Organic Chemistry of Explosives

Aromatic nitramines 241

N

H 3 C CH 3

N

H 3 C CH 3

NO 2

NO 2

227

N

H 3 C

NO 2

NO 2

229

NH

H 3 C

NO 2

NO 2

230

N

H 3 C NO 2

NO 2

NO 2

8

O 2 N

90

H 2 SO 4 , HNO 3

(tetryl)

O 2 N

NO 2

N

H 3 C

NO 2

NO 2

228

H

Figure 5.93

acid at 80◦C,^172 more concentrated nitric acid at lower temperature,^173 mixed acid^174 and a

mixture of nitric acid in acetic anhydride.^175 Studies have shown that the nitration ofN, N-

dimethylaniline with mixed acid proceeds in five steps –N, N-dimethylaniline (90) first under-

goes aromatic ring nitration to (227), followed by oxidation of one of the methylamino groups

to a carbamic acid group which subsequently loses carbon dioxide to form (228), further nitra-

tion now generates nitramine (229) which undergoes N→C nitro group rearrangement to give

(230), and further nitration yields tetryl (8).^176 TheN-nitration of (228) to (229), and (230) to

(8) is promoted by the presence of the aromatic ring nitro groups which reduce the basicity of

the amino group.

The nitration ofN, N-dimethylaniline inevitably produces copious amount of nitrogen ox-

ides from the methyl group oxidation step and other side-reactions. Oxidation of the methyl

group is favoured by high reaction temperature but so are other oxidative side-reactions. Con-

sequently, the highest yields for the nitration ofN, N-dimethylaniline to tetryl are achieved with

mild nitrating agents like acetic anhydride in nitric acid; nitrating systems with more powerful

oxidizing potential give lower yields.

Cl

NO 2

NO 2

231

N

NO 2

NO 2

228

H 3 C

N

H 3 C NO 2

NO 2

NO 2

8

MeNH 2 , H 2 O O 2 N

NaOH, reflux

90 % HNO 3 , 50 °C

H

Figure 5.94

Tetryl (8) can be synthesized in two steps from 2,4-dinitrochlorobenzene (231). Thus,

reaction of the latter with methylamine under aqueous conditions yields 2,4-dinitro-N-

methylaniline (228), which readily undergoes nitration to tetryl (8) on treatment with mixed