A combined experimental and theoretical study of the homogeneous, unimolecular decomposition kinetics of 3-chloropivalic acid in the gas phase

Decomposition kinetics of 3-chloropivalic acid in the gas phase were determ ined in a static system over the temperature and pressure ranges of 380.5-4 30.1 degreesC and 43-120 Torr, respectively. The reaction, in vessel season ed with allyl bromide, and in the presence of free-radical suppresser tolue ne, is homogeneous, unimolecular, and follows a first-order rate law. The r ate coefficients are given by the following equation: log k(1) (s(-1)) = (1 2.42 +/- 0.36) - (205.8 +/- 4.7) kJ mol(-1) (2.303RT)(-1). The reaction mec hanism for the formation of isobutene, hydrogen chloride, and carbon dioxid e has been theoretically characterized. The theoretical study, at MP2/6-31G ** computational level, points out that the molecular mechanism corresponds to a concerted and highly synchronous process yielding the products. An an alysis of bond orders and NBO charges shows that the polarization of the C- Cl breaking bond can be considered the driving force for this fragmentation process. The rate coefficients obtained from experimental data and;theoret ical calculations are in good agreement.