Conjugation and thermally insensitive explosives 1772,2′,4,4′,6,6′-Hexanitrostilbene (HNS, m.p. 316◦C,d= 1 .74 g/cm^3 ,VOD∼7000 m/s)
(16) shows higher than expected thermal stability due to conjugation between the aromatic
rings. HNS finds wide application as a heat-resistant explosive and was used on the Apollo
spaceship for stage separation.^294 The Atomic Weapons Research Establishment at Aldermas-
ton in the UK has developed a plastic bonded explosive composed of HNS/Kel-F800 95/5
for specialized applications. HNS is synthesized industrially via the method of Shipp and
Kaplan^288 where TNT undergoes oxidative coupling on treatment with sodium hypochlorite
(see Section 4.9). Introduction of two amino groups into HNS in the 3- and 3′-positions gives
3,3′-diamino-2,2′,4,4′,6,6′-hexanitrostilbene (DAHNS) (146), an explosive with even higher
thermal stability.^241
NH 2ClClNO 2NO 2O 2 NO 2 NO 2 NClClClClNO 2NO 2O 2 NO 2 NO 2 NH 2 NH 2 NNH 2NH 2HNO 3NH 3147
148149NO 2NO 2NNNNFigure 4.66The conjugation in 2,2′,4,4′,6,6′-hexanitroazobenzene (HNAB) (90) is also reflected in
its thermal stability (m.p. 220◦C). The synthesis of HNAB from picryl chloride and 2,4-
dinitrochlorobenzene is discussed in Sections 4.8.1.2 and 4.8.1.3 respectively. 3,3′,5,5′-
Tetraamino-2,2′,4,4′,6,6′-hexanitroazobenzene (149) has been synthesized by an unusual but
efficient route which involves the nitration–oxidative coupling of 3,5-dichloroaniline (147) on
treatment with nitric acid, followed by reaction of the resulting product, 3,3′,5,5′-tetrachloro-
2,2′,4,4′,6,6′-hexanitroazobenzene (148), with ammonia.^295 Both the tetrachloro (148) and
tetraamino (149) derivatives exhibit high thermal stability.
Agrawal and co-workers^296 have reported the synthesis ofN,N′-bis(1,2,4-triazol-3-yl)-4,4′-
diamino-2,2′,3,3′,5,5′,6,6′-octanitroazobenzene (17) (BTDAONAB) via nitration–oxidative
coupling of 4-chloro-3,5-dinitroaniline (152) followed by nucleophilic displacement of the
chloro groups with 3-amino-1,2,4-triazole. BTDAONAB has the unique distinction of being
the most thermally stable explosive reported so far (DTA exotherm∼ 550 ◦C) as compared to
well known thermally stable explosives such as TATB (∼ 360 ◦C), TACOT (∼ 410 ◦C), NONA
(∼440–450◦C), and PYX (∼ 460 ◦C).
Amino derivatives of polynitrobiphenyls often exhibit high thermal stability. The
thermally insensitive explosive (156) is synthesized in three synthetic steps from 3,5-
dimethoxychlorobenzene (154) in a route employing nitration, Ullmann coupling and
ammonolysis.^297 3,3′-Diamino-2,2′,4,4′,6,6′-hexanitrobiphenyl (DIPAM) (157) is synthe-
sized from 3-chloroanisole by a similar route.^298 DIPAM (m.p. 304◦C,d= 1 .82 g/cm^3 )is