Organic Chemistry of Explosives

264 Nitramines and Their Derivatives

6.2 Cyclobutanes

H 2 N

OEt

OEt

H 2 N

H

O

OEt

OEt

NHHN

O

AcN NAc

O

AcN NAc

AcN NAc

O

O

7

HN NH

HN NH

O

O

8

O 2 NN

O 2 NN

NNO 2

NNO 2

O

O

9

O 2 NN

O 2 NN

NNO 2

NNO 2

NHNO 2

NHNO 2

O 2 NHN

O 2 NHN

KOCN, HCl (aq)

81 %

H 2 SO 4 (aq)

44 %

Ac 2 O,

reflux

68 %

hv, acetone

23 %

K 2 CO 3 , EtOH (aq)

86 %

80 % H 2 SO 4 ,

(CH 2 O)n

32 %

H 2 SO 4 (aq)

36 %

HNO 3 , N 2 O 5

97 %

3 4 5

6

11

10

N

Figure 6.2

Chapman and co-workers^2 have synthesized nitramino derivatives of cyclobutane. Their syn-

thesis starts from the reaction of aminoacetaldehyde diethylacetal (3) with potassium cyanate in

aqueous hydrochloric acid to give ureidoacetaldehyde diethylacetal (4) which undergoes ring

closure to the imidazolinone (5) on treatment with aqueous sulfuric acid. Acetylation of the

imidazolinone (5) with acetic anhydride, followed by a photo-induced [2+2] cycloaddition,

yields the cyclobutane derivative (7). Deacetylation of (7) with ethanolic potassium carbon-

ate, followed by treatment of the resulting bis-urea (8) with absolute nitric acid or dinitrogen

pentoxide in fuming nitric acid, yields octahydro-1,3,4,6-tetranitro-3a,3b,6a,6b-cyclobuta[1,2-

d:3,4-d′]diimidazole-2,5-dione (9), a powerful explosive with a detonation velocity of 8400

m/s and a high crystal density of 1.99 g/cm^3 , both properties typical of the energetic and

structurally rigid nature of cyclicN,N′-dinitroureas.

The N,N′-dinitrourea (9) is a precursor to the nitramine explosives (10) and (11).^2

Thus, refluxing (9) in aqueous sulfuric acid yieldsN,N′,N′′,N′′′-tetranitro-1,2,3,4-cyclo-

butanetetramine (10), an explosive which is isomeric with HMX. Treatment of (10) with