Kinetics and the mechanism of oxidation of methoxy benzaldehydes by benzimidazolium fluorochromate in an aqueous acetic acid medium

The oxidation of benzaldehyde (BA) as well as 4-methoxy (4-MBA), 3-methoxy (3-MBA), 2-methoxy (2-MBA), 2,6-dimethoxy (2,6-DMBA), 2,4-dimethoxy (2,4-DMBA), 3,4-dimethoxy (3,4-DMBA), 2,4,6-trimethoxy (2,4,6-TMBA), 3,4,5-trimethoxy (3,4,5-TMBA) and 2,3,4-trimethoxy (2,3,4-TMBA) benzaldehydes by benzimidazolium fluorochromate (BIFC) have been studied in a 50% acetic acid–50% water medium. The oxidation leads to the formation of the corresponding carboxylic acids. The reaction is first order with respect to [BIFC], [S] and [H+]. The reaction was catalysed by H+ ions. The reaction was studied at four different temperatures, and the thermodynamic parameters were calculated. The Exner plot indicated that all of the methoxy-substituted benzaldehydes were oxidized via the same mechanism. Based on the observed kinetics, a suitable mechanism has been proposed.