Kinetic and mechanistic studies on the Heck reaction using real-time near infrared spectroscopy

In this paper, Fourier-transform near infrared (FT- NIR) spectroscopy is used to monitor the kinetics of complex catalytic reactions in liquid phase. Gas chromatography ( GC) is used as a reference method. Spectroscopic measurements generate large amounts of data and the calibration is usually time-consuming and complex. To reduce the calibration effort the spectral data is analysed using the net analyte signal (NAS) approach. The reaction of interest is the Heck reaction of iodobenzene (PhI) and n-butyl acrylate (NBA) to give n-butyl cinnamate (NBC). This reaction is studied by means of FT-NIR and GC and the time-resolved reaction profiles obtained are compared. Results of the two techniques are consistent and the spectral results show an excellent reproducibility. It was observed that the reaction has an initiation period that decreases with the increase of temperature. With bulky monodentate palladium catalysts the presence of this initiation period has up to now gone unnoticed.