Reaction Kinetics of the Autocatalytic Hydrolyses of Alkyl Lactates

Abstract

Kinetic description of the hydrolysis reaction of alkyl lactates has been limited to acid-catalyzed conditions even though the reverse reaction, esterification of lactic acid with alcohols, has been well studied in the presence and absence of added acidic catalysts. Methyl lactate and ethyl lactate, like most esters, undergo spontaneous hydrolysis in aqueous solution. As the reaction progresses, the generated lactic acid serves to catalyze ester hydrolysis, while the rate of the reverse reaction to form esters increases with the accumulation of acid product. The reaction sequence of lactate hydrolysis can be described in three regimes: initiation/neutral hydrolysis, autocatalytic hydrolysis, and equilibrium. In these experiments, the evolution of lactate hydrolysis was measured for varying temperatures (6°C to 40 °C) and initial methyl or ethyl lactate concentrations (3 to 40 mol%) to quantify the kinetics transition in reaction regimes with time.