Control of Chemical Selectivity by Effect of Shape Similarity between Solute and Solvent Molecules

为了开发一种更“精确”和新颖的方法来控制化学选择性，我们研究了一对缔合硫醇（I和II）的氧化选择性的相关性和温度依赖模式，每个都有R^1或R^2作为取代基，溶质分子和溶剂分子的取代基之间的形状相似。甲醇-正丙醇的选择性（R^1=Ph, R^2=n-C_5H_<11>）高于甲醇-异丙醇（20和35‰）。在烃类摩尔分数=0.50时，烃类水-正丙醇从环己烷、正己烷和异己烷的选择性（R^1=Ph, R^2=i-C_5H_<11>）均有所提高。在苯-乙醇（乙醇的摩尔分数=0.50）中，R^1=Ph, R^2=i-C_5H_<11>)的选择性在ca.35 oc时最高，在异己烷-乙醇中最低，在正己烷-乙醇中随温度升高而降低。甲醇-正丁醇（甲醇摩尔分数=0.50）和甲醇-异丁醇的选择性（R^1=环c_5h_9， R^2=n-C_4H_9）均随温度升高而升高。从这些结果可以明显看出：(1)当硫醇取代基与溶剂分子的取代基形状相似时，选择性增加；(2)选择性的温度依赖模式随着溶质分子和溶剂分子取代基形状相似的程度而显著改变。这表明形状相似效应成为控制化学选择性的一种新型方法。

In order to develop a more "precise" and novel type of method for control of chemical selectivity, we examined correlation of the selectivity and the pattern of temperature dependence of the selectivity in oxidation of a pair of associating thiols (I and II) , each having R^1 or R^2 as a substituent, with shape similarity between substituents of solute and solvent molecules.1. The selectivity (R^1=Ph, R^2=n-C_5H_<11>) was higher in methanol-n-propyl alcohol than in methanol-isopropyl alchol (at 20 and 35ﾟC).2. The selectivity (R^1=Ph, R^2=i-C_5H_<11>) in hydrocarbon-water-n-propyl alcohol (mole fraction of hydrocarbon=0.50) increased in going from cyclohexane, n-hexane, and to isohexane.3. The selectivity (R^1=Ph, R^2=i-C_5H_<11>) exhibited a maximum at ca.35ﾟC in benzene-ethanol (mole fraction of ethanol=0.50) , showed a minimum in isohexane-ethanol, and decreased with temperature in n-hexane-ethanol.4. The selectivity (R^1=cyclo-C_5H_9, R^2=n-C_4H_9) increased with temperature both in methanol-n-butyl alcohol (mole fraction of methanol=0.50) and in methanol-isobutyl alchol.It is evident from these results that (i) the selectivity increases when a substituent of a thiol is similar in shape to that of a solvent molecule and (ii) the pattern of temperature dependance of the selectivity alters markedly with the degree of shape similarity between substituents of solute and solvent molecules. This indicates that shape similarity effect becomes a novel type of method for control of chemical selectivity.