Organic Chemistry of Explosives

Nitrolysis 217

N, N′-Diacetylimidazolidine (87) undergoes nitrolysis on treatment with nitronium tetrafluo-

roborate to yield eitherN, N′-dinitroimidazolidine (88) orN-acetyl-N′-nitroimidazolidine (89)

depending on the reaction stoichiometry and conditions used.^103 N, N-Diacylmethylamines are

inert to reagents like trifluoroacetic anhydride–nitric acid but undergo nitrolysis with nitronium

salts, and hence, provide a route to alkyl-N, N-dinitramines.^103 The nitrolysis ofN-alkylamides

with nitronium tetrafluoroborate is more of a problem due to the instability of the primary

nitramine product in the presence of the strong acid liberated during the reactions.^104

5.6.2 Nitrolysis of N-alkyl bonds

HNO 3

R 2 NCH 2 R^1 +HNO 3 R 2 NNO 2 + R^1 CH 2 OH

R^1 CHO

R^1 CH 2 ONO 2

nitrolysis

(Eq. 5.15)

[O]

Figure 5.48

The nitrolysis of tertiary amines in the form oftert-butylamines and methylenediamines has

been used to synthesize numerous polynitramine-based energetic materials. In these reactions

one of the N–C bonds is cleaved to generate a secondary nitramine and an alcohol; the latter

is usuallyO-nitrated or oxidized under the reaction conditions (Equation 5.15). The ease in

which nitrolysis occurs is related to the stability of the expelled alkyl cation. Consequently, the

tert-butyl group and the iminium cation from methylenediamines are excellent leaving groups.

5.6.2.1 Primary and secondary alkyl groups

Tertiary amine substrates containing only primary or secondary alkyl functionality are reluctant

to undergo nitrolysis and often need pushing by increasing the reaction temperature. The

reaction of nitric acid–acetic anhydride mixtures with tertiary alkylamines containing only

primary and secondary alkyl groups usually generates the corresponding nitrosamine as the

main product.^105 Although nitrosamines can be oxidized^106 to the corresponding nitramine

their high toxicity makes their formation undesirable.

N

H 3 C CH 3 N

H 3 C NO 2

NO 2

NO 2

8

(tetryl)

O 2 N

90

H 2 SO 4 , HNO 3

Figure 5.49

A important exception is the synthesis of the practical high explosive known as tetryl

(8), prepared by treatingN, N-dimethylaniline (90) with nitric acid, mixed acid or acetic