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, CH 3, 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 CH 3). The Brønstedtype plot is also nonlinear with a change in slope from a small value (βnuc = 0.50) to a large value (βnuc = 1.29 at pKa = 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 (Eo) of the aniline nucleophiles and are consistent with the suggested mechanism.