Transfer Hydrogenation Reactions by Using Simple Biomass Alcohols as Hydrogen Sources

The reduction of different unsaturated compounds by transfer hydrogenation (TH) has emerged as a more efficient methodology than the classical method of using the molecular hydrogen in industry and laboratory. Transfer hydrogenation is more advantageous in terms of safety and convenience. Alcohols, formic acid, esters, H2O, etc. are the common molecules that are used as a hydrogen donor in the transfer hydrogenation reaction. Primary alcohols, namely methanol and ethanol were less explored as a hydrogen source in the TH reaction, probably due to the formation of aldehyde after dehydrogenation of these alcohols, which are more reactive and may undergo side reactions. However, methanol and ethanol are cheap, easily available, and easily handled compounds. They can be easily obtained from biomass, coal, etc. Because of these advantages, chemists became more interested in the application of methanol and ethanol as hydrogen sources in the transfer hydrogenation reaction. In this review, we present an overview of the work reported by different groups on the transfer hydrogenation reactions with methanol and ethanol as hydrogen sources.