The Gas-Phase Elimination Kinetics of 2-Hydroxy-2-Methylbutyric Acid and 2-Ethyl-2-Hydroxybutyric Acid

Article abstract of DOI:10.1002/kin.550270903

The elimination kinetics of the title compounds have been examined over the temperature range of 270 - 320 deg C and pressure range of 19 - 117 torr.The reactions, carried out in seasoned vessels, with the free-radical suppressor toluene always present, are homogeneous, unimolecular, and follow a first-order rate law.The products of 2-hydroxy-2-methylbutyric acid are 2-butanone, CO, and H2O; while of 2-ethyl-2-hydroxybutyric acid are 3-pentanone, CO, and H2O.The rate coeffcient is expressed by the following Arrhenius equation: for 2-hydroxy-2-methylbutyric acid, log k₁(s^-1) = (12.87 +/- 0.19) - (171.2 +/- 2.1) kJ mol^-1 (2.303 RT)^-1; and for 2-ethyl-2-hydroxybutyric acid, log k₁(s^-1) = (12.13 +/- 0.34) - (159.4 +/- 3.7) kJ mol^-1 (2.303 RT)^-1.Augmentation of alkyl bulkiness at the 2-position of the 2-hydroxycarboxylic acids showed an increase in the rate of dehydration.The electron release of alkyl groups, rather than steric acceleration, appears to enhance the pyrolysis decomposition of these substrates.These reactions are believed to proceed through a semi-polar five-membered cyclic transition type of mechanism.