物理化学学报 >> 1991, Vol. 7 >> Issue (02): 129-135.doi: 10.3866/PKU.WHXB19910201

研究论文    下一篇

乙基乙酰胺热解反应机理的MO研究

徐森; 傅孝愿   

  1. 江西上饶师专;北京师范大学,北京 100875
  • 收稿日期:1989-12-31 修回日期:1990-03-26 发布日期:1991-04-15
  • 通讯作者: 傅孝愿

A Molecular Orbital Study on the Mechanism for Homogenous Gas Phase Pyrolysis of Ethyl Acetamide

Xu Sen; Fu Xiao-Yuan   

  1. Department of Chemistry, Beijing Normal University, Beijing 100875
  • Received:1989-12-31 Revised:1990-03-26 Published:1991-04-15
  • Contact: Fu Xiao-Yuan

摘要: 对于烷基乙酰胺的初始热解反应机理, 通常认为与酯类的热解反应相类似。Maccoll和Nagra通过对该热解反应的动力学研究, 认为两者存在不同。差异之一, 烷基乙酰胺存在两种可能的热解途径【参见本文(129页)前述反应方程(1),(2)】。而在酯类热解反应中(2)的活化能过高, 且四元环过渡态极不稳定。差异之二, 极性溶剂(比如乙酸)对酰胺热解反应的催化作用不明显, 而对酯类等气相热解反应的催化作用是十分显著的。
为此, 我们用MINDO/3分子轨道法对乙基乙酰胺的初始热解反应进行了较全面的研究。用能量梯度法对此反应的反应物、中间体和生成物的平衡几何构型进行了全优化。(如图1所示)用极小能量途径法分别寻找反应(1)和反应(2)的初始过渡态, 继而用Powell法全优化过渡态的几何构型, 计算所得的过渡态TS1、TS2和TS3分别见图2a, 图3a和图4a。为了确证这些过渡态, 进行了振动分析研究, 结果表明这些过渡态的力常数矩阵的诸本征值中均只有一个负值, 且虚振动模式展示了走向各自的反应物和生成物的趋势, (如图2b,图3b和图4b所示)。它们的总能量及反应(1)和反应(2)的活化能列于表1. 对整个热解反应(1)作了内禀反应坐标(IRC)理论分析, 反应历程见图5所示. 与IRC相应的总能偶极矩以及部分关键的键长和原子净电荷变化一并列于表2.
本文研究结果表明, 在乙基乙酰胺的初始反应中主反应即反应(1)与酯类反应相类似, ...

关键词: 气相热解, 分子轨道法, 乙基乙酰胺

Abstract: The homogenous gas phase pyrolysis of ethyl acetamide is studied by MINDO/3 molecular orbital method.The results show that the major process proceeds via a six membered ring transition state (TS), but the four membered ring TS is also feasible, which is not accessible in the gas phase pyrolysis of esters. A detail analysis of Intrinsic Reaction Coordinate(IRC) is used to elucidate the reaction mechanism. The results also reveal that the change of activation energy in the polar solvent is not evident, in other words, the catalysis by carboxylic acid is not marked for the gas phase pyrolysis of ethyl acetamide.

Key words: Gas phase pyrolysis, Molecular orbital method, Ethyl acetamide