Aldehydes and ketones

Abstract

Oxidative Methods.-Further studies of oxidations using sodium hypochlorite in glacial acetic acid have shown that secondary alcohols may be oxidized to ketones in the presence of primary a1cohols.l In one example where epimerization of the ketonic product was possible, isomerization was not observed under the reaction conditions. The easily stored calcium hypochlorite also oxidizes secondary alcohols to ketones.2 Yields are high in dichlorornethane or acetronitrile containing acetic acid. cr-Diols are cleaved oxidatively to aldehydes or ketones, depending on the starting materiaL3 A hypochlorite may be used as an oxidant for secondary alcohols in various solvents (dichloromethane, carbon tetrachloride, ether, or ethyl acetate) in the presence of catalytic amounts of the hypochlorite form of the commercial resin IRA goo.* This method, allowing a non-aqueous work-up to be employed, may prove advantageous for the preparation of water-soluble products. Sodium bromate, in the presence of cerium(1v) ammonium nitrate or cerium(1v) sulphate, also oxidizes secondary alcohols in preference to primary alcohol^.^The uses of the versatile oxidant pyridinium chlorochromate have been reviewed.6 Pyridinium chlorochromate has been used for the oxidation of methyl 5-hydroxypentanoate to the aldehyde,' an intermediate useful in the synthesis of leukotrienes, and the same reagent oxidatively cleaves secondary vicinal diols to the corresponding aldehydes.8 The reactivity of the chlorochromate ion as an oxidant can be influenced by the counter-ion. For example, the 4-dimethylaminopyridinium salt is a mild, selective reagent for the oxidation of allylic and benzylic alcohols. Pyridinium fluorochromate oxidizes primary and secondary alcohols to aldehydes and ketones respectively in dichloromethane solution, and shows a less pronounced acidity compared with the chloro-