Sodium hydrosulfite nitro phenols

Nitro alcohols were reduced to amino alcohols by catalytic hydrogenation over platinum [632] and with iron [JJ9], and nitrosophenols [255] and nitro-phenols [256] to aminophenols with sodium hydrosulfite, sodium sulfide [238] or tin [176]. Bromine atoms in 2,6-di-bromo-4-nitrophenol were not affected [176]. 

The reduction of azo compounds using sodium hydrosulfite (Na2S204) and NaOH is an important reaction, as it provides an indirect method for the amination of phenols and naphthols (Fig. 13.49). The reduction of nitro groups in anthraquinone compounds works best when a mild reducing agent (e.g., sodium hydrosulfide, NaSH) is used. In this way one avoids reducing the quinoid system. 

The naphthylamines may be prepared by reduction of the corresponding nitro compound, but they are readily accessible from naphthois by the Bucherer reaction The naphthol is heated, preferably under pressure in an autoclave, with ammonia and aqueous sodium hydrogen sulfite solution, when an addition-elimination sequence occurs. The detailed mechanism is not completely elucidated, but the Bucherer reaction is restricted to those phenols that show a tendency to tautomerize to the keto form, such as the naphthois and 1,3-dihydroxybenzene (resorcinol). Using 1-naphthol for illustration, the first step is addition of the hydrosulfite across the 3,4-double bond of either the enol or keto tautomer (Scheme 12.9). Nucleophilic attack by ammonia at the carbonyl group... 

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