溶液中甲醇和二氯亚砜的化学反应

用B3LYP方法和SCIPCM模型(模拟溶剂效应)研究了甲醇和二氯亚砜在两种非极性(ε<15)和两种极性(ε>15)溶剂中的反应(最终产物为氯代甲烷和二氧化硫). 反应过程由反应(1)和反应(2)组成, CH3OS(O)Cl是反应(1)的主要产物和反应(2)的反应物. 反应(2)有“前面取代”(经过渡态TS3f)和“背后取代”(先经CH3OS(O)Cl的电离, 再经过渡态TS3b)两种机理. 计算表明, 在气相和四种溶剂中反应(1)和(2)都是放热反应, 反应(1)具有相同的反应途径(经过渡态→中间体→过渡态), 溶剂的极性对反应(2)有很大的影响. 在气相和非极性溶剂中, TS3f的能量比(CH3OSO++Cl-)离子对(中间体IM2)的能量低, 反应(2)应为前面取代机理; 在极性溶剂中, IM2和TS3b的能量都比TS3f低, 反应(2)应为背后取代机理.

Reaction of Methyl Alcohol with Thionyl Chloride in Solution

Reaction of CH3OH with SOCl2 producing CH3Cl and SO2 in two nonpolar (ε<15) and two polar (ε>15) solvents was studied using the B3LYP method and the SCIPCM model of the SCRF theory for simulating solution effects. The reaction process consists of reaction (1) and reaction (2) with CH3OS(O)Cl being a product of reaction (1) and the reactant of reaction (2). Reaction (2) has front-side substitution (via transition state TS3f) and back-side substitution (ionization of CH3OS(O)Cl followed by substitution via transition state TS3b) mechanisms. The calculations predicted that in gas phase and in the four solvents reactions (1) and (2) were exothermic and reaction (1) had the same reaction path (TS1→IM1→TS2). The calculations indicated that reaction (2) experienced very strong effects of solvent. In gas phase and in nonpolar solvents the front-side substitution was favored over the back-side substitution since TS3f is lower in energy than the (CH3OSO++Cl-) ion pair (IM2); and in polar solvents the back-side substitution was favored over the front-side substitution since IM2 and TS3b are lower in energy than TS3f.