Advances in homogeneous and heterogeneous catalytic aerobic oxidation of isophorone to ketoisophorone

Homogeneous and heterogeneous systems for the catalytic aerobic allylic oxidation of alpha- and beta-isophorone (alpha- and beta-IP) to ketoisophorone (KIP) have been investigated. A detailed study has been conducted on the influence of several parameters for the phosphomolybdic acid (PMA)/DMSO/potassium tert-butoxide combination which provides KIP in high yield (68% isolated) from alpha-IP. Metal(bis-salicylaldehyde)s (M(sal)(2)) are new homogeneous catalysts for alpha- and beta-IP oxidation. (M(sal)(2)) immobilized on aminopropyl-modified silica gel and metal(salen) incorporated in silica aerogels, prepared in our laboratory, have also been investigated for isophorone oxidation. The combined study suggests that the base/solvent plays a pivotal role in directing selectivity in the allylic oxidation of highly substituted cyclic olefins in homogeneous catalysis. In addition, the solvent/additive combination can also dictate the stability of heterogeneous catalysts under conditions necessary for facile dioxygen activation for allylic oxidation. Differences in the activities of the homogeneous and immobilized systems may be associated with the phenomenon of site isolation leading to different reaction pathways. (C) 2002 Elsevier Science B.V. All rights reserved.