Single electron transfer in SNAr process: Reactions of 2,4,6-tris(trifluoromethanesulfonyl)anisole with anilines in dimethyl sulfoxide

Abstract

Second-order rate constants ( k1) have been measured spectrophotometrically for reactions of 2,4,6-tris(trifluoromethanesulfonyl)anisole 1 with 4-X-substituted anilines (X = OH, OCH3, CH3, H, I and Cl) 2a–f in dimethyl sulfoxide (DMSO) at 25 °C. The Hammett plot is nonlinear, i.e. the anilines having an electron-donating substituent exhibit positive deviations from the log k1 versus correlation. The Hammett plot consists of two intersecting straight lines, i.e. ρ=– 1.40 for electron-withdrawing substituents (X = I and Cl) while ρ=– 3.26 for electron-donating substituents (X = OH, OCH3 and CH3). The Brønsted-type plot is also nonlinear with a change in slope from a small value (βnuc=0.50) to a large value (βnuc = 1.29 at p Ka=4.58). This change could be interpreted in terms of a change in mechanism from a polar SNAr process to a single electron transfer. On the other hand, the experimental data show that the rate constants ( k1) values exhibit good correlation with the oxidation potentials ( E°) of the aniline nucleophiles and are consistent with the suggested mechanism.