Oxovanadium(IV)-Salen Ion Catalyzed H2O2 Oxidation of Tertiary Amines to N-Oxides - Critical Role of Acetate Ion as External Axial Ligand

The oxovanadium(IV)-salen ion catalyzed H2O2 oxidation of N,N-dimethylaniline forms N-oxide as the product of the reaction. The reaction follows Michaelis-Menten kinetics and the rate of the reaction is accelerated by electron donating groups present in the substrate as well as in the salen ligand. This peculiar substituent effect is accounted for in terms of rate determining bond formation between peroxo bond of the oxidant and the N-atom of the substrate in the transition state. Trichloroacetic acid (TCA) shifts the (max) value of the oxidant to the red region and catalyzes reaction enormously. The cleavage of NO bond by vanadium complex leads to moderate yield of the product. But the percentage yield of the product becomes excellent in the presence of TCA.