Studies on kinetics and thermodynamics of oxidation of 3,4,5-trimethoxy benzaldehyde, benzaldehyde and N,N-dimethylamino benzaldehyde by tetraethylammonium bromochromate in dimethyl formamide and acetic acid mixture

Abstract

The oxidation of 3,4,5-trimethoxy benzaldehyde (TMBA), benzaldehyde (BA) and dimethylamino benzaldehyde (DMABA) in N,N-dimethyl formamide (DMF) by tetraethylammonium bromochromate (TEABC) resulted in the formation of the corresponding acids. The reaction is first order with respect to both TEABC and the aldehydes. The reaction is catalyzed by toluene-p-sulfonic acid (p-TsOH). The hydrogen ion dependence has the form: kobs = a + b [H+]. The reaction has been studied in different percentage of DMF–acetic acid mixture. The effect of dielectric constant of the medium indicates the reaction to be of ion–dipole type. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of isokinetic relationship. Reason for high rate in the case of oxidation of N,N-dimethylamino benzaldehyde is also described. A mechanism involving formation of a chromate ester intermediate in the slow step has been proposed. Keywords: Aldehydes, Tetraethylammonium bromochromate, Kinetics, Isokinetic relationship