Combined on-line transmission FTIR measurements and BTEM analysis for the kinetic study of a consecutive reaction in aqueous–organic phase medium

Abstract

Combined on-line transmission FTIR spectroscopy and band-target entropy minimization (BTEM) analysis were employed in order to monitor and analyze the kinetics of the alkaline hydrolysis reaction of diethyl phthalate (DEP) in aqueous–ethanol solvent mixture. This reaction is irreversible and involves two consecutive steps with the formation of the observable mono-ion intermediate species. The pure component mid-FTIR spectra of the reactive species involved in this reaction, namely DEP, mono-ion intermediate and di-ion product were successfully reconstructed using BTEM. Their corresponding concentrations were also calculated and subsequently employed to derive the kinetic rate parameters. The effect of temperature and the solvent mixture compositions on these two consecutive reaction steps were also discussed. The temperature variation study showed that both reaction rate coefficients increased with temperature. Both rate coefficients were also affected by the solvent mixture compositions and reached minimum values at certain water–ethanol solvent composition (circa 60% (v/v)). This study shows the utility of combined on-line transmission FTIR spectroscopy and chemometric techniques for the present, rather complex, consecutive organic reaction. Moreover, the present type of approach could facilitate better understanding of a wide variety of organic reactions that are performed in aqueous and mixed aqueous–organic solvents.