Mechanistic investigation of oxidation of aromatic anils by isonicotinium dichromate in acidic medium. A kinetic study

Under identical experimental conditions the kinetics of oxidation of aromatic anils to benzaldehyde and nitrosobenzene, by isonicotinium dichromate, has been studied in aqueous acetic acid medium. The low dielectric constant of the medium facilitates the reactivity. Ionic strength has no significant effect on the conversion. The added Mn(II) decreases the rate of the reaction. The added acrylonitrile has no effect on the reaction rate indicating the absence of free radical mechanism. Highly negative Delta S-# values indicate a structured transition state. The deviation of Hammett plot is noted and a concave downward curve is obtained for the anils with substituents in the aniline moiety. The observed break in the log k(obs) versus sigma is attributed to the change in the transition state whereas the linear plot is observed for the substituents in the benzaldehyde moiety. A suitable mechanism has been proposed.