Oxidation of Alcohols, Carbohydrates and Diols

Abstract

This is one of the most important classes of oxidation effected by Ru complexes, particularly by RuO 4 , [RuO 4 ] − , [RuO 4 ] 2− and RuCl 2 (PPh 3 ) 3 , though in fact most Ru oxidants effect these transformations. The chapter covers oxidation of primary alcohols to aldehydes (section 2.1), and to carboxylic acids (2.2), and of secondary alcohols to ketones (2.3). Oxidation of primary and secondary alcohol functionalities in carbohydrates (sugars) is dealt with in section 2.4, then oxidation of diols and polyols to lactones and acids (2.5). Finally there is a short section on miscellaneous alcohol oxidations in section 2.6.In this chapter the first of the two most important categories of oxidations catalysed by Ru complexes (the other being alkene and alkyne oxidations in Chapter 3) are considered. The approach in this and subsequent chapters differs from that of Chapter 1, concentrating here on the substrate rather than on the oxidant. The text is divided into the categories of alcohols and their oxidations. There are summaries in section 2.3.6 of systems of limited applicability which are mentioned only in Chapter 1, and in section 2.3.7 of large-scale (>1 g) oxidations.The first oxidations of alcohols by stoicheiometric RuO 4 /H 2 O were reported in 1958, of primary alcohols to aldehydes or carboxylic acids and secondary alcohols to ketones [1]. The first Ru-catalysed oxidation of an alcohol was reported in 1965 when Parikh and Jones used RuO 2 /aq. Na(IO 4 )/CCl 4 1 ( Table 2.3) [2] to oxidise secondary alcohol groups in carbohydrates.Oxidation of alcohols is the most frequently reviewed topic for Ru-catalysed oxidations [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Mechanisms of alcohol oxidation by Ru complexes have been reviewed [21].