Mechanism and kinetic study of Paal-Knorr reaction based on in-situ MIR monitoring

Abstract

An in-depth understanding of reaction processes is beneficial to the development and quality control of chemical products. In this work, the mechanism and kinetics of the Paal-Knorr reaction for pyrrole derivatives are thoroughly studied using in-situ Fourier transform infrared (FTIR) spectroscopy. The hemiacetal amine intermediate, reactants, and products were identified and quantified by the treatment of real-time infrared spectra via chemometrics method and two-dimensional correlation spectroscopy (2DCOS) technique. Based on the IR quantitative models, influences of operating conditions on reaction processes were investigated, and the reaction kinetic model was built with kinetic parameters of two rate-limiting reaction steps calculated. This approach of analysis on the in-situ FTIR data demonstrated the ability to extract useful information on reaction components, especially the intermediate spectrum, from the confounding real-time IR data. The in-situ FTIR monitoring combined with the IR analysis methods is proved as a powerful tool for revealing the reaction mechanism and kinetics.