Nitrosamines nitrolysis

The scope of nitrolysis is huge, with examples of nitramine formation from the cleavage of tertiary amines, methylenediamines, carbamates, ureas, formamides, acetamides and other amides. The deflnition of nitrolysis must be extended to the nitrative cleavage of other nitrogen bonds because sulfonamides and nitrosamines are also important substrates for these reactions. The nitrative cleavage of silylamines and silylamides is also a form of nitrolysis (Section 5.7). 

The high performance nitramine explosive known as CL-20 (5) has been synthesized via a two-stage nitrolysis starting from the key intermediate (83). The first stage uses dinitrogen tetroxide or nitrosonium tetrafluoroborate for nitrosolysis. The second step, involving nitrolysis of the acetamide and nitrosamine bonds, is achieved with nitronium tetrafluoroborate (>90 %) or mixed acid at 75 °C to 80 °C (93 %). The synthesis of CL-20 is discussed in more detail in Chapter 6. 

Secondary nitramines are conveniently prepared from the nitrolysis of A, A-dialkylamides with nitronium salts in acetonitrile or ethyl acetate at 20 °C where the acyl group is converted into an acylium tetrafluoroborate (Equation 5.14). Problems can occur if commercial nitronium salts like the tetrafluoroborate are used without purification. The presence of nitrosonium salts can then lead to nitrosamines via nitrosolysis. Yields of secondary nitramine up to 90 % have been reported with solutions of nitronium tetrafluoroborate in acetonitrile di-n-butylnitramine is obtained in 82 % yield from the nitrolysis of corresponding acetamide. ... 

Methylenediamines are readily synthesized from the reaction of secondary amines with formaldehyde. Many aliphatic amines are too basic for direct nitration without a chloride catalyst, and even then, nitrosamine formation can be a problem. Their conversion into intermediate methylenediamines before nitration is therefore a useful route to secondary nitramines. The success of these nitrolysis reactions is attributed to the inherent low basicity of the methylene-diamine nitrogens. 

The conversion of a nitrosamine to a nitramine can be affected by either nitrolysis or oxidation. While the results of these two reactions are identical, they are mechanistically very different. For this reason, the oxidation of nitrosamines is discussed separately in Section 5.9. 

The choice of reagent determines whether a nitrosamine undergoes conversion to a nitramine by either nitrolysis or oxidation. An example is given for the conversion of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) to l,3,5-trinitro-l,3,5-triazacyclohexane (3) (RDX) - the use of 30 % hydrogen peroxide in 99 % nitric acid at subambient temperature goes via oxidation of the nitrosamine functionality, whereas dinitrogen pentoxide in pure nitric acid makes use of a nitrolysis pathway via C-N bond cleavage. 

The nitrolysis of nitrosamines has been relatively unexplored because of the high toxicity of such substrates. Atkins and Willer have prepared a number of cyclic 1,3-dinitrosamines... 

Krimmel and co-workers ° have reported the synthesis of 2,4,6-tris(trifluoromethyl)-l,3,5-trinitro-l,3,5-triazacyclohexane (123) from the nitrolysis of the nitrosamine (122). 

The reaction of hexamine dinitrate (241) with 98% nitric acid at —30°C, followed by quenching with aqueous sodium nitrate, yields the nitrosamine (244). When the same reaction is cautiously quenched with ethanol the ethoxyether (245) is obtained. Treatment of the ethoxyether (245) with cold absolute nitric acid yields the bicyclic ether (246). ° Treatment of any of the cyclic nitramines (242)-(246) with nitric acid and ammonium nitrate in acetic anhydride yields RDX. ° Hexamine dinitrate is often used in low temperature nitrolysis experiments in order to avoid the initial exotherm observed on addition of hexamine to nitric acid. 

At present there are four good methods for preparing secondary nitramines. They are the oxidation of nitrosamines by peroxytrifluoro-acetic acid (5), the chloride-ion catalyzed direct nitration of amines (3), the nitrolysis of dialkylamides with nitric acid (16), and the alkaline nitration of amines with acetone cyanohydrin nitrate (6). We have found that treating two equivalents of several secondary aliphatic amines... 

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