Kinetics and mechanism of the oxidation of substituted benzaldehydes by benzyltrimethylammonium chlorobromate

The oxidation of 35 monosubstituted benzaldehydes by benzyltrimethylammoniu m chlorobromate (BTMACB) in aqueous acetic acid leads to the formation of t he corresponding benzoic acids. The reaction is first order with respect to both benzaldehyde and BTMACB. The reaction failed to induce the polymeriza tion of acrylonitrile. There is no effect of benzyltrimethylammonium chlori de or potassium bromide on the reaction rate. The oxidation of [H-2]benzald ehyde (PhCDO) indicated the presence of a substantial kinetic isotope effec t. The effect of solvent composition indicated that the reaction rate incre ases with an increase in the polarity of the solvent. The rates of oxidatio n of meta- and para-substituted benzaldehydes were correlated in terms of C harton's triparametric LDR equation, whereas the oxidation of ortho-substit uted benzaldehydes was correlated with the tetraparametric LDRS equation. T he oxidation of para-substituted benzaldehydes is more susceptible to the d elocalization effect, whereas the oxidation of ortho-and meta-substituted. compounds displayed a greater dependence on the field effect. The positive value of eta suggests the presence of an electron-deficient reaction center in the rate-determining step. The reaction is subjected to steric hindranc e by the ortho substituents.