Metal Complexation and Extraction Studies of bis-dithiophosphinite Ligands 
 
by 
 
Michael Alan DeVore II 
 
 
 
 
A thesis submited to the Graduate Faculty of 
Auburn University 
in partial fulfilment of the 
requirements for the Degree of 
Master of Science 
 
Auburn, Alabama 
December 12, 2011 
 
 
 
 
Keywords: Extraction, Uranyl, 
bis-dithiophosphinite 
 
 
Copyright 2011 by Michael Alan DeVore II 
 
 
Approved by 
 
Anne Gorden, Chair, Asociate Profesor of Chemistry and Biochemistry 
Rik Blumenthal, Asociate Profesor of Chemistry and Biochemistry 
Christopher Easley, Asistant Profesor of Chemistry and Biochemistry 
Christian Goldsmith, Asistant Profesor of Chemistry and Biochemistry 
 ii 
Abstract 
 
 
 Six bis(dithiophosphonite) ligands OR1a-OR3b were synthesized using 
Laweson?s Reagent and analogs of Laweson?s Reagent.  Two of the ligands OR2a and 
OR3a, were used in extraction studies with uranyl nitrate.  UV-Vis measurements were 
taken to determine how much uranyl was extracted into the organic layer from the 
aqueous layer at pH 2, 3, 4, and 5.  The extraction studies indicated that a longer time 
frame of extractions would be beneficial for these ligands.  There were modest 
extractions of 70% for most of the ligands however, it would be best to confirm with ICP 
in a continuing study.  These ligands could also be used for future studies of separating 
the trivalent lanthanides from the trivalent actinides because of the sulfur donors.     
 iii 
Acknowledgments 
 
 
 I would like to thank Dr. Anne Gorden, for putting up with me and geting me 
through al this work, I have learned a lot about the actinide series of elements and look 
forward to continuing to work with her.  Dr. John Gorden for giving me off the wal ideas 
of things to try from a coordination chemist?s standpoint.  My felow lab mates for 
support and answering any questions I may have had.  My parents and family for support 
and encouragement.  My commite members, Dr. Christopher Easley, Dr. Christian 
Goldsmith, and Dr. Rik Blumenthal, for taking time out of their busy schedules to read 
this and listen to my presentation, I hope to work with each of you more in the future. 
 iv 
Table of Contents 
 
 
Abstract...............................................................................................................................ii 
Acknowledgments.............................................................................................................iii 
List of Tables....................................................................................................................vii   
List of Figures..................................................................................................................vii 
List of Schemes................................................................................................................xiii 
List of Abbreviations.......................................................................................................xiv 
Uranium Extractions  ..........................................................................................................1 
            Introduction..............................................................................................................1  
 PUREX Proces  .....................................................................................................2 
 Cyanex 301  ............................................................................................................5 
 Laweson?s Reagent  ..............................................................................................7 
 Bis(dithiophsophinite) Ligands  ..............................................................................8 
 Experimental  ..........................................................................................................9 
 Synthesis of Ligands  ..............................................................................................9 
  OR1b..................................................................................................................9  
  OR2b................................................................................................................10 
  OR2a................................................................................................................10  
  OR3b................................................................................................................11  
  OR3a................................................................................................................11
 v 
 
 Laweson?s Reagent Analogs................................................................................12 
 Metal Complexes...................................................................................................14 
 Results and Discussion..........................................................................................16 
 Hydrolysis..............................................................................................................16 
 Extractions.............................................................................................................19 
  OR2a pH 2.......................................................................................................21 
  OR2a pH 3.......................................................................................................31 
  OR2a pH 4.......................................................................................................39 
  OR2a pH 5.......................................................................................................46  
  OR3a pH 2.......................................................................................................55 
  OR3a pH 3.......................................................................................................64 
  OR3a pH 4.......................................................................................................72 
  OR3a pH 5.......................................................................................................81 
 Extractions with SDS.............................................................................................89  
  OR3a pH 3 SDS...............................................................................................89 
  OR2a pH 3 SDS...............................................................................................97 
 Sequential Extraction...........................................................................................103 
  OR2a pH 3.....................................................................................................104 
  OR2a pH 4.....................................................................................................104 
  OR3a pH 3.....................................................................................................105 
  OR3a pH 4.....................................................................................................106 
 Conclusions  ........................................................................................................108 
 vi 
 Future Work  .......................................................................................................111 
References  ......................................................................................................................112 
Appendix   .......................................................................................................................114
 vii 
List of Tables 
 
 
Table 1  Diference in extinction betwen the first measurement and the last 
         measurement for each ligand and phase at corresponding pH..........................110 
Table 2  Maximum shift observed from the blank for each ligand and phase at 
 corresponding pH..............................................................................................110 
 
 
  
 vii 
List of Figures 
 
Figure 1  Tri-butyl Phosphate............................................................................................3 
Figure 2  Typical PUREX proces used with TBP...........................................................4 
Figure 3  Cyanex 272, 301 and 302 structures..................................................................5 
Figure 4  Plot of ?U(reorg) values versus number of methylene groups in the 
 linkage.
36
............................................................................................................7 
Figure 5  Structural reorganization as a two-step proces.................................................7 
Figure 6  Laweson?s Reagent structure...........................................................................8 
Figure 7  Hydrolysis of OR2a as extinction vs. wavelength...........................................17 
Figure 8  Hydrolysis of OR3a as extinction vs. wavelength...........................................18 
Figure 9  Close-up of extinction maximum that forms at 330 nm with pH 3-10............19 
Figure 10  Graph of the control absorbance vs. wavelength of OR2a (10 ?M) at pH 2 
        to determine the wavelength of the ligand in the aqueous phase (no uranyl)..22 
Figure 11  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
        from the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the 
        organic phase (DCM).......................................................................................24 
Figure 12  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M)  
         from the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the 
        organic phase (DCM).......................................................................................26 
Figure 13  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) 
     from the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the 
   organic phase (DCM).......................................................................................29
 ix 
Figure 14  Graph of extinction vs. time for OR2a at pH 2 in the organic phase...............30  
Figure 15  Graph of the control extinction vs. wavelength of OR2a (10 ?M) at pH 3 to 
        determine the wavelength of the ligand in the aqueous phase (no uranyl)......31 
Figure 16  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
        from the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) in the 
           organic phase (DCM).......................................................................................33 
Figure 17  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
            from the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) in the 
            organic phase (DCM).......................................................................................35 
Figure 18  Graph of extinction vs. wavelength for the extraction of 
            uranyl (5 ?M) from the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) 
         in the organic phase (DCM).............................................................................37 
Figure 19  Graph of extinction versus time for OR2a at pH 3 in the organic phase.........38 
Figure 20  UV-Vis spectrum absorbance vs. wavelength of the control of OR2a 
      at pH 4..............................................................................................................39 
Figure 21  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
      from the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the 
          organic phase (DCM).......................................................................................41 
Figure 22  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
       from the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the 
         organic phase (DCM).......................................................................................42 
Figure 23  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) 
       from the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the  
          organic phase (DCM).......................................................................................44 
Figure 24  Graph of extinction versus time for OR2a at pH 4 in the organic phase.........46 
Figure 25  UV-Vis spectrum of the control of OR2a at pH 5...........................................47 
Figure 26  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
       from the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the 
       organic phase (DCM).......................................................................................49 
Figure 27  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
         from the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the 
        organic phase (DCM).......................................................................................51 
 x 
Figure 28  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) 
         from the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the 
          organic phase (DCM).......................................................................................54 
Figure 29  UV-Vis spectrum absorbance vs. wavelength of the control of 
       OR3a at pH 2...................................................................................................56 
Figure 30  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
        from the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the 
         organic phase (DCM).......................................................................................58 
Figure 31  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
           from the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the 
          organic phase (DCM).......................................................................................60 
Figure 32  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) 
  from the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................62 
Figure 33  Graph of extinction versus time for OR3a at pH 2 in the organic phase.........63 
Figure 34  UV-Vis spectrum absorbance vs. wavelength of the control of OR3a 
  at pH 3..............................................................................................................64 
Figure 35  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................66 
Figure 36  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................68 
Figure 37  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................70 
Figure 38  Graph of extinction versus time for OR3a at pH 3 in the organic phase.........71 
Figure 39  Graph of extinction versus time for OR3a at pH 3 in the aqueous phase........72 
Figure 40  UV-Vis spectrum of the control of OR3a at pH 4...........................................73 
 
 
 xi 
Figure 41  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
  from the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................75 
Figure 42  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................77 
Figure 43  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
  the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................79 
Figure 44  Graph of extinction versus time for OR3a at pH 4 in the organic phase.........81 
Figure 45  UV-Vis spectrum of the control of OR3a at pH 5...........................................82 
Figure 46  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
  from the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................84 
Figure 47  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M)  
  from the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................86 
Figure 48  Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M)  
  from the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the 
  organic phase (DCM).......................................................................................89 
Figure 49  UV-Vis spectrum of OR3a with SDS control at pH 3.....................................91 
Figure 50  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) 
  in the organic phase (DCM).............................................................................92 
Figure 51  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) 
  in the organic phase (DCM).............................................................................95 
Figure 52  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M)  
  in the organic phase (DCM).............................................................................96 
Figure 53  UV-Vis spectrum of OR2a SDS control at pH 3.............................................97 
 
 
 xii 
Figure 54  Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) with SDS (5 ?M) 
  in the organic phase (DCM).............................................................................99 
Figure 55  Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) 
  from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) 
  in the organic phase (DCM)...........................................................................100 
Figure 56  Graph of extinction coeficient vs. wavelength for the extraction of uranyl 
  (5 ?M) from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) 
  with SDS (5 ?M) in the organic phase (DCM)..............................................102 
Figure 57  Aqueous layer contains uranyl nitrate (5 mM), organic layer contains 
  OR2a (5 mM) in DCM; Left:  Before shaking.  Right: Layers separated 
  after shaking...................................................................................................104 
Figure 58  Aqueous layer contains uranyl nitrate (5 mM), organic layer contains 
  OR2a (5 mM) in DCM; Left:  Before shaking.  Right: Layers separated  
  after shaking...................................................................................................104 
Figure 59  Aqueous layer contains uranyl nitrate (5 mM), organic layer contains 
  OR3a (5 mM) in DCM; Left:  Before shaking.  Right: Layers separated 
  after shaking...................................................................................................105 
Figure 60  Aqueous layer contains uranyl nitrate (5 mM), organic layer contains 
  OR3a (5 mM) in DCM; Left:  Before shaking.  Right: Layers separated 
  after shaking...................................................................................................106 
Figure 61  Proposed modes of binding that would result in > 20 nm 
  wavelength shift.............................................................................................107 
Figure 62  Possible modes of secondary binding............................................................108 
 xii 
List of Schemes 
 
Scheme 1 Synthesis of amonium salt OR1b.....................................................................9 
Scheme 2 Synthesis of amonium salt of OR2b..............................................................10 
Scheme 3 Synthesis of organicaly soluble OR2a.............................................................10 
Scheme 4 Synthesis of amonium salt of OR3b..............................................................11 
Scheme 5 Synthesis of organicaly soluble OR3a.............................................................11 
Scheme 6 Synthesis of tert-butyl Laweson?s...................................................................12 
Scheme 7 Synthesis of sec-butyl Laweson?s....................................................................12 
Scheme 8 Synthesis of hexyl Laweson?s.........................................................................13 
 xiv 
List of Abbreviations 
 
An Actinide(s)    
DCM Dichloromethane or methylene chloride 
DMF N,N-dimethylformamide 
DI  Deionized 
DMSO Dimethylsulfoxide 
D2EHPA di-(2-ethylhexyl)phosphonic acid 
FP Fision Products 
HSAB Hard soft acid base theory 
ICP-MS Inductively Coupled Plasma-Mas Spectrometry 
Ln Lanthanide(s) 
L.R. Laweson?s Reagent 
LWR Light Water Reactor 
MOX Mixed Oxide Fuel 
PUREX Plutonium Uranium Recovery by Extraction 
SDS Sodium Dodecyl Sulfate 
SNF Spent Nuclear Fuel 
TBP Tri-n-butyl phosphate 
UV-VIS Ultra Violet-Visible Spectroscopy 
 
 
 
 1 
Uranium Extractions 
Introduction 
The availability of adequate energy at a reasonable price is considered a requirement of 
modern society.
1
 Experts predict that the maximum alowable oil production using 
current methods wil occur in the next 5 to 25 years, and consequently, the need to have 
alternative energy sources to eventualy replace oil is growing.
1
 Currently 25-30% of the 
world?s electricity is produced using nuclear sources, and nuclear power is the dominant 
source of electrical power for most of Europe.
2
 As of January 1, 2010, there were 437 
nuclear power reactors in operation worldwide with 104 in the United States alone.
3
 At 
the end of 2005, 85% of the domestic energy in the United States was produced from 
fossil fuels, while 8% was from nuclear power, and 6% from renewable energy such as 
hydroelectric, solar and wind power.
1
 The applications of nuclear energy for the 
production of electricity for general civilian use, military applications, as wel as in 
satelite and space exploration applications are plagued with waste management risks that 
must be addresed.
2
 Fifty-years of nuclear weapons production has generated more than 
100 metric tons of purified plutonium in the United States alone.
4
 The production of 
plutonium from power reactors amounts to perhaps as much as 7000 metric tons 
worldwide most of which is dilute and contained in spent reactor fuel.
4
 
 
In a typical light-water reactor, the operational life-span of a fuel rod is only three years,
5
 
and only about 5% of the energy content of the nuclear fuel rod is used.
1
   Although 
recycling the remaining 95% of fisile material sems reasonable from an eficiency 
standpoint, the generation of weapons grade plutonium and proliferation risks led to the 
cesation of this technology in the United States during the cold war.
1,6
 Other nations 
using nuclear power technology reproces their spent fuel to recycle remaining fisile 
fractions.
1
 Such a proces can provide up to 96% more energy than the once-through 
cycle using the same initial amount of enriched uranium fuel.
1
    
