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Title of Thesis

Abida Perveen
Institute/University/Department Details
Department of Chemistry/ University of Karachi
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
diphenylamine, diphenylbenzidine, dpbd, sodium thiosulphate, ascorbic acid, arsenic oxide, amines, vitamin c, arsenic oxide

The kinetic investigation between diphenylbenzidine (DPBD) and different reductants i.e. sodium thiosulfate, ascorbic acid and arsenic trioxide is being reported. The results of these reactions in triplicate have been interpreted through the statistical calculation using Standard deviation in MS excel 2000. The characterization of diphenylbenzidine has also been undertaken. It was prepared using mole ratio method by allowing interaction between diphenylamine (DP A) and cerium (IV) sulfate tetra hydrate and the product DPBD was identified through spectral analysis.

The reduction of DPBD with sodium thiosulfate has been investigated and the rate of reaction with respect to DPBD, S2O32- and H+ has been determined. Kinetic order of the system with respect to each of the DPBD, S2O32- and H+ has been observed and it has been found that the reaction follows first order kinetics in DPBD and similar results were recorded for the other reactants Le. thiosulfate and H+. The redox mechanism has been explained through the bimolecular step reaction proceeding through an intermediate ion pair resulting from the interaction of oxidizing and reducing species. The suggested rate law for the system is as follows,

Rate = {k1[C12H10 N2 C12 H10 ]+ k2 K[C12H10 N2 C12 H10] [H+]} [S2O32-]

Having the values of k1 and k2 AS 1.07 X102 ± 1.52 dm3. mol-1 s-1 and 7.45 X102± 0.14 dm3. mol-1 .s-1 respectively.

Activation parameters, for the reaction, have also been determined by varying temperature between 15 - 30°C. The values of energy of activation, enthalpy and entropy were subsequently evaluated. These values have been calculated by using the Arrhenius and Eyring plot and are found to be as with standard deviation Ea = 28.73 ± 0.5 kJ / mol , ”H‰ = 26.33 ± 0.10 kJ / mol and ”S‰ = -113 ± 0.33 J/mol. K.

The redox reaction between diphenylbenzidine and ascorbic acid (ASC) has been spectrophotometrically investigated with in pH range of 3.5-5.0. To find out the effect of single species on rate of reaction the study has been under taken using pseudo first order condition. It is found that the rate of reaction increased with the increase of hydrogen ion concentration and the first order is found w.r.t [H+]. The rate law for the redox reaction has been suggested. Experimental results confirm the validity of the suggested mechanism. The rate law for the reaction is as follow,

Rate = {k1[C12H10 N2 C12 H10 ]+ k2 K[C12H10 N2 C12 H10] [H+]} [C6H8O6]

Where k1, and k2 are the rate constants, having the value of kl = 7.71x102 ± 1.05 dm3 .mol-1 s-1 and k2 = 4.201 x 103 ± 4.93 dm3 .mol-1 s-1 . K is the equilibrium constant of protonated and deprotonated forms of diphenylbenzidinc having value of 476 dm3.mol-l. The over all order of reaction is two.

Effect of temperature with in a range of 15 - 30°C has been examined for the determination of the activation parameters. They are found to be Ea = 30.00 ± 0.56 kJ / mol. ”H‰ = 28.00 ± 0.34kJ/ mol and ”S‰ = -99 ± 0.05 J/ mol. K.

The work was also extended to the study pertaining to electron transfer reaction between diphenylbenzidine and arsenic (III) oxide. The reaction has been scrutinized under pseudo first order condition keeping the concentration of arsenic (III) oxide constant and varying the concentration of DPBD. To find out the effect H+ and temperature the reaction was carried out in between a pH of 3.0 to 4.5 and at temperature 15-30°C. Effect of pH and temperature on the order of reaction with respect to each of DBPD , arsenic (III) oxide and H+ has been evaluated and has been found to be first. The rate law for the system mechanism has been recommended as follows,

Rate = k2 [C12H10 N2 C12 H10] [As2O3] 1+K[H+]

From the slope the value for the rate constant k2 has been calculated as = 1.01 x 102 ±2.46 dm3 .mol-1s-1 Activation parameters for the redox system have also been calculated using Arrhenius and Eyring equations. In these Ea= 26.41 ± 0.34 kJ.mol-1 and that the values of ”H‰ and ”S‰ have been found to be 23.49± 0.80 kJ.mol-1 and -117± 2.79 J mol-1 K-1 .

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3256.5 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
416.72 KB
2 1 Introduction 1
1436.06 KB
  1.1 Redox Theory 1
  1.2 Oxidation Reduction Reactions 2
  1.3 Electron Transfer Reactions 9
  1.4 Solvent Exchange Reactions 23
  1.5 Mechanism Of Redox Reactions 24
  1.6 Chemical Kinetics 34
  1.7 Reaction Mechanism And The Rate Law 47
  1.8 Amines 62
  1.9 Vitamin €˜C€™/ Ascorbic Acid 67
  1.9 Arsenic (III) Oxide 71
3 2 Experimental 75
150.88 KB
  2.1 Preparation Of Sodium Thioulfate Stock Solution 75
  2.2 Preparation Of Stock Solution Of Ascorbic Acid 75
  2.3 Stock Solution Of Arsenic Tri Oxdie 75
  2.4 Preparation Of Sodium Hydroxide Solution 75
  2.5 Preparation Of Sodium Sulfate Salt Solution 76
  2.6 Preparation Of Dpbd Solution 76
  2.7 Kinetic Measurements 82
  2.8 Instrumentation 82
4 3 Results And Discussion 83
994.91 KB
  3.1 Reduction Of DPBD Through Sodium Thiosulfate 83
  3.2 Reaction Of Diphenylbenzidine With Ascorbic Acid 109
  3.3 Reduction Of Diphenylbenzidine With Arsenic( Iii) Oxide 129
5 4 Conclusion 149
210.98 KB
  4.1 Formation Of Activated Diphenylbenzidine 149
  4.2 Effect Of Molecular Structure And Electron Transfer Reactivity On Rate Of Reaction 150
  4.3 Effect Of Ionic Strength 150
  4.4 Marcus Theory 152
  4.5 Electron Tunneling Theory 153
  4.6 Libby€™s Theoretical Discussion 154
  4.7 Entropy Of Activation 155
6 5 Publications And Related To The Thesis 158
272.13 KB
  5.1 References 159