Kinetic studies for the reactions of N1-methyl-4-nitrobenzofurazanium tetrafluoroborate 1a with a series of 4-X-substituted anilines 2a-d (X = OH, OMe, Me and H) have been carried out in MeCN at 20 °C. The derived second-order rate constants (k1) have been combined with the pKa values of the conjugate acids of the anilines 2a-d to calculate the Brönsted parameters βnuc according to the linear free-energy relationship log k1 vs. pKa. The large Brönsted βnuc of 1.40 obtained suggest that the reactions proceed trough a single electron transfer (SET) mechanism. On the other hand, the finding of satisfactory correlation between the log k1 of the reactions and the oxidation potentials (Eo ) of anilines 2a-d supports this mechanism.
S. Ben Salah, R. Goumont, T. Boubaker
Kinetics, Linear Free Energy Relationships, Substituent Effects, SET Mechanism