正硅酸乙酯水解过程的半经验量子化学研究

Semi-empirical Studies on Hydrolysis Process of TEOS

通过半经验量子化学方法研究了正硅酸乙酯的最优化分子几何结构并推断了催化水解机理。通过用MNDO方法求得正硅酸乙酯在不同条件下水解反应过程的位能曲线,研究了不同催化剂对正硅酸乙酯水解反应过程的影响。计算结果表明,碱催化过程是一个放热过程,硅原子可从原先的4配位的正四面体结构向6配位的八面体结构转变。而在酸性条件下,水合质子作为亲电试剂,可以使正硅酸乙酯的烷氧基质子化,从而增加了正硅酸乙酯的亲电能力。质子化后的正硅酸乙酯容易被亲核试剂所进攻,进攻过程是一个SN2亲核取代反应过程。计算结果表明,在有氟离子参与的反应过程中,氟离子对正硅酸乙酯亲核进攻所形成的6配位结构易与亲核试剂水分子发生亲核反应。这些结论对实验研究将起到很重要的指导意义。

Semi-empirical calculations have been performed to investigate the geometries structure and hydrolysis mechanism of tetraethoxysilane(TEOS). Applying MNDO calculations, the potential curve along the reaction coordinate in the hydrolysis of TEOS was provided. Catalysis effects on the hydrolysis process have been widely studied. The calculated results suggested that coordination number of Si atom can change from 4 to 6 during alkaline hydrolysis process of TEOS. And this process is an exothermic process. Under acid condition, protoned H2O can proton OR group of TEOS, then nucleophilic reagent nucleophilic displace the protoned OR group (S(N)2). With F-, the coordination number, of Si atom can change from 4 to 6, then H2O can nucleophilic attacked the 6-coordination structure caused by F-. These conclusions are very helpful to the experimental studies.