ABSTRACT
An aromatic nitro group is generally the most easily hydrogenated of all functional groups. Reduction to the aniline takes place under mild conditions over virtually all hydrogenation catalysts. This hydrogenation usually proceeds best in neutral solution. In acidic or basic media it takes place more slowly. Aryl diazomethanes and ethyl diazoacetate lose nitrogen completely when hydrogenated over palladium in neutral medium at room temperature and atmospheric pressure. The hydrogenation of azines takes place in a stepwise fashion over platinum with the hydrazone formed on absorption of one equivalent of hydrogen. The selective hydrogenation of semicarbazones to semicarbazides, and azines and hydrazones to hydrazines takes place over platinum and nickel, but less readily over palladium. Further hydrogenolysis to the primary amine, while occurring over all catalysts, is particularly favored with palladium.
