SELECTIVE OXIDATION OF HYDROCARBONS via C-H BOND ACTIVATION BY SOLUBLE AND SUPPORTED PALLADIUM CATALYSTS

Aidehydes. ketones and vinylic oxidation products such as acetaldehyde. acetone and vinyl acetate are manufactured by related heterogeneous and homogeneous catalytic reactions involving nucleophilic attack on Pd(ll) olefin lrcomplexes. Carbon-hydrogen bond activation (beta-hydrogen elimination) always occurs after nucleophilic attack in these cases. Another family of industrially important products: alpha,beta-unsaturated alcohols, esters and acids such as acrylic acid, allyl acetate and methacrylic acid can be produced by reactions involving nucleophilic attack on a palladium-olefin pi-allyl complex. In these cases C-H bond activation recedes nucleophilic attack. The oxidation state of the metal is a critical factor in determuung when C-H bond activation will occur and therefore which direction these reactions will take. Liquid phase palladium catalyzed oxidation of aromatic substrates via aromatic C-H bond activation gives either phenols and aryl acetates or products of oxidative dimerization. Oxidative coupling is favored by lower oxidation state catalysts whereas ring oxidation is favored by high oxidation state systems. Alkyl aromatic compounds undergo oxidation at the alkyl side chain. Benzylic oxidation is favored by low oxidation state palladium whereas more electrophilic high oxidation state species attack the ring.