The oxidation of DL-methionine (MT) by benzimidazolium dichromate (BIDC), in dimethyl sulfoxide, leads to the formation of the corresponding sulfoxide. The reaction is first order with respect to BIDC. Michaelis - Menten type kinetics were observed with respect to MT. The reaction is catalysed by hydrogen ions and the dependence is of the form kobs = k‘[H+]. The rate of oxidation of MT was determined in 19 organic solvents. An analysis of the solvent effect by solvatochromic equations indicated that though both the anion- and cation-solvating powers of the solvent contribute to the observed solvent effect, the role of cation-solvation is much the major. A suitable mechanism has been proposed.

The oxidation of some alkyl phenyl sulfides by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide, to the corresponding sulfoxides, is first order with respect to BIDC. Michaelis–Menten type kinetics was observed with respect to sulfide. Thermodynamic parameters for the complex formation and activation parameters for the decomposition of the complex were calculated. The reaction is proton-catalyzed and the order is less than one. It appears that the BIDCH+ is the active electrophile. An intermediate of composition sulfide–BIDC–H+ has been envisaged. The high value of negative entropy of activation suggests a cyclic transition state in the rate-determining step. The reaction exhibited negative polar reaction constants and a small degree of steric hindrance. The rate of oxidation of sulfide was determined in 19 organic solvents. An analysis of the solvent effect by Swain’s equation indicated that though both the anion and cation solvating powers of the solvent contribute to the observed solvent effect, the role of cation solvation is major. A mechanism involving the rate-determining oxygen atom transfer in complex, formed by a nucleophilic attack of sulfide-sulfur on BIDCH+ in a rapid pre-equilibrium, is suggested to give corresponding sulfoxide via. a cyclic transition state.

The oxidation of a number of para-, meta- and ortho-substituted benzaldehydes by butyltriphenylphosphonium dichromate (BTPPD), in dimethyl sulphoxide, leads to the formation of the corresponding benzoic acid. The reaction is first-order with respect to BTPPD. Michaelis-Menten type kinetics were observed with respect to the aldehyde. The formation constants of the aldehyde-BTPPD complexes and the rates of their decomposition were determined at different temperatures. The reactions are catalysed by hydrogen ions and the dependence is of the second order. The oxidation of [2H] benzaldehyde (PhCDO) exhibited the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzaldehydes were correlated in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated with tetraparametric LDRS equation. The oxidation of para- and ortho-substituted benzaldehydes are more susceptible to the delocalization effect than is the oxidation of meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric hindrance by the ortho-substituents. The rates of oxidation of benzaldehyde were determined in nineteen organic solvents. An analysis of the solvent effect by multiparametric equations indicated the greater importance of the cation-solvating power of the solvents. Suitable mechanisms have been discussed.