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 s ubstituted styryl.-fluorenyl ketones by pyridinium chlorochromate (PCC) hav e been studied in 90% acetic acid- 10% water (v/v) containing perchloric ac id and NaClO4 at 10 degrees, 20 degrees, 30 degrees and 40 degrees C. The r eactions are first order in styryl ketones and PCC. The second order rate c onstants an well correlated only with sigma(+) constants implying developme nt of positive charge adjacent to benzene ring in the transition state. The effects of varying [HClO4] and the percentage of acetic acid on the reacti ons have also been analysed. A mechanism involving nucleophilic attack of P CC leading to an unsymmetric intermediate from which epoxides are formed is proposed.