溶剂对 Menshutkin 反应的影响,The Journal of Physical Chemistry B

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溶剂对 Menshutkin 反应的影响
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2022-02-23 , DOI: 10.1021/acs.jpcb.1c09710
Haydar Taylan Turan ₁ , Sebastian Brickel ₁ , Markus Meuwly ₁

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Menshutkin 反应是与从生物化学到化学合成等领域相关的甲基转移反应。在目前的工作中，NH _{3的能量和溶剂分布}通过反应分子动力学模拟，在显式溶剂（水、甲醇、乙腈、苯、环己烷）中研究了 +MeCl 和 Pyr+MeBr 反应。对于极性溶剂（水、甲醇和乙腈）和苯，发现这两种反应都具有强到中等的催化作用，而非极性和庞大的环己烷与溶质的相互作用较弱，并且没有显示出明显的屏障减少。Pyr+MeBr 反应在乙腈和环己烷中的计算势垒高度分别为 23.2 和 28.1 kcal/mol，而实验测量的势垒分别为 22.5 和 27.6 kcal/mol。溶剂分布在反应物和 TS 之间变化很大，但在 TS 和溶质的产物构象之间变化相对较小。当系统接近过渡状态时，发生相关的溶剂运动，使溶剂-溶剂相互作用不稳定。这是系统克服障碍所必需的。最后，发现反应物、TS 和产物状态几何形状中的平均溶剂-溶剂相互作用能与溶质周围溶剂结构的变化相关。

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Solvent Effects on the Menshutkin Reaction

The Menshutkin reaction is a methyl transfer reaction relevant in fields ranging from biochemistry to chemical synthesis. In the present work, the energetics and solvent distributions for NH₃+MeCl and Pyr+MeBr reactions were investigated in explicit solvent (water, methanol, acetonitrile, benzene, cyclohexane) by means of reactive molecular dynamics simulations. For polar solvents (water, methanol, and acetonitrile) and benzene, strong to moderate catalytic effects for both reactions were found, whereas apolar and bulky cyclohexane interacts weakly with the solute and does not show pronounced barrier reduction. The calculated barrier heights for the Pyr+MeBr reaction in acetonitrile and cyclohexane are 23.2 and 28.1 kcal/mol compared with experimentally measured barriers of 22.5 and 27.6 kcal/mol, respectively. The solvent distributions change considerably between reactant and TS but comparatively little between TS and product conformations of the solute. As the system approaches the transition state, correlated solvent motions occur which destabilize the solvent–solvent interactions. This is required for the system to surmount the barrier. Finally, it is found that the average solvent–solvent interaction energies in the reactant, TS, and product state geometries are correlated with changes in the solvent structure around the solute.

更新日期：2022-02-23

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