Abstract
AbstractThe mechanism of the catalyzed reaction between alcohols and isocyanates was investigated by means of NMR, infrared, and ultraviolet spectroscopy. The shift of the OH proton resonance in the NMR spectra indicated the existence of a 1 : 1 complex in the system dibutyltin dilaurate (DBTDL)–1‐methoxy‐2‐propanol. Complex formation was also observed when lead naphthenate or triethylamine (TEA) were substituted for the DBTDL. Mixtures of the DBTDL–TEA catalysts caused a shift of the OH proton resonance greater than that observed for either catalyst alone. This correlates with the synergistic effect noted when preparing urethanes with a mixture of these catalysts. No direct evidence of alcohol–catalyst complex formation could be obtained by infrared spectroscopy. Efforts were also made to detect complex formation in mixtures of phenyl isocyanate and catalysts. These complexes could not be detected by NMR, infrared, or ultraviolet spectroscopy.
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