Kinetics and mechanism of Ru(Ill) catalysed oxidation of substituted cinnamic acids by cerium(IV )

Abstract

Ruthenium(III) catalysed oxidation of substituted cinnamic acids by [Ce(IV)] in aqueous acetic acid-sulphuric acid medium follows a complex rate law, the reaction being zero order in [Ce(IV)], first order in [Ru(III)] and fractional order in [substrate]. Increase in the proportion of acetic acid in the reaction medium retards the reaction rate. The Hammett plot shows a break with p values of -1.65 (electron-releasing groups) and 0.03 (electron with drawing groups). Activation parameters have been computed. A mechanism involving rate-determining rearrangement of the Ru(III)-substrate π-complex to the σ-complex and its cleavage in a concerted manner has been suggested.