Spectroscopy of Hydrothermal Reactions 16: Kinetics of Decarboxylation/Hydrolysis of Methyl Propiolate Ester and Decarboxylation of Propiolic Acid at 150-210 deg C and 275 Bar

摘要

The coupled kinetics of decarboxylation and hydrolysis of methyl propiolate were determined in real time at 160-210 deg C and 275 bar by using a titanium-cell flow-reactor equipped with sapphire windows for direct IR spectral detection. The rate constats were calculated from the formation of CO_2 and the disappearance of methyl propiolate at the natural pH of the solution. The product acid (propiolic) also decarboxylates, and its kinetics were determined at 150-200 deg C and 275 bar for use in the overall model. At 180 deg C, the relative rates are in the order propiolic acid decarboxylation > methyl propiolate decarboxylation > methyl propiolate hydrolysis. Hence, the hydrolysis step is rate-determining over most of the temperature range studied. Because of the instability of the propiolic acid product, the hydrolysis of methyl propiolate is not acid-catalyzed. Instead, the Arrhenius activation energy for the ester hydrolysis more closely resembles those previously reported for base catalysis.