The nitrile oxide–isocyanate rearrangement

Abstract

The thermal rearrangement of 2,4,6-trimethylbenzonitrile N-oxide to the corresponding isocyanate has been investigated by double isotopic (²H and ¹⁸O) labelling and kinetic experiments. Rearrangement proceeds with exchange of oxygen atoms, and this exchange occurs exclusively between nitrile oxide molecules. Kinetic results suggest that the pathway involves a polymerisation, catalysed either by electrophiles or by nucleophiles, followed by decomposition of the polymer. The rearrangement is catalysed at room temperature by trifluoracetic acid. A synthesis of ¹⁸O-labelled hydroxylamine is reported.