Transfer hydrogenolysis of aromatic alcohols using Raney catalysts and 2-propanol

Abstract

Raney nickel in refluxing 2-propanol is an effective catalytic system for cleaving CO bonds in aromatic alcohols by transfer hydrogenolysis. Deoxygenation of alcohols substituted at the α-, β-, γ-, δ-, and ε-positions was accomplished. The reaction appears not to be sensitive to substitution about the carbinol carbon. Aliphatic alcohols do not undergo hydrogenolysis with this system. Some dehydromethylation is found in the hydrogenolysis of primary alcohols. With extended reaction times, ring reduction accompanies hydrogenolysis of alcohols containing more than one aromatic ring. Raney cobalt is shown to catalyze hydrogen transfer from 2-propanol. Raney cobalt in refluxing 2-propanol is an effective system for deoxygenating α-substituted alcohols only. Although Raney cobalt is less reactive than Raney nickel in transfer hydrogenolysis, it exhibits greater selectivity as illustrated by the lack of ring reduction in alcohols containing more than one aromatic ring.