Alexander Johnstone

The solvent-free side chain oxidation of 4-t-butyltoluene via a photolytically assisted HBr/H2O2 system†

A process has been developed for the oxidation of 4-t-butyltoluene to 4-t-butylbenzaldehyde via an indirect route involving the formation of either 4-t-butylbenzyl bromide or 4-t-butylbenzal bromide. The organic bromides were formed using a photolytic HBr/H2O2 route in the absence of solvent. The bromination steps were found to be highly efficient in that all the substrate could be converted, consuming all the hydrogen peroxide at this stage of the reaction. Partial hydrolysis (up to 50%) of the benzyl bromide to the aldehyde was achieved employing the Sommelet route using hexamethylenetetramine. However, up to 58% aldehyde yield could be afforded from the benzal bromide using a suitable phase transfer agent and a small amount of co-solvent. In both cases, the extent of over-oxidation to 4-t-butylbenzoic acid was reduced by careful control of the bromination step and eliminating dioxygen from the reactor.

Novel Catalysts for Olefin Cleavage Using Hydrogen Peroxide

Abstract Transition metal oxides are well-known reagents for cleaving olefinic double-bonds. Due to toxicity and expense, catalytic amounts of the metal species, along with a co-oxidant are favoured. Whilst hydrogen peroxide and ruthenium give good results for many olefins, poor results are obtained for, amongst others, terminal double bonds. This paper reports the use of a second metal to extend the range of cleavage reactions using hydrogen peroxide as oxidant, with good efficiency of peroxide usage.

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.