Rovibrational Energy Transfer in the 4νCH Manifold of Acetylene, Viewed by IR−UV Double-Resonance Spectroscopy. 4. Collision-Induced Quasi-Continuous Background Effects

Density functional theory study on the cycloaddition of carbon dioxide with propylene oxide catalyzed by alkylmethylimidazolium chlorine ionic liquids

The cycloaddition of carbon dioxide (CO2) with propylene oxide (PO) in the absence and presence of alkylmethylimidazolium chlorine ([C(n)mim]Cl, n = 2, 4, and 6) ionic liquids has been studied in detail by performing density functional theory calculations at the B3PW91/6-31G(d,p) level. It is found that in the absence of [C(n)mim]Cl the reaction proceeds via two possible channels (each of them involves one elementary step) and the corresponding barriers are found to be as high as 59.71 and 55.10 kcal mol(-1), while in the presence of [C(n)mim]Cl there exist five possible reaction channels (each of them involves two or three elementary steps) and the barriers of the rate-determining steps are reduced to 27.93-38.05 kcal mol(-1), clearly indicating that [C(n)mim]Cl promotes the reaction via modifying the reaction mechanism and thereby remarkably decreases the barrier. The origination of the catalytic activity of [C(n)mim]Cl has been analyzed in detail. The present theoretical study rationalizes the early experimental findings well and provides a clear profile for the cycloaddition of CO2 with PO promoted by [C(n)mim]Cl.

Theoretical Study of the Mechanism for the Markovnikov Addition of Imidazole to Vinyl Acetate Catalyzed by the Ionic Liquid [bmIm]OH

By performing density functional theory calculations, we have studied the Markovnikov addition of imidazole to vinyl acetate catalyzed by 1-butyl-3-methylimidazolium hydroxide, [bmIm]OH, a novel basic ionic liquid. The purpose is to show the detailed reaction mechanism, to rationalize the experimental observations, and in particular to better understand the role of [bmIm]OH played in the reaction as a catalyst. Two different reaction pathways (stepwise and concerted) have been characterized and analyzed in detail. It was found that both the cation and anion of [bmIm]OH play important roles in the Markovnikov addition, which decrease the barrier and increase the selectivity of Markovnikov addition. The present results rationalize the early experimental findings well and provide a prototype for theoretically understanding the Markovnikov addition catalyzed by room-temperature ionic liquids.

Choline saccharinate and choline acesulfamate: ionic liquids with low toxicities

Choline saccharinate and choline acesulfamate are two examples of hydrophilic ionic liquids, which can be prepared from easily available starting materials (choline chloride and a non-nutritive sweetener). The (eco)toxicity of these ionic liquids in aqueous solution is very low in comparison to other types of ionic liquids. A general method for the synthesis and purification of hydrophilic ionic liquids is presented. The method consists of a silver-free metathesis reaction, followed by purification of the ionic liquid by ion-exchange chromatography. The crystal structures show a marked difference in hydrogen bonding between the two ionic liquids, although the saccharinate and the acesulfamate anions show structural similarities. The optimized structures, the energetics, and the charge distribution of cation-anion pairs in the ionic liquids were studied by density functional theory (DFT) and second-order (Møller-Plesset) perturbation theory calculations. The occupation of the non-Lewis orbitals was considered to obtain a qualitative picture of the Lewis structures. The calculated interaction energies and the dipole moments for the ion pairs in the gas phase were discussed.

Surface Orientation of 1-Methyl-, 1-Ethyl-, and 1-Butyl-3-methylimidazolium Methyl Sulfate as Probed by Sum-Frequency Generation Vibrational Spectroscopy

The orientation of the ions at the surface of ionic liquids has been determined by the surface-sensitive technique sum-frequency generation vibrational spectroscopy. The results indicate that both ions are present at the first layer of the gas-liquid interface. Furthermore, the alkyl chains are found to be extended toward the gas phase and away from the liquid phase. The proposed models for the preferred orientation of the ions are in good agreement in comparison with the results obtained from the recent MD simulation studies. The salts considered here are 1,3-dimethylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium methylsulfate, and 1-butyl-3-methylimidazolium methylsulfate.