 
 2 
Reprocesing refers to the chemical separation of fisionable uranium and plutonium 
from irradiated nuclear fuel.
6
 The two main reasons for commercial reprocesing are: (1) 
to increase the available energy from fisile and fertile atoms and (2) to reduce hazards 
and costs for handling the high level wastes from fision products (FP).
7
 The economic 
advantage of reprocesing depends on the cost and availability of natural uranium, on 
enrichment and making fuel rods, and the prevailing energy price (usualy based on fossil 
fuels).
7
 
 
One of the first problems asociated with the separation of Spent Nuclear Fuel (SNF) is 
separating lanthanides from actinides.  This is dificult due to their similar oxidation 
states and ionic radii.
8
 The first separation of uranium and plutonium was done by the 
chemists of the Manhatan Project in the 1940s.
7
 In the early separations, the stability of 
UO
2
2+
 was exploited as wel as the redox lability of plutonium (+3, +4, and +6 oxidation 
state).
4,7
 In these earliest proceses, only plutonium was isolated by precipitating it in the 
reduced state as PuF
3
 or PuF
4 
along with al the other FP insoluble fluorides.
7
 In order to 
get relatively pure plutonium, this precipitation proces had to be repeated several times.
4
   
 
This precipitation technique is not suitable for large-scale, continuous remote operations, 
in which uranium and plutonium both have to be isolated in a very pure state.
7
 In the late 
1940?s this proces was replaced by solvent extraction methods in which the fuel rods 
where disolved in nitric acid, and contacted with an organic solvent which selectively 
extracted the desired elements.
7
 Because actinide production in reactors is acompanied 
by fision, the ability to isolate the transuranium actinides from both fision products and 
uranium, remains a separation problem central to actinide production.
4
 Acordingly, 
eficient separation proceses continue to be sought.
4,9
 
 
PUREX Proces 
The most widely used and efective proces for the removal of plutonium and uranium 
around the world is the PUREX proces, which stands for Plutonium Uranium Recovery 
by EXtraction.
10-12
 This proces utilizes the extractant tributyl phosphate (TBP) (Figure 
1) in a hydrocarbon solvent (usualy kerosene or dodecane) (Se Figure 2).
7,13
 It relies on 
 3 
the extraction of plutonium and subsequent reduction to the trivalent state, leaving the 
exces uranium in the extractant phase for subsequent recovery.
4
 
 
Figure 1: Tri-butyl Phosphate 
 
As a result of using PUREX, the volume and radiotoxicity of highly radioactive and long-
lived waste to be disposed were significantly reduced as compared to a once-through fuel 
cycle.
13
 TBP acts like an adduct and is normaly used as a 30% solution in kerosene.
7
 It 
takes three purification cycles for both uranium and plutonium to be extracted eficiently, 
and the first cycle is where >99% of the fision products are separated as wel as where 
high levels of beta and gama activity are present.
7
 The aqueous phase of the first 
separation is prepared in 3-4M HNO
3
.   The next two cycles are the same as the first but 
at lower acid concentration and are used to achieve additional decontamination and 
overal purity.
7
      
 
After using this proces for several decades with industrial fedback, there were several 
major milestones.  First, high eficiency and reliability is achieved through the procesing 
of large volumes of spent fuel with good statistics. Second is the production of high 
quality UO
2
 and mixed oxide (MOX) fuels for light water reactors (LWRs) and fast 
reactors. Finaly, continuous decrease of solid waste volume, efluents, and 
environmental impact in terms of radiation doses.
13
  Though it is the industry standard at 
present, the PUREX proces remains far from perfect, because it does not addres the 
isolation of other actinide cations.
4
 
 
 
 
 4 
   
Figure 2: Typical PUREX proces used with TBP.  
ww.euronuclear.org/info/encyclopedia/p/purex-proces.htm 
   
TBP works very wel at binding uranium and plutonium because the two metals are hard 
acids.  Oxygen being a hard base forms a very stable complex.  In 1963, Pearson came up 
with the Hard Soft Acid Base Theory (HSAB theory) that esentialy describes the 
binding afinity of a hard Lewis acid (UO
2
2+
, Mg
2+
, Co
3+
, Pu
4+
...etc.) wil more 
selectively bind with a hard Lewis Base (F, O, N?etc.) and the same for soft Lewis acids 
and bases.
14
 Ni
2+
 and Co
2+
, being soft Lewis acids, should be atracted to soft donors, 
sulfur substitution and the organophosphorous reagents began to emerge.  This proved 
beneficial to the extraction of these metal ions.
15
 Al known An(III) | Ln(III) group 
separations are based on the stronger interactions of actinide with soft donor atoms like 
Cl
-
, S, or N.
4,16
 
 
Organophosphorous extractants have played a major role in actinide extraction.
9
 These 
extractants are generaly stable, cheap, and commercialy available, and have been widely 
studied in the past few decades, in particular with respect to cobalt-nickel separation in 
weakly acidic sulfate media.
15
 The earliest work was performed by Ritley and co-
workers, as wel as Flet and co-workers where they used an alkylphosphoric acid, di-(2-
ethylhexyl)-phosphoric acid (D2EHPA).  This resulted in a number of patents, and the 
commercial implementation of several proceses with D2EHPA.
15,17
 Next came the 
development of the phosphonic and phosphinic acid extractants 2-ethylhexylphosphonic 
 5 
acid mono-2-ethylhexyl ester (PC88A) and bis-(2,4,4,-trimethylpentyl)-phosphinic acid 
(Cyanex 272) which led to beter separation factors in the order: phosphoric< 
phosphonic< phosphinic acid.
15,18,19
 Handley and Dean lead the way into the 
investigation of the extraction of a number of metals from H
2
SO
4
 and HCl by 
trialkthiophosphates,
20
 a dialkylthiophosphoric acid,
21
 and dialkyldithiophosphoric 
acids.
22
 
 
Cyanex 301 
Cyanex 301 and 302 are the respective dithio and monthio analogs of Cyanex 272 with 
the main components of the reagents shown below:
15
 Cyanex 301 was originaly 
developed for the selective extraction of zinc from efluent streams containing calcium.
15
 
Increasing sulfur substitution increases the acidity of the extractants, making them more 
suited to the extraction of soft Lewis acid metal ions such as Ag(I), Ni(II), Zn(II), Cu(I), 
Au(I), and platinum group metals in acordance with the HSAB theory.
23
 
 
 
 
Figure 3: Cyanex 272, 301 and 302 structures 
 
 
In recent years, Cyanex 302 and Cyanex 301 have received considerable atention both 
for their ability to extract soft transition metals,
23
 and for their ability to diferentiate 
betwen chemicaly similar trivalent lanthanides and actinides.
24
 Recently, there have 
been numerous publications using thiosubstituted organophosphinic reagents to extract 
 6 
metal ions such as cobalt (II)
25
, nickel (II),
25
 titanium (IV),
26
 silver,
27
 mercury (II),
28
 
molybdenum (VI),
29
 actinides and lanthinides,
30
 copper,
31
 and halfnium.
32,33
 
 
With the sulfur atoms on Cyanex 302 and 301, these compounds are much stronger acids 
than Cyanex 272, and as such, are capable of extracting many metals at low pH (<2).  At 
this low pH, they show a high degree of selectivity for heavy metals vs. alkaline and 
alkali earth metals,
33
 however, Cyanex 301 wil only diferentiate betwen Am(III) and 
lanthanides in solutions les acidic than pH of 3 (pK
a
 of Cyanex 301 is 2.6).
34
 Because 
the waste stream of the Cyanex proces contains sulfur, a problem arises during 
incineration which can lead  to the release of coke ash and sulfur dioxide, major 
contributors, to acid rain.
13
   
 
To date, separations of SNF have focused on extraction agents containing a single 
dithiophosphinic acid group like Cyanex 301.  We wanted to se if we could synthesize a 
ligand with two or more of these groups, such that they structuraly complement the 
metal, and provide a chelate efect that would dramaticaly enhance the extraction 
eficiency.
35
 Using computational calculations from Dr. Benjamin Hay,
36
 we were able to 
identify a series of target ligands with two thiophosphonates to synthesize. A summary of 
his calculations in a graph of ?U(reorg) vs. number of CH
2 
groups in linkage are shown 
in figure 4.  The structural reorganization is convenient to partition into a two-step 
proces as shown in figure 5.  In the first step, the ligand (host) goes from the free form, 
defined as the lowest energy conformation of the host, to the binding form.  The 
diference in the strain energy of these two forms on the ligand, ?U(conf), is a measure 
of the degree of pre-organization.  The second step, where the host goes from the binding 
form to the bound form, the diference in the strain energy betwen these two forms is 
?U(comp), is a measure or the degree of complementarity offered by the binding 
conformation.  The sum of the two energies ?U(reorg) = ?U(conf) + ?U(comp), 
provides a measuring stick for determining the degree of structural reorganization that 
occurs on binding the guest (metal).
36
   In this research, Laweson?s reagent and analogs 
of Laweson?s Reagent have been used to synthesize bisdithiophosphonate ligands for 
metal complexation as wel as extraction studies of uranium.  
 7 
 
 
Figure 4: Plot of ?U(reorg) values versus number of methylene groups in the linkage.
36
 
?U(reorg) = ?U(conf) + ?U(comp)
36
 
 
 
Figure 5: Irrespective of the actual complexation mechanism, the structural 
reorganization in the host that occurs upon binding the guest can be viewed as taking 
place in two steps defining three distinct structural states for the host: bound form, 
binding form, free form.  The bound form is the structure of the host when complexed 
with the guest, the binding form is the host conformation obtained after removing the 
guest and optimizing the host, and the free form is the global minimum conformation of 
the host.
36
 
 
Laweson?s Reagent 
The chemical conversion of carbonyl to thiocarbonyl has been an area of interest in 
synthetic organic chemistry for over a century.
37
 The usual method involves boiling 
toluene, xylene, or pyridine as solvent, and a large exces of a carbonyl reagent and long 
reaction times, resulting in variable yields.
37-39
 Previous investigations have shown that 
 8 
the reaction of carbonyl compounds with phosphorous pentasulfide can be carried out at 
30?C in polar solvents such as acetonitrile or tetrahydrofuran in the presence of a base 
catalyst.
37
 
 
In the search for new, useful, and general thionation reagents, the chemistry of 2,4-bis(p-
methoxyphenyl)-1,3-dithiadiphosphetane-2,4-disulfide (Laweson?s Reagent, LR) 
appeared to indicate that it could be a superior reagent for the conversion of a wide 
variety of carbonyl to thiocarbonyl compounds.
37
 The first report on the synthesis of 
arylthionophosphine sulfides dates back to 1956, when Lecher and co-workers described 
the reaction of phosphorous pentasulfide with a number of aromatic substrates at elevated 
temperatures.
39,40
 The crystaline products were isolated in varying yields.
40
 
 
Laweson?s reagent has a couple of advantages over phosphorous pentasulfide.  First, it 
easily and safely prepared by the reaction of phosphorous pentasulfide with refluxing 
anisole in a 1:10 molar ratio at 155?C for 6 hours for a 70-80% yield,
39,41
 both are 
commercialy available.  The second advantage is that it can react with a wide range of 
carbonyl compounds in nearly equimolar proportions.
37
 The atractivenes of this system 
is asociated with its availability, simplicity and convenience of use, the high yields of 
sulfur-containing products, and a comparative ease of isolating the products from the 
reaction mixture;
42
 however, LR is not stable for very long in a solution at temperatures 
at over 110?C, because it slowly undergoes polymerization or decomposes.
37,39
   
 
 
 
Figure 6: Laweson?s Reagent structure 
 
Bis(Dithiophosphinite) Ligands 
Organodithio derivatives of phosphorous compounds, such as dithiophosphinates, 
dithiophosphonates, and dithiophosphates have been studied for many years.
43,44
 
 9 
Phosphodithioates and their corresponding acids and metal complexes, have been used as 
additives to lubricant oils,
45,46
 floatation reagents for the recovery of metals from 
solutions,
47
 pesticides,
47,48
 and for chemical warfare.
43
 Mono(dithiophosphinates), 
mono(dithiophosphonates), and mono(dithiophosphates) and their complexes with 
various metals have been extensively studied;
44
 however, the properties of the 
bis(dithiophosphinates, bis(dithiophosphonates), and bis(dithiophosphates), with special 
regard to containing bridging moieties, have not been investigated in detail.
44,47
 The 
inspiration for this research was to prepare bid(dithiophosphonates) and to evaluate these 
in simple extractions systems to develop new targets for novel selective extraction 
systems.   
 
Experimental 
Laweson?s reagent, uranyl nitrate, uranyl sulfate, ethylene glycol, 1,3-propanediol, 1,5-
pentanediol, phosphorous pentasulfide, and tert-butyl benzene were purchased from 
Acros and used without any purification.  The pH was recorded on a Fischer Scientific 
AR15 pH meter.  UV-Vis data was collected on a Cary 50 UV-Vis spectrophotometer 
with a xenon lamp in the range of 200-1200 nm.  The 
1
H, 
13
C, and 
31
P NMR was 
recorded on a Bruker AV 250 spectrophotometer with d
1
-MEOD, d
1
-CDCl
3
, or d
6
-DMSO 
as the solvent with tetramethylsilane as the reference.  Al melting points were recorded 
on a Mel-temp II melting point apparatus, and the values are uncorrected. 
 
