The pyrolysis of oxindoles at 850°C

Pyrolysis of oxindole at 850�C/0.7 mm with short contact time gives a complex mixture of products including benzene, benzonitrile, 2-vinylpyridine, o-toluidine, aniline, and o-aminostyrene. The pyrolysis has been investigated by using 1% and 13C labelling and by studying the effects of methyl and phenyl substituents. The nitrile carbon of benzonitrile thus formed is derived from C7a of oxindole, and not from C3. Pyrolysis of 7-phenyloxindole forms 1-methylcarbazole, and 4-phenyl-oxindole forms 1-aminofluorene. These results are interpreted in terms of the formation and subsequent rearrangement of arylnitrenes and arylcarbenes. The pyrolysis of oxindole is compared with pyrolyses of o-tolyl azide and tropyl azide. The mass spectrum of oxindole is reinterpreted in the light of the pyrolytic results; the spectrum of [3-13Cloxindole shows that loss of H13CN is a minor process (25-30%).