N-Benzylidene-2-nitrobenzenesulfenamide and 1-Nitro-2-(phenylthio)benzene: Comparison of Their Behavior on Flash Vacuum Pyrolysis and Under Electron Impact

The molecular ion of N-benzylidene-2-nitrobenzenesulfenamide (1) loses SO2 and N2 and gives a base peak at m/z 165, C13H9, and another abundant peak at m/z 166, C13H10. Analysis, by gas chromatography/mass spectrometry and by preparative thin-layer chromatography, of the products of flash vacuum pyrolysis at 500-800°C of (1) showed no detectable hydrocarbon, but dibenzothiophen (mol. wt 184) was isolated and identified. The abundance of m/z 184 in the positive-ion mass spectrum of (1) is about 1%. In the mass spectrum of 1-nitro-2-( phenylthio )benzene (2a) the base peak is at m/z 167, C12H9N, and there is a fragment ion at m/z 184, C12H8S (35%). However, carbazole (3) could not be isolated from the flash vacuum pyrolysis products, but dibenzothiophen (4) was obtained in increasing yield as the pyrolysis temperature was raised from 500 to 800°C. It is clear from these results that drawing analogies between electron impact mass spectra and flash vacuum pyrolysis results is somewhat hazardous.