Kinetics and mechanism of the oxidation of aliphatic aldehydes by tetrabutylammonium tribromide

The oxidation of six aliphatic aldehydes by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid resulted in the formation of corresponding carboxylic acids. The reaction is First order with respect to TBATB and the aldehydes. The oxidation of deuterlated acetaldehyde (MeCDO) showed the presence of substantial kinetic isotope effect (k(H)/k(D) = 5.92 at 298 K). Addition of tetrabutylammonium chloride has no effect on the reaction rate Tribromide ion has been proposed as the reactive oxidizing species. The rate constants correlate well with Taft's sigma* values, the reaction constant being negative. A mechanism involving a hydride-ion transfer from the aldehyde hydrate to the oxidant in the rate-determining step has been suggested. (C) 2001 John Wiley & Sons, Inc.