Reduction of Nitrate Esters

There are many methods to reduce nitrate esters from ester groups to alcoholic hydroxyl groups, most likely to obtain the corresponding alcohols. The oldest, also the most common, reduction method is the reductive hydrolysis by alkali sulfide or alkali sulfhydrate, such as sodium sulfide, ammonium sulfide, or corresponding sulfhydrate [39]. Transesterification reaction would happen in the hydrolysis of nitrate esters by sulfuric acid to form sulfate esters [40]. 

The corresponding alcohols can be obtained in several reaction conditions for nitrate esters. For examples, in acetic acid solvent, iron is used as a reducer for nitrate esters [41]. In pressure condition, iron and zinc are used to reduce nitrate esters in acetic acid solvent, and palladium is used as a catalyst in the hydrogenation process. By using palladium or platinum catalysts, nitrate esters is reduced by hydrazine. The yield of reduction is up to 60-80 %. Some gases, such NO, N2, and H2O, are also obtained in the reduction process. 

Nitrate esters can be reduced in acetic anhydride if zinc is used in the reaction, or reduced by electrolysis. They are prone to be reduced if lithium aluminum hydride is used. The reaction is finished in ether solution and the corresponding alcohols are 

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The basic feature of nitrate esters is the nitroxyl group of -C-O-NO2. The ester group in nitrate esters is of an oxygen atom connecting with a carbon atom, that is, the nitrate esters belong to (9-nitro compounds. This was confirmed by the hydrolysis or reduction of nitrate esters to alcohols [3, 13, 14], as the following reaction equation. 

Analytical. Mannitol Hexanitrate can be hydrolyzed in basic soln and the soln acidified in the presence of NITRON to quanty ppt NITRON nitrate (Ref 16). A procedure is described for. the quant detn of nitrate esters, including Mannitol Hexanitrate, in the presence of aromatic nitro compds in Ref 17. It gives a yellow color when treated in et ale or acet with 5% aq K hydroxide, then 5% aq ammonia (Ref 24), It can be quanty detd by reduction with Devarda s alloy (Encycl 5, D-l 110) or A1 wire in aq et ale and titration of the evolved... 

A group of flavoenzyme reductases mediate the reduction both nitrate esters and C= C double bonds generally activated with carbonyl or nitro functions. The structures of the substrates vary widely (references in Faber 1997). 

The enantiomeric reduction of 2-nitro-l-phenylprop-l-ene has been studied in a range of Gram-positive organisms including strains of Rhodococcus rhodochrous (Sakai et al. 1985). The enantiomeric purity of the product depended on the strain used, the length of cultivation, and the maintenance of a low pH that is consistent with the later results of Meah and Massey (2000). It has been shown that an NADPH-linked reduction of a,p-unsaturated nitro compounds may also be accomplished by old yellow enzyme via the flcf-nitro form (Meah and Massey 2000). This is formally analogous to the reduction and dismutation of cyclic enones by the same enzyme (Vaz et al. 1995), and the reductive fission of nitrate esters by an enzyme homologous to the old yellow enzyme from Saccharomyces cerevisiae (Snape et al. 1997). 

Hydrazine salts have been prepared by the action of hypochlorites on ammonia1 or urea 2 by the hydrolysis of salts of sulfohydrazimethylene disulfonic acid 3 by the hydrolysis of triazoacetic acid 4 by the reduction of diazoacetic ester 5 by the reduction of nitroguanidine followed by hydrolysis 6 by the reduction of the nitroso derivatives of hexamethylene tetramine 7 by the reduction of nitrates or nitrites with zinc in neutral solution 8 by the action of sodium bisulfite on hyponitrous acid... 