Synthesis of Ligands 
 
OR1b
47
 
 
Scheme 1:  Synthesis of amonium salt OR1b 
 
Laweson?s Reagent (2.0 g, 5 mol) was mixed with toluene (5 mL) in a 100 mL round 
bottom flask.  To this mixture ethylene glycol (0.275 mL, 5 mol) was added.  The 
 10 
temperature was set to 80?C and stirred until al of the solids had disolved.  The solution 
turned a dark green and more toluene (75 mL) was added. A white precipitate formed 
imediately upon the bubbling of dry amonia gas converting the acid to the amonium 
salt.  Bubbling of the gas continued for 30 minutes.  The white precipitate was filtered, 
washed with cold toluene and dried at room temperature under vacuum.  Crystals for x-
ray difraction were grown from methanol but were not suitable for difraction.  The yield 
was 2.05g  (82 %); product did not melt below 200?C  
 
OR2b
47
 
 
Scheme 2:  Synthesis of amonium salt of OR2b. 
 
Laweson?s Reagent (4.2 g, 10 mol) was mixed with toluene (5 mL) in a 150 mL round 
bottom flask.  To this mixture 1,3-propanediol (0.74 mL, 10 mol) was added.  The 
temperature was set to 80?C and stirred until al the solids had disolved.  At this point 
the mixture was a dark green color and more toluene (125 mL) was added. A white 
precipitate formed imediately upon the bubbling of dry amonia gas converting the 
acid to the amonium salt.  Bubbling of the gas continued for 30 minutes.  The white 
precipitate was filtered, washed with cold toluene and dried at room temperature under 
vacuum. Crystals for x-ray difraction were grown from methanol but were not suitable 
for difraction.  The yield was 4.05 g (80  %); mp 157-162 ?C  
 
OR2a
44
 
 
Scheme 3:  Synthesis of organicaly soluble OR2a. 
 
 11 
To a solution of 1,3-propanediol (0.7232 mL, 10 mol) in toluene (30 mL), 4.0 g (10 
mol) of Laweson?s Reagent was added.  The mixture was stirred at 60?C until al the 
solids had disolved and left overnight.  The solvent was removed on a roto-vap until the 
remaining volume was ~10 mL.  Hexane (30 mL) was added to precipitate the product as 
a green oil.  Yield 4.206 g (88%). 
 
OR3b
47
 
 
Scheme 4: Synthesis of amonium salt of OR3b. 
 
Laweson?s Reagent (4.2 g, 10 mol) was mixed with toluene (5 mL) in a 100 mL round 
bottom flask.  To this mixture 1,5-pentanediol (1.05 mL, 10 mol) was added.  The 
temperature was set to 80?C and stirred until al the solids had disolved. At this point the 
mixture was a dark green color and more toluene (150 mL) was added. A white 
precipitate formed imediately upon the bubbling of dry amonia gas converting the 
acid to the amonium salt.  Bubbling of the gas continued for 30 minutes.  The white 
precipitate was filtered, washed with cold toluene and dried at room temperature under 
vacuum.  Crystals for x-ray difraction were grown from methanol but were not found to 
be suitable for characterization by single-crystal X-ray difraction.  The yield was 4.1 g 
(80 %); mp 171-176?C 
 
OR3a 
 
Scheme 5:  Synthesis of organicaly soluble OR3a. 
 
To a solution of 1,5-pentanediol (1.05 mL, 10 mol) in toluene (30 mL), 4.0 g (10 
mol) of Laweson?s Reagent was added.  The mixture was stirred at 70?C until al the 
 12 
solids had disolved and left overnight.  The solvent was removed on a roto-vap until the 
remaining volume was ~10 mL.  Hexane (30 mL) was added to precipitate the product as 
a green oil.  Yield was 4.2 g (84%). 
 
Laweson?s Reagent Analogs 
 
tert-butyl Laweson?s 
 
Scheme 6: Synthesis of tert-butyl Laweson?s. 
 
In a 100 mL round bottom flask, 158 mL (1mol) of tert-butyl benzene and 6.6 g (7.5 
mol) of phosphorous pentasulfide (P
2
S
5
) and 20 mL of 1,2-dichlorobenzene as solvent 
were heated to 170?C and stirred until al the solid had disolved.  The solution was 
decanted into a 250 mL beaker and cooled to room temperature, where a yelow 
precipitate formed.  The product was filtered and washed three times with 10 mL each of 
50:50 mixture of ethyl ether:methylene chloride.  The product became crystaline like and 
was dried in a vacuum oven at room temperature overnight.  Yield 0.79 g (23 %). mp - 
decomposed   
 
sec-butyl Laweson?s 
 
Scheme 7: Synthesis of sec-butyl Laweson?s 
 
In a 100 mL round bottom flask, 50 mL (0.32 mol) of sec-butyl benzene and 4.3 g (9.67 
mol) of phosphorous pentasulfide (P
2
S
5
), and 20 mL of 1,2-dicholorbenzene as solvent 
were heated and stirred at 170?C until there was no more evolution of hydrogen sulfide.  
The solution was decanted into a 250 mL beaker and cooled to room temperature where 
 13 
the product precipitated as a yelow solid.  The product was filtered and washed three 
times with 10 mL each of 50:50 mixture  of ethyl ether:dichloromethane.  The product 
became crystaline like and was dried in a vac-oven at room temperature overnight. Yield 
0.16g (15%) mp Decomposed at 200?C 
 
hexyl Laweson?s 
 
Scheme 8:  Synthesis of hexyl Laweson?s 
 
In a 100 mL round bottom flask, 50 mL (265 mol) of hexyl benzene, 2.4 g (5.4 mol) 
of phosphorous pentasulfide, and 20 mL of 1,2-dichlorobenzne as solvent were heated 
and stirred at 170?C until there was no more evolution of hydrogen sulfide.  The solution 
decanted into a 250 mL beaker and cooled in an ice bath, where the product precipitated 
as a brown solid.  The precipitate was filtered and washed three times with 10 mL of 
50:50 mixture of ethyl ether:dichloromethane mixture.  The precipitate was dried in a 
vac-oven at room temperature overnight. Yield 0.5876 g (21%) mp decomposed. 
 
The NMR data can be located in appendix; OR1a, OR2a, and OR3a were found to 
compare wel to the literature values.   
 
Using the analogs of Laweson?s reagent, we tried to make the bisdithiophosphonate-
linked ligand soluble in other organic solvents; however, due to the analogs not being 
soluble in solvents other than DMF or DMSO, we could not synthesize the ligands, 
because reactions with the solvent led to numerous side products generated by thionation 
of the solvent. 
 
 
 
 
 
 14 
Metal Complexes 
 
Al metal complexes were formed using the amonium salts of the ligands. 
 
OR1a: Cu(II) 
In a 20 mL scintilation vial, 0.200 g (0.4 mol) of OR1a was disolved in 5 mL of DI 
water.  In a second vial, 0.100 g (0.4 mol) of copper (II) sulfate was disolved in 5 mL 
of DI water.  The copper solution was added dropwise to the OR1a solution.  
Immediately a brown precipitate formed.  The solid was filtered off and washed with cold 
DI water.  This precipitate was not found to be soluble in standard organic solvents such 
as toluene, methylene chloride, or DMSO. 
 
OR1a: Ni(II) 
In a 20 mL scintilation vial, 0.200 g (0.4 mol) of OR1a was disolved in 5 mL of DI 
water.  In a second vial, 0.159 g (0.4 mol) of Nickel (II) amonium sulfate was 
disolved in 5 mL of DI water.  The Nickel solution was added dropwise to the OR1a 
solution and a light brown/light purple precipitate formed almost imediately.  The 
precipitate was filtered off and washed with cold DI water.  The solid was slightly soluble 
in DMSO.     
 
OR2a: Cu(II) 
In a 20 mL scintilation vial, 0.209 g (0.4 mol) of OR2a was disolved in 5 ml of DI 
water.  In a separate vial, 0.101 g (0.4 mol) of Copper sulfate was disolved in 5 mL of 
DI water.  The copper solution was added dropwise to the OR2a solution.  A brown 
precipitate formed imediately.  The solid was filtered and washed with cold DI water.  
The dried solid was slightly soluble in DMSO. 
 
OR2a: Ni(II) 
In a 20 mL scintilation vial, 0.202 g (0.4 mol) of OR1a was disolved in 5 mL of DI 
water.  In a second vial, 0.155 g (0.4 mol) of Nickel (II) amonium sulfate was 
disolved in 5 mL of DI water.  The Nickel solution was added dropwise to the OR1a 
 15 
solution and a light brown/light purple precipitate formed almost imediately.  The 
precipitate was filtered off and washed with cold DI water.  The solid was slightly soluble 
in DMSO. 
 
OR2a:UO
2
2+
 
In a 20mL vial, 0.2 g (0.4 mol) of OR2A was disolved in 5mL of DI water.  In a 
separate 20mL vial, 0.15 g (0.4 mol) of Uranyl (VI) Sulfate was disolved in 5mL of 
deionized water.  The uranyl solution was added dropwise to the ligand solution and 
imediately a yelow precipitate formed.  The uranyl vial was washed with 2mL of 
deionized water and added to the now OR2A: Uranyl solution.  The precipitate was 
filtered, washed with cold water and air-dried.  The solid was recrystalized from 
difusion of DMSO: Ether. 
 
OR3a:UO
2
2+ 
 In a 20 mL vial, 0.22 g (0.4 mol) of OR3a was disolved in 5 mL of DI water.  In a 
separate 20 mL vial, 0.15 g (0.4 mol) of Uranyl (VI) Sulfate was disolve in 5 mL of DI 
water.  The uranyl solution was added drop wise to the ligand solution and a yelow 
precipitate imediately formed. The uranyl vial was washed with 2 mL of DI water and 
added to the solution.  The precipitate was filtered, washed with cold water, and air-dried.  
The solid was recrystalized from difusion of DMSO: Ether.  No crystals were good 
enough for single x-ray difraction. 
 
Extractions 
Two-phase extraction studies (DCM:H
2
O) were performed to determine the extraction 
capability for the removal of UO
2
2+
 ion from aqueous solution.  The ligands OR2a and 
OR3a, soluble in DCM were used for extraction studies.  Fresh solutions of 
UO
2
(NO
3
)
2
?6H
2
O were prepared in DI water, and the pH was adjusted with HNO
3
 and 
KOH (? 0.05).  Two diferent methods were employed for studying extraction.   
 
 
 
 16 
Hydrolysis Study 
Stock solutions of OR2a, and OR3a were prepared by disolving the respective 
compound in dichloromethane solution (100 mL each).  An equivalent amount of 
aqueous solution at pH 1-14 (? 0.05) was added to separate vials containing 5 mL of 
OR2a or OR3a in organic solvent and shaken for 60 seconds.  The solution was left 
undisturbed overnight, and the organic layer isolated for hydrolysis studies employing 
UV-Vis.  The extent of hydrolysis at diferent pH was interpreted relative to the spectra at 
neutral pH. 
 
Results and Discusion 
 
Hydrolysis 
The two-phase hydrolysis study of OR2a indicates that the ligand hydrolyzes in extreme 
pH conditions (pH 1,2 and 12-14) while OR3a also hydrolyzes in extreme pH conditions 
(pH 1,2 and 11-14).  The hydrolysis profile of compounds OR2a and OR3a are shown in 
figures 7-9. 
 
 17 
 
Figure 7: Hydrolysis of OR2a as extinction vs. wavelength.  The band indicated by the x 
corresponds to neutral pH. 
 
In the UV-VIS spectra of OR2a, there is a significant change in extinction maximum at 
pH 1 and 2 compared to that observed at pH 7.  Another significant change in extinction 
is also observed in pH 12-14 compared to pH 7 as wel as the characteristic extinction 
maximum wavelength peak around 245 nm is absent. 
 
 18 
 
Figure 8: Hydrolysis of OR3a as extinction vs. wavelength.  The band indicated by x 
corresponds to neutral pH. 
 19 
 
Figure 9: Close-up of extinction maximum that forms at 330 nm with pH 3-10.  X 
indicates neutral pH in the hydrolysis of OR3a 
 
In the UV-VIS spectra of OR3a, there is a significant change in extinction maximum 
betwen pH 1 and pH 2.  Then there is another extinction maximum change betwen pH 
10 and 11.  Perhaps even more significant is the formation of extinction maximum at 330 
nm.  This extinction maximum is only formed for pH 3-10 giving indication that the 
ligand would stil hydrolyze at pH 2.  For pH 11-14, the characteristic extinction 
maximum at 245 nm is absent. 
 
Extractions 
Based on the hydrolysis of the ligand and literature reference, simple extractions were 
tested in the pH range of 2-5 with ratios of 2:1, 1:1, and 1:2 uranyl (as UO
2
2+
) to ligand 
for compounds OR2a and OR3a. The phases were agitated by stirring for time periods 
indicated on graphs, stopped, alowed 10 minutes to equilibrate, and each layer drawn off 
into a cuvete for UV-Vis measurement.   
 20 
 
Typicaly, in these types of uranyl extractions, the eficacy of the ligand is quantified by 
the disappearance and eventual absence of the characteristic UO
2
2+
 extinction maximum 
at ca. 420 nm;
8
 however, due to the high absorbencies (i.e. extinction coeficients) of 
these ligands, the concentration of the ligand must be decreased to micro molar scale and 
the smaler extinction coeficient of the characteristic extinction maximum is such that it 
cannot be distinguished from that of the ligand.  Therefore, extraction eficacy is 
characterized by the formation of the metal/ligand complex and characterization of the 
organic and aqueous layers.  Typicaly binding would be indicated by a shift of 20-25 nm 
from the ligand peak.  With such a significant shift, it is commonly acepted that the 
ligand binds the metal tightly and is not partialy binding.  An equilibrium equation for 
metal binding in the aqueous phase is shown in equation 1; however, this only works at 
pH 3 or higher, as there is hydrolysis at pH 2. 
 
