Organic Chemistry of Explosives

208 Synthetic Routes toN-Nitro

acetic anhydride during the nitration of alkyldichloramines is essential in keeping the reaction

conditions anhydrous –N-chloronitramines are readily hydrolyzed in the presence of aqueous

acid and it is unlikely that the resulting primary nitramine would survive the acidic conditions

of the nitration.

N-Chloronitramines can be isolated or the diluted nitration liquors treated directly with an

aqueous solution of sodium bisulfite to generate the corresponding nitramine in good yield.

The presence of a reducing agent during hydrolysis is essential because the conversion of a

N-chloronitramine to a nitramine and hypochlorous acid is a reversible process.

5.5 N-Nitration of amides and related compounds

The directN-nitration of N-alkylamides is the most important of the synthetic routes to

secondary nitramides. Hydrolysis of these secondary nitramides is an important but indirect

route to primary nitramines, a reaction discussed in Section 5.10.

Numerous studies have shown that amide substrates containing the – CONHCH 2 – group

are readily nitrated to the corresponding nitramide with a range of nitrating agents. The facile

nitration of such amides is mainly due to the weakly basic nature of the nitrogen atom in

these substrates. Substrates containing the – CONHCO – urea group are far less susceptible

toN-nitration. HeterocyclicN-nitroureas andN, N′-dinitroureas are recognised as a class of

energetic materials (Chapter 6). Consequently, the nitration of ureas has been well studied.

5.5.1 Nitration with acidic reagents

Secondary nitramides are relatively stable in highly acidic media and so their synthesis from

the direct nitration ofN-substituted amides with nitric acid and its mixtures is feasible. The

synthesis of primary nitramides from the nitration ofN-unsubstituted amides is usually not

possible in acidic media, although this class of compounds have no practical value as explosives

anyway.

O

O

NCH 3

NCH 3

NO 2

NO 2

9

O

O

NHCH 3

NHCH 3

53

100 % HNO 3

Figure 5.30

Pure nitric acid (98–100 %) has long been the classic reagent for theN-nitration ofN-

alkylamides, and in some cases, this reagent gives excellent yields of the corresponding sec-

ondary nitramide. ManyN-alkyl carbamates and sulfonamides have been successfully nitrated

in this way.62–70Treatment of the oxamide (53),^69 the sulfonamide (54)^69 and the carbamate

(55)^70 with pure nitric acid at 0◦C yields the secondary high explosives, (9), (10) and (56)

respectively.N, N′-Dinitro-N, N′-dimethyloxamide (9) (m.p.= 124 ◦C) forms a convenient eu-

tectic with TNT and the melt solidifies to give charges free of gross cavities. A eutectic mixture