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用核磁共振法研究了亚胺型杂卓1和烯胺型杂卓2在不同质子溶剂—甲醇、乙醇、叔丁醇、乙酸及CF3CO2D的DMSO-d6溶液中的稳定性及互变异构.结果表明,烯胺型杂卓2在上述溶剂中稳定,亚胺型杂卓1在酸性较弱的质子溶剂中(乙醇、叔丁醇)及较低的温度下(≤30℃)基本稳定,在酸性较强的质子溶剂中(甲醇、乙酸、CF3CO2D的DMSO-d6溶液)向烯胺转化,而且随着溶剂酸性的增强、温度的升高以及反应物与溶剂接触时间的延长,亚胺向烯胺的转化进一步加强.本文还以1a和1b为例,研究了在乙酸溶液中亚胺型杂卓向烯胺型杂卓转化的热力学和动力学特征.研究表明,在283~333 K范围内,该转化的焓变(△H)和熵变(△S)均大于零,吉布斯自由能变(△G)小于零,因此其是吸热、自发及熵增加的过程,该过程可用二级动力学方程来描述,质子对亚胺向烯胺的转化起催化作用.
The stability and tautomerism of imine-type 1 and enamine-type 2 in DMSO-d6 solutions of different protic solvents-methanol, ethanol, t-butanol, acetic acid and CF3CO2D were studied by NMR. The results showed that the enamine type 2 was stable in the above solvents and the imine type 1 was basically stable in the acidic proton solvent (ethanol, t-butanol) and the lower temperature (≤30 ℃) In the more acidic protic solvent (methanol, acetic acid, CF3CO2D in DMSO-d6 solution) to enamine conversion, and with the increase of solvent acidity, temperature and reactants and solvent exposure time extension, the imine to Enamine conversion further strengthened.In this paper, 1a and 1b are also used as an example to study the thermodynamic and kinetic characteristics of conversion of imine to enamine in the acetic acid solution.The results show that in the range of 283 ~ 333 K , The enthalpy change (ΔH) and entropy change (ΔS) of the transformation are both greater than zero. The Gibbs free energy change (ΔG) is less than zero, so it is an endothermic, spontaneous and entropy increasing process. Available second-order kinetic equation to describe the proton on the conversion of imine to enamine catalytic role.