The estimated extraction percentage was calculated by taking the diference in the 
absorbance betwen the final measurement in the organic phase and the first 
measurement in the organic phase at 15 minutes.  This was divided by the extinction 
coeficient of the ligand and then divided by the concentration of the ligand to get the 
estimated percent extraction.  Without the characteristic uranyl peak, the percent 
extraction is much more complicated to estimate. 
 
? 
yUO
2
(H
2
O)
8
2
x
+
xL
2?
   
 
 
 
 
 
 
 
 
 
 21 
OR2a pH 2 
A)  
 
B)  
 22 
C)  
Figure 10: Graph of the control absorbance vs. wavelength of OR2a (10 ?M) at pH 2 to 
determine the wavelength of the ligand in the aqueous phase (no uranyl).  A) Organic 
phase, time plot at 245 nm B) Overal aqueous phase spectrum; C) Close up of aqueous 
phase around 240 nm.  Time plotted at 240 nm. 
 
The UV-Vis spectra above in figure 10, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time. 
 
 23 
A)  
 
 
B)  
 
 24 
C)  
Figure 11: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase time plotted at 245 nm; B) aqueous phase; C) close up of aqueous phase 
around 240 nm. 
 
In the figure above, with OR2a at pH 2 and a ratio of 2-1 (metal to ligand), in the organic 
layer (DCM), the extinction maximum is increasing at a steady rate based on the time 
betwen measurements.  Up until the 24
th
 hour, there is an increase of 20000 extinction 
units from the first measurement, indicative of the metal-ligand complex transferring into 
the organic phase; however betwen the 24
th
 hour and the 48
th
 hour there is only an 
increase of 1000 extinction units indicating that the ligand may be close to maximum 
extraction eficiency.   The extinction maximum in the aqueous layer is decreasing, 
confirming that the ligand coordination and metal complex is being taken into the organic 
phase.  The decrease betwen the 12
th
 hour and the 24
th
 hour is about 5000 extinction 
units, and betwen the 24
th
 hour and 48
th
 hour there is a decrease of just a litle over 1000 
extinction units, just like the organic phase.  Unlike other similar systems, there is no 
wavelength shift in the extinction; however the change in extinction is far greater than 
efects sen due to changes in pH.  This indicates that at this ratio of metal to ligand 
maintained at this pH, the ligand binding is not very strong for uranyl.  Instead of al four 
 25 
sulfurs coordinating to uranyl, it is possible that only two, or only one sulfur is binding.  
From the hydrolysis data above, a second possibility is that the ligand could by 
hydrolyzing with the addition of the metal salt (decreasing below pH 2), the ligand-metal 
complex is not stable for very long.  In comparison to control solutions containing ligand 
in the organic phase, we find that at this pH there is some evidence for the transfer of the 
ligand into the aqueous phase.  This makes it dificult to interpret the data, as there is not 
clear evidence of the formation of metal complex and subsequent sequestration of the 
metal-ligand complex entirely in the organic phase.  With the control as a basis for the 
shift in the aqueous phase, the maximum extinction in the controls is at 240 nm, and it is 
the same for the aqueous phase.  From the data above, we presume that there is about 50-
60% uranyl extraction, but is dificult to say this with certainty because of the potential 
for hydrolysis. 
 
A)  
 
 26 
B)  
 
C)  
Figure 12: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 240 nm. Time plotted at 240 nm 
 
 27 
When the ratio of uranyl to ligand is equal, there is no change in the 
maximum extinction wavelength typicaly indicative of binding betwen 
the ligand and metal. At this ratio, as time of exposure is increased, 
there is evidence of the metal complex continuing to separate into the 
organic layer. This hypothesis is confirmed in both the aqueous and 
organic layers by the 12, 24, and 48-hour measurements. Significant 
increases in extinction maximum of 10000 extinction units betwen 6 and 
12 hours, 7000 extinction units betwen 12 and 24 hours, and 11000 units 
betwen 24 and 48 hours at 245 nm are noted in the organic phase. Based 
on the diference from the control, the change of 28000 extinction units 
to reach equilibrium, it is estimated to indicate that 60-70% of the uranyl has been 
extracted. 
 
Significant decreases in extinction maximum of 5000 extinction units 
betwen 6 and 12 hours, 10000 extinction units betwen 12 and 24 hours, 
and 9000 extinction units betwen 24 and 48 hours in the aqueous phase 
at 240 nm are noted. In neither phase does the maximum extinction shift from the initial 
extinction wavelength sen in the control with the ligand at the target pH. 
 
 28 
A)  
 
 
B)  
 
 29 
C)  
Figure 13: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 240 nm. Time plotted at 240 nm 
 
Comparing the organic phase to the UV-Vis spectra sen in a system with an exces of 
ligand, as depicted in figure 13, an increase in the extinction maximum at each time 
interval at 245 nm is noted. The extinction wavelength shift at its maximum of 245nm is 
minimal. The ligand may be coordinating the uranyl ion, but not strongly enough to cause 
a shift in the extinction wavelength.  From the blank, there is an initial increase of 
approximately 18000 extinction units at 15 minutes.  The total increase in extinction after 
48 hours is 76900 extinction units from the blank.  Since the extinction is stil increasing, 
this is indicative of the ligand not reaching equilibrium or maximum extraction eficiency 
yet. 
 
The spectral changes with time of the aqueous layer are also quite interesting.  In the 
control experiment the ligand wil freely go into the aqueous layer at pH 2 and remain 
there.  With an exces of ligand, ligand goes into the aqueous layer, and some of the 
ligand wil remain there, while the rest wil coordinate metal and equilibrate with the 
 30 
organic layer. During the first two hours, the extinction maximum has decreased about 
6700 extinction units, but increased by 8000 extinction units from the 2
nd
 to the 4
th
 hour.  
After the 5
th
 hour, there is a dramatic drop of 15000 extinction units followed by a smal 
subsequent increase in the 6
th
 hour of 6000 extinction units.  The extinction decreased by 
11000 extinction units from the 6
th
 hour to the 48
th
 hour.  From the data above, we 
believe to be about 70-80% extraction of uranyl, but with the hydrolysis of the ligand, it 
is inconclusive. 
 
With the dramatic drop of extinction maximum after the 5
th
 hour, there is not a dramatic 
increase in extinction in the organic layer as one might expect, possibly indicating that 
the ligand-metal complex is soluble both in the organic and aqueous phases, or that some 
of the complex is precipitating or forming a third-phase system. 
 
 
Figure 14: Graph of extinction vs. time for OR2a at pH 2 in the organic phase. ?? 2-1 
ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
 
 
 
 
0"
20"
40"
60"
80"
100"
120"
140"
160"
180"
?
*1
0
3
&M
(1&
cm
(1&
Time&
OR2a&pH&2&ORG&
 31 
OR2a pH 3 
 
A)  
 
B)  
Figure 15: Graph of the control extinction vs. wavelength of OR2a (10 ?M) at pH 3 to 
determine the wavelength of the ligand in the aqueous phase (no uranyl). A) Organic 
phase, time plotted at 245 nm. B) Aqueous phase, time plotted at 240 nm. 
 
 32 
The UV-Vis spectra above in figure 15, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time. 
 
A)  
 
 
B)  
 33 
Figure 16: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase 
 
At pH 3 with OR2a and a ratio of 2-1 (metal to ligand), (as shown in figure 16) al of the 
recorded extinction measurements are not above the blank at 39000 extinction units but 
are increasing in extinction maximum at every interval in the organic phase.  The 
extinction increased by 19600 extinction units from 15 minutes to the 2
nd
 hour 
measurements; however, after 3 hours, the extinction maxima tightly overlay again, 
possibly indicating the ligand is geting close to maximum extraction eficiency at this 
pH, having already extracted al the uranyl it can into the organic layer.  The extinction 
peaks are also broadening at time increases, which could indicate binding of the uranyl in 
the organic phase.  However, without the shift, the ligand binding is not very strong for 
uranyl.  Instead of al four sulfurs binding to uranyl, possibly only one or two sulfurs are 
binding.  In comparison to control solutions containing ligand in the organic phase, we 
find that at this pH there is some evidence for the transfer of the ligand into the aqueous 
phase. 
 
In figure 15b, depicting the extinction of the aqueous phase from the extraction at pH 3 
with a two-fold exces of uranyl is not straightforward.  The overal trend is that the 
extinction maximum decreases with time.  While the first few measurements at 15 
minutes, 30 minutes, and 1-3 hours are extinction maxima at a wavelength of 240 nm, the 
5, 6, 12, and 24 hour extinction maxima appear to have shifted to approximately 230 nm.  
This is promising but it does not indicate a strong binding and shift of 20-25 nm, as one 
would expect.  This is a definite improvement over the results sen in the characterization 
of extraction at pH 2. In comparison to control solutions containing ligand in the organic 
phase, we find that at this pH there is some evidence for the transfer of the ligand into the 
aqueous phase. The ligand does fluctuate betwen the organic and aqueous layers at this 
pH, which is a problem if it does not form a hydrophobic complex with uranyl. From the 
data above, we believe that there is about 5-65% extraction of uranyl. 
 
 34 
A)  
 
B)  
 
 35 
C)  
Figure 17: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 240 nm. Time plotted at 240 nm 
 
In the UV-Vis spectral data from the organic phase (figure 17) for an extraction of 
ligand:metal 1:1 for the aqueous layer at pH 3, a demonstrable increase in extinction 
maximum at 245 nm is noted.  Also noted is a shift of approximately 10 nm after 12 
hours with an extinction of 30350 a diference of 12400 extinction units from the first 
measurement.  Again this is indicative of a kinetics problem asociated with the ligand 
binding.  If it requires 12 ? 24 hours to bind efectively, although not fully, this wil not 
be good for extractions on an industrial scale.  Betwen the 12
th
 and 24 hour 
measurement, there is only a smal increase of 2000 extinction units indicating that the 
ligand may be reaching full extraction eficiency and equilibrium. 
 
In the aqueous phase, the decrease in maximum extinction
 
of 800 extinction units at 240 
nm is noted, and then at the 12 hour measurement, an increase in maximum extinction of 
4100 extinction units from the 5
th
 hour, but at 235 nm indicating a shift in the wavelength 
of 5 nm from the initial measurements.  At the 24-hour mark, a decrease in extinction 
 36 
maximum to 46700 (overal decrease of 3100 extinction units) was observed also at 235 
nm, indicating that the metal complex was transitioning back into the organic phase.  This 
helps confirm that there is a metal complex in the organic phase as indicated by the shift 
as stated earlier.  It is believed that 30-40% of the uranyl was extracted into the aqueous 
phase. 
 
A)  
 
B)  
 37 
 
C)  
Figure 18: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase Time plotted at 245 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 240 nm. 
 
In figure 18, with an exces of ligand is a similar as compared to the data shown in figure 
15 with exces uranyl.  The early measurements stil feature the extinction maxima at the 
same wavelength as the control without any uranium, and later measurements such as the 
6, 12, and 24-hour measurements, have a shift of 5, 5, and 15 nm respectively.  This 15 
nm shift is indicative of metal complexation and extraction into the organic phase, but the 
slow change confirms slow coordination, a kinetic problem with the ligand.  The shift is 
stil not in the 20-25 nm range typical of strong binding.  Further investigations would be 
needed to probe the nature of this reaction, given the initial slow kinetics and if the rate 
can be improved with heat.  Betwen the 15
th
 minute and 12
th
 hour, there is an increase in 
extinction of 19000 extinction units.  The slowing of the increase extinction maximum 
betwen 12 and 24 hours appears to indicate that the extraction is complete or has 
achieved equilibrium. 
 
 38 
Changes sen in the UV-Vis spectra for the aqueous phase at pH 3 and exces ligand in 
figure 16 are quite remarkable.  It demonstrates that even with exces ligand, more of the 
ligand is likely to remain in the aqueous phase than to transfer back into the organic 
phase.  As time increases, the extinction maximum is decreased and there is a smal shift 
of 5 nm indicating binding in the aqueous phase, although not very strong.  Because 
binding is indicated at the 4
th
 hour, uranyl coordinating ligand may drop imediately into 
the organic layer which is why at the 5
th
 hour, there is a decrease in extinction maximum 
of 4000 extinction units and shift back to the original 240 nm wavelength.  The overal 
decrease in extinction betwen the 15
th
 minute and 24
th
 hour is 5700 extinction units, 
much les than the increase sen in the organic phase. Based on the aqueous phase of the 
control, it is believed that 50-60% of the uranyl is extracted.  This is dificult to confirm 
because of the smal decrease in extinction in the aqueous phase. 
 
 
Figure 19: Graph of extinction versus time for OR2a at pH 3 in the organic phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
 
 
 
5"
10"
15"
20"
25"
30"
35"
40"
45"
15"
Mi
n
u
t
e
s
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Mi
n
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t
e
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Ho
u
r
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Ho
u
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"
Ho
u
r
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4
"
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u
r
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5
"
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"
6
"
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?
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&M
(1&
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OR2a&pH&3&ORG&
 39 
OR2a pH 4 
 
A)  
 
B)  
Figure 20: UV-Vis spectrum absorbance vs. wavelength of the control of OR2a at pH 4. 
A) Organic phase, time plotted at 245 nm. B) Aqueous phase, time plotted at 235 nm. 
 
 40 
The UV-Vis spectra above in figure 20, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  The 
ligand even takes some time before equilibrium is reached in the aqueous phase. It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time. 
 
A)  
 
 
B)  
 41 
Figure 21: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase; B) Aqueous phase. Time plotted at 235 nm. 
 
