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, ML(n) -SiO₂, have been prepared by the sol-gel technique and have been used as heterogeneous catalysts for the side-chain oxidation of alkyl arches 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(OSV)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.