I= REDOX PROCESS IN U(IV) COMPLEXES
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Title of Thesis
REDOX PROCESS IN U(IV) COMPLEXES

Author(s)
Rashida Parveen
Institute/University/Department Details
Department of Chemistry/ University of Karachi
Session
2006
Subject
Chemistry
Number of Pages
182
Keywords (Extracted from title, table of contents and abstract of thesis)
redox process, u(iv) complexes, tris -orthophenanthroline iron, polyaminocarboxylate complexes, uranium, uranium polyaminocarboxylic acid, uranyl polyaminocarboxylate, tetravalent uranium, ceric sulphate, uranous dtp, uranous dcta, uranous hedta

Abstract
Kinetic study of reduction of tris -orthophenanthroline iron (III) complex with U(IV) and a series of its polyaminocarboxylate complexes has been investigated. The rate constant found to vary with charge and stability of metal ion and metal -ion complexes. All the reactions followed outer sphere mechanism transfer reaction. The data supports the issues underlined in Frank Condon principle, Marcus theory and the Electron Tunneling Theory

U(IV) solution was prepared in 0.lM hydrochloric acid ( Eº = 0.3V). pH of U(IV) solution was maintained up to 3.5. Order of U(IV) oxidation with ferric 1,10 orthophenanthroline was established under pseudo first order conditions. It was found that reaction follows first order kinetics with respect to both the reactants The redox mechanism relating to U(IV) oxidation could not be established., through kinetic evidences because of complex solution chemistry of U(IV) at higher pH. A vague behavior toward ionic strength and non linear graph between log of hydrogen ion concentration Vs log kobs may be related to the complex solution chemistry of U(IV). The second order rate constants were found to be k1 = 41.09 57.3, 80.14, 97.28 mol-1 dm3 S-1 at 4.0, 3.8, 3.5 and 3.2 respectively. .Activation parameter have also been computed and were found to be Eº = 85kJ mol-1, ”S# =-63.2 JK-1, ”H# =83.1kJ mol-1, ”G#= 102.4kJ mol-1

The kinetic reduction of tris(l, 10 orthophenanthroline ) iron(III) by uranium (IV) N-hydroxyethyl ethylenediamine triactate [U(IV) HEDTA]+ has been investigated in aqueous medium at 30±0.5 °C and correlated with the redox potentials values. Measurements were recorded under pseudo first order conditions. The rate of electron transfer reaction between [U(IV) HEDTA]+1 and [Fe (opt)3]3+ was measured by varying pH and ionic strength, between 2.5-3.0 and 0.01-0.05 M respectively. It was found that pH directly influenced the kl and values were found to be111.8, 193.7,344.7478.93 mol-1 dm3 S-1 at pH 3.2, 3.0,2.8,2.5 respectively. The value of k€™ was evaluated as 6.35x 106 mol-1 dm3 S-1. The observed rate law

Rate= d[Fe(opt)3]2+ = k1 [U (IV) HEDTA]+1 [Fe (Opt)3]3+dt

At different pH

Rate= d[Fe(opt)3]2+ = Kk [H+]n [U (IV) HEDTA]+1 [Fe (Opt)3]3+dt

Activation parameter have been evaluated and were found to be Eº = I9.3kJ mol-1 ”S# =150.6 JK-1, ”H# =15.3kJ/mol, ”G#= 60.8kJ mol-1 The kinetics and mechanism of the reduction of ferric 1,10 orthophenanthroline by uranium (IV) trans - 1,2 - cyclohexanediaminetetraacetate ([U (IV)DCT A]) was investigated in aqueous hydrochloric acid at 30ºC, at ionic strength 0.01-mole dm-3and pH 3.5. Rate law for the formation of [Fe (Opt)3 ]2+ was established through spectroscopic measurements at constant and varying pH by isolation method. Order of reaction with respect to each reactant ([U(IV) DCTA] and [Fe (Opt)3]3+ was investigated by plotting a graph of In Aˆž;-At vs time at different temperature ranges. Each reactant was found to obey first order. Rate law is suggested to be

d [Fe(opt)3]+2 = k, [U(IV) DCTA ][Fe (Opt)3]+3dt

At different pH

Rate= d[Fe(opt)3]2+ = Kk [H+] [U (IV) DCTA]+1 [Fe (Opt)3]3+dt

Different thermodynamic functions for the reaction were Eº = 35.1 kJ mol-1, ”H# = 33.7IkJ mol-1 and ”S# = -136.2 J mol-1 and ”G#= 75 kJ mol-1 .At different pH values the rate law was observed as rate = Kk [H+] [U (IV) DCTA]+1 [Fe (Opt)3]3+, where K is equilibrium constant for the reaction [U (IV) DCTA]+ [H+] = [U(IV) DCT A(H+)] and k' is the specific rate constant for the reaction [U (IV) DCTA (H+)]+ [Fe(opt)3]+3†’[U (V) DCTA(H+)]+1 + [Fe (Opt)3]2+. At pH4.0, 3.8,3.5,3.2,3.0, kl found to be 0.26,0.53, 1.19,2.06, 3.21dm3 mol-1 S-1 respectively. The value of k€™ found to be 3.29 x 105 dm3 mol-1 S-1

The reduction of ferric 1,10 orthophenanthroline by uranium (IV) complex of diethylenetriamine-pentaacetic acid was investigated in aqueous 'hydrochloric acid at 30ºC, ionic strength 0.01-mole dm-3and pH 3.5. The mechanism and rate law for the formation of [Fe (Opt)3]2+ was established by isolation method at constant and varying pH. Spectroscopic method was employed for this investigation. The rate constant and order of reaction with respect to each of reactant the [U(IV) DTPA]-l and [Fe (Opt)3]3+ was established by plotting a graph In( Aˆž-At ) vs. time. The reaction was observed to be following first order with respect to each of the reactants