In the figure above, with OR2a at pH 4, and a ratio of 2-1 (metal to ligand) in the organic 
layer, an imediate shift of 5 nm and an extinction of 27300 units are noted.  At the 1-
hour measurement, the extinction maximum is decreased to an extinction of 4870 and the 
shift is returned to the ligand blank at 245 nm.  At the 2
nd
 hour measurement a shift of 10 
nm is noted with an extinction of 6450, an increase of 1580 extinction units over the 1
st
 
hour.  At the 3
rd
 hour, a shift in extinction maximum of 5 more nm is noted with an 
increase in the extinction maximum by 4000 units. At the 4
th
 hour measurement a 5 nm 
shift back towards the ligand blank and a decrease in extinction maximum is noted.  An 
increase of 10600 extinction units at a wavelength of 230 nm betwen the 5
th
 and 24
th
 
hour is a good indication of extraction of uranyl into the organic phase and binding of the 
metal-ligand complex.  More measurements past this time frame would be good for 
determining if the ligand had reached its extraction eficiency at this pH. 
 
This is very diferent from the aqueous phase in figure 20c, where there is a decrease in 
extinction maxima without any fluctuations.  Similar to what was sen in the control with 
OR2a and no uranyl, the first measurement at 15 minutes an extinction maximum at 240 
nm is noted.  After this measurement, a shift of 5 nm to 235 nm is noted for al 
measurements up until the 12
th
 hour measurement where another shift of 5 nm of 
extinction maximum wavelength is noted.  An overal decrease of 1000 extinction units, 
while smal compared to the organic phase, is stil an indication of the bound metal-
ligand complex, going from the aqueous phase into the organic phase.  The shift shows 
the ligand is binding stronger than at pH 2 or 3 in the aqueous phase.  While it is good for 
the ligand to bind to uranyl in the aqueous phase, it is not good if the metal-ligand 
complex is hydrophilic, as that wil hinder extraction.  It does not sem to have afected 
extraction in this case as the extinction maximum increases in the organic phase and 
decreases in the aqueous phase as noted.  65-75% of the uranyl is believed to be extracted 
after 24 hours. 
 42 
 
A)  
 
B)  
Figure 2: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase; Time plotted at 235 nm. B) Aqueous phase. Time plotted at 240 nm 
 
 43 
In figure 2 above, with OR2a (10 ?M) at pH 4 and that ratio now equal (1:1 metal to 
ligand), in the organic layer, there are a lot of similarities to both the exces ligand in 
figure 21 and exces uranyl in figure 19, in that there are wel defined maximum 
extinction shifts with increasing time.  While there is an extinction maximum wavelength 
shift at 30 minutes, and an increase in extinction maximum by 300 extinction units, the 1 
hour time measurement the extinction maximum is shifted back to the extinction 
maximum wavelength of the blank and a decrease of 1000 extinction units.  An overal 
increase of 12000 extinction units from the lowest extinction measurement at 1 hour, and 
an increase in the maximum extinction wavelength shift to 10 nm from the blank confirm 
an extraction and binding of uranyl by the ligand in the organic phase. Since the 
extinction maximum is increasing and decreasing over time, coupled with the wavelength 
shifts, it can be concluded that a complex is being formed.  However, the binding cannot 
be determined as it would appear some of the metal ligand complexes being formed are 
not stable for very long.  There could also be a third phase formation hindering the 
extraction kinetics.   
 
This aqueous phase spectrum is slightly diferent than what is sen in the organic phase.  
In the aqueous phase, there is a decrease of 1700 extinction units betwen the first 
measurement and the last measurement.  Although a greater increase is sen in the 
organic phase, it is correlated wel with the data in the aqueous phase.  No shift in the 
extinction maximum wavelength from the blank is noted in the aqueous phase, and while 
this is not indicative of strong binding to uranyl in the aqueous phase, the metal-ligand 
complex could be somewhat hydrophobic and transfer into the organic phase as soon as it 
is formed.  Instead of al four sulfurs coordinating to uranyl, only two, or possibly even 
one sulfur is binding, which would cause the extinction to shift in the organic phase.  
With a decrease in extinction as time increases, the hypothesis of third layer formation 
could be dispeled.  After 24 hours, only 60-70% of the uranyl is believed to have been 
extracted into the organic phase. 
 
 
 44 
A)  
 
 
B)  
Figure 23: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase; B) Aqueous phase. Time plotted at 235 nm.; 
 
 45 
In figure 23 above, with OR2a at pH 4 and a ratio of 1-2 (metal to ligand) in the organic 
layer, the extinction maximum is increasing as an overal trend.  An overal increase in 
extinction of 15100 extinction units is indicative of good extraction.  With the initial 
measurement at 15 minutes, we se a 10 nm shift to 230 nm is noted.  This is a shift of 10 
nm from the ligand blank.  This shift stays consistent throughout al the measurements 
indicating binding with uranyl, although it is not strong, thus indicating that not al four 
sulfurs are binding uranyl.  Perhaps, only one or two sulfurs are binding uranyl.  Further 
investigation is needed to probe the rate of extraction, as the biggest increase in 
extinction maximum was not sen until the 24-hour measurement.   The extinction 
maximum in the aqueous phase is decreasing, indicating that the ligand coordination and 
metal complex is being taken into the organic phase.  A decrease of 1300 extinction units, 
while not a lot compared to the organic phase, confirms that the metal-ligand complex is 
transitioning into the organic phase.   It is not until the 5
th
 hour that a shift of 5 nm is 
noted.  This indicates that at this ratio and pH, the ligand binding is not very strong for 
uranyl in the aqueous phase.  However, when the metal complex is transferred into the 
organic phase, the binding sems to be stronger as indicated by the longer shift in 
extinction maximum wavelength of 10 nm.  After 24 hours, it is believed that 70-80% of 
the uranyl was extracted. 
 
 46 
 
Figure 24: Graph of extinction versus time for OR2a at pH 4 in the organic phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
OR2a pH 5 
 
A)  
 
0"
5"
10"
15"
20"
25"
30"
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*1
0
3
&M
(1&
cm
(1&
Time&
OR2a&pH&4&ORG&
 47 
B)  
 
C)  
Figure 25: UV-Vis spectrum of the control of OR2a at pH 5. A) Organic phase, time 
plotted at 240 nm. B) Overal aqueous phase spectrum; B) Close up around 235 nm. Time 
plotted at 235 nm. 
 
The UV-Vis spectra above in figure 25, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  The 
ligand is not reaching equilibrium as evidenced by the changing betwen increases and 
 48 
decreases in extinction maximum at diferent time measurements.  With a longer time 
frame, we would expect to se equilibrium reached and decrease in extinction indicating 
the ligand would transfer back into the organic phase.   
 
A)  
 
 
B)  
 49 
 
 
 
C)  
Figure 26: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase; Time plotted at 245 nm. B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
In the organic phase with OR2a at pH 5 and a ratio of 2-1 (metal to ligand) in figure 26, 
there is a general increase in extinction maximum especialy for the 6, 12, and 24-hour 
measurements. An overal increase of 3800 extinction units from the first measurement at 
15 minutes til the 24
th
 hour is noted.  A shift of 5 nm in extinction maximum wavelength 
is noted at 15 minutes, as wel as a shift of 5 nm more for 30 minutes.  This shift remains 
there until the 6
th
 hour measurement when it shifts back towards the blank extinction 
maximum wavelength of 5 nm.  This shift at 240 nm remains for the 12 and 24-hour 
measurements.  The 10 nm shift would indicate stronger coordination, but since it does 
not remain at that wavelength for very long, we can conclude that the metal-ligand 
complex is not very stable with stronger binding, and is more stable with a weaker 
binding over a long period of time. 
 
 50 
The aqueous phase indicates that the ligand takes at least an hour to equilibrate at this pH 
and ratio or metal to ligand.  15 Minutes is the lowest extinction maximum with 11700 
extinction units.  The overal increase in extinction maximum of 2600 units is not typical 
of what has been observed before.  It would appear as though the ligand is establishing 
equilibrium in the aqueous phase with any metal-ligand complexes formed being 
hydrophobic and transferring into the organic phase. To correlate the two phases, there 
would need to be a decrease in extinction maximum in the aqueous phase, at the same 
time as in increase in the organic phase.  No shift in extinction maximum wavelength is 
noted; indicating coordination of the uranyl ion is not weak, when using the maximum 
extinction in the controls at 235 nm.  The % extraction at pH 5 and with an exces of 
uranyl is estimated to be roughly 80%. 
 
 
A)  
 
 51 
B)  
 
C)  
Figure 27: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase;Time plotted at 240 nm. B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
 52 
In the organic phase with OR2a at pH 5 and a ratio of 1-1 (metal to ligand) in figure 27, 
there is a general increase in extinction maximum especialy for the 12 and 24-hour 
measurements.  A significant increase of 13100 extinction units from lowest extinction 
measurement (1 hour) til the 24
th
 hour is noted.  It is not until the 4
th
 hour that an 
extinction maximum shift in wavelength of 5 nm is noted.  This shift increases at the 12-
hour measurement by 10 nm to 230 nm.  That is an overal shift of 15 nm from the 
extinction maximum wavelength of the ligand.  While this indicates stronger binding than 
anything sen before, it is not in the 20-25 nm extinction maximum wavelength shift that 
would indicate strong binding.  To speculate, the 15 nm shift could be three of the sulfurs 
coordinated to one uranyl, or one sulfur coordinated to one uranyl and one sulfur 
coordinated to another uranyl.  It is hard to determine from the data what the binding is. 
 
In the aqueous phase, there are increases in extinction maxima for the first 30 minutes 
before decreasing at the 1 and 2 hour measurements.  The sharp increase in the 3
rd
 and 4
th
 
measurements is noted, as wel as the decrease in the next two hours.  This increase and 
decrease in maximum extinction is indicative of the ligand trying to find equilibrium in 
the aqueous phase, or possibly, there is a hydrophilic metal-ligand complex but is not 
coordinated strongly to cause a shift in the extinction maximum wavelength.  Instead of 
al four sulfurs binding to uranyl, only one or two sulfurs are binding to uranyl, if it is 
binding at al in the aqueous phase.  At an equimolar ratio at pH 5, like the other 1-1 
ratios at other pHs, there is les extraction compared to exces uranyl or exces ligand, 
and in this case, it is estimated that only 50-60% uranyl was extracted. 
 
 53 
A)  
 
 
B)  
 
 54 
C)  
Figure 28: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR2a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 240 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
In the figure above, with OR2a at pH 5 and a ratio of 1-2 (metal to ligand) in the organic 
layer, an overal decrease in extinction maximum of 4000 extinction units for 15 minutes, 
30 minutes, and 1 hour at a wavelength of 245 nm is noted.  An increase of 19100 
extinction units from the lowest maximum extinction measurement at 1 hour is noted.  
The 12
th
 hour measurement is also when the first maximum extinction wavelength shift 
of 5 nm is noted.  The ligand was able greatly increase extraction, but it took 24 hours for 
it to happen, leading to a belief of a kinetic problem.  The wavelength shift is an 
indication of binding in the metal-ligand complex, but only 1 or 2 sulfurs is binding, and 
not al four that would cause a 20-25 nm shift. 
 
The aqueous phase is very similar to the aqueous phase of the control sen in figure 22.  
The extinction maximum is increasing and decreasing trying to establish equilibrium.  
When there is the significant increase in extinction maximum in the organic layer, there 
is not a decrease in extinction maximum in the aqueous phase, there is actualy an 
 55 
increase of 2000 extinction units. No shifts in extinction maximum wavelength are noted 
for the aqueous layer indicative of not weak coordination of uranyl by the ligand.  With 
the increase of extinction maximum betwen the 12
th
 and 24
th
 hour, it can be concluded 
that, because there is an exces of ligand in solution, when the metal-ligand complex 
forms and transfers into the organic phase, more or equal amount of free ligand is 
equilibrated in the aqueous phase. While it is estimated that only 10-15% of the uranyl 
was extracted after 12 hours, the % extraction jumps up to about 80-90% after 24 hours. 
 
OR3a pH 2 
 
A)  
 
 56 
B)  
 
C)  
Figure 29: UV-Vis spectrum absorbance vs. wavelength of the control of OR3a at pH 2.  
A) Organic phase, time plotted at 245 nm B) Overal aqueous phase spectrum; B) Close 
up around 250 nm. Time plotted at 250 nm. 
 
 
 57 
The UV-Vis spectra above in figure 29, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there and even 
form an equilibrium for a relatively short period of time.  It wil however, transition back 
into the organic phase slowly over time as evidenced by the decrease in extinction over 
time.     
 
 
A)  
 
 
 58 
B)  
 
C)  
Figure 30: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm.; B) Aqueous phase; C) Close up of aqueous 
phase around 245 nm. Time plotted at 245 nm. 
 
 59 
In the figure above, with OR3a at pH 2 and a ratio of 2-1 (metal to ligand), in the organic 
layer, the extinction maximum is generaly increasing.  The largest increase in extinction 
maximum is betwen the 12
th
 and 24
th
 hour measurements where the increase is 18200 
extinction units.  This correlates to the decrease of 2600 extinction units of extinction 
maximum sen in the aqueous phase at the same time frame.  This is an indication that 
the metal-ligand complex is being taken into the organic phase.  The organic phase does 
not exhibit an extinction maximum wavelength shift; however the change in extinction 
maximum is far greater than the efects sen due to changes in pH.  This indicates that at 
this ratio of metal to ligand maintained at this pH, the ligand binding is not very strong 
for uranyl.  Instead of al four sulfurs coordinating to uranyl, only two, or possibly even 
one sulfur is binding. 
 
In the aqueous phase we se an increase in extinction maximum until the 6
th
 hour when 
we start geting dramatic drops in extinction maximum.  There is a consistent decrease 
from the 6
th
 hour on of 1600 extinction units each measurement.  While we se the 
increases in the organic phase at these times, we se a drop at the 24-hour measurement 
in the organic phase.  From the hydrolysis data above, a second possibility is that the 
ligand could by hydrolyzing with the addition of the metal salt (decreasing below pH 2), 
the ligand-metal complex is not stable for very long. It is believed that only 60% uranyl 
was extracted at this pH.  It is dificult to ascertain precisely at such a low concentration 
and the ligand hydrolyzing.   
 
