Hydrolysis of nitramides and nitroureas

The instability of primary nitramines in acidic solution means that the nitration of the parent amine with nitric acid or its mixtures is not a feasible route to these compounds. The hydrolysis of secondary nitramides is probably the single most important route to primary nitramines. Accordingly, primary nitramines are often prepared by an indirect four step route (1) acylation of a primary amine to an amide, (2) A-nitration to a secondary nitramide, (3) hydrolysis or ammonolysis with aqueous base and (4) subsequent acidification to release the free nitramine (Equation 5.17). Substrates used in these reactions include sulfonamides, carbamates (urethanes), ureas and carboxylic acid amides like acetamides and formamides etc. The nitration of amides and related compounds has been discussed in Section 5.5. 

A particularly useful synthesis of primary nitramines involves the nitration of the appropriate carbamate ester followed by ammonolysis with gaseous ammonia in diethyl ether. The ammonium salt of the nitramine precipitates in pure form and is carefully acidified to give the free nitramine. The corresponding carbamate esters are readily synthesized from the action of chlorocarboxylic acid esters on alkylamines in the presence of alkali hydroxides. 

Nitramine (161), the simplest member of the nitramines, can be prepared from ethyl carbamate (158) in three synthetic steps nitration of the latter with mixed acid or a solution of ethyl nitrate in concentrated sulfuric acid, followed by isolation of the resulting ethyl N-nitrocarbamate as the ammonium salt (159), hydrolysis with aqueous potassium hydroxide and subsequent acidification, yields nitramine (161).  

Methylnitramine (1) can be prepared from the hydrolysis of an appropriate secondary nitramide. One route involves the nitration of Ai, Ai -dimethylsulfamide (54) to Ai,Ai -dinitro-iV,iV -dimethylsulfamide (10) with absolute nitric acid, followed by ammonolysis and subse- 

Methylnitramine (1) has also been synthesized from the hydrolysis of ethyl Ai-methyl-A -nitrocarbamate (163), Al,Al -dinitro-Ai,Ai -dimethyloxamide (9) and A Ai -dinitro-Ai.Al -dimethylurea (165) the latter, synthesized from the mixed acid nitration of N,N -dimethylurea (164), has been suggested as a possible industrial route to methylnitramineX  

---