The catalytic mechanism of KI and the co-catalytic mechanism of hydroxyl substances for cycloaddition of CO2 with propylene oxide
The catalytic mechanism of KI and the co-catalytic mechanism of hydroxyl substances for cycloaddition of CO2 with propylene oxide
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KI与羟基物质共催化CO2与环氧丙烷环加成反应机理
DOI：
10.1039/c2gc35711a
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发表时间：
2012-01-01
期刊：
影响因子：
9.8
通讯作者：
Han, Buxing
中科院分区：
文献类型：
--
作者：
Ma, Jun;Liu, Jinli;Han, Buxing
大量实验表明，KI/-OH催化体系对CO2与环氧化合物环加成反应生成环状碳酸酯非常有效，是将CO2转化为高附加值化学品的重要途径之一。但催化机理尚不清楚。本工作首次对KI的催化机理和羟基物质的助催化机理进行了理论研究。采用密度泛函理论（DFT）方法，选择环氧丙烷（PO）作为环氧化合物，甘油和丙二醇（PG）作为羟基化合物。确定了气相和溶剂环境下的过渡结构、速率控制步骤和最低能垒反应途径。发现羟基、钾离子和碘离子形成三元协同催化体系I-（-OH）-K+。羟基物质提供的极性溶剂环境也有利于环加成反应的进行。结果为KI/羟基催化体系促进的CO2与环氧化物的环加成反应提供了清晰的轮廓，并能满意地解释以前的实验观察。
Many experiments have demonstrated that KI/hydroxyl (-OH) substance catalytic systems are very effective for the cycloaddition of CO2 with epoxides to produce cyclic carbonates, which is among the most successful and important routes to convert CO2 into value-added chemicals. But the catalytic mechanism is not clear. In this work, we conducted the first theoretical research to clarify the catalytic mechanism of KI and the co-catalytic mechanism of hydroxyl substances. Density functional theory (DFT) method was used, propylene oxide (PO) was selected as the epoxide, and glycerol and propylene glycol (PG) as the hydroxyl substances. The transition structures, rate-determining steps and lowest energy barrier reaction pathways were identified for both gas phase and solvent environments. It was found that the hydroxyl groups, the potassium cation and the iodine anion form a ternary synergistic catalytic system, I--(-OH)-K+. The polar solvent environment provided by the hydroxyl substance was also favorable to the cycloaddition reaction. The results provide a clear profile for the cycloaddition of CO2 and epoxides promoted by KI/hydroxyl substance catalytic systems, and can explain satisfactorily the previous experimental observations.