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Updated: Mar 15, 2026

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
Published on: October 18, 2019
The Importance of Methyl Positioning and Tautomeric Equilibria for Imidazole Nucleophilicity
Renan B Campos1,2,3, Leociley R A Menezes1, Andersson Barison1
1Department of Chemistry, Universidade Federal do Paraná, CP 19081, CEP, 81531-990, Curitiba-PR, Brasil.
Abstract:
Imidazole (IMZ) rings catalyze many biological dephosphorylation processes. The methyl positioning effect on IMZs reactivity has long intrigued scientists and its full understanding comprises a promising tool for designing highly efficient IMZ-based catalysts. We evaluated all monosubstituted methylimidazoles (xMEI) in the reaction with diethyl 2,4-dinitrophenyl phosphate by kinetics studies, NMR analysis and DFT calculations. All xMEI showed remarkable rate enhancements, up to 1.9×105 fold, compared with spontaneous hydrolysis. Unexpectedly, the electron-donating methyl group acts to decrease the reactivity of the xMEI compared to IMZ, except for 4(5)methylimidazole, (4(5)MEI). This behavior was attributed to both electronic and steric effects. Moreover, reaction intermediates were monitored by NMR and surprisingly, the reactivity of the two different 4(5)MEI tautomers was distinguished.
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