Theoretical Studies on the Mechanism of Chloro-carboxylic Acids Gas-phase Elimination Process

3-chloropropionic acid and 2-chlorobutyric acid elimination processes have been studied by semi-empirical MO theory AM1 method. The calculated results are consistent with the experimental reports and can be summed up as the following two points: (1) 3-chloropropionic acid gas-phase elimination is a parallel pyrolytic process and occurs via a concerted process with a four-membered cyclic transition state or via a two-step process with a six-membered and a four-membered cyclic transition states. The former is easier to proceed. (2) 2-chlorobutyric acid elimination proceeds in terms of a four-membered cyclic transition state or a five-membered transition state. The former is a concerted process. The five-centred transition state forms an intermediate and eliminate CO further. It is more favored than the four-centered transition state in a dehydrochlorination process.