Oxidation of alcohols with molecular oxygen on platinum metal catalysts in aqueous solutions

Abstract

The platinum-catalyzed oxidation of alcohols with molecular oxygen in aqueous medium was discovered one and a half centuries ago [ 1,2]. The method has been improved with the general development of heterogeneous catalysis. At the beginning of this century it was found [ 31 that not only platinum, but dispersed palladium was also a good catalyst for the reaction. Platinum on various supports was tested and compared by Heyns [ 41 when he extended the method to the synthesis of L-ascorbic acid. The next milestone was the promotion of platinum metals with heavy metals such as Bi or Pb to overcome the deactivation problems and change the direction (selectivity) of the reaction [ 5-71. The present review will be focused on the application of biand multi-metallic catalysts in the aqueous phase oxidation of alcohols with molecular oxygen. The reactions discussed are the transformation of primary alcohols to aldehydes or carboxylic acids, and secondary alcohols to ketones. Special attention will be given to the various reasons for the loss of catalytic activity and the role of promoters in the suppression of deactivation. A detailed discussion of the earlier results of alcohol oxidation on platinum metal catalysts, especially in the field of carbohydrate chemistry, can be found in previous reviews [ 818 1. The mild reaction conditions and high selectivity in the oxidation of polyols made the method very attractive for carbohydrate chemistry. As an example, the catalytic route for the oxidation of D-glucose to D-gluconic acid based on the application of promoted Pd catalysts in aqueous alkaline medium can compete economically with the generally applied biochemical oxidation [ 19,201. Various chelating agents, detergent builders or food additives may be prepared by this way from relatively cheap starting materials of natural origin.