Mechanisms of solvolyses of acid chlorides and chloroformates. Chloroacetyl and phenylacetyl chloride as similarity models
Mechanisms of solvolyses of acid chlorides and chloroformates. Chloroacetyl and phenylacetyl chloride as similarity models
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DOI：
10.1021/jo0514366
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发表时间：
2005-10-28
影响因子：
3.6
通讯作者：
Szajda, SR
中科院分区：
文献类型：
--
作者：
Bentley, TW;Harris, HC;Szajda, SR
报道了在乙醇/和甲醇/水混合物中，氯乙酰氯（3）在-10 ℃和苯乙酰氯（4）在0 ℃溶剂分解的速率常数和产物选择性（S = [酯产物]/[酸产物]）×（[水]/[醇溶剂]）。另外的动力学数据报告溶剂分解在丙酮/水，2，2，2-三氟乙醇（TFE）/水，和TFE/乙醇的混合物。3的选择性和溶剂效应，包括甲醇的动力学溶剂同位素效应（KSIE）为2.18，与对硝基苯甲酰氯的溶剂分解相似（1，Z = NO2）;丙酮/水中的速率常数与三级机理一致，乙醇/和甲醇/水混合物中的速率和产物可以通过竞争的第三-有序机制，其中一个溶剂分子（醇或水）充当亲核试剂，另一个充当通用碱（加成/消除反应通道）。当水加入到醇中时，3的选择性增加。溶剂对3的溶剂分解反应速率常数的影响与氯甲酸甲酯非常相似，但乙酰氯的KSIE较低，对溶剂电离能力的敏感性较高，这可以通过改变S（N）2/S（N）1（电离）反应通道来解释。4的溶剂分解经历了从乙醇中的加成/消除通道到含水乙醇（<80%v/v乙醇）中的电离通道的变化。用Gaussian 03（HF/6- 31 G（d），B3 LYP/6- 31 G（d），B3 LYP/6 - 311 G（d，p）MO理论）计算了酰基离子的气相稳定性，讨论了反应通道变化的原因.
Rate constants and product selectivities (S = [ester product]/[acid product]) x ([water]/[alcohol solvent]) are reported for solvolyses of chloroacetyl chloride (3) at - 10 degrees C and phenylacetyl chloride (4) at 0 degrees C in ethanol/ and methanol/water mixtures. Additional kinetic data are reported for solvolyses in acetone/water, 2,2,2-trifluoroethanol(TFE)/water, and TFE/ethanol mixtures. Selectivities and solvent effects for 3, including the kinetic solvent isotope effect (KSIE) of 2.18 for methanol, are similar to those for solvolyses of p-nitrobenzoyl chloride (1, Z = NO2); rate constants in acetone/water are consistent with a third-order mechanism, and rates and products in ethanol/ and methanol/water mixtures can be explained quantitatively by competing third-order mechanisms in which one molecule of solvent (alcohol or water) acts as a nucleophile and another acts as a general base (an addition/elimination reaction channel). Selectivities increase for 3 as water is added to alcohol. Solvent effects on rate constants for solvolyses of 3 are very similar to those of methyl chloroformate, but acetyl chloride shows a lower KSIE, and a higher sensitivity to solvent-ionizing power, explained by a change to an S(N)2/S(N)1 (ionization) reaction channel. Solvolyses of 4 undergo a change from the addition/elimination channel in ethanol to the ionization channel in aqueous ethanol (< 80% v/v alcohol). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions, calculated using Gaussian 03 (HF/6-31G(d), B3LYP/6-31G(d), and B3LYP/6-311G(d,p) MO theory).