A Kinetic Analysis Of The Oxidations Of Hydrazine And Its Derivatives By Iridium(?)

In this thesis,a kinetic study of the oxidations of hydrazine and its derivertives by the single electron oxidant [IrCl6]2-has been carried out by the stopped-flow spectrometric technique.The reactions proved to be first-order each in [IrCl62-] and [Reductant]tot,leading to overall second-order kinetics.The variation in the observed second-order rate constant k?with pH was explored in a wide pH range and the k? versus pH profile has been established for each of the reductants.Spectrophotometric titrations reveal a general stoichiometry:?[Ir Cl62?]/?[Reductants]tot = 4:1.Based on the rate laws,the redox stoichiometry and the rapid scan spectra,reaction mechanisms are proposed.The proposed reaction mechanism in the case of semicarbazide(SEM)involves parallel attacks of [IrCl6]2-on both H2NCONHNH3+ and H2NCONHNH2 as rate-determining steps,followed by several rapid reactions.The rate expression,derived from the reaction mechanism,was utilized to simulate the k?-pH profile yielding a virtually perfect fit,indicating that the reaction path involving H2NCONHNH3+ does not make a significant contribution to the overall rate.The reaction between [IrCl6]2-and H2NCONHNH2 was further studied as a function of both temperature and ionic strength.From the temperature dependence,activation parameters were obtained as: ?H2? = 34.9 ± 1.5 kJ?mol-1 and ?S2? =-78 ± 5 J?K-1?mol–1.The observed strength dependence suggests that the rate-determining step is between [IrCl6]2-and a neutral species of SEM.Hence,both the temperature and ionic strength dependency studies are in good agreement with the proposed reaction mechanism,in which the rate-determining step involves an outer-sphere electron transfer.The oxidation products for the oxidations of hydrazine,cyclohexylhydrazine and tert-butylhydrazine by [IrCl6]2-are nitrogen cyclohexanol and tert-butylalcohol,respectively,which were confirmed by gas chromatography.The reaction mechanisms also involve two parallel reactions which are the rate-determining steps.The rate expressions are derived from the reaction mechanisms,and the rate constants of rate-determining steps have been calculated from the k? versus pHprofiles.Moreover,the influence of substituted groups on the reaction rate is examined and discussed.