ABSTRACT
A carbon-carbon double bond is one of the more easily hydrogenated functional groups. An isolated double bond is more readily hydrogenated than any other functional group with the exception of acetylenes, polyenes and, under certain conditions, aromatic nitro groups. Strained double bonds are hydrogenated more readily than unstrained alkenes and exocyclic double bonds are generally more easily hydrogenated than are endocyclic olefins. Under conditions of low hydrogen availability such as low pressure, slow agitation and/or a large quantity of catalyst, insufficient hydrogen is present at the catalyst surface so rapid transfer of both adsorbed hydrogens is not possible. The hydrogenation of enol ethers, esters, enamines and enamides is commonly run using a palladium catalyst at room temperature and atmospheric pressure. Isolated double bonds and double bonds conjugated with the enol are, however, preferentially hydrogenated. The selective hydrogenation of the double bond of an a,ß-uiisaturated carbonyl compound is rather easily accomplished over most metal catalysts under moderate conditions.
