Oxidation of l-sorbose with molecular oxygen on platinum modified by metals, amines and phosphines

Abstract The oxidative dehydrogenation of l -sorbose to 2-keto- l -gulonic acid in aqueous medium is reviewed with special emphasis on the use of promoted platinum catalysts. The activity of alumina- or carbon-supported platinum can be increased by selective deposition of bismuth or lead onto the supported platinum particles, and by preadsorbed strongly basic tertiary and quaternary amines. Both methods have a negative influence on the selectivity, but the effect of supported N-bases is less detrimental. Aromatic and cycloaliphatic amines, some phosphines and aminophosphines improve the selectivity to 2-keto- l -gulonic acid. The amine and phosphine modifiers are used in very small amounts, less than 600 ppm related to sorbose. The best modifier is hexamethylenetetramine, which provides 99-95% selectivity up to 30% conversion. The efficiency of metal, amine and phosphine type promoters is compared.