Elimination of carbon monoxide by electron impact on quinoline N-oxide, carbostyril and 8-hydroxyquinoline

Under electron impact, the molecular ions of quinoline N‐oxide, carbostyril and 8‐hydroxyquinoline lose carbon monoxide giving a fragment ion C8H7N (m/z 117), which was shown by collision‐activated dissociation in each case to have the structure of the molecular ion of indole. Its formation from 8‐hydroxyquinoline requires an unusual rearrangement. Isoquinoline N‐oxide loses HCN rather than CO and gives a fragment which has the structure of the molecular ion of benzofuran. When the first three compounds were subjected to flash vacuum pyrolysis, quinoline N‐oxide at 500–700°C gave carbostyril and indole was detected by gas chromatography/mass Spectrometry. At 900°C carbostyril and 8‐hydroxyquinoline both gave indole in small amounts, detected by gas chromatography/mass Spectrometry.