Silicate xerogels containing cobalt as heterogeneous catalysts for the side-chain oxidation of alkyl aromatic compounds with tert-butyl hydroperoxide

New transition metal substituted silicate xerogels, MLn-SiO2, have been prepared by the sol-gel technique and have been used as heterogeneous catalysts for the side-chain oxidation of alkyl arenes with anhydrous t-butylhydroperoxide. The cobalt substituted silicates were the most active and selective, for example, ethylbenzene was cleanly oxidized to acetophenone at 65% conversion and > 99% selectivity. The metal salt precursor used was a key factor in determining the activity of the metallosilicate. Diffuse reflectance UV-vis and IR measurements indicated that when using Co(OAc)(2) as metal precursor, the acetate group was detached from the metal and Co(II) was tetrahedral and site substituted in the silicate network. Addition of the oxidant led to stabilization of a Co(III) oxidation state and/or retention of the tetrahedral configuration. (C) 1999 Elsevier Science B.V. All rights reserved.