Monitoring the alcoholysis of isocyanates with infrared spectroscopy

Abstract The alcoholysis reaction of phenylisocyanate with cyclohexanol ( I ) and of 2,4-toluene-diisocyanate with chloraldhydrate ( II ) is studied by infrared absorption spectroscopy in combination with anharmonic frequency calculations using density functional theory. It is shown that the progress of the reaction can be monitored by measuring infrared marker bands in the isocyanate NCO and alcohol OH stretching regions. Analysis of spectra obtained as a function of time for different temperatures yields a second-order kinetics with an Arrhenius activation energy of 6.7 ± 0.2 and 2.8 ± 0.3 kcal/mol for reaction I and II , respectively.