Monitoring the alcoholysis of isocyanates with infrared spectroscopy

- Alcoholysis reactions of isocyanates are investigated using IR spectroscopy.
- Spectral changes are assigned with the help of anharmonic frequency calculations.
- Marker bands are monitored to extract data on reaction kinetics.
- Arrhenius activation energies between 3 and 7 kcal/mol are observed.

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.

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