Determination of reaction mechanism and rate constants of alkaline hydrolysis of phenyl benzoate in ethanol–water medium by nonlinear least squares regression

In the reaction system of alkaline hydrolysis of phenyl benzoate in the ethanol–water media, high performance liquid chromatography-diode array detector (HPLC-DAD) is used to measure the reaction and kinetic profiles are obtained. Nonlinear least squares regression (NLLS) is used to fit the kinetic profiles and then investigate the mechanism. Genetic algorithm (GA) is adopted to optimize the parameters of the postulated mechanisms, and when the minimum standard deviation of mechanical model matches the noise level of measurement, the mechanism of the reaction system can be determined, and parameters, such as rate constants of every reaction step, are resolved simultaneously. The true mechanism of the reaction system that a parallel reaction coexists with a consecutive reaction is determined. In the ethanol–water media, phenyl benzoate hydrolyzes to benzoic acid and phenol, as well as produces a transesterification that ethanyl is substituted for phenyl, and ethyl benzoate, the product of transesterification, consecutively hydrolyzes to benzoic acid and ethanol. The method to resolve online spectroscopic–kinetic data is also studied and the results show that it is hard to obtain the kinetic parameters of all components if their kinetic concentration profiles can be combined linearly in some cases whose pure spectra of components are unknown beforehand.