Kinetics and Correlation Analysis of Reactivity in the Oxidation of Some α-Hydroxy Acids by Benzimidazolium Dichromate

Abstract

Kinetic and mechanistic studies of the oxidation of mandelic acid and nine monosubstituted mandelic acids by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide are discussed with an emphasis on correlation of structure and reactivity. The reactions were of first order with respect to BIDC. However, Michaelis-Menten type kinetics were observed with respect to hydroxy acids. The reactions are catalysed by protons. The deuterium isotope effect for the oxidation of mandelic acid ( kH/ kD = 5.91 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. An analysis of the solvent effect showed that the role of cationsolvation is major. The reaction showed an excellent correlation with the Hammett σ values, the reaction constant being negative. Based on the kinetic data, analysis of the solvent effect and results of structure-reactivity correlation along with some non-kinetic parameters, a mechanism involving rate-determining oxidative decomposition of the complex through hydride-ion transfer via a cyclic transition state to give the corresponding oxoacid is suggested.

Kinetics and Mechanism of Oxidation of Aliphatic Secondary Alcohols by Benzimidazolium Fluorochromate in Dimethyl Sulphoxide Solvent

“…Therefore, the transfer of hydride-ion from secondary alcohol to the BIFC is suggested. The bigger role of cation-solvating power of the solvents also supports the hydride ion transfer mechanism 41 . The hydride ion transfer can occur either via an acyclic bimolecular reaction or may occur due to the involvement of a cyclic, planner and symmetrical transition state of chromate ester.…”

“…The polar transition state is also supported by the observed negative value of entropy of activation 28 . The solvent effect has also indicated that the intermediate state is more polarized than the reactant [40][41][42][43][44][45][46][47][48] . Finally, we can say that BIFC is a very effective, mild oxidant, which can be used for the synthesis of ketonic compounds.…”

Comparative Study of Solvent Effect for Mandelic acid Oxidation by Different Oxidants

“…For this study, many Cr(VI) derivatives have been reported [1][2][3][4][5] . The oxidation study of a-hydroxy acids by PBC 6 , PDC 7 , PCC 8 , IDC 9 , QCC 10 , PzCC 11 , MCC 12 , TEACC 13 , IFC 14 , PipCC 15 , MFC 16 , BIDC 17 etc. has been reported in DMSO.…”