Organic Chemistry of Explosives

Nitroureas 279

Li and co-workers^43 recognised the potential of cyclicN-nitroureas as energetic materi-

als and reported the synthesis of 2,4,6,8-tetranitro-2,4,6,8-tetraazabicyclo[3.3.0]octane-3-one

(109) (K-55) from the nitration of 2,4,6,8-tetraazabicyclo[3.3.0]octane-3-one dihydrochloride

(108) with absolute nitric acid in acetic anhydride at room temperature; the latter obtained from

the condensation ofN,N′-diformyl-4,5-dihydroxyimidazolidine (107) with urea in aqueous

hydrochloric acid. Pagoria and co-workers^21 ,^44 reported the synthesis of 2,4,6-trinitro-2,4,6,8-

tetraazabicyclo[3.3.0]octane-3-one (110) (HK-55) in 72 % yield from the nitration of (108)

with 90 % nitric acid in acetic anhydride at subambient temperature (Table 5.3). HK-55 has a

relatively high density (1.905 g/cm^3 ) coupled with a low sensitivity to shock.

N

N

CHO

CHO

111

OH

OH

H 2 N

O

N

H

H

N

N

H

H

N

O

N

N

N

N

O

NO 2

NO 2

NO 2

NO 2

. 2HCl

+

113

(K-56/TNABN)

112

20 % N 2 O 5

HCl (aq) in 100 % HNO 3

NH (^2) 75 % 82 %
Figure 6.30
Graindorge and co-workers^45 reported the synthesis of 2,5,7,9-tetranitro-2,5,7,9-tetraaza-
bicyclo[4.3.0]nonane-8-one (113) (K-56, TNABN) from the nitration of 2,5,7,9-tetraazabi-
cyclo[4.3.0]nonane-8-one dihydrochloride (112) with dinitrogen pentoxide in absolute nitric
acid, the latter obtained from the condensation of urea with 1,4-diformyl-2,3-dihydroxy-
piperazine (111) in hydrochloric acid.^31 Treatment of (112) with nitronium tetrafluoroborate
in nitromethane results in the nitration of the piperazine ring nitrogens only and the isolation
of (114) in 86 % yield (Table 5.2).
115
(HK-56)
N
N
N
H
H
N
O
NO 2
NO 2
114
N
N
N
N
O
NO (^2) NO
2
NO 2 H
Figure 6.31
Agrawal and co-workers^46 also conducted extensive studies into the synthesis, character-
ization and thermal and explosive behaviour of (113) (K-56, TNABN). 2,5,7,9-Tetraazabi-
cyclo[4.3.0]nonane-8-one (112) was synthesized from the direct reaction of ethylenediamine
with glyoxal, followed by reaction of the resulting cyclic imine with urea in concentrated
hydrochloric acid; nitration of (112) was achieved in 51 % yield with a mixture of nitric
acid–acetic anhydride. Agrawal showed that K-56/TNABN is significantly more resistant to
hydrolytic destruction than TNGU.
Pagoria and co-workers^21.^44 also reported the synthesis of (113) (K-56, TNABN) and the tri-
nitrated derivative, 2,5,7-trinitro-2,5,7,9-tetraazabicyclo[4.3.0]nonane-8-one (115) (HK-56).
Their route to the bicycle (112) was via bromination of 1,3-diacetyl-2-imidazolone, followed
by reaction with ethylenedinitramine and nitrolysis of the acetyl groups.