Organic Chemistry of Explosives

Direct nitration of amines 199

acceptable yield.^3 Some nitramines can be prepared via the sole addition of zinc chloride to a

slurry of the amine nitrate in acetic anhydride, which is a method discussed in Section 5.11.^4

The chloride-catalyzed nitration of secondary amines has its disadvantages. The most se-

rious disadvantage being the formation of nitrosamines as by-products, a consequence of

the redox reaction between chlorine anion and nitric acid (Equation 5.5). The toxicity of

nitrosamines cannot be stressed enough, and in the case of diisopropylamine, the correspond-

ing nitrosamine is exceedingly toxic and a very powerful carcinogen. The same is true of

N, N-dimethylnitrosamine which is biologically reduced to the powerful carcinogenN, N-

dimethylhydrazine. It is found that an increase in the amount of chloride ion present in these

nitration reactions increases the amount of nitrosamine formed, a scenario which is grim for

the nitration of diisopropylamine. Additionally, the nitration of strongly basic amines, even

under chloride ion catalysis, is slow and allows competition with slow side-reactions such as

nitrosation and acetylation of the amino functionality.^3

HN

CH 2 CH 2 OH

N

CH 2 CH 2 ONO 2

CH 2 CH 2 ONO 2

O 2 N

ZnCl 2 , 90 %

7

(DINA)

CH 2 CH 2 OH

31

HNO 3 , Ac 2 O

Figure 5.13

Chloride-catalyzed nitration is used for the industrial synthesis ofN-nitrodiethanolamine

dinitrate (DINA) (7), an explosive plasticizer with VOD∼7580 m/s. The synthesis of DINA (7)

uses a mixture of nitric acid in acetic anhydride to nitrate diethanolamine (31) in the presence

of catalytic zinc chloride or a small portion of the diethanolamine as the hydrochloride salt;

the yield of DINA from this process is usually about 90 %.^4 Note that diethanolamine is only

a moderately basic amine, but enough so to prevent its direct nitration with acetic anhydride–

nitric acid mixtures in the absence of chloride anion. As expected, a small amount of nitrosamine

impurity (<5 %) is formed during the synthesis of DINA. Fortunately, this nitrosamine is

unstable and is readily decomposed by the action of boiling water or the injection of stream

into the crude molten product. The important role of chloride anion in the synthesis of DINA is

illustrated by the following observation – if the reaction mixture is vented, so that the volatile

sources of electropositive chlorine can escape, the yields of DINA are very poor and the reaction

can cease altogether.^4 DINA is a desirable explosive with a conveniently low melting point to

permit melt casting. DINA is also an excellent gelatinizing agent for nitrocellulose.

The founder of the chloride-catalyzed nitration of amines, G. F. Wright, has extensively

reviewed chloride-catalyzed nitration.^24 Even 50 years later, the importance and success of

this method as a route to nitramines is illustrated by the number of examples which can be

found in the literature.

Br

H 2 N

OH

90 %

N

H

OH

N

ONO 2

NO 2

HNO 3 , Ac 2 O,

ZnCl 2

32 80 %

33

34

(Bu-NENA)

Figure 5.14