Nitrates reductive denitration

Denitration can be effected by chemical reducing agents (134)- For monomolecular nitrates, reductive denitration with hydrogen and Raney nickel (135) is preferable. Ammonium hydrogen sulfide effectively denitrates the nitrated polysaccharides. 

Purified mtALDH catalysed the stoichiometric formation of 1,2-GDN and nitrite from GTN, in a reaction that was shown to be dependent on the presence of thiols. It was argued that reductive denitration of GTN involves interaction of one of two adjacent active site thiols with GTN to yield an -SNO2 group, which then reacts with the other thiol to yield nitrite and a disulfide. In a final, essential step the inactive disulfide is converted back to two thiols by external thiol compounds (Scheme 2.2). It is interesting to note that this mechanism is essentially that foreseen by Needleman and colleagues in their proposed nitrate receptor (see earlier). 

Scheme 2.2 Mechanism of reductive denitration of organic nitrates (RONO2) to nitrite, catalysed by mtALDH. Adapted from Chen et al. [95].

Fig. 9.6. Postulated mechanisms in the cytochrome P450 catalyzed reductive denitration of organic nitrates. Pathway a shows the hypothetical mechanism for the reduction of organic nitrates to organic nitrites, whereas Pathway b presents the same reaction for organic nitrites.

Further work by Baum and co-workers showed that the nitration of l,l-diamino-2,2-dinitroethylenes with trifluoroacetic anhydride and nitric acid in methylene chloride yields 1,1,1-trinitromethyl derivatives via addition of nitronium ion to the double bond of the enamine such treatment also resulting in the A-nitration of the products. In this way, trini-tromethyl derivatives like (185) and (188) are obtained. Further treatment of these trinitromethyl derivatives with aqueous potassium iodide results in reductive denitration and the formation... 

Sugar nitric acid esters are also subject to reductive denitration (see p. 9) and to the chemical reactions typical of sugar nitrates. 

Recently, Baum and coworkers154 reported the nitration of 1,1-diamino-2,2-dini-troethylene. On treatment with nitric acid and trifluoroacetic anhydride in methylene chloride at 0 °C, 1,1-enediamines 42 are converted to 3-nitro-2-(trinitromethyl)-l,3-diazacyclic compounds 192 in good yields (equation 79). Compounds 192 have also been prepared from the nitration of 7, although the yields are lower (16-22%). Denitration of 192 to 193 includes a reductive denitration of 192 with potassium iodide and acidification of initially formed salts of 193. Nitration of 193 regenerates 192 (equation 79). 

Methylation of free OH groups, followed by denitration, hydrolysis, reduction, and glc analysis has been suggested as a method for determining the location of nitrate (82). This method has been suggested for CP and CS (82) as the phosphate and sulfate groups are stable to methylation and can then be removed. Periodate oxidation has been used to determine the DS of CS (81). 

Precipitation Processes. Plutonium peroxide precipitation is used at Rocky Flats to convert the purified plutonium nitrate solution to a solid (14) the plutonium peroxide is then calcined to Pu02 and sent to the reduction step. The chemistry of the plutonium peroxide precipitation process is being studied, as well as alternative precipitation processes such as oxalate, carbonate, fluoride, and thermal denitration. The latter method shows the most promise for cost and waste reduction. 

The denitration system works satisfactorily only for spent acid from the nitration of glycerine and similar alcohols. In spent acid from trinitrotoluene production the high content of dissolved nitrated hydrocarbons causes an excessive reduction of nitric arid at the top of the denitrating tower. Thus spent acid from the nitration... 

Clement and Riviere [59] also reported that cellulose acetate or a mixed ester — a nitrate-acetate — can be obtained by reacting cellulose nitrate with acetic anhydride, acetic acid, and sulphuric acid. According to more recent contributions, e.g. Wolfrom, Bower and Maker [60], the reaction should be performed as follows Cellulose nitrate is dissolved in the cold in a little sulphuric add and acetic anhydride, the surplus of acetic anhydride is then hydrolysed also in the cold, and cellulose acetate is extracted with a suitable solvent, such as chloroform. Other methods of acetylating nitrocellulose consist in reduction, for instance with zinc and hydrogen chloride, which entails denitration of the ester, followed by acetylation with acetic anhydride. All these reactions are carried out in the same vessel. Further, it is possible to synthesize mixed esters, cellulose nitrate-acetates, by subjecting cellulose to the action of a mixture that includes nitric acid, acetic add and acetic anhydride in the presence of sulphuric acid (Kruger [61]). The use of a large amount of nitric acid favours the formation of nitrocellulose only. Mixed esters are formed... 

The chief chemical use of such nitrates has arisen from opportunities to take advantage of their stability, the easy, selective removal of the nitrate groups from certain positions, and their ready and complete denitration by reductive processes. These properties have permitted preparation of several new methyl ethers of D-glucose, D-galactose, and D-fructose. ... 

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