基于苯并硫氮杂卓的亚胺、烯胺在质子溶剂中的稳定性及其互变异构
摘要
The stability and tautomerism of imines (<bold>1</bold><bold>a</bold>-<bold>1c</bold>) and enamines (<bold>2a</bold>-<bold>2c</bold>) in various protic solvents (methyl alcohol, ethyl alcohol, <italic>tert</italic>-butyl alcohol, acetic acid and CF<sub>3</sub>CO<sub>2</sub>D DMSO-<italic>d</italic><sub>6</sub> solution) were investigated via <sup>1</sup>H NMR spectral data. It was found that enamines (<bold>2a</bold>-<bold>2c</bold>) were stable in above solvents and imines (<bold>1a</bold>-<bold>1c</bold>) were stable at lower temperature (≤30 ℃) in weak acid solvents (ethyl alcohol, <italic>tert</italic>-butyl alcohol), but imines converted into enamines in methyl alcohol, acetic acid and CF<sub>3</sub>CO<sub>2</sub>D DMSO-<italic>d</italic><sub>6</sub> solution. It was also found that along with the increase of acidity in solution, the extension of time and the temperature rising, more and more imines converse to enamines. The kinetic and thermodynamic characteristics of the conversion of imines to enamines in acetic acid were studied by taking <bold>1a</bold> and <bold>1b</bold> as examples. The results showed that transformation from imines (<bold>1a</bold> and <bold>1b</bold>) to enamines (<bold>2a</bold> and <bold>2b</bold>) is endothermic and thermodynamically feasible in the temperature range of 283-333 K (Δ<italic>H</italic> > 0, D<italic>G</italic> < 0), and the values of entropy change are positive (Δ<italic>S</italic> > 0). The transformation follows the second-order kinetic equation at above temperatures and the proton in solution catalyzes the conversion of imines to enamines.