Formic acid nitro compounds

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Formic acid, anhydrous (M.W. 46.03, m.p. 8.5°, b.p. 100.8°, density 1.22), or a 90% aqueous solution, is an excellent hydrogen donor in catalytic hydrogen transfer carried out by heating in the presence of copper [77] or nickel [77]. Also its salt with triethylamine is used for the same purpose in the presence of palladium [72, 73], Conjugated double bonds, triple bonds, aromatic rings and nitro compounds are hydrogenated in this way. 

Some studies seeking preferred conditions for this reaction have been made. Optimum yields are obtained when the amount of water present is appreciable, and it was noted that the rate of hydrogen evolution increases with increasing water content. A 75% formic acid system appears generally preferred. Under the reaction conditions examined by the submitters, olefins, ketones, esters, amides, and acids are inert, but nitro compounds are reduced to the formamide derivative. 

Selective reduction to hydroxylamine can be achieved in a variety of ways the most widely applicable systems utilize zinc and ammonium chloride in an aqueous or alcoholic medium. The overreduction to amines can be prevented by using a two-phase solvent system. Hydroxylamines have also been obtained from nitro compounds using molecular hydrogen and iridium catalysts. A rapid metal-catalyzed transfer reduction of aromatic nitroarenes to N-substituted hydroxylamines has also been developed the method employs palladium and rhodium on charcoal as catalyst and a variety of hydrogen donors such as cyclohexene, hydrazine, formic acid and phosphinic acid. The reduction of nitroarenes to arylhydroxyl-amines can also be achieved using hydrazine in the presence of Raney nickel or iron(III) oxide. ... 

Nitro-3-h5 droxybenzaldehyde also yields a mixture of compounds. The dimercurated product appears to be a hydroxymercuri-acetoxy-mercuri-4-nitro-3-hydroxybettzaldehyde. It is insoluble in most solvents, but gives 2 Q-diformomydimercuri- -nitro-Z-hydroccybenzahk-hyde from hot formic acid solution. It crystallises in pale yellow needles, which darken at 120° C. and explode at 257° C. When boiled with formic acid, metallic mercury separates. It gives a red solution in potassium hydroxide, from which hydrochloric acid precipitates the 2 Q-dichloro-dimercuri derivative This crystallises from alcohol in bundles of minute, pale yellow needles, which darken at 240° C. but do not melt at 300° C. When heated in vacuo it loses a molecule of water at 60° C., and decomposes at 282° C. (corr.). Its potassium hydroxide solution is decomposed by carbon dioxide with precipitation of 2 3-anhydro-2 6-dihydroxymercuri"4-nitro-3-hydroxybenzaldehyde. The dimercurated compound may be converted by the usual means into a di-iodo-4-nitro-3-hydroxybenzaldehyde,... 

There now exists evidence for the extension of two-phase catalysis into the new area of Ci-chemistry. Thus, Leitner an co-workers [206] described the biphase hydrogenation of CO2 to formic acid (cf. Section 3.3.4). Two-phase hydrogenations of aromatic nitro compounds with Pd or Rh catalysts are examined by Tafesh and co-workers [207] and others [212 f, 218 d, 226]. 

The Taft analysis has the working disadvantage that it requires two measurements to define a a value, and it also suffers from the problem that the parameters of some substituents cannot be obtained either because the ester decomposes too quickly for measurements to be made or because it would not decompose by ester hydrolysis. Such restrictions apply to the halogen substituents, nitrile or the nitro group, which would require study of such compounds as Hal-CO-OR, NC-CO-OR and O2N-CO-OR. This problem can be solved by use of Taft analysis of esters of the type X-CH2-CO-OR instead of X-CO-OR. In this analysis the similarity coefficient, p, for the substituted acetic acid derivatives is attenuated by 0.41 from the set value of p = 2.48 for the formic acid derivatives (Equations 8 and 9). The a constants based on formic acid derivatives are recorded in Table 1 in Appendix 3. ... 

Amount of Acid Used. This reaction requires the presence of small amounts of ferrous ion to act as a catalyst. Generally about 0.05-0.2 of an equivalent of acid is used. The acids usually employed in the reduction process are hydrochloric and sulfuric. It should be borne in mind that hydrochloric acid sometimes causes the formation of small amounts of chlorinated amines whereas sulfuric acid may rearrange the intermediate arylhydroxylamines to hydroxyarylamines and cause the formation of darker amines in lower yields, particularly in the case of solid amines. Where the danger of hydrolysis or contamination by such products exists, acetic or formic acid is employed instead. The disadvantages in the use of sulfuric acid appear to be minimized when the sulfuric acid is introduced as sodium acid sulfate (niter cake). When used alone or preferably in conjunction with a calculated quantity of sodium chloride, a very economical and satisfactory promoter is obtained. For example, 2.4 lb of sodium chloride with 6 lb of niter cake per 100 lb of nitro compound gives satisfactory results. The niter cake is first ground and is added, along with the sodium chloride, to the water and finely divided iron in the reducer. 

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