甲苯热解机理的AM1研究(Ⅰ)热力学分析

AM1 Thermodynamic Research of the Pyrolysis Mechanism of Toluene?

在实验的基础上,本文用Gaussian98程序包中AM1法UHF计算,对碳材料用碳前驱体甲苯的热裂解反应机理进行了研究。在对反应物、产物自由基的结构进行能量梯度法全优化的同时,计算了不同温度下的标准热力学参数(298～1073K)。热力学计算结果表明:(1)当甲苯的热裂解温度相对较低时(773K左右),热力学计算结果首先支持苯环上甲基C-H键的断裂生成苄基自由基并继而生成联二甲苯的反应;随着温度的提高(达1073K时),生成苯自由基和甲基自由基的反应比例将大于生成苄基自由基的比例;该反应机理与实验结果基本一致。(2)采用Gaussian98程序包中AM1法中的UHF计算,较适合低级芳香烃热裂解反应机理的理论研究。

Based on the experiment, the pyrolysis mechanism of the carbon matrix precursor toluene used for carbon material was studied with semi empirical method AM1 of Gaussian 98 package,the equilibrium geometry of the reactants and free radicals were optimized. The standard thermodynamic parameters in different temperatures range were calculated. The thermodynamic calculation results show: when the pyrolysis temperature of toluene is relatively low(below 1073K),C H bonds of the methyl on the benzene ring is broken firstly, and the reaction path of producing phenylmethyl is the main one(path 1).With temperature increasing(being above 1073K), C C bond between phenyl and methyl is easy broken,the reaction path that produces phenyl and methyl is a chief one(path 2). This mechanism is in accord with the experiment. When studying the pyrolysis carbonization mechanism and initial pyrolysis carbonization reaction process of low molecularly organic compounds used quantum chemistry calculation theory, semi empirical method AM1 is still an efficient method.