title: Ionic Liquid Solvation versus Catalysis: Computational Insight from a Multisubstituted Imidazole Synthesis in [Et2NH2][HSO4].
abstract: The mechanisms of a tetrasubstituted imidazole [2-(2,4,5-triphenyl-1 H-imidazol-1-yl)ethan-1-ol] synthesis from benzil, benzaldehyde, ammonium acetate, and ethanolamine in [Et2NH2][HSO4] ionic liquid (IL) are studied computationally. The effects of the presence of the cationic and anionic components of the IL on transition states and intermediate structures, acting as a solvent versus as a catalyst, are determined. In IL-free medium, carbonyl hydroxylation when using a nucleophile (ammonia) proceeds with a Gibbs free energy (ΔG≠) barrier of 49.4 kcal mol-1. Cationic and anionic hydrogen-bond solute-solvent interactions with the IL decrease the barrier to 35.8 kcal mol-1. [Et2NH2][HSO4] incorporation in the reaction changes the nature of the transition states and decreases the energy barriers dramatically, creating a catalytic effect. For example, carbonyl hydroxylation proceeds via two transition states, first proton donation to the carbonyl (ΔG≠=9.2 kcal mol-1) from [Et2NH2]+, and then deprotonation of ammonia (ΔG≠=14.3) via Et2NH. Likewise, incorporation of the anion component [HSO4]-of the IL gives comparable activation energies along the same reaction route and the lowest transition state for the product formation step. We propose a dual catalytic IL effect for the mechanism of imidazole formation. The computations demonstrate a clear distinction between IL solvent effects on the reaction and IL catalysis.
authors: Department of Chemical Engineering Qafqaz University Hasan Aliyev Str. 120 Baku Absheron AZ0101 Azerbaijan; Institute of Petrochemical Processes Azerbaijan National Academy of Sciences Baku AZ1025 Azerbaijan.
authors: Yusif
authors: Y
authors: Abdullayev
authors: Institute of Petrochemical Processes Azerbaijan National Academy of Sciences Baku AZ1025 Azerbaijan.
authors: Vagif
authors: V
authors: Abbasov
authors: Department of Fundamental Chemistry Institute of Chemistry University of São Paulo Av. Prof. Lineu Prestes, 748 05508-000 São Paulo Brazil.
authors: Lucas C
authors: LC
authors: Ducati
authors: Department of Chemical Engineering Qafqaz University Hasan Aliyev Str. 120 Baku Absheron AZ0101 Azerbaijan; Institute of Petrochemical Processes Azerbaijan National Academy of Sciences Baku AZ1025 Azerbaijan.
authors: Avtandil
authors: A
authors: Talybov
authors: Department of Chemistry University at Buffalo State University of New York Buffalo NY 14260-3000 USA.
authors: Jochen
authors: J
authors: Autschbach
keywords: catalysis; density functional calculations; ionic liquids; multisubstituted imidazole; solvation