Bismuth Catalyzed Aqueous Alcohol Oxidation Reaction Study

Carbonyl compounds widely exist in pharmaceutical and fine chemical industries, and often serve as intermediates for organic synthesis. The oxidation of alcohols to carbonyls is a straightforward method for accessing this important class of compounds. Traditionally, stoichiometric amount of strong oxidants are often employed to accomplish the oxidation of alcohols. However, such oxidants are often hazardous and produce a large amount of waste after reaction. Catalytic oxidation of alcohols with green oxidants, such as H2O2, oxygen or air, is a more desirable process, which only generates H2O as the only by-product. The acceptorless dehydrogenation of alcohols is another green alternative, in which hydrogen gas is released as the only by-product which could be used as a fuel.Chapter 1 of the thesis introduces catalytic systems for oxidation of alcohols with green oxidants such as H2O2, oxygen or air, as well as acceptorless dehydrogenation of alcohols without oxidants.In Chapter 2, a water-soluble binuclear rhodium(II) complex was identified to be an efficient catalyst for oxidation of alcohols to carboxylic acids or ketones in water. The catalytic syetem could operate via either acceptorless dehydrogenation or aerobic oxidation with air. The water soluble catalyst could be removed from the product by simple phase separation and reused for 19 times without significant loss of catalytic activity. The catalytic system has broad substrate scope and could work at gram scale with a substrate/catalyst ratio of 5000.Mechanistic studies were carried out to shed some light on the reaction mechanism. Hydrogen gas was detected from the head gas of the reaction under Ar, but not from the reaction under air, suggesting that the reaction under Ar proceeds via an acceptorless dehydrogenation pathway and oxygen would act as an oxidant to remove the hydrogen atoms from alcohols for the reaction under air. The oxidation of primary alcohols to carboxylic acids procceds mainly via a hemiacetal intermediate instead of the base promoted Cannizzaro reaction.