Nucleophilic attacks on carbon–carbon double bonds. Part XIII. Vinylic substitution of 1,1-dicyano-2-p-dimethylaminophenyl-2-halogenoethylenes by aromatic amines in acetonitrile

Abstract

The substitution of 1,1-dicyano-2-p-dimethylaminophenyl-2-chloro- and -2-fluoro-ethylenes by substituted anilines in acetonitrile is of the second order in the amine for the fluoro-compound and of increasing first order in the amine for the chloro-compound. The reactions are slower with sterically hindered amines, have low ΔH‡ and high negative ΔS‡, and show high negative Hammett's ρ values. The reaction of the fluoro-ethylene with p-toluidine is catalysed by pyridine. The order in the amine is higher than two in benzene and in cyclohexane. The results are discussed in terms of initial nucleophilic attack to form the zwitterion Ar(ArN⁺H₂)CX–C^–(CN)₂ followed by competition between (i) expulsion of the halide ion followed by N–H bond cleavage, and (ii) amine-catalysed N–H bond cleavage followed by a carbon–halogen bond cleavage. Process (i) governs the behaviour of the chloro-compound and (ii) the behaviour of the fluoro-compound. The differences are due to the much easier C–Cl bond cleavage.