DFT Studies on Reaction Mechanism of the Double Bond Isomerization of Butene Catalyzed by 1-ethyl-3-methyl-imidazolium of the Ionic Liquid (II)

Abstract

The possible reaction paths of butene isomerization catalyzed by 4-H and 5-H of 1-ethyl-3-methyl-imidazolium (EMIM(superscript +)) have been studied by using density functional theory (DFT) at B3LYP/6-3G(superscript **) levels. The geometries of the reactants, transition states and products are fully optimized by energy gradient technology and the equilibrium states and transition states are verified according to the number of imaginary frequency obtained through vibrational analysis. The computed results indicate that the butene molecule approaches to 4-H or 5-H of EMIM(superscript +) at the first and then forms a supermolecule due to physical adsorption. Whereafter the isomerization of butene double bond is catalytically performed. The forward energy barriers of the rearrangement reaction catalyzed by 4-H and 5-H atom of EMIM(superscript +) are 204.2 and 207.3 kJ•mol^(-1), and the reverse energy barriers are 220.9 and 223.8kJ•mol^(-1), respectively. The isomerization of outene catalyzed by the proton of the imidazolium ring may proceed through multi-channel at one-step process.