 60 
A)  
 
B)  
Figure 31: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase. Time Plotted at 240 nm. 
 
In the organic phase of figure 31 above, with OR3a at pH 2 and a ratio of 1-1 (metal to 
ligand), the extinction maximum at 30 minutes decreases by 5100 extinction units.  It 
 61 
then increases at 1 hour to 67000, a diference of 9100 extinction units.  At the 2 hour 
measurement is another decrease of 2800 extinction units, followed by an increase of 
1700 extinction units at the 3
rd
 hour measurement. A diference of 36500 extinction units 
separates the highest maximum extinction at 48 hours from the lowest at 30 minutes.  The 
drop at 24
th
 hour measurement in the organic phase is confirmed with an increase in 
extinction maximum of 8800 units in the aqueous phase at the same time interval.  The 
increase and decrease of extinction sen in the organic phase could be because of the 
ligand hydrolyzing, or the formation of a third phase, that would make extractions 
dificult.  The only real diference betwen the two phases is that besides the drop in 
extinction maximum at 24 hours, the aqueous phase is constantly increasing in maximum 
extinction.  A shift of 5 nm from the aqueous control experiments for 15 and 30 minutes 
is noted.  After this time, al extinction maximum wavelengths have shifted 10 nm from 
the aqueous control.  While this is not in the 20-25 nm extinction wavelength shift that 
indicates strong coordination, a smal shift is indicative of weak coordination of uranyl to 
the ligand.  Since it occurs in the aqueous phase, we can asume that the ligand-metal 
complex could be somewhat hydrophilic, before being transferred into the organic layer.  
The ligand is believed to have only extracted 70-80% of the uranyl, while it undergoes 
hydrolysis. 
 
 
 62 
A)  
 
B)  
Figure 32: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 2 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase. Time plotted at 240 nm. 
 
 
In figure 32 above, with OR3a at pH 2 and a ratio of 1-2 (metal to ligand), in the organic 
layer, an overal increase in extinction maximum of 12300 extinction units from the first 
 63 
measurement at 15 minutes.  An unexpected decrease in extinction maximum in the 
organic phase, would lead to formation of a third phase, but there is a correlation in the 
aqueous phase where the extinction maximum increases by 6000 extinction units at the 
same time interval.  This is followed by a decrease of 6900 extinction units at the 48 hour 
measurement in the aqueous phase, similar to the 8900 extinction units increase noted in 
the organic phase.  There is not an observed shift of extinction maximum in the organic 
phase; however, in the aqueous phase, we se an imediate 10 nm extinction maximum 
wavelength shift for al measurements except for the 48-hour measurement, where there 
is an extinction maximum wavelength shift of 15 nm.  While there is also a shift of 15 nm 
sen at the 3
rd
 hour, with the next five measurements having only a 10 nm shift from the 
controls, this could be an anomaly but is duly noted.  The extinction maximum 
wavelength shifts are indicative of stronger coordination with uranyl than was sen in a 
similar ratio with OR2a.  A reason could be with the extra two carbon atoms in the linker, 
the ligand is able to wrap around the uranyl ion beter and promote binding. The ligand is 
hypothesized to have only extracted 20-30% of the uranyl in this case. 
 
 
Figure 33: Graph of extinction versus time for OR3a at pH 2 in the organic phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
0"
50"
100"
150"
200"
250"
300"
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*1
0
3
&M
(1&
cm
(1&
Time&
OR3a&pH&2&ORG&
 64 
OR3a pH 3 
 
A)  
 
B)  
Figure 34: UV-Vis spectrum absorbance vs. wavelength of the control of OR3a at pH 3. 
A) Organic phase, time plotted at 245 nm. B) Aqueous phase time plotted at 240 nm. 
 
 
 65 
The UV-Vis spectra above in figure 34, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time. 
 
A)  
 
B)  
 
 66 
C)  
Figure 35: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 240 nm; B) Aqueous phase; B) Close up of aqueous phase 
around 240 nm. Time plotted at 240 nm. 
 
In the organic phase with OR3a at pH 3 and ratio of 2-1 (metal to ligand) (figure 35A), 
the majority of the measurements overlap each other at 245 nm until the 3
rd
 hour, when 
there is a more noticeable increase in extinction maximum to an extinction of 44800 
extinction units.  An increase of 6500 extinction units occurs betwen 15 minutes and 12 
hours.  However in the 24
th
 hour, there is a demonstrable decrease in extinction 
maximum of 7400 and a shift in extinction maximum wavelength of 5 nm more, a total of 
10 nm from the ligand blank.  Next though, is a decrease in the maximum extinction 
wavelength of 5 nm, but a monumental increase of 10500 extinction units, indicative of 
extraction.  With the time length to cause significant increases in extinction, a kinetic 
problem may be indicated. 
 
In the aqueous phase, betwen 15 minutes and 48 hours, there is an increase of 1900 
extinction units.  We want to se the spectra decrease in extinction, indicative of ligand 
 67 
metal complex transferring into the organic phase.  There is a decrease in the extinction 
maximum after the ligand establishes equilibrium at the 24-hour measurement.  The 
sudden increases and shifts correspond to the shift and increase noted in the organic 
phase at the same time interval.  It can be concluded that while there was strong 
coordination of uranyl by the ligand, it was not a stable complex in either phase.  It is 
hypothesized that OR3a extracted approximately 20-30% of the uranyl from the aqueous 
phase into the organic phase. 
 
A)  
 
 
 68 
B)  
Figure 36: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 245 nm; B) Aqueous phase. Time plotted at 240 nm. 
 
In the figure above, with OR3a at pH 3 and a ratio of 1-1 (metal to ligand) in the organic 
phase, there is an increase in extinction maximum betwen 15 minutes and 48 hours of 
20300 extinction units.  The most significant increase in extinction maximum is at 12 
hours where there is an increase of 5600 extinction units before a sharp decrease of 5500 
extinction units and a shift of 5nm more in extinction maximum for a total of 10 nm from 
the blank.  The 48-hour measurement shows a shift of 5 nm back towards the ligand 
blank and an increase in extinction maximum of 10800 extinction units.  The decrease 
and shift in extinction sen at the 24
th
 hour, is what has been observed in al ratios at this 
pH.  The ligand could have stronger coordination but is not a stable complex for long 
which is why there is a shift back towards the ligand blank at 48 hours.  Another 
explanation could be of a third layer formation, causing the extra shift and decrease in 
extinction. 
 
In the aqueous phase, there are some overlaps in extinction maxima at 30 minutes and 1-3 
hours, 4-6 hours, and 12 and 24 hours.  It would sem as though the ligand established 
and equilibrium, and then maybe some extraction happens, and it has to establish another 
 69 
equilibrium.  There is a general decrease in the extinction with a change of 10300 
extinction units betwen the first measurement at 15 minutes and the last measurement at 
48 hours.  At the even ratio, there is much les extraction and is predicted that about 40-
50% of the uranyl was extracted. 
 
A)  
 
 
 
 
 
 70 
B)  
Figure 37: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase. Time plotted at 240 nm. 
 
In the figure above, with OR3a at pH 3 and a ratio of 1-2 (metal to ligand), in the organic 
phase there is an overal increase in extinction maximum as time increases.  While the 
15-minute measurement exhibits no shift in extinction maximum wavelength, subsequent 
measurements measure a 5 nm shift except for the 24-hour measurement, where a 10 nm 
shift in extinction maximum wavelength is noted.  The extra 5 nm shift at the 24
th
 hour 
would indicate a stronger coordination of ligand to uranyl, however, it does not appear to 
be stable for more than a day as the 48 hour measurement is equal to the 5 nm extinction 
maximum wavelength shift sen in previous measurements in this spectra.  The 
extinction maxima at 30 minutes and 1 hour almost overlap each other.  Also the 
extinction maxima at the 3rd and 4
th
 hour almost overlap each other, indicative of very 
litle or no increase of metal-ligand complex coming into the organic phase.  An overal 
increase in extinction maximum of 20400 extinction units shows that there is an excelent 
amount of extraction as compared to pH 2.   
 
There is almost the same overlap in extinction maxima that is sen in the organic phase, 
but in the aqueous phase, it?s betwen 30 minutes and 2
nd
 hour, 3
rd
 and 1
st
 hour, and 4
th
, 
 71 
5
th
, and 6
th
 hour.  What is interesting is that none of these correlate with the overlaps in 
extinction maxima sen in the organic phase. A diference of 20200 extinction units 
separates the first measurement at 15 minutes from the last measurement at 48 hours.  
The extinction maximum in the aqueous phase does not have a shift off of the controls 
aqueous phase at 240 nm.  This would mean that the ligand binding is not very strong for 
uranyl in the aqueous phase, or when the ligand binds to uranyl, it is a hydrophobic 
complex and transfers into the organic phase. The ligand could be binding with just one 
or two sulfurs, instead of al four sulfurs.  We believe that about 50-60% of the uranyl 
was extracted from the aqueous phase. 
 
 
Figure 38: Graph of extinction versus time for OR3a at pH 3 in the organic phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
25"
30"
35"
40"
45"
50"
55"
?
*1
0
3
&M
(1&
cm
(1&
Time&
OR3a&pH&3&ORG&
 72 
 
Figure 39: Graph of extinction versus time for OR3a at pH 3 in the aqueous phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
OR3a pH 4 
 
A)  
 
0"
10"
20"
30"
40"
50"
60"
70"
?
*1
0
3
&M
(1&
cm
(1&
Time&
OR3a&pH&3&Aq&
 73 
B)  
 
C)  
Figure 40: UV-Vis spectrum of the control of OR3a at pH 4. A) Organic phase, time 
plotted at 250 nm. B) Overal aqueous spectrum; B) Close up around 235 nm. Time 
plotted at 235 nm. 
 
The UV-Vis spectra above in figure 40, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
 74 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time and form an equilibrium as sen in the smaler decreases 
in extinction betwen 12, 24, and 48 hours. 
 
A)  
 
B)  
 
 75 
C)  
Figure 41: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm 
 
In figure 41, with OR3a at pH 4 and a ratio of 2-1 (metal to ligand), in the organic phase, 
there is an increase of 10600 extinction units betwen 15 minutes and 72 hours.  The 
smaler increase noted betwen 48 and 72 hours could be an indication that the ligand is 
beginning to reach maximum extraction eficiency.  There is a smal 5 nm extinction 
maximum wavelength shift that is indicative weak coordination of uranyl to the ligand. 
 
In the aqueous phase, there is an overal increase in extinction until the 12
th
 hour when 
there are decreases in extinction.  The absorbencies overlap with each other, indicative of 
the ligand being in equilibrium betwen the two phases.  When there is the monumental 
decrease in absorbencies betwen 12 and 24 hour and 24 and 48 hours is a good 
indication of the metal-ligand complex transferring into the organic phase.  The decreases 
are 300 and 200 extinction units respectively, also an indication that the ligand may be 
reaching extraction eficiency, especialy since the 72
nd
 hour measurement goes back to 
the equilibrium extinction sen in the earlier measurements. These decreases in extinction 
maxima correlate wel with the increase of extinction maxima in the organic phase.  
 76 
There is not a shift a shift from the control containing no uranyl, indicative of weak 
coordination betwen uranyl and the ligand.  With the extinction being higher, it is 
estimated that extraction is in the 20-30% range. 
 
A)  
 
B)  
 
 77 
C)  
Figure 42: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
With OR3a at pH 4 and a ratio of 1-1 (ligand to metal) (figure 42) in the organic layer, 
there is an always-increasing extinction maximum at 250 nm at each measurement, a 5 
nm shift from the blank.  An increase of 12900 extinction units betwen 15 minutes and 
72 hours is noted.  The 12 and 24-hour measurements overlap each other, indicative of no 
increase of ligand-metal complex in the organic phase. It would appear that the ligand 
takes up to 48 hours to provide significant extractions and then could be slowing down, 
indicative of reaching extraction eficiency.  More data at longer time intervals would be 
needed to support that hypothesis. 
 
The spectral changes with time of the aqueous layer are quite interesting.  In the control, 
the ligand wil freely go into the aqueous layer at pH 4 and remain there.  With an exces 
of ligand or uranyl, ligand goes into the aqueous phase, and some of the ligand wil 
remain there, while the rest wil coordinate metal and equilibrate with the organic phase. 
There should be a decrease in extinction maximum in the aqueous phase, but instead 
 78 
there is an increase as noted. There is a decrease until the 72
nd
 hour, when the extinction 
goes back to the equilibrium extinction sen at earlier measurements. This would be an 
indication of the ligand reaching the maximum extraction eficiency.  This is the first 
time that a 1-1 ratio has a higher extinction than an exces of either ligand or uranyl, and 
therefore estimated to have 30-40% extraction. 
 
 
A)  
 
 
 79 
B)  
 
 
C)  
Figure 43: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 4 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
 
 80 
With OR3a at pH 4 and a ratio of 1-2 (ligand to metal) in the figure above, in the organic 
phase, there is a constant increase in extinction maximum at each measurement.  Each 
measurement has also had an extinction maximum wavelength shift of 5 nm indicative of 
coordination, although weak.  The overal increase in maximum extinction is 7000 
extinction units, this constant increase in maximum extinction indicates that the uranyl is 
being extracted, but is disconcerting that it does take up to 24 hours to se a significant 
diference in the extinction indicative of beter extractions.  A longer time frame would 
be needed to se if and when maximum extraction eficiency is achieved. 
 
