Tetrazole compounds, neutral

Out of the different possible derivatives of tetrazoles, we have so far only discussed (A) and nitriminotetrazole (D) (Fig. 9.14) in more detail. Although the azide-substituted tetrazole compound of type C is very energetic, it is still not useful for practical application since it is extremely sensitive. Additionally of interest are the neutral and ionic nitrotetrazole derivates of type F, which are more stable (Fig. 9.14). 

A very interesting approach to the synthesis of new, ethyl-bridged, energetic tetrazole compounds, both neutral and ionic has been reported recently by Shreeve and co-workers [56a,b]. They react in situ generated cyanazide, N3CN, with 1,2-diaminoethane to form the bridged tetrazole derivative A (Fig. 9.17), which can sub-... 

Compound (159) has an IR band at 1070 cm-1, in neutral solution or the solid state, consistent with the tetrazole structure. In trifluoroacetic acid this band is replaced by a typical azide absorption at 2140 cm-1. Only in this solvent will photolysis give a good yield (91%) of the pyrimidinoindole (160) (72JOC3216). 

Disconnection of tetrazoles with a 1,3-dipolar cycloaddition in mind is easy to see once we realize that a nitrile (RCN) is going to be one of the components. It can be done in two ways disconnection of the neutral compound would require hydrazoic acid (HN3) as the dipole but the anion disconnects directly to azide ion. 

The diazotization products of 2- and 4-aminophenols, -naphthols (etc.), possess a mesomeric (zwitterionic) phenolate-diazonium and quinone-diazide structure. We discussed these structures in the context of aromatic diazotization (Zollinger, 1994 Sect. 2.4) because the synthetic methods used are closely related to those used for aromatic diazonium salts. This is also the case for the diazotization of amino-di-, tri- and tetrazoles, which, in their neutral form, contain a heterocyclic NH group in the )8-position to the amino group. After diazotization, the NH group is very acidic. Following deprotonation the product corresponds to a heterocyclic diazoalkane. Similarly, the diazotization product of 4-(dicyano)methylaniline ((4-amino-phenyl)malonitrile) may lose the CH proton. This compound is, therefore, sometimes called a vinylene homolog of diazomalonitrile (Regitz and Maas, 1986, p. 205). 

In this chapter we want to discuss the possibility of new high explosives that are neutral compounds and are based on nitrogen-rich tetrazole building blocks. 

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