Kinetics and Mechanism of Os(VIII)-Catalysed Oxidation of some Substituted trans-Cinnamic Acids by Chloramine-T in Alkaline Medium - A Non-Linear Hammett Plot

Article abstract of DOI:10.1016/S0040-4020(01)85705-7

The kinetics and mechanism of Os(VIII) catalysed oxidation of some substituted trans-cinnamic acids by chloramine-T in presence of alkaline medium has been investigated.The order with respect to is zero and is one.The reaction is fractional order in .The rate dependence on is inverse first order.Both the electron-releasing and withdrawing substituents facilitate the reaction rate.The observed rate constants for substituents are plotted against Hammett constant ?, a non-linear, 'V' shaped curve is obtained.The electron-withdrawing substituents fall on one side of the curve having a negative ρ value, and electron-releasing substituents fall on the otherside with positive ρ value.The break in the Hammett plot is due to change in the nature of transition state.The mechanism proposed and the derived rate law are in confirmity with the observed results.