A Study of Conformational Effects on Oxidation Kinetics of N-H- and N-Methyl-4-piperidones with N-Bromosuccinimide : A Comparative Analysis

Department of Chemistry, Seethalakshmi Ramaswami College (Autonomous), Trichy-620 002

Manuscript received 26 March 1993, revised 25 October 1994, accepted 18 January 1995

A comparative oxidation kinetics of six pairs of N-H and .V-methyl-2,6-diphenyl-4-piperidones with N-bromosuccinimide (NBS) in aqueous acetic acid medium (20-80%, v/v) at constant ionic strength in presence or mercuric acetate has been investigated. The effect of alkyl substituents on the rates or oxidation in N-H series parallels their effects in N-H series. The enhanced rates N-Me compounds compared to their N-Il counterparts and the least reactivity of 3,5-dimethyl-2,6-diphenyl-4-piperidones have been rationalised on the basis of their conformation. The reactions are second order, first order each in (piperidone) and [NBS]. Negative salt effect, positive dielectric effect and nil succinimide effect have been observed suggesting NBS itself as the reactive species. A mechanism involving formation of a cyclic transition slate by the interaction between the enol form of piperidone and NBS, consistent with reaction stoichiometry has been proposed.