Organic Chemistry of Explosives

Nitroureas 281

Boyer and co-workers^48 also reported the synthesis of the guanidine tricycle (122), prepared

as the tetrahydrochloride salt from the condensation of two equivalents of guanidine with 1,4-

diformyl-2,3,5,6-tetrahydroxypiperazine in concentrated hydrochloric acid. Treatment of the

tricycle (122) with absolute nitric acid yields the bis-nitrimine (123), whereas the same reaction

with nitric acid–acetic anhydride yields HHTDD (117).

HN

N

NH

O

t-Bu

124

N

O

NO 2

125

(Keto-RDX or K-6)

N

NO 2

H N

2 N

O

HNO 3 , Ac 2 O

+ 2 CH 2 O + t-BuNH 2 57 %

50–55 °C

52 %

NH 2

O 2 N

Figure 6.35

Chemists at Lawrence Livermore National Laboratory (LLNL) synthesized the RDX ana-

logue 1,3,5-trinitro-2-oxo-1,3,5-triazacyclohexane (125) (Keto-RDX or K-6) from a Mannich

reaction between urea, formaldehyde andt-butylamine, followed by nitrolysis of the resulting

2-oxo-5-tert-butyltriazone (124) with nitric acid in acetic anhydride or dinitrogen pentoxide

in absolute nitric acid.^20 ,^21 Nitrolysis with other nitrating agents has also been reported, in-

cluding nitronium tetrafluoroborate (40 %), TFAA–nitric acid (43 %) and mixed acid (0 %) –

see Table 5.6.^21 ,^49 Keto-RDX is not as hydrolytically labile as otherN,N′-dinitroureas and its

ease of preparation and relatively high performance (4 %>HMX) makes its future application

attractive.

OEt

OEtOEt

EtO

H 2 N

O

CH

CH 2

HN NH

CH NHHN

OCO

CH

CH 2

N

CH NN

OCO

NO 2

NO 2

O 2 N

O 2 N

HCl (aq), 50 °C

+

(^126127)
(TNPDU)
Ac 2 O, HNO 3
45 % 82 % - see text
NH 2
C
N
C
Figure 6.36
Tetranitropropanediurea (127) (TNPDU) is a high performanceN,N′-dinitrourea explosive
(VOD∼9030 m/s) synthesized from the nitration of propanediurea (126) with nitric acid in
acetic anhydride,^50 the latter readily synthesized from the condensation of urea with 1,1,3,3-
tetraethoxypropane. Agrawal and co-workers^46 conducted extensive studies into the synthesis,
characterization and thermal behaviour of TNPDU. The nitration step was significantly im-
proved by using a ‘slow nitration procedure’ which involves the slow addition of propanediurea
to 98 % nitric acid followed by slow addition of acetic anhydride. This gave a higher yield of
TNPDU than previously reported, and excellent product purity which avoids the need for a
lengthy purification step. Agrawal noted that the hydrolytic stability of TNPDU is better than
similar compounds and, in particular, TNGU. The impact and friction sensitivity of TNPDU
and its formulations were also explored.