A kinetic model for water reactivity (avoiding activities) for hydrolyses in aqueous mixtures - selectivities for solvolyses of 4-substituted benzyl derivatives in alcohol-water mixtures
A kinetic model for water reactivity (avoiding activities) for hydrolyses in aqueous mixtures - selectivities for solvolyses of 4-substituted benzyl derivatives in alcohol-water mixtures
复制标题
水性混合物中水解的水反应性（避免活性）的动力学模型 - 醇-水混合物中 4-取代的苄基衍生物的溶剂分解的选择性
DOI：
10.1002/poc.1308
复制
发表时间：
2008
影响因子：
1.8
通讯作者：
Bentley T
中科院分区：
文献类型：
--
作者：
Bentley T
对于各种苄基底物在乙醇-水（EW）和甲醇-水（MW）混合物中的溶剂分解，在75°C下氯化物的产物选择性(S)被报道，用摩尔浓度定义如下：S=（[醚产物]/[醇产物]）×（[水]/[醇溶剂]）。该结果支持了先前的证据，即4‐硝基苯底物的溶剂裂解是SN2过程，该过程不受从水到醇的整个溶剂范围内的机制变化的影响。在25°C和/或45°C的EW和MW中，报告了额外的动力学数据，包括动力学溶剂同位素效应（KSIE），用于甲酰亚硝基苄基和甲酰亚苄基的溶剂裂解。提出了一个既能解释速率又能解释产物的动力学模型；由溶剂极性引起的一般介质效应与溶剂对SN2反应中充当亲核试剂的水和醇分子亲核性的影响结合在一个参数中。根据该模型，当醇加入水中时，由于溶剂极性降低，反应速率降低，但水的亲核性相对于醇增加。从酒精到水的整个溶剂组成范围的实验速率和产品数据的可用性显示了利用活性的替代方法的局限性。版权所有©2008 John Wiley & Sons， Ltd
For solvolyses of various benzyl substrates in ethanol–water (EW) and methanol–water (MW) mixtures, product selectivities (S) are reported for chlorides at 75 °C defined as follows using molar concentrations:S= ([ether product]/[alcohol product]) × ([water]/[alcohol solvent]). The results support earlier evidence that solvolyses of 4‐nitrobenzyl substrates are SN2 processes, which are not susceptible to mechanistic changes over the whole range of solvents from water to alcohol.Svalues at 25 and/or 45 °C in EW and MW, and additional kinetic data including kinetic solvent isotope effects (KSIE) are reported for solvolyses of 4‐nitrobenzyl mesylate and tosylate. A kinetic model, explaining both rates and product, is proposed; a general medium effect due to solvent polarity is combined in one parameter with solvent effects on the nucleophilicity of the water and alcohol molecules acting as nucleophiles in SN2 reactions. According to this model, as alcohol is added to water the rate of reaction decreases due to a decrease in solvent polarity, but the nucleophilicity of water increases relative to alcohol. The availability of experimental rate and product data over the whole range of solvent compositions from alcohol to water, reveals limitations of alternative approaches using activities. Copyright © 2008 John Wiley & Sons, Ltd.