In the aqueous phase, there is an overal trend of decreasing extinction with increasing 
time.  The extinction decreases for the first two hours, but then suddenly increases by 400 
extinction units in the third hour, before decreasing by 1400 extinction units in the 4
th
 
hour.  It?s not until the 12
th
 hour before there is a consistent decrease in the extinction 
with a diference of 4400 extinction units betwen the 12
th
 hour and the 48
th
 hour. No 
shift from the aqueous control is noted, where it can be concluded that in the aqueous 
phase, coordination of uranyl by the ligand is weak, and that the metal-ligand complex 
could be hydrophobic and imediately transfer into the organic phase when the complex 
is formed. At this higher pH, the ligand does not appear to extract uranyl as wel as at pH 
3, and therefore it is estimated that only 20-30% of the uranyl is extracted.  
 
 81 
 
Figure 44: Graph of extinction versus time for OR3a at pH 4 in the organic phase. ?? 2-
1 ratio, ++ 1-1 ratio, - - 1-2 ratio (metal to ligand) 
 
OR3a pH 5 
 
A)  
 
0"
5"
10"
15"
20"
25"
30"
35"
?
*1
0
3
&M
(1&
cm
(1&
Time&
OR3a&pH&4&ORG&
 82 
B)  
 
C)  
Figure 45: UV-Vis spectrum of the control of OR3a at pH 5. A) Organic phase, time 
plotted at 250 nm.  B) Overal aqueous spectrum; C) Close up around 235 nm. 
 
The UV-Vis spectra above in figure 45, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
 83 
decrease in extinction over time.  The extinction decrease appears to happen in groups of 
a few measurements at a time.  The first 1-hour measurements are al closely asociated 
with each other, and then hours 2-4, then hours 5-24, and finaly 48 and 72 hours.  
Perhaps the ligand is equilibrating after a certain amount is transferred back into the 
organic phase. 
 
 A)  
 
B)  
 84 
 
C)  
Figure 46: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 235 nm; B) Aqueous phase; C) close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
In figure 46, with OR3a at pH 5 and a ratio of 2-1 (metal to ligand), in the organic phase, 
there is a consistent increase in steady increase in extinction maximum for the first 24 
hours of 700 extinction units each measurement.  It?s not until the 48
th
 hour is there a 
dramatic increase in maximum extinction and an overal increase of 6700 extinction 
units. The smaler increase at 72 hours compared to 48 hours is indicative of the ligand 
reaching maximum extraction eficiency.  For al measurements, there is a 5 nm 
extinction maximum wavelength shift, indicating weakly coordinated uranyl to the 
ligand.  Instead of al four sulfurs binding, only two or perhaps even one sulfur is binding 
the metal. 
 
The spectral changes with time of the aqueous layer are quite intriguing.  The maximum 
extinction has a decrease of 1900 extinction units betwen 15 minutes and 72 hours.  The 
aqueous layer does correspond to the smaler increase of extinction maximum in the 
 85 
organic phase with a smaler decrease in the aqueous phase betwen 48 and 72 hours of 
200 extinction units as compared to the previous measurement.  The aqueous phase 
shows no extinction maximum wavelength shift from the aqueous layer of the control, 
containing only ligand and no uranyl.  This could be from weakly coordinated uranyl to 
the ligand, or the formation of a hydrophobic metal-ligand complex in the aqueous layer.  
At pH 5, more than likely out of the best pH for extractions, it is estimated that only 10-
20% of the uranyl is extracted based on the data above.  
 
A)  
 
 86 
B)  
 
C)  
Figure 47: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
With OR3a at pH 5 and a ratio of 1-1 (metal to ligand) in figure 47, in the organic layer, 
much like what was sen at the other ratios of exces ligand and exces uranyl, there is a 
consistent increase in extinction maximum with the biggest increases coming betwen the 
 87 
24
th
 and 48
th
 hour, and the 48
th
 and 72
nd
 hour, with an increase overal of 6100 extinction 
units. There is also a shift of 5 nm in extinction maximum wavelength from the very first 
measurement indicative of a weakly binding metal-ligand complex in the organic phase.  
The late increase in extinction maximum at the 48-hour measurement indicates a kinetic 
isue with the extraction and the smaler increase in the 72
nd
 hour, would be indicative of 
the ligand possibly reaching maximum extraction eficiency at this pH and ratio. 
 
In the aqueous phase, as is sen in al the other aqueous phases at this pH, the extinction 
maximum fluctuates until the 12
th
 hour where there is consistently a decrease.  The most 
important spectra are the 48
th
 and 72
nd
 hour measurements.  These spectra correlate wel 
with the organic phase, where there were big increases in extinction maximum betwen 
24 and 48 hours, and a smaler increase betwen the 48
th
 and 72
nd
 hours, there are big 
decreases in the aqueous phase betwen 24 and 48 hours, and a smaler decrease betwen 
the 48
th
 and 72
nd
 hour measurements.  While this decrease is smal compared to the other 
ratios at this pH, it does fal in line with what would be expected.  The overal decrease in 
extinction is 2700 extinction units betwen the measurements at 15 minutes and 72 hours.  
While les than what is sen in the organic phase, this could just be an indication of 
ligand at equilibrium in the aqueous phase.  Acording to the data, it is hypothesized that 
only 10-20% of the uranyl was extracted. 
 
 88 
A)  
 
 
B)  
 
 89 
C)  
Figure 48: Graph of extinction vs. wavelength for the extraction of uranyl (5 ?M) from 
the aqueous phase (H
2
O) at pH 5 by OR3a (10 ?M) in the organic phase (DCM). A) 
Organic phase. Time plotted at 250 nm; B) Aqueous phase; C) Close up of aqueous phase 
around 235 nm. Time plotted at 235 nm. 
 
In figure 48 above, with OR3a at pH 5 and a ratio of 1-2 (metal to ligand) in the aqueous 
phase, an imediate shift in extinction maximum wavelength from the ligand blank of 5 
nm at the first measurement is noted.  This is indicative of a weakly coordinated uranyl to 
the ligand where only two, or possibly even one sulfur is bound to the metal instead of al 
four sulfurs.  There is an always-increasing maximum extinction at each time 
measurement except for the 12
th
 hour measurement.  An overal increase of 7600 
extinction units is noted.  As was sen in the 2-1 (metal to ligand) ratio, al the 
measurements are grouped together with a slight increase over time, and then at 48 hours, 
there is a huge increase in extinction maximum, with a slightly les increase in the 72
nd
 
hour.  
 
While the general trend of the aqueous phase is decreasing extinction maximum, it?s not 
until the 24
th
 hour that there is a consistent decrease. An overal decrease of 6600 
 90 
extinction units betwen 15 minutes and 72 hours, with a note that at 6 hours the 
extinction is actualy lower, which could be an outlier.  This could be an indication that 
the ligand is in equilibrium, and because of the exces ligand, the equilibrium hypothesis 
makes sense because the overal decrease is also consistent with the overal increase sen 
in the organic phase, indication extraction of uranyl. Using the data above, it is estimated 
that only 20-30% of the uranyl was extracted from the aqueous phase.  
 
Extractions with SDS 
To se if there was a possibility of the ligand aggregating with itself, we had a surfactant, 
sodium dodecyl sulfate (SDS) or sodium lauryl sulfate, as it is also known.  These 
extractions were done at a pH of 3, and a 5?M concentration of SDS in the organic layer. 
 
OR3a pH 3 SDS 
A)  
 
 91 
B)  
Figure 49: UV-Vis spectrum of OR3a with SDS control at pH 3. A) Organic phase, time 
plotted at 240 nm. B) Aqueous phase 
 
The UV-Vis spectra above in figure 49, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time 
 
A)  
 92 
 
B)  
 
C)  
Figure50: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) in the organic 
phase (DCM). A) Organic phase. Time plotted at 240 nm; b) aqueous phase; c) close up 
of aqueous phase around 235 nm. Time plotted at 235 nm. 
 93 
In the organic phase of figure 50, with OR3a, SDS, and a ratio of 2-1 (metal to ligand), 
there is a general decrease in extinction maximum until the 5
th
 hour, where an increase in 
extinction maximum in noted.  Another decrease in maximum extinction at the 6
th
 hour 
measurement, before there is a consistent increase in extinction for the 12, 24, 48, and 72-
hour measurements.  What there should be is a consistent increase in maximum 
extinction and not a fluctuation to have good extractions data.  The fluctuation could be 
the ligand establishing equilibrium before any binding.  It is not until the 6
th
 hour is there 
a shift in maximum extinction wavelength of 5 nm.  The 5
th
 hour measurement, that is 
high in extinction and has a shift in wavelength of 10 nm from the ligand blank, would be 
an indication of a stronger coordinating complex, but is not stable in the organic phase for 
long, as evidenced by the sharp decrease and maximum extinction wavelength shift back 
towards the ligand blank by 5 nm. 
 
In the aqueous layer, there is a shift in maximum extinction wavelength of 15 nm from 
the aqueous control, which contained no uranyl and only ligand with SDS.  This shift 
disappears after 1 hour and goes back to the control wavelength of 235 nm.  There may 
have been a complex formed in the aqueous layer, but it was not stable and did not 
transfer into the organic phase.  There is a decrease of 1500 extinction units in the 
extinction maximum betwen the 48 and 72
nd
 hour measurements.  This shift and 
decrease in maximum extinction are indicative of a weakly binding metal-ligand complex 
and that it is transferring into the organic phase, much like the increases sen in the 
organic phase.  The fluctuation would indicate that the ligand is trying to reach 
equilibrium or is at equilibrium.  With the data in hand, it is estimated that about 30-40% 
of the uranyl was extracted. 
 
 94 
A)  
 
 
B)  
 
 95 
C)  
Figure 51: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) in the organic 
phase (DCM). A) Organic phase. Time plotted at 235 nm; B) Aqueous phase; C) Close 
up of aqueous phase around 235 nm. Time plotted at 230 nm 
 
In the figure above with OR3a and SDS at pH 3 and a ratio of 1-1 (metal to ligand), in the 
organic phase, up until the 24-hour measurement, there is no shift in extinction maximum 
wavelength, a shift of 15 nm after which is observed.  There is a possible shift of 10 nm 
back towards the ligand blank at 48 hours, but the shift goes back to 15 nm from the 
ligand blank at the 72-hour measurement.  Perhaps, the complex at the 48-hour 
measurement was not as stable as it could be, and went back to the stronger coordinating 
complex.  The biggest increase of extinction maximum is 2800 extinction units betwen 
the 48
th
 and 72
nd
 hour measurement.   
 
In the aqueous phase, the ligand takes a few hours to come to equilibrium, but this could 
be due to the extraction of uranyl into the organic phase. The overal diference betwen 
15 minutes and 72 hours was an increase in the extinction of 2100 extinction units.  The 
72-hour measurement was actualy on a decline in the extinction from the two previous 
measurements.  While it is tough to tel, there appears to be a shift of 5 nm from the 
aqueous controls, indicating that ligand is weakly coordinating uranyl in the aqueous 
 96 
phase.  The shift along with the increases and decreases in extinction maxima would 
indicate a slightly hydrophilic metal-ligand complex, but it does not sem to detract from 
the extraction sen in the organic phase.  At this ratio, it is estimated that about 60-70% 
of the uranyl was extracted at this ratio. 
 
         
 
Figure 52: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) in the organic 
phase (DCM). Time plotted at 230 nm. 
 
In the figure above, with OR3a, SDS, at pH 3 and a ratio of 1-2 (metal to ligand), in the 
organic phase, there is an imediate shift of 15 nm in extinction maximum wavelength 
from the ligand blank.  Then there is an ever-increasing extinction maximum as wel.  
This is great extraction data, although there is not the 20-25 nm shift that would indicate 
strong coordination of the uranyl ion, but much stronger than there was without SDS.  
The biggest increase occurs betwen 48 and 72 hours with an increase in extinction of 
7500 extinction units.   The reason for there not being an aqueous phase is that in the 
aqueous phase, there was some problem, that caused it to be cloudy and therefore would 
make the UV-Vis spectra go off the chart.  
 97 
 
OR2a pH 3 SDS 
A)  
 
 
B)    
Figure 53: UV-Vis spectrum of OR2a SDS control at pH 3. A) Organic phase, time 
plotted at 245 nm. B) Aqueous phase 
 
 98 
The UV-Vis spectra above in figure 53, shows that even though the ligand should be 
somewhat hydrophobic; it wil transfer into the aqueous layer and remain there.  It wil 
however, transition back into the organic phase slowly over time as evidenced by the 
decrease in extinction over time 
 
A)  
 
B)  
 
 99 
C)  
Figure 54: Graph of extinction vs. wavelength for the extraction of uranyl (20 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR2a (10 ?M) with SDS (5 ?M) in the organic 
phase (DCM). A) Organic phase. Time plotted at 240 nm; B) Aqueous phase; C) Close 
up of aqueous phase around 230 nm. Time plotted at 230 nm. 
 
In the figure above, with OR2a and SDS at pH 3 and a ratio of 2-1 (metal to ligand), in 
the organic layer, the maximum extinction is increasing at every measurement with an 
overal increase of 8600 extinction units.  Even with the SDS to help prevent aggregation 
of the ligand, there is stil a kinetic isue asociated with extractions.  The first shift in 
extinction wavelength doesn?t occur til the 24
th
 hour, a 5 nm shift, and doesn?t last 
because the spectra shifts back at the 48
th
 hour and doesn?t increase in extinction; 
however, at the 72
nd
 hour, the shift returns along with an increase in extinction, indicative 
that the complex is possibly more stable with the increase in time, and with stronger 
coordination than was noted at previous measurements.  
 
