Kinetics and mechanism of the oxidation of aliphatic aldehydes by benzyltrimethylammonium dichloroiodate

The oxidation of six aliphatic aldehydes by benzyltrimethylammonium dichlor oiodate (BTMBCI) in glacial acetic acid, in the presence of zinc chloride, results in the formation of the corresponding carboxylic acids. The reactio n is first order with respect to BTMACI, the aldehyde and zinc chloride. Th e oxidation of deuterated acetaldehyde shows the presence of a substantial kinetic isotope effect (k(H)/k(D) = 6.32 at 288 K). Addition of benzyltrime thylammonium chloride enhances the reaction rate. It is proposed that the r eactive oxidizing species is [PhCH2Me3N](+) [IZn2Cl6](-). The rates correla te well with Taft's sigma* substituent constants, with negative reaction co nstant. A mechanism involving a hydride-ion transfer from the aldehyde to t he oxidant in the rate-determining step, has been postulated.