KINETICS AND MECHANISM OF OXIDATION OF PHENOLS BY PEROXYDISULPHATE ION

Abstract

Study of the kinetics of reactions is one of the important tools to help a chemist to unravel the mysteries of a reaction. Besides this being fascinating in itself, such kinetic studies are important from the industrial point of view too, since a complete understanding of kinetic behaviour of a reaction enables a chemist to work out the optimum conditions for carrying out a reaction. In a chemical change, the molecular dynamics of making and breaking of chemical bonds is looked upon at the microscopic level as a two way reversible process of reactants and products interconverting, but at the macroscopic level the reaction is seen as a one way process of a non-equilibrium system irreversibly relaxing towards equilibrium. Although chemical kinetics provides the most powerful method of investigating the mechanism of a process, it is, however, not always possible to get absolute information through kinetic studies. Therefore, theories based on certain postulates are put forward to explain the facts obtained by experiments. Consequently, mechanisms are modified or changed when some new information is uncovered or some new concept is developed. Nevertheless, the data on kinetic studies coupled with other techniques provide one of the most satisfactory way for obtaining information about the mechanism and pathways involved. To an organic chemist, kinetic studies also help in predicting the conditions required for the formation of the desired product when several competing steps are occurring. Thus, kinetic studies help the organic chemist in two ways - firstly, to investigate the pathways of several competing reactions occurring and secondly to work out the favourable conditions for obtaining the desired product. It must be admitted that, in many cases, it is not always possible to provide complete information about the course of a chemical reaction. Sufficient data can, nevertheless, often be gathered to show that one mechanism is more likely than the other. Besides the kinetic results, additional information is required to establish the assumed mechanism of a reaction. One of the first and certainly most important pieces of data needed is the stoichiometry of the reaction; usually the stoichiometry is the sum of various terms and the slower among them is said to be rate-determining1. The knowledge of the energy of activation and available energies of possible reaction steps is also essential in arriving at the correct mechanism.