Autocatalysed Oxidative Decarboxylation of Propionic and Succinic Acid by Permanganate ion. A Kinetic Study

摘要

A study of oxidative decarboxylation of propionic and succinic acids by permanganate ion in moderately concentrated acidic medium has shown that it is a two-stage reaction, i.e. a slow first stage is followed by a relatively faster second stage. The lg (a-x) versus t curve displays an infection. In the both stages the reaction follws first order behaviour with resepct to each, substrate and the oxidant. The cause of autocatalysis has been attributed to Mn(II) ions,which was further substantiated by the initial addition of MnSO_4. The oxidation reactions are acid catalysed and, therefore, various hypotheses for the mechanism of acid catalysis were tested. Thus, the role of water molecule as proton abstracting agent has been established. On addition of fluoride ions,known complexing agents, there is a decrease in the reaction rate. The stoichiometry for the propionic acid reaction is 5CH_3CH_2COOH + 2MnO_4~- + 6H~+ -> 5CH_3CH_2OH + 3H_2O + 5CO_2 + 2Mn~(2-). The effect of ionic srength has also been studied. Thermodynamic parameters have been computed by studying the reaction at diffrent temperatures. On the basis of the various observations and product characterisation a most plausible mechanism has been envisaged.