Organic Chemistry of Explosives

Ring-opening nitration of nitrogen heterocycles 227

compounds, known as NENAs, find use as energetic plasticizers; then-butyl analogue (145)

is known as Bu-NENA and finds use in some LOVA propellant formulations.^46 ,^127 Carba-

mate derivatives of aziridine also give good yields of 1,2-nitramine-nitrate product, although

the formation of acyl nitrate impurities is found to be a problem when using an excess of

dinitrogen pentoxide (Table 5.9, Entries 2a and 2b). Such impurities are derived from the

trans-esterification of the carbamate ester functionality and can be considerably reduced by

limiting the amount of dinitrogen pentoxide used in the reaction. Carbamates like (147) are

excellent plasticizers for use in energetic formulations.^46 High yields of 1,2-nitramine-nitrate

product are also obtained fromN, N-dialkylureas (Table 5.9, Entry 3). Amides are found to be

poor substrates in these reactions.

Substrates with acidic/labile hydrogens are found to give low yields of 1,2-nitramine-nitrate

product because of the liberation of nitric acid on reaction with dinitrogen pentoxide, which in

turn, promotes acid-catalyzed aziridine ring opening and the formation of polymeric material.

Consequently,N-alkylureas containing free N–H bonds give poor yields of nitramine product.

Similar results are seen for other substrates containing labile hydrogen; 2-aziridineethanol

(150) reacts with dinitrogen pentoxide to generate DINA (7) but the yield is less than 10 %

(Table 5.9, Entry 4).

96 %

N

N

N

N

N N

N

N

N

N

NN

NO 2

O 2 NOCH 2 CH 2

O 2 N

O 2 N

(^153154)
N 2 O 5 , CHCl 3
CH 2 CH 2 ONO 2
CH 2 CH 2 ONO 2
Figure 5.62
A fairly recent application of this chemistry involves the reaction of the triazine (153) with
dinitrogen pentoxide; the product (154), known as Tris-X (VOD∼8700 m/s, m.p. 69◦C), is an
energetic material of low melting point.^128 The high explosive known as pentryl (152) (VOD
∼8100 m/s) is also synthesized in good yield from the reaction ofN-picrylaziridine (151)
with dinitrogen pentoxide (Table 5.9, Entry 5).^124
Recent advances in the technology used to synthesize dinitrogen pentoxide means that such
reactions may achieve industrial importance, although aziridines are not as readily available
as the corresponding epoxides.

5.8.2 Azetidines

N

R

O 2 NO N

NO 2

R R = CH 2 CH 2 CN (79 %)

R = CH 2 CH 2 CH 2 CH 3 (41 %)

R = CO 2 Et (88 %)

N 2 O 5 , CH 2 Cl 2

Figure 5.63

The reaction of azetidines with dinitrogen pentoxide is found to reflect the reduced ring strain

in this system compared to aziridines.^125 ,^126 Accordingly, while the carbamate andN-alkyl