Kinetics and Mechanism of Oxidation of Styryl Biphenyl and Styryl Fluorenyl Ketones by Pyridinium Chlorochromate

The kinetics of oxidation of substituted styryl 4-biphenyl ketones and of substituted styryl 2-fluorenyl ketones by pyridinium chlorochromate (PCC) have been studied in 90% acetic acid- 10% water (v/v) containing perchloric acid and NaClO₄ at <TEX>$10^0,;20^0,;30^0$</TEX> and 40℃. The reactions are first order in styryl ketones and PCC. The second order rate constants are well correlated only with σ<TEX>$^+$</TEX> constants implying development of positive charge adjacent to benzene ring in the transition state. The effects of varying [HClO₄] and the percentage of acetic acid on the reactions have also been analysed. A mechanism involving nucleophilic attack of PCC leading to an unsymmetric intermediate from which epoxides are formed is proposed.