The reactivity of halogenobenzofurazans and halogenonitrobenzofurazans with nucleophiles. Part I. Methoxy-dehalogenation

Abstract

The reactivity in methanol of methoxide ion with each of 4-fluoro-, 4-chloro-, 4-bromo-, 5-chloro-, 4-chloro- 5-nitro-, 5-chloro-4-nitro-, and 5-bromo-4-nitro-benzofurazan, and 5-chloro- and 5-chloro-4-nitro-benzothiadiazole has been studied. The results indicate that the reaction proceeds through a two-step mechanism of S_NAr type.

In benzofurazans a nitro-group, ortho to the leaving group, increases the substitution rate by a factor of 10⁶–10⁸ except in the case of 5-halogeno-6-nitrobenzofurazans which are practically inert. The increase in velocity is less in the case of the corresponding benzothiadiazole derivatives and is explained by the different situation in the two cases of the fixed double-bond between C(4) and C(5). Some of the results are compared with the other recent work.