壳聚糖催化正丁醛自缩合反应性能

Catalytic performance of chitosan for n-butyraldehyde aldol self-condensation

为克服工业上强碱水溶液催化正丁醛自缩合反应的缺点,选择可生物降解的壳聚糖催化该反应。活性评价结果表明,壳聚糖具有良好的催化性能:在催化剂与正丁醛质量比为0.05:1、反应温度80℃和反应时间8 h的条件下,产物辛烯醛的收率和选择性分别为86.0%和89.6%。红外光谱分析发现,壳聚糖在反应中失活是因为表面氨基被破坏,采用氨水处理可恢复其催化活性。阐明了壳聚糖催化正丁醛自缩合反应的酸碱协同作用机理,在此基础上,采用密度泛函理论(DFT)对该反应速率控制步骤(C─C键形成)进行了模拟计算,其表观活化能为82 kJ×mol^-1。

In order to overcome the shortages of alkali aqueous catalysts in industrial n-butyraldehyde self-condensation reactions,a biodegradable natural polymer chitosan was selected for catalyzation.Activity evaluation results show that chitosan exhibits an excellent catalytic performance for n-butyraldehyde self-condensation.Under the conditions of catalyst to n-butyraldehyde mass ratio=0.05:1,temperature=80℃and reaction time=8 h,the yield and selectivity of 2-ethyl-2-hexenal reached 86.0%and 89.6%,respectively.FI-IR analysis shows that the destruction of amino group on chitosan surface is the main reason for chitosan deactivation and the catalytic activity could be recovered by ammonia treatment.A possible reaction mechanism of chitosan catalyzed n-butyraldehyde self-condensation is thus established.Density function theory(DFT)calculation results show that the apparent activation energy of the rate-limiting step as carbon-carbon bond formation in n-butyraldehyde self-condensation is 82 kJ×mol^-1.