Mechanisms of pyrolysis for a specifically labeled deuterated urethane

The pyrolysis products of a model urethane prepared from trimethylolpropane (TMP) propoxylated with 3,3,3-d3-propylene oxide and isocyanate have been extensively studied by gas chromatography in conjunction with electron-impact, chemical-ionization, and field-ionization mass spectrometry. The isotope distributions for some of the lower-molecular-weight species (determined by electron-impact and/or field-ionization mass spectrometry) showed a greater amount of H/D mixing than was expected from previously postulated concerted mechanisms. The deuterium distributions of the higher-molecular-weight TMP species were, in general, consistent with previously described mechanisms. The results from this study support the proposal that pyrolytic degradation of urethanes occurs mainly by a systematic sequence of concerted reactions. However, the deuterium distributions in some compounds indicate that free-radical reactions are important in the formation of some pyrolyzates