The aqueous phase is similar to the aqueous phases sen with OR3a and SDS.  After 15 
minutes, there is a shift in extinction maximum wavelength of 5 nm from the control 
aqueous phase, but this quickly goes away after 30 minutes.  The extinction maximum 
increases in the 1
st
 hour but then decreases in the 2
nd
 hour.  It decreases even more in the 
third hour but this could be an outlier.  The maximum extinction increases in the 4
th
 and 
 100 
5
th
 hour before decreasing in the 6
th
 hour.  It then increases once again in the 12
th
 and 24
th
 
hour before decreasing in the 48
th
 and 72
nd
 hours.  This does not correlate wel with the 
organic phase, a consistent decrease in extinction maximum would be expected, but the 
fluctuations could indicate and equilibrium trying to be established by free ligand and 
possibly a partialy hydrophilic metal-ligand complex.  Using the data above, it is 
predicted that 70-80% of the uranyl was extracted from the aqueous phase after 72 hours. 
 
 
Figure 55: Graph of extinction vs. wavelength for the extraction of uranyl (10 ?M) from 
the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) in the organic 
phase (DCM). Time plotted at 230 nm. 
 
In the figure above, with OR2a and SDS at pH 3 and a ratio of 1-1 (uranyl to ligand), in 
the organic phase, the general trend is an increase in extinction maximum at each time 
measurement.  There is a shift in extinction maximum wavelength of 10 nm from the 
ligand blank at 240 nm.  A shift of only 5 nm at the 12
th
 hour is noted.  The last 4 
measurements could be considered outliers, as they were above the absorbencies of the 
other measurements at the higher wavelengths.  The increase in maximum extinction and 
the shift is indicative of both good extraction and a somewhat stronger coordination 
metal-ligand complex.  There is not any aqueous phase data for this run, as there was a 
mishap in the aqueous phase, causing it to be cloudy, and would make the extinction of 
 101 
that layer to go off the charts.  Since the organic layer semed unafected for the most 
part, we decided to measure the organic layer and look for the trends. 
 
 
A)  
 
B)  
 
 102 
C)  
Figure 56: Graph of extinction coeficient vs. wavelength for the extraction of uranyl (5 
?M) from the aqueous phase (H
2
O) at pH 3 by OR3a (10 ?M) with SDS (5 ?M) in the 
organic phase (DCM). a) Organic phase; b) aqueous phase; c) close up of aqueous phase 
at 235 nm. Time plotted at 230 nm 
 
In figure 56 above, with OR2a and SDS at a ratio of 1-2 (metal to ligand), in the organic 
phase, there are similarities to what was noted at the 2-1 ratio like there is not a shift in 
extinction wavelength until the 12
th
 hour, and then there is a shift of 5 nm.  There is an 
increase of 12200 extinction units overal in the organic phase.  The shift noted would be 
rationale for a weakly coordinated uranyl to the ligand, as it is not in the 20-25 nm range 
of a strongly coordinated complex.  Two sulfurs, or perhaps even one sulfur could be 
binding to uranyl, instead of the four that would cause the 20-25 nm shift.  While it is 
unclear if the SDS is helping with the binding or acting as a co-extractant. 
 
The aqueous phase is no diferent than any of the other aqueous phases that have been 
noted with either OR3a or OR2a with SDS.  There is an increase in extinction for the first 
2 hours, while a decrease is sen at the 3
rd
 hour (possible outlier).  There are increases in 
both the 4
th
 and 5
th
 hour before another decrease in extinction in the 6
th
 hour.  There are 
increases until the 72
nd
 hour, when there is a decrease, although smal.  The fluctuation in 
the extinction maximum is more than likely the ligand trying to equilibrate in the aqueous 
 103 
phase.  This does not correlate to what is noted in the organic phase, where there is a 
constant increase in maximum extinction.  At the later measurements, there is an 
extinction maximum wavelength shift of 5 nm, indicative of a weakly binding slightly 
hydrophilic metal-ligand complex. With the extinction of the last measurement higher at 
this ratio than with exces uranyl, we believe that 80-90% of the uranyl may have been 
extracted after 72 hours. 
 
After al the extraction data with SDS, while there is help in binding as indicated by the 
increased extinction maxima shifts, it is tough to tel if the SDS is helping with the 
binding by preventing the ligand from aggregating, or acting as a co-extractant.  More 
data would be needed to fully understand the efect. 
 
Sequential Extraction 
 
Since it is sometimes dificult to quantify uranyl extraction, much can be said for the 
value of empirical observations. Uranyl in solution is yelow and it is this color that wil 
turn clear in the aqueous phase indicating extraction.  The organic phase with the ligands 
is clear to slightly cloudy. This phase should turn yelow.  These solutions were 5mM 
ligand in methylene chloride and 5 mM uranyl at pH 3 and 4.  10 mL of each was put into 
a separatory funnel and mixed by shaking for 30 seconds, with venting every 15 seconds.  
The layers were alowed to separate for 10 minutes, and the organic layer siphoned off.  
Fresh organic solvent with ligand was added and the procedure repeated.  Below the 
observations are described. 
 
 
 
 
 
 
 
 
 104 
OR2a pH 3 
   
Figure 57:  Aqueous layer contains uranyl nitrate (5 mM), organic layer contains OR2a 
(5 mM) in DCM; Left:  Before shaking.  Right: Layers separated after shaking. 
 
As can be sen in the first picture, the aqueous (top) layer is a slight shade of yelow 
although hard to se and the organic (bottom) layer is clear. We can se that most of the 
uranyl is extracted after the first organic layer, and then more in the second organic layer.  
Based on clarity of the final solution, it may be completely extracted based on the 
aqueous layer; however, at this pH, this ligand formed a third layer that would not go 
away. Because of this, both the organic and aqueous layers are cloudy and why we 
cannot acquire meaningful UV-Vis data.  This indicates a solvent problem when a third 
layer forms, or the third layer is forming a polymer of ligand and uranyl.  This could be 
the best pH for extractions with this ligand. 
 
OR2a pH 4 
   
Figure 58: Aqueous layer contains uranyl nitrate (5 mM), organic layer contains OR2a (5 
mM) in DCM; Left:  Before shaking.  Right: Layers separated after shaking. 
 
 105 
The first picture like the rest of the first pictures shows a yelow aqueous layer and a clear 
organic layer.  After the first extraction, we se that most of the uranyl was extracted into 
the organic phase by the darker yelow color as compared to the second organic layer.  
The aqueous layer has no tint of yelow, but however is slightly cloudy and would 
prevent any data on the UV-Vis.   
 
OR3a pH 3 
   
Figure 59: Aqueous layer contains uranyl nitrate (5 mM), organic layer contains OR3a (5 
mM) in DCM; Left:  Before shaking.  Right: Layers separated after shaking. 
 
For this ligand, we se a darker yelow, almost orangish yelow organic layer.  There was 
very litle of a third layer formed in the first extraction.  The second extraction shows 
more uranyl being extracted with a slightly lighter yelow color.  This second extraction 
also formed a third layer although not nearly as much as OR2a.  The aqueous layer after 
the second extraction stil has a tint of yelow indicating there is stil uranyl in the 
aqueous phase that would take further extractions remove al of it. 
 
 
 
 
 
 
 
 
 
 106 
OR3a pH 4 
   
Figure 60: Aqueous layer contains uranyl nitrate (5 mM), organic layer contains OR3a (5 
mM) in DCM; Left:  Before shaking.  Right: Layers separated after shaking. 
 
At this pH, we se the dark, almost clear organic layer after the first extraction.  There 
was a litle bit of a third layer formed.  After the second extraction, the yelow color is of 
a lighter tint and therefore not as much uranyl was extracted.  The aqueous layer stil 
shows a tint of yelow indicating there is stil some uranyl left, which could be extracted 
with fresh solution of ligand.  This could be the best pH for extractions with this ligand. 
 
There are at least seven possible ways the ligand may be binding and there are probably 
more.  A shift of 20-25 nm in the UV-Vis data is expected for specific binding.   
 
 
         
  
 
 107 
   
 
Figure 61:  Proposed modes of binding that would result in > 20 
nm wavelength shift. 
 
Since the peak shift was les than 20-25 nm, one must consider additional modes of 
interaction.  In the figure below, are possibilities of how the ligand might bind to uranyl.  
These are not complete binding and therefore would not cause the complete shift that we 
want to se, and therefore might cause a less significant shift of 5-15 nm.   
 
         
 
 
 
 
 
 108 
 
 
 
Figure 62:  Possible modes of secondary binding 
 
Conclusions 
 
From this data one can observe that the ligand may not be the best for uranyl extraction.  
While possible, this ligand is not an improvement over current methods. The amonium 
salt of the ligand was recrystalized from methanol, but single crystals were not suficient 
for single crystal x-ray difraction experiments.  At no point could a metal complex be 
crystalized except for the amonium salt of OR2a with uranyl nitrate, with the single 
crystals not being of high quality for single crystal x-ray difraction.   
 
With the extraction data, we determined that there is both a solubility problem and a 
kinetic problem.  There is a solubility problem, because while methylene chloride is 
imiscible with water, there is stil a smal fraction that interacts with water, and could 
be part of the reason with the third phase formation.  There was also the problem that 
 109 
when the concentrations were increased, there was a third layer formed betwen the 
organic and aqueous phases of the sequential extractions.  While this was present in 
diferent amounts, it was nonetheles present and is a problem for extractions, if the third 
layer consists of an inorganic polymer with uranyl in it, it would take away from the 
overal extraction eficiency and recovery of uranyl. 
 
There is also the possibility of a kinetic problem. Often, it took 12-24 hours to se a shift 
in either the organic phase or the aqueous phase.  There were a few times that an 
imediate shift was observed at a higher pH, than are typical for SNF extractions.  Most 
PUREX extractions are done at 3-6 M HNO
3
 at significantly lower pH than the 2-5 that 
the extractions were done.  The SDS surfactant added semed aid in the binding but not 
necesarily the kinetics or rate of reaction.  The SDS increased the shift by 5 nm to 15 nm 
from the blank as compared to extractions without SDS was only a 10 nm shift from the 
blank.  This could mean it is acting as a co-extractant and not necesarily keeping the 
ligands from aggregating.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 110 
The tables below show the overal diferences in extinction betwen the first 
measurement and the last measurement.   
 
Diference in 
Extinction ? M
-1
 
cm
-1
 pH 2 pH 3 
Ligand/phase 2-1 1-1 1-2 2-1 1-1 1-2 
OR2a/Aq -2800 -24400 -14800 -6800 -3100 -6800 
OR2a/Org 40800 54200 57000 24600 14100 19600 
OR3a/Aq 6500 44400 8500 1900 -10400 -16200 
OR3a/Org 30400 31400 11200 7700 19400 20400 
 
Diference in 
Extinction ? M
-1
 
cm
-1
 pH 4  pH 5 
Ligand/phase 2-1 1-1 1-2 2-1 1-1 1-2 
OR2a/Aq -1000 -1600 -4000 1600 1500 2700 
OR2a/Org 14400 11300 14000 13600 11800 16500 
OR3a/Aq 50 70 16500 2600 1500 2800 
OR3a/Org 10500 12800 7100 16300 11800 16500 
 
Table 1: Diference in extinction betwen the first measurement and the last 
measurement for each ligand and phase at corresponding pH. 
 
Max Shift (nm) pH 2 pH 3 
Ligand/Phase 2-1 1-1 1-2 2-1 1-1 1-2 
OR2a/Aq 0 0 0 5 5 5 
OR2a/ Org 0 0 0 0 10 15 
OR3a/Aq 0 0 5 0 5 0 
OR3a/Org 0 0 0 10 10 10 
 
Max Shift (nm) pH 4  pH 5 
Ligand/Phase 2-1 1-1 1-2 2-1 1-1 1-2 
OR2a/Aq 0 0 5 0 0 0 
OR2a/ Org 15 10 10 10 15 5 
OR3a/Aq 0 0 0 0 0 0 
OR3a/Org 10 5 5 10 15 15 
 
Table 2: Maximum shift observed from the blank for each ligand and phase at 
corresponding pH. 
 
 111 
To prove in a way that can be sen with one?s own eyes, we increased the concentration 
of both the ligand and uranyl to se if the yelow color of uranyl in aqueous solution 
would transfer to the organic phase.  As it turns out, the uranyl appears to be transferred 
relatively quickly, and would not require too require significant quantities of fresh 
solvent to extract al of the uranyl from the aqueous phase.  If we can eliminate the third 
layer formation, we can do UV-Vis and determine just how much is extracted after each 
fresh solvent is added. 
 
Future Work 
 
Future work in these eforts would include making these compounds more soluble in 
organic solvents other than methylene chloride or chloroform.  One option could be 
including an ether linkage as opposed to a pure carbon tail on the phenyl rings.  TBP has 
three such ether linkages with butyl groups atached and is soluble in kerosene or 
dodecane. 
 
Another possible piece of the puzzle would be addresing the kinetic efect 
thermodynamicaly, can modest increases in temperature aid in extraction. There is an 
energy cost, however, and one must consider the costs for increasing the temperature.  
Also, a deeper look at the sequential extractions to determine how many times fresh 
solvent with ligand would have to be applied to achieve the maximum extraction of 
uranyl from the aqueous phase. Ultimately, future work would include extractions of the 
trivalent actinides (Am
3+
) and trivalent lanthanides.  Most of the ligands in the literature 
used for those extractions contain soft donors and more specificaly sulfur donors.   
 
Using inductively couple plasma mas spectrometry (ICP-MS), we could perform 
extractions on UO
2
2+
, Gd
3+
, Ce
3+
, and Fe
3+
 with these ligands at higher concentrations.  
ICP-MS wil give clear percent extraction regardles of either the ligand or the binding 
modes. This would be used to determine how selective the ligand could be betwen the 
actinides and lanthanides and how it can be applied towards trivalent actinide and 
lanthanides. 
 112 
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Appendix
 
 115 
 
 116 
 
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