丙烯腈水解反应机理的理论研究

采用密度泛函方法研究了丙烯腈的水解反应,设计了2条水解途径,并在B3lyp/6-31++G(d,p)水平上优化了反应过程中的反应物、中间体、过渡态及产物的几何构型.途径A的第1步是水分子先进攻丙烯腈的C≡C中的C原子,同时H转移到CC的另一个C原子上,在第2步中,另一个水分子进攻C≡N中的C原子,H原子转移到N上.经历一个扭转过渡态后,在第4步中,与N原子邻近的羟基上的H原子转移到N原子上,形成最终的产物酰胺.其中第1步的能垒最高,为52 kcal/mol,故为途径A的速度控制步骤.途径B的第1步是水分子先进攻C≡N,然后第2个水分子进攻CC,后面的过程与途径A类似.该途径也是第1步的能垒最高47 kcal/mol,故为途径B的速度控制步骤.研究结果表明途径B比途径A更优势.

Theoretical study of the reaction mechanism of acrylonitrile hydrolysis

The hydrolysis of acrylonitrile has been studied by using the density functional theory,and two reaction pathways have been designed. The geometries for the reactants,intermediates,transition states and products have been optimized at B3 lyp/6-31 + + G(d,p) level. In the pathway-A,the first step involves the water molecule attacking the C atom of C C in acrylonitrile,and the H atom of water transfers to the other C atom of C C at the same time. In the second step,another water molecule attacks the C atom of C≡N with the H atom transferring to the N atom. The next step corresponds a rotational transition state. The H atom in the hydroxyl group adjacent to the N atom transfers to the N atom to form the final product amide in the fourth step. The free energy barrier of the first step is the highest,which is equal to 52 kcal/mol,and therefore the first step is proved to be the rate-controlling step for the pathway-A. The first step of process B is that the water molecule attacks C≡N first,and then the second water molecule attacks C C. The following processes are similar to the pathway-A. In the pathway-B,the free energy barrier of the first step is also the highest,which is equivalent to 47 kcal/mol. Consequently,the first step of process B is verified to be the rate-controlling step. In conclusion,the pathway-B is more favorable than the pathway-A.