Dinitroaniline, reduction

Eizember (1978) and Eizember et al (1979 and 1980) investigated other contingencies for the additional reduction of nitrosamine impurities in a wide variety of dinitroaniline analogs. Trifluralin is chosen as being typical of the dinitroanilines. 

Owing to its low water solubility and high octanol/water partition coefficients, dinitroaniline herbicides adsorb and bind to soil macromolecules and show minimal leaching potential. Dinitroanilines herbicides show good soil residue activities with soil half-lives ranging from 30 days for benfluralin and oryzalin to 6-7 months for trifluralin. Al-Dealkylation (aerobic conditions) and reduction of the nitro group to an amino moiety (anaerobic conditions) have been reported as major soil degradation pathways. 

Dinitroaniline herbicides show minimal plant systematic translocation properties with the majority of the absorbed residues in the root tissues. Metabolites identified include traces of Al-dealkylation, alkyl and aryl hydroxylation and nitro reduction products. Low levels of dinitroaniline herbicide residues have been reported in raw agricultural commodities according to Good Agricultural Practice. 

The fate of the dinitroaniline herbicides in soil is extremely complex and many metabolites have been identified. Golab and Althaus reported 28 metabolites identified in a degradation study of trifluralin in soil. Major degradation products of dinitroaniline herbicides were formed by nitro reduction, A-dealkylation (mono-dealkylated and completely dealkylated) and the ring formation of benzimidazole. 

The synthesis of TATB (14) from the reaction of 2,3,4,5,6-pentanitroaniline (31) with ammonia has been reported. " In one route, 2,3,4,5,6-pentanitroaniline (31) is synthesized from the nitration of 3,5-dinitroaniline (30) " the latter is obtained from the selective reduction of TNB ° or via a Schmidt reaction with 3,5-dinitrobenzoic acid. Another route to 2,3,4,5,6-pentanitroaniline (31) involves the selective reduction of TNT (1) with hydrogen sulfide in ammonia followed by nitration of the resulting 4-amino-2,6-dinitrotoluene (46), during which the methyl group is lost by oxidation-decarboxylation. 

The mixture is heated to 450, and with good stirring hydrogen sulfide is passed into the reaction mixture while its temperature is maintained between 450 and 550 (Notes 2 and 3). The yellow suspended particles of 2,4-dinitroaniline dissolve slowly to form an intensely red-colored solution. The reaction is complete when all the yellow particles have disappeared reduction should be complete in thirty to sixty minutes (Note 4). 

Reduction. sym-Trinitrobenzcne, when reduced with sodium- or ammonium sulphide, forms 3,5-dinitroaniline. By treating it with hydrogen sulphide in alcoholic solution dinitrophenylhydroxylamine may be formed ... 

Dinitroaniline is usually obtained from 1,3,5-trinitrobenzene by reduction of a nitro group with sodium hydrosulphide. It may be used as starting material for the preparation of pentanitroaniline. 

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

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... 

Nitroaminocompounds or Nitroamines. Compds containing both —NO2 and —NH2 radicals attached to different C atoms, eg, nitroaniline, O2N.C5H4.NH2, etc. Nitroamines can be prepd either by the nitration of amines, or by partial reduction of nitrocompounds contg several —NO2 groups. Another method is to treat a chloronitrocompound with ammonia, as in the prepn of dinitroaniline... 

Diamino-4-nitrobenzene can be prepared by the partial reduction of 2,4-dinitroaniline in alcohol solution using sodium hydrosulfide or ammonium sulfide. - The method described here is a modification of that given by Kehrmann. ... 

It appears that resistance to the aryloxyphenoxypropionate herbicides, the cyclohexanedione herbicides and to the sulfonylurea herbicides is unlikely to be due to reductions in the sensitivity or increases in the amounts of their respective target enzymes (Figures 2 3). Studies have not yet been performed to examine if die resistance to the dinitroaniline herbicide trifluralin is associated with any change at the tubulin polymerization site. 

Selective hydrogenation of one or two nitro groups in an aromatic dinitro compound is the basis for the synthesis of otherwise unattainable molecules. Carefully chosen catalysts, under totally different reaction conditions, have been met with success. Partial reduction of 2,6-dinitroanilines to nitrophenylenediamines occurs in 60-90% yield over 10% palladium-on-carbon at RT [equation (a)], although most heterogeneous catalysts do not afford such selectivity. 

Selective reduction of polynitro compounds. 2,6-Dinitroanilines can be reduced to nitrophenylenediamines by partial hydrogenation with 20% Pd on... 

The reduction of 2-bromo-4,6-dinitroaniline (BDNA), an important intermediate in the preparation of textile dyes that has been detected in river waters (Maguire and Tkacz, 1991), in anaerobic sediment-water systems occurred in an analogous manner to that of 2,4-dinitroaniline and 2,4-dinitrophenol (Equation 3.27). 

The reduction of BDNA was very selective for the nitro group in the 2-position (Weber, 1988). Also, as was the case for the reduction of trifluralin, 2,4-dinitroaniline, and 2,4-dinitrophenol, the resulting diamino benzene was much more persistent than the parent compound. Reduction of the second nitro group to give the triamino benzene did occur, but very slowly. Only trace amounts of this compound were observed in the sediment slurries. 

The reduction of several water-insoluble disperse azo dyes in anaerobic sediment-water systems also has been reported. For example, reduction of Disperse Blue 79, the largest volume textile dye on the market today, was reduced in anoxic sediment slurries with half-lives on the order of 1 to 5 hours (Weber, 1988). Reduction appears to occur initially across the azo linkage and results in formation of 2-bromo-4,6-dinitroaniline (BDNA) and the substituted 1,4-phenylenediamine, (A) (Figure 3.5). 

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