Homogeneous, heterogeneous and nanocatalysis

For the conversion of raw materials into fine chemicals and high-value building blocks, reliable oxidation methods have been found to be indispensable tools in modern organic synthesis. Various methods with remarkable efficiencies have been developed for a wide array of oxidative transformations which are now well established. However, since most of these standard protocols rely on the use of hazardous terminal oxidants or cause the generation of significant amounts of waste products, there is still an evident need for methodological improvements with respect to environmental and economic issues. Especially in terms of waste product minimization and the use of renewable materials, catalytic aerobic transformations offer some ideal features of a ‘green’ process towards sustainability. In particular, the oxidation of alcohols is one of the most important synthetic operations in both the organic chemistry laboratory and the chemical industry. Although classic oxidation reactions can be very efficient and selective, they often involve the use of stoichiometric reagents and halogenated solvents, resulting in the generation of large quantities of wastes. The urgent need for more sustainable chemical processes hasprompted the development of mild and selective oxidation methods based on the use of green reagents and solvents. In this context, the direct use of oxygen as an oxidizing reagent is a very desirable feature for modern synthetic methods. Hence new catalysts for the aerobic oxidation of alcohols have attracted much attention in recent years. Transition metal-based systems have been successfully used for the aerobic oxidation of alcohols to the corresponding carbonyl compounds with excellent performances of several transition metal catalysts. Homogeneous, heterogeneous and nanocatalysis are the subject of intense research in this field and, rather than aspiring to be exhaustive, this chapter deals with the comparison of those macro-areas within the context of efficiency in reaction design, by following the principles of green and sustainable chemistry for oxidation processes.