Selective benzylic oxidation catalyzed by chromium carboxylate complexes

Abstract

Screening for chromium carboxylate complexes disclosed that chromium(III) stearate coupled with TBHP could catalyze the transformation of ethylbenzene to acetophenone in high yield with excellent selectivity. The optimum conditions for the oxidation of benzylic methylene compounds including amount and type of catalyst, solvents, oxidants, additive, reaction time and reaction temperature were conducted. Under optimum conditions, selected benzylic methylene compounds: n-propylbenzene, n-butylbenzene, n-pentylbenzene, benzyl alcohol, benzaldehyde, tetralin, xanthene, acenaphthene, dibenzyl hexyl ether, benzyl acetate, ethyl 4-ethylbenzoate, ethyl phenylacetate, 1-bromo-2-ethylbenzene, 1-ethyl-2-nitrobenzene and 4-ethylbenzoic acid could be converted to the corresponding carbonyl compounds in high yield. Particularly, the transformation of 1,2,3,4-tetrahydroquinoline (as amide of pivalic acid) and ethyl phenylacetate to the corresponding keto compounds were among prominent instances. This developed oxidation reaction was believed to undergo via free redical process.