Benzofurazans nitration

Some nitro derivatives of benzofurazan have been investigated for their explosive properties. 4-Amino-5,7-dinitrobenzofurazan (56) has been prepared by a number of routes including (1) the thermally induced cyclodehydration of l,3-diamino-2,4,6-trinitrobenzene (55), (2) the nitration of 4-amino-7-nitrobenzofurazan and (3) the reduction of 4-amino-5,7-dinitrobenzofuroxan with triphenylphoshine. The isomeric 5-amino-4,7-dinitrobenzofurazan (57) has been prepared along similar routes. ... 

The furoxan ring is notably resistant to electrophilic attack and reaction normally takes place at the substituents. Thus aryl groups attached to monocyclic furoxans and the homocyclic ring of benzofuroxans are nitrated and halogenated without disruption of the heterocycle. Reaction with acid is also slow protonation is predicted to occur at N-5 <89KGS1261> and benzofuroxans have pKj, values of ca. 8, similar to those of benzofurazans. Monosubstituted furoxans are, as expected, less stable and can be hydrolyzed to the corresponding carboxylic acid. Treatment of the parent furoxan (3) with concentrated sulfuric acid results in rearrangement to (hydroxyimino)acetonitrile oxide (HON=CHC=N —O ) and subsequent dimerization to bis(hydroxyiminomethyl)furoxan... 

Note No higher nitrated derivs of benzofurazan were found in Beil or in CA thru 1956... 

Substituted benzoxazoles are also nitrated with nitric-sulfuric mixture into the 6 position, if it is vacant [143, 144], In earlier publications it has been stated that benzofurazans (2,1,3-benzoxadiazoles) are nitrated exclusively to the 4(7) position... 

Nitrated benzotriazole and benzofurazan were obtained as a result of an interesting rearrangement in the reaction of 5-dimethylaminobenzofuroxan with 2,4-dinitroben-zenediazonium sulfate or with HN02 in H2S04/H20-C2H50H (Scheme 2.137) [671],... 

Benzofurazans, except for nitrated ones, at reduction on a dropping mercury electrode (in acetonitrile or DMF) on polarogram, have the one-electron wave, which corresponds to reduction of furazan cycle (Scheme 3.42) [1005] ... 

NBD-Q was noted as a possible fluorescent label during the examination of benzofurazans as potential antileukaemic agents and blockers of thiol groups [192]. NBD-Q is prepared by nitrating 4-chlorobenzofurazan [193], It is commercially available. NBD-CI is a stable, non-fluorescent pale yellow solid, m.p. 97 °C, readily soluble in organic solvents and somewhat more soluble in water than Dns-CI. 

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