All bacteria where nitrate ester degradation has been characterized have very similar enzymes. The enzymes eatalyze the nicotinamide cofactor-dependent reductive eleavage of nitrate esters that produces alcohol and nitrite. Purification of the PETN reduetase from Enterobacter cloacae yielded a monomerie protein of around 40 kilo Daltons, which required NADPH as a co-faetor for aetivity. Similar enzymes were responsible for the nitrate ester-degrading activity in Agrobacterium radiobacter (Snape et al. 1997) - nitrate ester reductase - and in the strains of Pseudomonas fluorescens and Pseudomonas putida (Blehert et al. 1999) - xenobiotic reduetases . All utilize a non-covalently bound flavine mononucleotide as a redox eofactor. 

As is evident from experimental measurements, most kinds of nitrate esters appear to decompose to NOj and C,H,0 species with the breaking of the O-NOj bond as the initial step. A strong heat release occurs in the gas phase near the decomposing surface due to the reduction of NO2 to NO accompanied by the oxidation of C,H,0 species to HjO, CO, and COj. NO reduction, however, is slow and this reaction is not observed in the decomposition of some nitrate ester systems. Even when the reaction occurs, the heat release does not contribute to the heat feedback to the surface because the reaction occurs at a distance far from the surface. 

Nitrogen Concent of Nitrate Esters by Ferrous Reduction... 

Alkylation of potassium enolates is not always fruitful, and so counterion exchange with lithium bromide prior to addition of the electrophile has been recommended. Reduction of aromatic esters instead of acids provides a number of potential advantages. The esters tend to be more soluble than carboxylate salts, hydrogenolysis of 2-alkoxy substituents does not appear to present the s me problem, and the products are more stable. This can be important when enol ether functions are generated, allowing the necessarily acidic work-up procedures for carboxylic acids to be avoided. Indeed, the hydrolysis of enol ether functions may be very slow in aqueous acid and is best achieved through catalysis by mercury(II) nitrate. ... 

Hydrazine salts have been prepared by the action of hypochlorites on ammonia (1) or urea (2) by the hydrolysis of salts of sulfohydrazimethylene disiilfonic acid (3) by the hydrolysis of triazoacetic acid (4) by the reduction of diazoacetic ester (5) by the reduction of nitroguanidine followed by hydrolysis (6) by the reduction of the nitroso derivatives of hexamethylene tetramine (7) by the reduction of nitrates or nitrites with zinc in neutral solution (8) by the action of sodium bisulfite on hyponitrous acid followed by reduction (9) by the reduction of K2S03N202 (10) by the action of ammonia on dichlorourea (11) by the reduction of nitrosoparaldimin (12) by the action of copper sulfate on ammonia at high temperatures (13) by the reduction of methylene diisonitrosoamine (14) by the hydrolysis of the addition product of diazoacetic ester and fumaric or cinnamic esters (15). 

If sodium sulfhydrate, equal to basicity of pH 10-11, is used in hydrolysis, 93 % A -ester group of nitrate esters is hydrolyzed to nitrous acid ions and 7 % is hydrolyzed to ammonium. If ammonium sulfhydrate is used, the concentration of nitrous acid ions will be increased to a maximum first and then decreased to zero because of the reduction of ammonium sulfhydrate. The reduction effect would be increased with increasing pH value, especially at pH over 10. The reaction can be expressed as following chemical equations. 

Compared with nitrous acid ions, nitric acid ions can be slowly reduced in sodium sulfhydrate. The nitrous acid ions are produced from the hydrolysis of nitrate esters, other than from the reduction of nitric acid ions. Thus, the nitrous acid ions are formed, most likely, by the breakage of bonds between oxygen and nitrogen atoms. The effect of sulfhydrate on the hydrolysis of nitrate esters is to reduce the reactants, as expressed in the following reaction mechanism equations. 

When the concentration of alcohol is increased, the reduction is displaced towards more negative potentials. The reduction of polynitrate esters will occur at more positive potentials when the number of nitrate ester groups in the molecule is increased. The change will be approximately 0.1 V per each new nitrate ester group. Under certain conditions (water/methanol solutions), the reduction of the separate nitrate ester groups can be detected. 

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... 

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