Hydrogenation of Dinitrobenzenes to Aminonitrobenzenes

Lyle and LaMattina selectively hydrogenated 4-substituted 2,6-dinitroanilines to the corresponding nitrophenylenediamines over 10% Pd-C in 1,2-dimethoxyethane-chloroform as solvent (eq. 9.56).135 With use of ethanol instead of 1,2-di-methoxyethane, 4-trifluoromethyl-2,6-dinitroaniline was completely hydrogenated to give the corresponding triaminobenzene. 

Aromatic dinitro compounds may be selectively reduced by hydrazine in the presence of transition metal catalysts.136 Pitre and Lorenzotti obtained 3-amino-5-nitrobenzoic acid in 82% yield by treating 3,5-dinitrobenzoic acid with Raney Ni and an appropriate amount (3.6 equiv) of hydrazine in water (eq. 9.57).137 Similarly, 2,4-dinitrophe-nol and 2,4-dinitroaniline were reduced to 2-amino-4-nitrophenol and 2-amino-4-nitroaniline, respectively, with 10% Pd-C and hydrazine in ethanol solution. 

TABLE 9.6 The Reduction of 4-Trifluoromethyl-2,6-dinitroaniline with Hydrazine in the Presence of Catalyst in Ethanol  

5% Pd-C in both ethanol and DMF, little, if any, selectivity was obtained product ratios were 50 50 in ethanol and 60 40 in DMF. Palladium black in ethanol, which afforded 4-amino-5-nitroveratrole in 70-75% yield from 4,5-dinitroveratrole, provided no selectivity with 2,4-dinitroaniline, as well as with o- and m-dinitrobenzenes both nitro groups were hydrogenated.140 Reduction by sodium borohydride and Pd-C in methanol also does not appear to be selective, as 1,2,4-triaminobenzene is formed.141 It is of interest that over Pt-C in acidic alcohol 2,4-dinitroaniline is selectively hydrogenated at the 4-nitro group to give 4-amino-2-nitroaniline in 70% yield.142 

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