Quantification of the Electrophilic Reactivities of Benzotriazoles and Structure‐Reactivity Relationships

The kinetics of the coupling of 2‐N‐(4′‐X‐pheny1)‐4,6‐dinitrobenzotriazole 1‐oxides 1 a – d (X=OMe, H, Br and CN) with nitroalkyl anions 2 a – c have been investigated in aqueous solution at 20 °C. Using the derived second‐order rate constants and this series of nucleophiles 2 a – c as reference, the electrophilicity parameters E of the four electrophiles 1 a – d have been determined according to the linear free enthalpy relationship log k (20 °C)= s N ( E + N ). With the electrophilicity parameters E range from −9.72 to −11.78, the substituent effects on the electrophilic reactivity was examined quantitatively, leading to linear correlation of E with Hammett substituent constants (σ). Based on this correlation, the unknown electrophilicity parameters E of other 2‐N‐(4′‐X‐pheny1)‐4,6‐dinitrobenzotriazole 1‐oxides (X=CF 3 , Me and OH) were evaluated. Excellent linear correlation (r 2 =0.9962) between the electrophilicity parameters E of benzotriazoles 1 a – d and their pK a values for σ‐complexation has also been observed and discussed.