Electron‐impact fragmentation of triaryl‐ s ‐trithianes: A novel skeletal rearrangement involving sulphur‐sulphur bond formation

The mass spectral fragmentation of seven substituted 2,4,6‐triaryl‐ s ‐trithianes has been studied and the fragmentation modes confirmed by deuterium labelling. Triphenyl‐ s ‐trithiane shows some interesting features in its mode of cleavage and does not eliminate S, S 2 , SH ˙ , H 2 S or S 2 H ˙ from its molecular ion. The prominent radical ions in the mass spectrum are at m / e 180 (52.3%) and m / e 186 (45.2%), corresponding to stilbene and PhCHS 3 . Their compositions have been established by deuterium labelling and accurate mass measurements. The formation of stilbene indicates a relationship between pyrolytic and electron‐impact studies. The origin of [PhCHS 3 ] +˙ suggests that one of the sulphur atoms attaches itself to the other two sulphur atoms in the molecular ion, eliminating a stilbene radical ion. The other important fragmentation corresponds to the monomer radical ion (thiobenzaldehyde) and the thiobenzoyl cation. Among the other substituted triaryl‐ s ‐trithianes with substituents such as chloro, methoxy, methylenedioxy and hydroxy groups on the phenyl ring (IV to IX), only the tris‐( p ‐chlorophenyl)‐ s trithiane shows an insignificant molecular ion. Unlike the triphenyl derivative, the chloro, methoxy and methylenedioxy derivatives show the loss of HS ˙ and/or H 2 S from the molecular ion. The spectrum of tris‐( p ‐hydroxyphenyl)‐ s ‐trithiane corresponds to the spectrum of p ‐hydroxythiobenzaldehyde.