Oxidation catalysis using supported gold nanocrystals

Oxidation is a key process for commercial applications, in the production of chemical intermediates, high tonnage commodity chemicals, high value fine chemicals, agrochemicals and pharmaceuticals. These oxidations often use stoichiometric oxygen donors such as chromate or permanganate, oxygen donors that give rise to pollutants of considerable environmental concern. Free solvent oxidation of 1-hexene with air using supported gold catalysts with a catalytic amount of tert-butyl hydroperoxide (TBHP) as initiator has been conducted in the liquid phase. Reaction conditions such as radical initiator concentration and reaction temperature were varied to obtain optimum conditions. The gold supported on graphite is an effective catalyst for such oxidations and that graphite was the best of the supports studied. Preparation of catalysts using modified sol-immobilisation including washing under reflux resulted in enhanced catalyst activity by a solvent treatment prior to the reaction. Gold, palladium and gold-palladium catalysts supported on TiO2 has been used for oxidation of trans-2-hexen-1-ol and 1-hexene-3-ol with air at 50 ˚C. The effect of the preparation method, catalyst mass, support, gold: palladium ratio and temperature have been investigated. The main aim was to determine if either the alcohol or alkene functional group can be oxidised selectively. However, based on the reaction products observed trans-2-hexen-1-ol forms trans-2-hexene, hexanal, trans-2-hexenal, trans-3-hexen-1-ol, 4-hexen-1-ol and trans-2-hexanoic acid. 1-hexen-3-ol forms 1-hexene, 3-hexanone, 1hexen-3-one and 3-hexenol), the main pathway in these reactions is isomerisation and, in addition, significant yields of the products are due to a VI disproportionation reaction. Controlling the selectivity in molecules with multiple function groups by manipulating the catalyst composition and reaction conditions can promote or hinder the various reaction pathways, thereby increasing the selectivity to the desired oxidation products. Oxidations of cyclic alkenes were carried out using supported gold nanoparticles under mild solvent-free conditions. The influences of support, preparation method and choice of metal have been investigated. The selectivity to the epoxide is dependent on the size of the cyclic alkene ring. In particular, the epoxide selectivity is very low for < C7, and the origins of this effect are discussed. The influence of the removing stabiliser form cycloalkene has been demonstrated that cycloalkene can be oxidized in the absence of radical initiators when cycloalkene is free of stabilisers