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Platinum Metals Rev., 1971, 15, (1), 8

Further Advances in Catalytic Hydrogenation

New Reactions with Palladium and Rhodium Catalysts

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Workers from Hoffman-La Roche reported to a recent symposium held by the New York Academy of Sciences that acid chlorides can be converted to aldehydes by a modified Rosenmund reaction using palladium on charcoal catalyst poisoned with quinoline-sulphur inhibitor. The development of this reaction at 50 lb/in2 has reduced catalyst requirements and it opens the way to manufacture of pharmaceutical chemicals from cheaper aldehyde intermedidates by using cheap hydrogen instead of expensive hydrides for hydrogenation of pure acid chlorides. The end point of the reaction was determined by seeing how much hydrogen had been used. The conventional Rosenmund reaction barium sulphate moderator was not needed.

A group from Monsanto showed that optically active phosphine complexes of rhodium(III) can catalyse hydrogenation of olefins to optically active products. For example, 28 per cent optical purity, i.e., 64 per cent of one optical isomer and 36 per cent of the other, was obtained during hydrogenation of α-phenylacrylic acid to α-phenylpropionic acid at 300 to 400 lb/in2. The group has not yet finalised the reaction mechanism. The catalyst was formed in situ by reacting the 1,5-hexadiene complex of rhodium(III) with an optically active phosphine-based ligand such as methylphenyl-N -propylphosphine.

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