Possible heterocyclic ions in the reaction zones of flames with added nitrogen or sulfur

Abstract

Ions of m/z 80 and 94 are observed in the reaction zone of a C₆H₆/N₂O/H₂ flame, by flame ionization/mass spectroscopy. These are confirmed, by deuteration, as protonated pyridine and aniline. These ions are also detected in the reaction zone of a CH₄/N₂O flame, along with ions of m/z 44, 56, 68 and 72, which, it is proposed, are formed by protonation of the heterocyclic species aziridine, dihydroazete, pyrrole and pyrrolidine. This series of N-containing ions is in keeping with the postulate that HCN is formed in flames of hydrocarbons and N-compounds, and that the associated CN radicals undergo addition and hydrogenation reactions. Cyano compounds are not, however, detected, because their proton affinities tend to be lower than that of NH₃. In a C₆H₂/CS₂/H₂ flame, a series of S-containing ions are observed, beginning at m/z 97, for which the thiopyrylium structure is proposed. The detection of this stable aromatic species is in contrast to the absence of protonated thiophene. It is postulated that the active S-containing species in this flame is CS.