Uncatalysed and HClO4 catalysed oxidation of unsaturated alcohols by pyridinium chlorochromate in aquo-acetic acid medium

The uncatalysed and perchloric acid catalysed oxidation of unsaturated alcohols (Alc), viz., allyl alcohol, crotyl alcohol and cinnamyl alcohol by PCC in aquo-acetic acid medium leads to the formation of the corresponding aldehydes. Both the reactions were found to be first order each in [PCC] and [Alc]. In the uncatalysed reaction, the rate decreased with increase in acetic acid in the reaction medium, i.e. with decrease in dielectric constant of the medium indicating a dipole-dipole reaction, i.e. the participation of unprotonated PCC and a molecule of alcohol in the rate-determining step. In the perchloric acid catalysed oxidation, the rate of reaction increased with increase in [perchloric acid] and the order in [H+] was found to be fractional indicating the involvement of protonated PCC in the rate-determining step. Activation parameters along with k" at different temperatures are calculated.