Chloride-ion promoted dehydrochlorination of 1,1-diaryl-2,2,2-trichloroethanes in dipolar aprotic solvents

Abstract

Rate constants are reported for the second-order dehydrochlorination reactions of Ar₂CH·CCl₃ compounds promoted by Buⁿ₄NCl in acetone and by LiCl in dimethylformamide. Rate data for the dehydrochlorination reactions of Ar(Ph)CH·CCl₃ compounds in the latter system are also presented. A modified Hammett-equation analysis yields ρ values of 1·31 (acetone) and 0·99 (dimethylformamide). It is considered that these parameters are diagnostic of a significant degree of β-carbanionic character in the E2 transition states, and that the system provides the first clear example of a halide-promoted E2H reaction. The E2C mechanism can be definitely rejected for this particular case.