Secondary amides, nitrations, nitric acid

Secondary nitramides are relatively stable in highly acidic media and so their synthesis from the direct nitration of A -substituted amides with nitric acid and its mixtures is feasible. The synthesis of primary nitramides from the nitration of A -unsubstituted amides is usually not possible in acidic media, although this class of compounds have no practical value as explosives anyway. 

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. 

Direct nitration with anhydrous nitric acid (98%) can be accomplished most conveniently in the presence of monosubfctituted N-alkylamides. A secondary nitr-amide is then formed ... 

Direct N-nitration of secondary amines by nitric acid is possible only for weakly basic amines. The more basic amines can be nitrated under neutral conditions widi reagents such as dinitrogen pentoxide and nitronium tetrafluoroborate, but nitrosamines are significant by-products. The nitrate ester CF3CMe20N02 has been recommended as a nonacidic nitrating agent for secondary amines which avoids the problem of contamination of the products by A(-nitrosamines piperidine and pyrrolidine were nitrated in yields of 75% and 72%, respectively. Amides and imides are efficiendy N-nitrated using ammonium nitrate in trifluoroacetic anhydride. ... 

Nitration of Heteroatoms. Secondary amines and primary and secondary amides can be converted to A -nitro compounds by direct nitration with nitric acid. 46 Although most primary amines cannot be nitrated directly, it is possible to obtain primary nitramines by nitration of the corresponding dichloroamines (eq 9). Treatment of pyrrolidone with nitric acid and acetic acid in the presence of copper provides lV-nitroso-2-pyrrolidone in 70% yield note that this transformation represents A -nitrosation. 

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