Nitramine, reduction

Aromatic nitro and nitroso compounds are easily reduced at carbon and mercury electrodes. Other nitro compounds such as nitrate esters, nitramines, and nitrosamines are also typically easily reduced. The complete reduction of a nitro compound consists of three two-electron steps (nitro-nitroso-hydroxylamine-amine). Since most organic oxidations are only two-electron processes, higher sensitivity is typically found for nitro compounds. Several LCEC based determination of nitro compounds have been reported... 

The diastereomerically related keto esters 53 and 55, activated for removal of the chiral auxiliary, were obtained from 5 and 9. The requisite nitrogen atom was introduced by an azide displacement of chloride and at an opportune stage of the synthesis an intramolecular aminolysis of the carboxylic ester provided the enantiomerically related keto lactams 54 and 56. Although shorter routes to these popular synthetic targets have been reported in recent years, the conversion of 9 to (—)-iso-nitramine (ten steps, 50% overall yield) clearly illustrates the efficiency of the asymmetric Birch reduction-alkylation strategy for construction of the azaspiroundecane ring system. 

While nitramines are formed from the reaction of secondary amines with nitronium salts the success of the reaction depends on the basicity of the amine (Equation 5.11). Thus, amines of low to moderate basicity are A-nitrated in good yields. The nitration of more basic amines is slow and the nitrosamine is often observed as a significant by-product, a consequence of the partial reduction of the nitronium salt to the nitrosonium salt during the reaction. Increased reaction temperature is also found to increase the amount of nitrosamine formed. The amine substrate is usually used in excess to compensate for the release of the strong mineral acid formed during the reactions. Both nitronium tetrafluoroborate and the more soluble hexafluorophosphate are commonly used for A-nitrations. Solvents like acetonitrile, methylene chloride, nitromethane, dioxane, sulfolane, ethyl acetate and esters of phosphoric acid are commonly used. 

The bis-nitramine (155) has been prepared from the reaction of 1,5-diaminotetrazole (152) with glyoxal, followed by reduction of the resulting fused heterocycle (153) with sodium borohydride and subsequent A-nitration of the piperazine nitrogens of (154). ... 

Preparative scale reduction of nitramines and nitrosamines in acid solution is a convenient route to substituted hydrazines. Early workers used a cathode of tinned copper [120], More recently mercury has been employed as cathode material, although tin would probably be equally suitable. Nitrosamines are conveniently reduced in dilute hydrochloric acid and evaporation of the electrolyte at the end of the reaction affords the hydrazine hydrochloride [121]. Some nitroso compounds are unstable to these acidic conditions. In the case of N-nitrosoindoles, this problem has been overcome in an ingenious manner [122]. The nitroso compound and aqueous sulphuric acid are mixed just prior to reaction and then forced through a porous cathode of bronze coated with mercury at such a rate that the reduction is completed in one pass through the cathode. Other workers have overcome the instability of N-benzyl-N-nitrosoanthraniiic acid towards acid by working in an acetate buffer at below room temperature [123],... 

Bratin, K., P. T. Kissinger, R. Briner, and C. Bruntlett. Determination of nitro aromatic, nitramine, and nitrate ester explosive compounds in explosives mixtures and gunshot residue by liquid-chromatography and reductive electrochemical detection. Anal. Chim. Acta 130, 295-311 (1981). 

The existence of a bond in nitramines linking the nitrogen atom of the nitro group with that of the amino group is proved by the formation of hydrazine derivatives by the reduction of nitramines. Secondary nitramines give a particularly high yield of hydrazine derivatives. 

Various products are formed by the reduction of nitramines, depending on the reaction conditions. 

The reaction of primary aromatic nitramines with nitrous acid is specific and leads to the formation of diazonium nitrate (Bamberger [23]). According to Stevens [24] this reaction is also a kind of reduction, and presumably may be represented as follows ... 

X = S) is excluded on the basis of the reduction of the corresponding ureas (143) to the known 3-aryl-l-(isopropylideneamino-amidino)ureas (143a R = Ph). In the absence of rearrangement, the condensation products of isocyanates and nitroguanidine may thus be formulated as nitramines (143), and, by analogy, their sulfur analogs as 139.141... 

JV-Nitraminopyridines are reducible both in acid and alkali. In hydrochloric acid the main product from 2-nitraminopyridine was the hydrazino-pyridine, formed in a six-electron reduction, but 2-aminopyridine and 2-chloropyridine were side products, the latter possibly through reaction by an intermediate diazonium compound with chloride. Contrary to nitramines of most primary amines, 2-nitraminopyridine431 is reducible in alkaline solution uptake of the first two electrons forms the 2-pyridyl-N-nitrosamine, which is further reduced to 2-aminopyridine. 

K. Bratin, P. T. Kissinger, R. C. Briner, and C. S. Bruntlett, Determination of Nitro Aromatic, Nitramine and Nitrate Ester Explosive Compounds in Explosive Mixtures and Gunshot Residue by Liquid Chromatography and Reductive Electrochemical Detection, Analytica Chimica Acta 130, no. 2 (1981) 295. 

Keefer LK, Lunn G. 1985. Reductive destruction of nitrosamines, hydrazines, nitramines, azo- and azoxy-compounds. National Institute of Health, U.S. patent no. 4534154. 

Petrosyan VA, Frolovskii VA. 1989. Electrochemical generation of n-nitramine ions upon the reduction of n-nitramines. Bulletin of the Academy of Sciences of the USSR Division of Chemical Science 38 2439. 

The corresponding V-nitro derivatives behave similarly306-308 in acid solution the hydrazines are produced in a six-electron reaction, in alkaline medium the first two-electron reduction results in the formation of the A7-nitroso derivatives which at a more negative potential are further reduced. iV-Nitropyrazole behaves slightly differently as the reduction in acid solution also results in a cleavage of the N-N bond with formation of nitrous acid. 2-Nitraminopyri-dine309 in acid solution is reduced to the hydrazine. In alkaline solution the anion is reducible, in contradistinction to most nitramines derived from primary amines. The four-electron reduction yields 2-aminopyridine. Pyridine 1-nitroimide is reduced to pyridine.309... 

In alkaline solution most A-nitro derivatives of primary amines form an irreducible anion [R-bHSf02] , with nitraminopyridines as exceptions [205], whereas nitramines of secondary amines are reduced in two steps. [202]. The first reduction consumes 2F/mol and produces an A-nitrosamine. It is noteworthy that A-nitrosamines in alkaline solution are more difficult to reduce than the corresponding A-nitramines it seems to be the only class of nitro compounds in which the nitro group is more easily reducible than the nitroso group. 

For the quantitative estimation the nitrometer method is not in general applicable, though the nitramine group in tetiyl responds to this test. The Dumas method may be used under precautions, and the Kjeldahl method is sometimes used for the lower nitrocompounds. Titration methods depending on reduction with stannous chloride are described by Limpricht,... 

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