Nucleophilic attacks on carbon–carbon double bonds. Part XIV. Low-element effects and amine catalysis in the substitution of 1,1-dicyano-2-p-dimethylaminophenyl-2-halogenoethylenes by anilines in alcohols

Abstract

The substitution of 1,1-dicyano-2-p-dimethylaminophenyl-2-chloro- and -2-fluoro-ethylenes by substituted anilines in methanol, propan-2-ol, and t-butyl alcohol is of the first order in the amine for the chloride, and of higher than first order in the amine for the fluoride. The reactions have low ΔH^‡ and high negative ΔS^‡ and (especially for the chloride), high negative Hammett's ρ values. A mechanism is suggested in which a reversibly formed zwitterion Ar(Ar[graphic omitted;]H₂)CX–(CN)₂ reacts further by either (a) solvent-assisted expulsion of the halide ion followed by N–H bond cleavage, or by (b) amine-catalysed N–H bond cleavage followed by expulsion of the halide ion. The chloro-ethylene reacts via(a) and the fluoro-ethylene via both (a) and (b). The element effects (k_F/k_Cl) for route (a) are low (3·05–0·71) and decrease with increasing temperature, on increasing the basicity of the amine, and on decreasing the dielectric constant of the solvent.