Effects of β-cyclodextrin on the keto-enol equilibrium of benzoylacetone and on enol reactivity
Effects of β-cyclodextrin on the keto-enol equilibrium of benzoylacetone and on enol reactivity
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DOI：
10.1021/jo982407g
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发表时间：
1999-05-28
影响因子：
3.6
通讯作者：
Leis, JR
中科院分区：
文献类型：
--
作者：
Iglesias, E;Ojea-Cao, V;Leis, JR
β-环糊精和十二烷基硫酸钠胶束通过优先结合烯醇形式将苯甲酰丙酮酮-烯醇平衡转移到烯醇互变异构体。采用紫外-可见光谱法研究了温度和溶剂对苯甲酰丙酮在酸性水溶液中酮-烯醇平衡的影响。从结合的苯甲酰丙酮烯醇十二烷基硫酸钠胶束和从列入酮和烯醇互变异构体到β-环糊精空腔的热力学参数之间的比较，使我们能够绘制在每种情况下形成的可能的复合物的图片。1H-1 NMR结果表明，苯甲酰基丙酮-烯醇突出更深的β-环糊精空腔内，而酮互变异构体只能有苯环封闭在β-环糊精空腔内部。在β-环糊精存在下，苯甲酰丙酮在酸性介质中的亚硝化反应降低到低于游离苯甲酰丙酮的亚硝化反应，表明环糊精复合物保护了苯甲酰丙酮烯醇互变异构体，这与我们对烯醇β-环糊精复合物的描述完全一致。
Both beta-cyclodextrin and sodium dodecyl sulfate micelles shift the benzoylacetone keto-enol equilibrium to the enol tautomer by preferentially binding the enol form. The UV-vis spectroscopic method was used to quantify the temperature and solvent effects on the keto-enol equilibrium of benzoylacetone in aqueous acid medium. The comparison between the thermodynamic parameters resulting from the binding of the benzoylacetone enol to sodium dodecyl sulfate micelles and from the inclusion of both keto and enol tautomers into the beta-cyclodextrin cavity allows us to draw a picture of the possible complex formed in each case. H-1 NMR results suggest that benzoylacetone-enol protrudes deeper inside the beta-cyclodextrin cavity, whereas the keto tautomer could only have the phenyl ring enclosed in the beta-cyclodextrin cavity interior. Nitrosation in acid medium of benzoylacetone in the presence of beta-cyclodextrin is reduced below that of free benzoylacetone, indicating that the cyclodextrin complex protects the benzoylacetone enol tautomer, which is in perfect accordance with our picture of the enol beta-cyclodextrin complex.