On the high-temperature unimolecular decomposition of ethyl levulinate

The pyrolysis of ethyl levulinate (EL) was studied behind reflected shock waves over the temperature range of 1015-1325 K and pressures of 750-1650 Torr. The reaction progress was followed by measuring ethylene mole fraction using CO2 gas laser absorption near 10.532 μm. The rate coefficients for the unimolecular dissociation of EL were extracted from the initial slope method and further ascertained by using a complete kinetic model. Our data exhibited no discernible pressure dependence under the current experimental conditions. To rationalize our results further, high-level quantum chemical and master equation calculations were employed to calculate the pressure- and temperature-dependence of the reaction. Our calculations revealed that unimolecular dissociation of EL involves simultaneous 1,5-hydrogen shift of the β-hydrogen to the carbonyl group, rupture of the O-C ester bond and formation of the π-bond (Cα-Cβ). Our results present evidences that the C2H4 elimination from EL occurs in a concerted manner. To our knowledge, this work represents the first experimental and theoretical study of the thermal unimolecular dissociation of ethyl levulinate.