HNCO热解为CO2和HNCNH的反应机理理论研究

利用从头算ＲＨＦ／３－２１Ｇ方法研究了ＨＮＣＯ二聚后生成ＨＮＣＮＨ和ＣＯ２的反应机理。计算表明,该反应是分步反应,由反应物经第一过渡态生成四元环中间体,再经过第二过渡态分解为产物,与实验得到的结论一致。反应的第一步是速度控制步骤,计算得到的活化位垒为１７２．５５ｋＪ·ｍｏｌ＾－１,与实验上测得的１７６．４０±１６．３０ｋＪ·ｍｏｌ＾－１相吻合。反应的第二位垒为８３．６８ｋＪ·ｍｏｌ＾－１,在实验条

A Theoretical Study on the Thermo Decomposition of HNCO to HNCNH and CO2

Ab initio RHF/3-21G method has been employed to study the mechanism of the bimolecular thermolysis of HNCO. The results show that this reaction is a stepwise reaction. The first step is the dimerization of HNCO to form a four-membered ring intermediate, the second step is the dissociation of the intermediate to form the products HNCNH and CO2. The calculated activation barrier for the steps are 172.55kJ•mol-1 and 83.68kJ•mol-1, respectively. It can be seen that the first step is the rate determining step, its barrier is in good agreement with experimental data (activation energy: 176.40±16.30 kJ•mol-1). The second step is a fast step, the four-membered ring intermediate can not stay as a final product. The reaction can be described as a stepwise non-synchronous reaction.