Catalytic Reduction of Sterically Hindered Aromatic Nitro Compounds with Hydrogen in Sulfuric Acid-Methanol Solution

The catalytic reduction (5% platinum on carbon carrier and under 1 atm of H₂) of sterically hindered aromatic nitro compounds [1] (2, 3-dimethylnitrobenzene [la], 2,6-dimethylnitro-benzene [1b], 1-nitronaphthalene [1c] and 2-methyl-l-nitronaphthalene [1d]) with hydrgen was carried out in sulfuric acid-methanol solution at room temperature. The reaction products were the corresponding amino compounds [2] (2, 3-dimethylaniline [2a], 2, 6-dimethylaniline [2b], 1-naphthylamine [2c] and 2-methyl-l-naphthylamine [2d]) and 4-methoxyM-amino compounds [3] (4-methoxy-2,3-dimethylaniline [3a], 4-methoxy-2,6-dimethylaniline [3b], 4-methoxy-l-naphthylamine [3c] and 4-methoxy-2-methyl-l-naphthylamine [3d]), respectively. [3] were considered to form in terms of the Bamberger-type rearrangement of arylhydroxylamines which are the intermediates formed in the catalytic reduction of [1] to [2]. The maximum yields of [3] were [3a]=64%, [3b]=45%, [3c]=68% and [3d] = 55%, respectively, under the typical reaction conditions. The yield of [3b] increased to 72% by the addition of a small amount of dimethyl sulfoxide to a reaction medium.