ABSTRACT
The addition of a small amount of ferrous sulfate18 or ferric chloride to the reaction mixture facilitates carbonyl group hydrogenation. Since aliphatic aldehydes and ketones are not hydrogenated over palladium, this reaction provides a means of selectively removing an aromatic carbonyl group in the presence of an aliphatic aldehyde or ketone. The palladium catalyzed hydrogenolysis of aryl aldehydes and ketones is preferable to any of the chemical reduction procedures such as the Wolff-Kishner or Clemmenson reactions for the removal of an aryl carbonyl group. The ease with which the carbonyl group is hydrogenated depends on its environment. Steric factors are more important in the hydrogenation of aldehydes than with ketones. Bulky substituents hinder the adsorption of the carbonyl group on the catalyst surface, thus decreasing the rate of hydrogenation. Other compounds in which the aldehyde or ketone is a to another carbonyl function or a trifluoromethyl group have enhanced adsorption.
