HOMOGENEOUS PYROLYSIS KINETICS OF ETHYL 3-HYDROXY-3-METHYLBUTANOATE IN THE GAS-PHASE

The pyrolysis kinetics of ethyl 3-hydroxy-3-methylbutanoate have been examined over the temperature range of 286-330 degrees C and pressure range of 29-108 Torr. In a seasoned vessel and in the presence of the free radical inhibitor cyclohexene or toluene the reaction is homogene ous, unimolecular and obeys a first-order rate law. The elimination pr oducts are mainly acetone and ethyl acetate, and very small amounts of ethyl 3-butenoate, acetic acid, ethylene and H2O. The rate coefficien t is expressed by the following equation: log k(1) (s(-1)) = (12.39 +/ - 0.46) - (174.5 +/- 5.2) kJ mol(-1)(2.303RT)(-1). The mechanism appea rs to proceed via a six-membered cyclic transition state, where polari zation of the (CH3)C(OH)(CH2COOCH2CH3)-C-delta+...delta- bond is rate determining.