COBALT SCHIFF-BASE COMPLEX-CATALYZED OXIDATION OF ANILINES WITH TERT-BUTYL HYDROPEROXIDE

Cobalt Schiff base complexes [Co(SB)] catalyze the oxidation of anilin es (1) with tert-butyl hydroperoxide to give nitrobenzenes 2 and 4-(te rt-butylperoxy)-2,5-cyclohexadien-1-imine derivatives 3 in yield distr ibutions depending on the substitution mode of the substrate. 4-Alkyl- and 4-aryl-2,6-di-tert-butylanilines gave mixtures of 2 and 3, where the higher the bulkiness of the 4-substituent, the higher the yield of 2. With 2,4,6-trimethylaniline, the ratio of oxidations of the nitrog en and C-4 atoms was almost the same; but a hydrolyzed product 5 of th e imine was obtained. 2,4,6-Triphenylaniline gave only 2. Nitrobenzene derivatives were also obtained from 2,6-dialkylanilines and 4-substit uted anilines. The catalytic activity of Co(SB) depended on the nature of the SB ligand: the formal potential E degrees and steric factors s eem to affect the reaction rate. Kinetic studies showed that the key s tep may involve hydrogen abstraction from the aniline, presumably by t -BuO(.) generated from homolytic decomposition of initially formed Co- III(SB)(OO-t-Bu). A precursor of 2 was found to be the nitrosobenzene derivative.