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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Free Energy Profile of the Reaction between the Hydroxide Ion and Ethyl Acetate in Aqueous and Dimethyl Sulfoxide Solutions: A Theoretical Analysis of the Changes Induced by the Solvent on the Different Reaction Pathways
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Free Energy Profile of the Reaction between the Hydroxide Ion and Ethyl Acetate in Aqueous and Dimethyl Sulfoxide Solutions: A Theoretical Analysis of the Changes Induced by the Solvent on the Different Reaction Pathways

机译：水溶液和二甲基亚砜溶液中氢氧根离子与乙酸乙酯之间反应的自由能谱：溶剂在不同反应途径上引起的变化的理论分析

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An extensive analysis of the free energy profile for the reaction of the hydroxide ion with ethyl acetate in both aqueous and dimethyl sulfoxide (DMSO) solutions has been carried out using ab initio calculations and including the solvent effect by the polarizable continuum model. Different reaction pathways were investigated, such as the usual B_(AC)2 mechanism, the carbanion mechanism, the elimination mechanism, and the S_N2 mechanism. Our calculation agrees with the view that in aqueous and DMSO solution basic hydrolysis occurs by the B_(AC)2 mechanism. In water, the predicted activation free energy value is 17.6 kcal mol~(-1), which is in very good agreement with the experimental value of 18.8 kcal mol~(-1). Using a new parametrization of the polarizable continuum model adequate to describe anions and neutral species in DMSO, the present study predicts a rate enhancement by a factor of 435 in the reaction when going from water (protic solvent) to DMSO (dipolar aprotic solvent). In this solvent, the activation free energy is predicted to drop to 14.0 kcal mol~(-1). Furthermore, our results point out that the elimination mechanism is only 6.0 kcal mol~(-1) (Δ_(sol)~(++) = 20.0 kcal mol~(-1)) less favorable than the BAC2 mechanism in DMSO solution, and 8.4 kcal mol~(-1) less favorable in water. The S_N2 and the carbanion mechanisms have barriers above 30 kcal mol-1 in water and DMSO and are thus highly unfavorable. These results suggest the elimination mechanism can become the dominant pathway in the basic hydrolysis of sterically crowded esters at the carbonyl center.
机译：使用从头算计算并通过可极化连续体模型包括溶剂效应，对氢氧根离子与乙酸乙酯在水溶液和二甲基亚砜（DMSO）中反应的自由能曲线进行了广泛的分析。研究了不同的反应途径，例如通常的B_（AC）2机理，碳负离子机理，消除机理和S_N2机理。我们的计算与以下观点一致：在水溶液和DMSO溶液中，碱性水解是通过B_（AC）2机理发生的。在水中，预测的活化自由能值为17.6 kcal mol〜（-1），与实验值18.8 kcal mol〜（-1）非常吻合。使用足以描述DMSO中阴离子和中性物种的可极化连续体模型的新参数化，本研究预测从水（质子传递溶剂）到DMSO（偶极非质子传递溶剂）时，反应速率可提高435倍。在该溶剂中，活化自由能预计将下降至14.0 kcal mol〜（-1）。此外，我们的结果指出，在DMSO溶液中，消除机理仅比BAC2机理差6.0 kcal mol〜（-1）（Δ_（sol）〜（++）= 20.0 kcal mol〜（-1））。在水中不利于8.4 kcal mol〜（-1）。 S_N2和碳负离子机制在水和DMSO中具有大于30 kcal mol-1的势垒，因此非常不利。这些结果表明消除机理可以成为在羰基中心的空间拥挤酯的基本水解的主要途径。

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