丙烯酸气相热解机理的理论探讨

用自洽场分子轨道法(半经验AM1法及从头算HF/3-21G法)研究了基态丙烯酸脱羧的反应途径. 计算结果表明, 除前人从理论上已经得到的一步反应途径外, 尚有一个与之竟争的二步反应途径, 且两步反应的总速率大于一步反应的. 计算所得的反应速率常数很小, 与实验结果(丙烯酸在827 K仅有25%左右发生脱羧, 脱水等反应)是一致的. 研究表明, 有较稳定的中间体存在, 有可能在实验中被检测到, 但有待于进一步验证.

THEORETICAL STUDY OF PYROLYSIS MECHANISMS OF ACRYLIC ACID IN THE GAS PHASE

The decarboxylation reaction of acrylic acid in ground state has been investigated by using self-consistent-field molecular orbital method (Semi-empirical AMI and HF/3-21G ab initio methods). Our calculation showed that in addition to one-step process from reactant to product which has been reported by Ruelle, there is another reaction path which is a two-step reaction and the latter will be least competitive with the one step process. The rate constants of both the two reaction paths are very small, which is consistent with the experimental fact (at ca. 500 ℃ acrylic acid breaks down to the extent of ca. 25%). Furthermore, our investigation indicated that the intermediate is rather stable, therefore it can be expected that this substance might be observed. This needs to be confirmed by experiment.