PCl_5与NH_4Cl反应生成六氯环三磷腈的链引发反应机理的理论研究

Theoretical Study on Initiation Reaction Mechanism of Hexachlorocyclotriphosphazene Synthesized by PCl_5 and NH_4Cl

采用密度泛函理论(DFT)方法研究了五氯化磷与氯化铵反应生成六氯环三磷腈的链引发过程的微观反应机理.在GGA-HCTH/DND理论水平下优化了反应路径上存在的反应物、中间体、过渡态及产物的几何构型,并通过频率分析确认了过渡态的结构.计算结果表明,该链引发是一个非常复杂的反应过程,反应路径上存在多种中间体和过渡态,并且这一过程为吸热反应,必须在加热条件下才能发生.其中IM2经由过渡态TS2脱掉一个氯化氢生成IM3的路径的能垒最低,仅为12.18 kJ/mol.IM5+PCl5经由过渡态TS5脱掉一个氯化氢生成IM6的过程能垒最高,值为174.83 kJ/mol,故这一步骤是整个反应的速控步骤.得到的产物为[Cl3P…N…PCl3]+PCl-6,与实验吻合.

The chain initiation reaction mechanism of hexachlorocyclotriphosphazene,which was synthe-sized by phosphorus pentachloride and ammonium chloride was investigated by using the density functional theory（DFT） of quantum chemistry.At the GGA-HCTH/DND level,the geometry optimizations of reac-tants,intermediates,the transition states and the products were performed.All of the transition states were verified by the frequency analysis method.The results showed that the chain initiation reaction was a very complex procedure so there were various intermediates and transition states along reaction paths and the product was [Cl3P…N…PCl3]＋ PCl-6 which was agreed well with experimental results.This reaction was an endothermal process,and it only took place when heated.For this reaction paths,IM2→TS2→IM3＋HCl had the lowest energy barrier,only 12.18 kJ/mol;while the fifth procedure（IM5＋PCl5→TS5→IM6＋HCl） was the rate-controlling step,and it had the highest energy barrier 174.83 kJ/mol.