Organic Chemistry of Explosives

Hydrolysis of nitramides and nitroureas 229

5.10 Hydrolysis of nitramides and nitroureas

N-nitration

R NHR'

O

R

O

R'

NO 2

1. base (aq)


2. H+
   N R'NHNO^2 +RCO^2 H (Eq. 5.17)

Figure 5.66

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)N-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 (ure-

thanes), 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 appro-

priate 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.

NH 2 CO 2 Et

158

1. H 2 SO 4 , EtONO 2


2. NH 4 OH
   47–55 %

N

CO 2 Et

NO 2

NH 4

N

CO 2

NO 2

2 K

+EtOH

+EtOH+ H 2 O

2 KOH

65–80%

2 H 2 SO 4

75–85 %

NO 2 NH 2

161

+ CO 2 + 2 KHSO 4

159

N

CO 2 Et

NO 2

NH 4

159

160

N

CO 2

NO 2

2 K

160

Step 1

Step 2

Step 3

Figure 5.67 Synthesis of nitramine

Nitramine (161), the simplest member of the nitramines, can be prepared from ethyl car-

bamate (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 ethylN-

nitrocarbamate as the ammonium salt (159), hydrolysis with aqueous potassium hydroxide

and subsequent acidification, yields nitramine (161).^131