Over all reaction order was found to be second. The rate law is suggested to be

d [Fe(opt)3]+2 = k1, [U(IV) DTPA ]-1[Fe (Opt)3]+3dt

Hydrogen ion dependence of the reaction was determined by varying the pH and the. rate law was observed as

Rate= d[Fe(opt)3]2+ = Kk [H+] [U (IV) DTPA]-1 [Fe (Opt)3]3+dt

where K is equilibrium constant for the reaction [U(IV) DTPA]-l + [H+] = [U(IV) DTPA( H+)]-l and k€™ is the specific rate constant for the reaction [U (IV) DTPA (H+)]-l+ [ Fe(opt)3 ]3+ †’ [U (VI) DTPA(H+)]+ [Fe (Opt)3]2+. The value of second order rate constant kl determined at pH 3.0, 3.2, 3.5, 4.0 have the values 9.33, 7.24, 9.08, 19.35 and 31.0 mol-1 dm3 S-1 respectively. The value of k€™ was calculated 4.1 x 106 dm3mol-1S-l. Thermodynamic parameters for the reaction were determined to be Eº= 26.47 KJ mol-1, ”G# = 35.11 KJ mol-1, ”H# = 24.86 KJ mol-1and ”S# = 50.17 J mol-1. With the help of Arrhenius equation activation energy for the reaction was calculated. Change in enthalpy and entropy for the reaction (”S#, ”H#) were determined from the slope and intercept of Eyring plot

Download Full Thesis
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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
427.44 KB
2 1 Redox Reactions
865.68 KB
  1.2 Theories Related To The Electron Transfer Reaction 12
  1.3 Factors Affecting Rate Of Reaction 31
  1.4 Two Electron Transfer Reactions 36
  1.5 Suitable Reductants 37
3 2 Uranium
1006.31 KB
  2.1 Metallic State 39
  2.2 Solid Compounds 39
  2.3 Ionic Radii 41
  2.4 Solution Chemistry Of Uranium 41
  2.5 Hydrolysis : 45
  2.6 Complex Formation Of Uranium With Inorganic Ligand 46
  2.7 Organometallic Compounds Of Uranium 48
  2.8 Redox Properties Of Some Uranium Complexes By Cyclic Voltammetric Studies 51
  2.9 Properties Of The Polyaminocarboxylic Acid Ligand Complexes Of Uranium 52
  2.10 Behavior Of Ligand In Solution 52
  2.11 Kinetic Properties Of The Polyaminocarboxylic Acid Ligand Of Metal Ion In Solution 53
  2.12 Mechanism Of Exchange Reactions : 54
  2.13 Metal Ion Attack 54
  2.14 Hydrogen Ion Attack 56
  2.15 Metal Ion Catalysis 58
  2.16 Co-Ordinated Anion Effect 58
  2.17 Behavior Of Uranium Polyaminocarboxylic Acid Complexes In Solution 58
  2.19 Hydrolysis And Olation Of U( IV) Polyaminocarboxylate Complexes 59
  2.19 Oxidation Behavior Of The U( IV) Polyamino Carbooxylates 61
  2.20 Uranyl Polyaminocarboxylate In Solution 61
  2.21 Oxidation Of Tetravalent Uranium In Aquoes Solution
  2.22 Oxidation States 66
  2.23 Thennodynamic Parameter 67
  2.24 Iron( II) Oxidation State 70
  2.25 Iron( II) Oxidation State 71
  2.26 Iron( IV) Oxidation State 78
  2.27 Iron( V) Oxidation State 78
  2.28 Iron( VI) Oxidation State 78
4 3 Experimental
213.33 KB
  3.1 Preparation Of Tris 1, 10 Orthophenanthroline Iron (III) Perchlorate. 79
  3.2 Determination Of Molar Absorption Coefficient 79
  3.3 Determination Of Stability Of Tris (1, 10 Orthophenanthroline) Iron (Iii ) 79
  3.4 Uranium (VI) Stock Solution 80
  3.5 Stock Solution Of Uranium (IV ) 80
  3.6 Preparation Of Sodium Diphenylamine Sulphonate Solution : 80
  3.7 Ferroin Indicator : 80
  3.8 K 2 Cr 2 O 7 A The Standard : 81
  3.9 Ceric Sulphate As The Standard : 81
  3.10 Uranous DCTA Complex, [U(Iv) DCTA] 81
  3.11 Uranous DTP A Complex, K[ U(Iv) Dtp A]. 82
  3.12 Uranous HEDTA Complex [ U( IV) HEDTA]Cl 82
  3.13 Spectrophotometric Determination Of U( Iv)Hedta 84
  3.14 Analysis Of Complexes 85
  3.15 Semi Micro Analysis 86
  3.9 Apparatus 87
  3.10 Kinetic Measurements 87
5 4 Results And Discussion
1019.47 KB
  4.1 Kinetic Studies Of [ Uranium( Iv) Hedta ] + 88
  4.2 Kinetic Study Of [ U( IV)DCT A] 106
  4.3 Kinetics Of [ U( Iv)DTP A] + 124
  4.4 An Attempt To Study Uranium( IV) Kinetics 144
6 5 Conclusions
542.65 KB
  5.1 Dielectric Constant 159
  52 Ionic Strength 160
  5.3 Entropy Of Activation 161
  5.4 Molecular Orbital Theory 163
  5.5 Marcus Theory 164
  5.6 Electron Tunneling Theory 165