Homogeneous synthesis of hydroxyethyl acrylate catalyzed by organochromium(III) complexes: Kinetics and ligand effect

Abstract

The ring-opening reaction of ethylene oxide with acrylic acid catalyzed by organochromium(III) complexes is the most promising route for the industrial synthesis of 2-hydroxyethyl acrylate. However, the heterogeneous batch process with highly explosive gaseous ethylene oxide possesses difficulties on the process optimization and safety. To resolve these problems, homogeneous synthesis process is developed by pressurization and in-line mixing of ethylene oxide and acrylic acid. Stop-flow microreactor is applied to investigate the homogeneous reaction characteristics with high efficiency. A reduced kinetic model on the basis of the simplified reaction network is proposed with good calibration results. The catalytic process of ring-opening reaction is distinguished from the non-catalytic one according to the kinetic model parameters. After recognizing the activation process of catalyst during reaction and fulfilling it before reaction, the ligand effect is quantitatively studied by carefully comparing the catalytic features of four types of organochromium catalysts, chromium(III) acetate, chromium(III) 2-ethylhexanoate, chromium(III) picolinate and chromium(III) acetylacetonate, indicating a high efficiency catalyst might contain such ligand (or support) that possesses weak interaction with Cr metal center as well as considerable steric hindrance.