160 Synthetic Routes to AromaticC-Nitro Compounds
2,2′,4,4′,6,6′-Hexanitroazobenzene (HNAB) (90), an explosive exhibiting thermal
stability^213 (m.p. 220◦C, VOD∼7250 m/s,d= 1 .77 g/cm^3 ), is formed from the reaction
of hydrazine with picryl chloride (87) followed by oxidation of the resulting hydrazide (89)
with fuming nitric acid.^214 The commercial availability of picryl chloride limits such reactions.
However, 2,4-dinitrochlorobenzene is widely available and can be used to synthesize many of
the above products (Section 4.8.1.3).
Cl
O 2 N NO 2NO 2
87O Na
NO 2
O2 O 2 NNOO 2 NO 2 NNO 2NO 2
91O 2 NONO 2
92NO 2+HNO 3 ,
H 2 SO 4Figure 4.33The harsh conditions needed to introduce five or more nitro groups into diphenyl ether lead
to the destruction of the aromatic ring. Highly nitrated derivatives of diphenyl ether can be
prepared by an indirect route; 2,2′,4,4′,6-pentanitrodiphenyl ether (92) is the product from the
controlled nitration of (91), which is obtained from the reaction of picryl chloride (87) with
sodiumo-nitrophenolate.^215
Cl
NO 2NO 2
87O 2 NNNO 2O 2 NNO 2
93+ N ClFigure 4.34Picryl chloride (87) reacts with pyridine to form picrylpyridinium chloride (93), a use-
ful intermediate which reacts with a range of nucleophiles^216 ; 2,4,6-trinitrodiphenylamine
and 2,4,6-trinitrodiphenylether can be formed from aniline and phenol respectively.^217 2,4,6-
Trinitrodiphenylamine is readily nitrated with mixed acid to the high explosive 2,2′,4,4′,6,6′-
hexanitrodiphenylamine (hexyl).^218
O 2 N NO 2NO 2
87Cl
NO 2O 2 N NONONH 2
O 2 N NO 2NO 2
5394NH 2 OH.HCl NH 2 OH.HClNaOEtFigure 4.35