Scott William Brown

The selective oxidation of toluenes to benzaldehydes by cerium(III), hydrogen peroxide and bromide ion

Abstract 4- t -Butyltoluene can be oxidised in acetic acid to 4- t -butylbenzaldehyde by hydrogen peroxide in a process catalyzed by cerium(III) and bromide ions. The conversion proceeds via benzylic bromination, hydrolysis of the bromide to alcohol and the rapid oxidation of the alcohol to the aldehyde by bromine. The reaction is ineffective in the absence of bromide but is also inhibited by significant quantities of the ion, apparently because the hydrolysis step is reversible. The role of the cerium has not been clearly established. Cerium(IV) is formed in the system but the first step appears not to involve electron transfer from the aromatic ring. Nor can simple radical bromination explain the rate of formation of benzylic bromide.

New Oxidations of Organic Substrates Using Hydrogen Peroxide and Supported Heteropolyacid Catalysts

Oxidation processes employing aqueous hydrogen peroxide in the presence of heterogeneous catalysts offer significant advantages over traditional liquid-phase processes in terms of cost, safety and environmental impact. We have previously shown1 that catalysts prepared by depositing phosphotungstic acid on gamma-alumina, followed by calcination, are active for the selective epoxidation of olefins using 35% H2O2. These catalysts have been demonstrated conclusively to operate heterogeneously, with essentially no observable leaching of tungsten into the reaction solvent (aqueous t-butanol). They may also be recycled many times without significant loss of activity. Best results are obtained with cyclic alkenes, there being no detectable steric limitations on the substrates which can react.