Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 2008-11-27

Kinetics and mechanisms of the homogeneous, unimolecular gas-phase elimination of trimethyl orthoacetate and trimethyl orthobutyrate.

Edgar Márquez, Rosa Dominguez, María Tosta, Gabriel Chuchani

Index: J. Phys. Chem. A 112(47) , 12140-2, (2008)

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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.