Catalytic Reduction of o-Nitroanisole with Hydrogen in Sulfuric Acid-Methanol Solution

Catalytic reduction (5% platinum or 5% palladium placed on carbon and under 1 atm of H₂) of o-nitroanisole [1 ] with hydrogen was carried out in sulfuric acid-methanol solution at a room temperature. The reaction products were o-anisidine [2], 2,4-dimethoxyaniline [3], and 2,6-dimethoxyaniline [4]. The products [3] and [4] were considered to form in terms of the Bamberger-type rearrangement of o-methoxyphenylhydroxylamine, formed in the course of catalytic reduction of [1] to [2]. The yield of amines ([2], [3], [4]) was significantly dependent upon the amount of sulfuric acid. Pt-C catalyst is more effective than Pd-C to obtain significant amount of [3] and [4]. When catalytic reduction of [1] (4.0g) over Pt-C (120mg) was carried out in 40ml of methanol, the maximum yield of [4] achieved when 20.0 g of sulfuric acid was added (the yield of [2],[3] or [4] being 56%, 12%, or 27%, respectively) and that of [3] was achieved when 40.0g of sulfuric acid was added (the yield of [2], [3], or [4] being 33%, 26% or 2%, respectively). It was also found that addition of dimethyl sulfoxide, a catalyst poison, enhances significantly the yield of rearrangement products: for example, while the yield of [2], [3], or [4] being 81%, 18%, or 1%, respectively, in the case of 2.8 g of sulfuric acid and in the absence of dimethyl sulfoxide, the yeild of [2], [3], or [4] being 55%, 28%, 9%, respectively, in the presence of dimethyl sulfoxide (0.05 ml).