Kinetics and mechanism of oxidation of aliphatic aldehydes by quinolinium bromochromate

The oxidation of six aliphatic aldehydes by quinolinium bromochromate (QBC) in dimethyl sulphoxide (DMSO) leads to the formation of the corresponding carboxylic acids. The reaction is first order each in QBC and the aldehyde. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: k(obs) a + b[H+]. The oxidation of deuteriated acetaldehyde, MeCDO, exhibited a substantial primary kinetic isotope effect (k(H)/k(D) = 5.80 at 298 K). The oxidation of acetaldehyde has been studied in nineteen different organic solvents. The solvent effect has been analysed using the Taft's and Swain's multiparametric equations. The rate constants correlate well with Taft's sigma* values; reaction constants being negative. A mechanism involving transfer of hydride ion has been suggested.