5-苯基偶氮基苯并呋喃-2-甲酸乙酯的顺反异构现象

Cis/trans Isomerization of Ethyl 5-Phenylazo-Benzofuran-2-Carboxylate

5-苯基偶氮基苯并呋喃-2-甲酸乙酯的甲醇溶液刚配制好时其紫外-可见吸收光谱只显示两个吸收峰,一个是苯环的吸收峰,位于272 nm,另一个是偶氮基的吸收峰,位于344 nm,受光照射后,在该吸收光谱中多了一个吸收带,位于460 nm。质谱显示:在该溶液中没有新化合物生成,这表明5-苯基偶氮基苯并呋喃-2-甲酸乙酯在甲醇中受光照后会发生偶氮基团结构的顺反异构化。该异构化行为经一定时间后会达到平衡,HPLC分析表明:平衡时,反式异构体的含量为顺式异构体含量的2.7倍。

UV-Vis spectrum of ethyl 5-phenylazo-benzofuran-2-carboxylate in methanol indicates two absorption bands for fresh prepared solution.One is an absorption band of phenyl moiety,which is at 272 nm,the other is an absorption band of azo group,which is at 344 nm.Irradiated by light,a new absorption band at 460 nm appears for the solution.New compounds wasn＇t found in mass spectrum,thus,there occurs a cis/trans isomerization in azo group of ethyl 5-phenylazo-benzofuran-2-carboxylate in methanol.The cis/trans isomerization can reach an equilibrium,which is exposed in the room for 3 h.HPLC analysis shows the ratio of trans-isomer to cis-isomer is 2.7,when the isomerization is in equilibrium.