L. Di Nunno

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

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 SNAr 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.

Nucleophilic reactions in ethylenic derivatives. Part IX. “Direct substitution” and “elimination–addition” mechanisms in the reaction of arylsulphonylchloroethylenes with alkoxide ions

cis-p-Tolylsulphonylhalogenoethylenes react with alkoxide ions by “direct substitution” and by “elimination–addition” mechanisms. A method based on the determination of the equilibrium concentration of the intermediate p-tolylsulphonylacetylene was worked out which enabled the contributions of the two mechanisms to the overall reaction to be determined.The method was applied to a few typical cases and it was found that the participation of the “elimination–addition” process to the overall reaction is important in the cases studied. Some preliminary results on the base-catalysed addition of alcohols to p-tolylsulphonylacetylenes are also reported.