Abstract. Kinetic and mechanistic studies of the oxidation of aliphatic aldehydes, (in organic non-aqueous solvents), were discussed with an emphasis of correlation of structure and reactivity. The reactions were of first order with respect to BIDC and hydrogen-ion. However, Michaelis-Menten type kinetics were observed with respect to aldehyde. The deuterium isotope effect for the oxidation of acetaldehyde (k H /k D = 6.36 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. Based on kinetic data, analyses of the solvent effect and results of structure-reactivity correlation along with some nonkinetic parameters suggested a mechanism involving rate-determining oxidative decomposition of a aldehyde-BIDC complex via a cyclic transition state to give a carbocationic species through hydride-ion transfer from the aldehyde to the oxidant. (doi: 10.5562/cca1694)

Oxidation of some lower oxyacids of phosphorus by benzimidazolium dichromate results in the formation of the corresponding oxyacids containing phosphorus in a higher oxidation state, via an intermediate complex formation.

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.

Benzimidazolium dichromate (BIDC), in dimethylsulfoxide, oxidizes secondary alcohols to the corresponding ketones. The reaction is first order with respect to BIDC. The order with respect to alcohol is more than one but less than two. Michaelis -Menten type kinetics were observed with respect to alcohol. The formation constants of the alcohol -BIDC complexes and the rates of their decomposition were determined at different temperatures.The oxidation of deuterated 2-propanol indicated the presence of a substantial primary kinetic isotope effect. The reaction exhibited a second order dependence on hydrogen-ion concentration. The reaction was studied in nineteen organic solvents. The solvent effect was analyzed using multiparametric equations. It was found that the cation-solvating power of the solvent played the major role. The rates of oxidation exhibited an excellent correlation with polar and steric substituent constants. A suitable mechanism has been proposed.

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