Abstract: 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.

Key words: Acrylic acid, Pyrolysis mechanism, Self-consistent-field molecular orbital method