College of Chemistry, Key Lab of Green Chemistry and Technology in Ministry of Education, Sichuan University, Chengdu 610064, People's Republic of China.
Phys Chem Chem Phys. 2013 Jul 28;15(28):11846-55. doi: 10.1039/c3cp51048d. Epub 2013 Jun 13.
An "on water" environment, describing the reactions with insoluble reactants in water, has been reported to give high yields of products compared to organic solvents. The 1,3-dipolar cycloadditions of phthalazinium dicyanomethanide 1 with three different dipolarophiles, methyl vinyl ketone (MVK), methyl acrylate (MAC), and styrene (STY), have been investigated using QM/MM calculations in water, acetonitrile, and acetonitrile-water solvent mixtures, as well as at the vacuum-water interface. Monte Carlo statistical mechanics simulations utilizing the free-energy perturbation theory and PDDG/PM3 for the QM method have been used. The transition structures for all three reactions do not show large variations among different solvents. However, the calculated free energies of activation at the interface are found to be higher than those calculated in bulk water. Computed energy pair distributions and radial distribution functions reveal a uniform loss of hydrogen bonds for the reactants and transitions states in progressing from bulk water to the vacuum-water interface. The hydrophobic effects in the reactions of 1 with MVK and MAC are similar for both, and weaker than the effect in the reaction with STY. According to the results in water-acetonitrile mixtures at different molar ratios, it is clear that the special hydrogen bonding effects are the main reason which leads to the rapid rate enhancement in progressing from a water-acetonitrile molar ratio of 0.9 : 0.1 to pure water. New insights into solvent effects for 1,3-dipolar cycloadditions are presented herein.
一种“水相”环境，描述了在水中与不溶性反应物的反应，与有机溶剂相比，该环境下产物的产率更高。利用 QM/MM 计算方法，在水、乙腈和乙腈-水溶剂混合物中，以及在真空-水界面上，研究了邻苯二甲酰亚胺二氰基甲烷 1 与三种不同的偶极子（甲基乙烯基酮 (MVK)、甲基丙烯酸甲酯 (MAC) 和苯乙烯 (STY))的 1,3-偶极环加成反应。使用了蒙特卡罗统计力学模拟和自由能微扰理论以及 PDDG/PM3 进行 QM 方法。所有三种反应的过渡态结构在不同溶剂中没有很大差异。然而，在界面处计算的活化自由能被发现高于在本体水中计算的值。计算得到的能量对分布和径向分布函数表明，在从本体水到真空-水界面的过程中，反应物和过渡态的氢键均匀丧失。在 1 与 MVK 和 MAC 的反应中，疏水效应相似，均比与 STY 的反应弱。根据不同摩尔比的水-乙腈混合物的结果，很明显，特殊的氢键效应是导致从水-乙腈摩尔比 0.9:0.1 到纯水时反应速率迅速提高的主要原因。本文提出了 1,3-偶极环加成反应溶剂效应的新见解。
