Joint Experimental and DFT Study of the Gas-Phase Unimolecular Elimination Kinetic of Methyl Trifluoropyruvate

The elimination kinetics of methyl trifluoropyruvate in the gas phase was determined in a static system, where the reaction vessel was always deactivated with allyl bromide, and in the presence of at least a 3-fold excess of the free-radical chain inhibitor toluene. The working temperature range was 388.5-430.1 degrees C, and the pressure range was 38.6-65.8 Torr. The reaction was found to be homogeneous and unimolecular and to obey a first-order rate law. The products of the reaction are methyl trifluoroacetate and CO gas. The Arrhenius equation of this elimination was found to be as follows: log k(1) (s(-1)) = (12.48 +/- 0.32) - (204.2 +/- 4.2) kJ mol(-1)(2.303RT)(-1) (r = 0.9994). The theoretical calculation of the kinetic and thermodynamic parameters and the mechanism of this reaction were carried out at the B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31G++(d,p) levels of theory. The theoretical study showed that the preferred reaction channel is a 1,2-migration of OCH3 involving a three-membered cyclic transition state in the rate-determining step.