Organic Chemistry of Explosives

5-Membered rings – 3N 307

The tetraazapentalene ring system forms the core of the thermally insensitive explosive

TACOT (Section 7.10) and so its fusion with the furoxan ring would be expected to enhance

thermal stability and lead to energetic compounds with a high density.γ-DBBD (95) is prepared

from the nitration of tetraazapentalene (91), nucleophilic displacement of theo-nitro groups

with azide anion, further nitration to (94), followed by furoxan formation on heating ino-

dichlorobenzene at reflux.^56 The isomeric explosive z-DBBD (96) has been prepared via a

similar route.^57

7.4 5-Membered rings – 3N

7.4.1 Triazoles

O

O

97

N

N

N N

N

N

NO 2

NO 2

O 2 N NO 2

O 2 N

O 2 N

Figure 7.36

Incorporation of a triazole ring into a compound is a known strategy for increasing thermal

stability. Many triazole compounds show high thermal stability coupled with a low sensitivity

to shock and impact. 2,6-Dipicrylbenzo[1,2-d][4,5-d′]bistriazole-4,8-dione (97) (m.p. 430◦C)

is one such example.^58

Analyses of the structures and properties of a large number of energetic materials reveal

that a combination of amino and nitro groups in a molecule often leads to better thermal

stability, lower sensitivity to shock and impact, and increased explosive performance because

of an increase in crystal density. Such observations are attributed to both intermolecular and

intramolecular hydrogen bonding interactions between adjacent amino and nitro groups. Some

modern triazole-based explosives have been designed and synthesized with this in mind.

Cl

NO 2

NO 2

67

O 2 N

N

N

H

98

N

H 2 N NO 2

NO 2

99

(PATO)

O 2 N

N

H N

NH

+ N

DMF, 100 °C

85 %

Figure 7.37

3-Amino-1,2,4-triazole is a useful starting material for the synthesis of many 1,2,4-triazole-

based explosives. Jackson and Coburn^59 synthesized a number of picryl- and picrylamino-

substituted 1,2,4-triazoles. PATO (99) is synthesized from the reaction of 3-amino-1,2,4-

triazole (98) with picryl chloride (67).^59 ,^60 PATO has also been synthesized from the reaction

of 3-amino-1,2,4-triazole withN,2,4,6-tetranitromethylaniline (tetryl).^61 PATO has a low sen-

sitivity to impact and is thermally stable up to 310◦C. PATO (VOD∼7469 m/s) exhibits

lower performance to TATB (VOD∼8000 m/s) which is the common benchmark standard

for thermal stability and insensitivity in explosives.