title: Kinetics and mechanisms of the homogeneous, unimolecular gas-phase elimination of trimethyl orthoacetate and trimethyl orthobutyrate.
abstract: The gas-phase elimination kinetics of the title compounds have been examined over the temperature range of 310-369 degrees C and pressure range of 50-130 Torr. The reactions, in seasoned vessels, are homogeneous, unimolecular, and follow a first-order rate law. The products are methanol and the corresponding methyl ketene acetal. The rate coefficients are expressed by the Arrhenius equation: for trimethyl orthoacetate, log k1 (s(-1)) = [(13.58 +/- 0.10) - (194.7 +/- 1.2) (kJ mol(-1))](2.303RT)(-1)r = 0.9998; and for trimethyl orthobutyrate, log k1(s(-1)) = [(13.97 +/- 0.37) - (195.3 +/- 1.6) (kJ mol(-1))](2.303RT)(-1)r = 0.9997. These reactions are believed to proceed through a polar concerted four-membered cyclic transition state type of mechanism.
authors.affiliation: Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado 21827, Caracas 1020-A, Venezuela.
authors.forename: Edgar
authors.initials: E
authors.lastname: Márquez
authors.forename: Rosa
authors.initials: R
authors.lastname: Dominguez
authors.forename: María
authors.initials: M
authors.lastname: Tosta
authors.forename: Gabriel
authors.initials: G
authors.lastname: Chuchani