Kinetic Studies on Nucleophilic Addition Reactions of 4-X-substituted Anilines to N1-methyl-4-nitro-2,1,3 benzothiadiazolium terafluoroborate in Acetonitrile: Reaction Mechanism and Mayr's Approach

ABSTRACT The kinetics of the coupling of N1‐methyl‐4‐nitro‐2,1,3 benzothiadiazolium tetrafluoroborate 1 with a series of 4‐X‐substituted anilines 2a–f (X = OH, OMe, Me, H, Cl, and CN) have been investigated in acetonitrile at 20°C. The second‐order rate constants result in a nonlinear Brönsted‐type plot. The Hammett plot is also nonlinear, whereas the Yukawa–Tsuno plot exhibits an excellent linear correlation with ρ = –1.62 and r = 1.44. The large Brönsted (βnuc = 1.24) and Hammett (ρ = –5.16) values suggest that the reactions proceed trough a single electron transfer mechanism. The finding of satisfactory correlation between the log k1 of the reactions and the oxidation potentials (E°) of anilines 2a–d supports this mechanism. On the other hand, electrophilicity parameter E of benzothiadiazolium cation 1 as defined by the correlation log k20°C = s(E + N) has been determined and compared with the electrophilic reactivities of a large variety of electrophiles.