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首页> 外文期刊>Indian Journal of Chemistry, Section A. Inorganic, Physical, Theoretical & Analytical >Kinetics and mechanism of amine-catalysed solvolysis of azlactone in water-dioxan mixtures
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Kinetics and mechanism of amine-catalysed solvolysis of azlactone in water-dioxan mixtures

机译：胺催化水-二恶烷混合物中内酯的动力学和机理

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摘要

The effect of replacing solvent water by dioxan up to 50% v/v on the rate of catalytic-amine solvolysis of azlactone has been measured spectrophotometrically in the temperature range 40-60°C Addition of an organic solvent to water largely decreases the rate of ring- opening process. Such an effect was found to diminish in the region of lower relative permittivity. The reaction rate constants are analyzed and discussed in terms of solvent effect and nucleophilicity of amines. ΔG~≠ gradually decreases as a function of increasing [water], due to a complex and quasi-mirror image compensation of ΔH~≠ and ΔS~≠. The variation of ΔH~≠ versus ΔS~≠ is linear. The catalytic coefficient, k_(Am), for amine has been estimated from the general linear equation, k_(obs)= k_o + k_(Am) [Amine]. The binary solvent mixtures used give an unusual range of properties. The plot of log k_(Am) versus log [H2O] show two linear segments with intersection at 33.3 mol dm~(-3) [H2O]. The correlation between log k_(Am) and reciprocal of the relative permittivity is non-linear, while that between log k_(Am) versus pK_a is linear. All these observations are consistent with the suggested mechanism.
机译：在40-60°C的温度范围内，用分光光度法测量了用二恶烷代替溶剂水（高达50％v / v）对lac内酯催化胺溶剂分解速度的影响。开环过程。发现这种效应在较低的相对介电常数的区域中减小。根据溶剂作用和胺的亲核性对反应速率常数进行了分析和讨论。 ΔG〜≠由于[H]的增加而逐渐减小，这是由于ΔH〜≠和ΔS〜≠的复杂镜面图像补偿所致。 ΔH〜≠与ΔS〜≠的变化是线性的。胺的催化系数k_（Am）已根据一般线性方程式k_（obs）= k_o + k_（Am）[胺]估算。所用的二元溶剂混合物具有异常的性能范围。 log k_（Am）与log [H2O]的关系图显示了两个线性段，其交点为33.3 mol dm〜（-3）[H2O]。 log k_（Am）与相对介电常数的倒数之间的相关是非线性的，而log k_（Am）与pK_a之间的相关是线性的。所有这些观察结果与建议的机制一致。

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