Joint Experimental and Theoretical Studies of the Mechanism for the Gas Phase Elimination Kinetics of Methyl 2,2-Dimethyl-3-hydroxypropionate

Abstract

Methyl 2,2-dimethyl-3-hydroxypropionate was found to decompose, in a static system, mainly to methyl isobutyrate and formaldehyde. The reaction rates were affected in packed and unpacked clean Pyrex vessels, demonstrating little but significant surface effect. However, in vessels seasoned with allyl bromide this reaction was homogeneous and unimolecular and followed a first-order law. The working temperature range was 349-410 degrees C and the pressure range was 64-162 Torr. The variation of the rate coefficient with temperature is expressed by the following Arrhenius expression: log k(1) (s(-1)) = [(11.43 +/- 0.57) - (180.4 +/- 7.2) kJ mol(-1)] x (2.303RT)(-1). Methyl 2,2-dimethyl-3-hydroxypropionate was found to be 1.4 times greater in the rate of elimination than methyl 3-hydroxypropionate. Apparently, steric acceleration may be considered responsible in the process of decomposition. The theoretical calculation of the kinetics and thermodynamics parameters, at the B3LYP/6-211G** level of theory, are in reasonably good agreement with the experimental values obtained. These calculations imply a molecular mechanism involving a concerted nonsynchronous transition state where abstraction of the hydroxyl hydrogen by the oxygen of the carbonyl ester is a determining factor and the transition state is late in the reaction coordinate.