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

• Published in: ChemistrySelect (Weinheim) Vol. 6; no. 18; pp. 4424 - 4431
• Main Authors: Rammah, Mehdi, Mahdhaoui, Faouzi, Gabsi, Wahiba, Boubaker, Taoufik
• Format: Journal Article
• Language: English
• Published: 14.05.2021
• Subjects: Benzotriazole 1-oxides; Electrophilicity; Kinetics; Mayr's Approach. Structure-reactivity
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202100568

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)=sN (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=CF3, Me and OH) were evaluated. Excellent linear correlation (r2=0.9962) between the electrophilicity parameters E of benzotriazoles 1 a–d and their pKa values for σ‐complexation has also been observed and discussed. This work describes the kinetics of the reactions of benzotriazole 1‐oxides with nitroalkyl anions in aqueous solution. The second‐order rate constants (kC‐C) follow the linear free energy relationship log kC‐C (20 °C) = sN (E + N), which allowed us to quantify electrophilicity parameters E of the benzotriazoles 1a‐d (X = OMe, H, Br and CN). In addition, structure‐reactivity relationships are discussed, and it is shown that the electrophilicity parameters E are linearly related to the pKa values for water addition to these neutral electrophiles.