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Showing papers in "Chemical Reviews in 1985"




Journal ArticleDOI
TL;DR: In this paper, a review of transfer reduction using hydrogen donors is presented, focusing mainly on those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen.
Abstract: Reduction of organic compounds is important synthetically both in the laboratory and in industry. There are many methods of effecting reduction which may or may not lead to hydrogenation, but in this review only processes leading to the addition of hydrogen or replacement of a functional group by hydrogen will be considered. Further, this review will be concerned mostly with those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen. Reduction of organic functional groups can be categorized into (i) addition of hydrogen to unsaturated groups as, for example, in the reduction of ketones to alcohols and (ii) addition of hydrogen across single bonds leading to cleavage of functional groups (hydrogenolysis). Removal of oxygen as a reductive process, as in the deoxygenation of oxiranes to alkenes, will not be discussed. Of all the methods available for addition of hydrogen to organic compounds, heterogeneous catalytic transfer reactions have been relatively underutilized. This lack of popularity can be traced to the relatively meager success of much of the earlier research which suggested that the technique was of only limited scope and could provide only modest yields of products. The early pioneering work by Braude' was largely ignored because of poor yields and long reaction times, but the situation has changed considerably following the appearance4 of a stimulating review and the introduction of greater catalyst loadings and different hydrogen donors.2 Another reason for the underutilization of transfer reduction has been the very successful exploitation of molecular hydrogen and hydrides for reduction of organic compounds. In comparison with catalytic reduction using molecular hydrogen, transfer reduction using hydrogen donors has real and potential advantages. Molecular hydrogen, a gas of low molecular weight and therefore high diffusibility, is easily ignited and presents considerable hazards, particularly on the large scale; the use of hydrogen donors obviates these difficulties in that no gas

824 citations