Ci Chen

Catalytic performance of a series of guanidinium-based ionic liquids in the coupling reaction of carbon dioxide with epoxides

In order to gain more insight into the high catalytic activity of N′′-(2-aminoethyl)-N,N,N′,N′-tetramethylguanidine bromide ([TMGC2H4NH2]Br) and to select a more suitable catalyst for the synthesis of propylene carbonate (PC), the cycloaddition reaction of carbon dioxide (CO2) into the epoxide (EO), catalyzed by a series of functional guanidinium-based ionic liquids (FGBILs), is schematically studied by the Density Functional Theory (DFT). The calculated results indicate that the formation of carbamic acid is a common pathway with a lower barrier height when the NH2-functionalized IL encounters CO2. What is more, the formation of carbamic acid is helpful in decreasing the barrier height of the ring-opening step. Two ILs are involved in the process of forming carbamic acid. Sparked by this, the mechanism catalyzed by two ILs is explored for comparison with the model catalyzed by one IL. In addition, the catalytic activities of other functionalized guanidinium-based ionic liquids are investigated, the results indicate that the task-specified ILs have better catalytic activity than those without functional groups because of the increased acidity. Besides the cation, the influence of different anions and substrates is also investigated.

The mechanism research on the reaction HCNO + HO2: a theoretical investigation

The mechanism of reaction HCNOxa0+xa0HO2 is investigated by means of CCSD(T)/6-311xa0+xa0G(d,p)//B3LYP/6-311xa0+xa0G(d,p) method, in which Pi with the ixa0=xa01, 2, 3, …, 7 are involved, to determine a more reasonable pathway. Among four possible entrance patterns, the attack of oxygen to carbon is the most energetically feasible leading to complex a1. Starting from the a1, the rupture of O2–O3 bond to form P3 (HC(O)NOxa0+xa0OH) is the most favorable pathway. Alternatively, the a1 undergoes N–O1 bond rotation to form the isomer a2. A concerted O2–O3 bond and C–N bond cleavage leading to P4 (OHxa0+xa0HCOxa0+xa0NO) is the secondary feasible pathway. Other products are not energetically accessible because of higher barrier-consumed and/or complicated processes. We hope that the present work would be helpful to experimentally identify the product distributions and deeply understand the mechanism of the title reaction.

Protic pyrazolium ionic liquids for efficient chemical fixation of CO2: design, synthesis, and catalysis

The conversion of carbon dioxide into organic products under benign conditions is still challenging. Ionic liquids are regarded as efficient and “green” catalysts from a sustainability view point. However, little attention has been focused on pyrazolium ILs although they are structural isomers of imidazolium ILs. Even fewer studies have been performed on protic pyrazolium ILs. In this work, three new protic pyrazolium ILs, HTMPzBr, HMM3PzBr, and HMM5PzBr, have been synthesized to explore their catalytic activity for the coupling reaction of carbon dioxide and propylene oxide. Both theoretical calculations and experimental characterization have verified that HTMPzBr and HMM5PzBr have similar catalytic activity, which is higher than that of HMM3PzBr. The role of various weak interactions, especially hydrogen bonds, in the reaction is elucidated by detailed theoretical analysis. The sequence of catalytic activity predicted by the Double-IL theoretical model is totally consistent with the experimental result. It is reasonable to design ionic liquids from a molecular level if a suitable theoretical model is applied, and this would provide some guidance for further experimental study.