An electron ionization and fast‐atom bombardment mass spectrometric study of some N(10)‐substituted phenothiazine‐S‐oxides

Electron ionization mass spectral behavior of N R substituted phenothiazine-S-oxides (R:CH2CCH3CH2, CH2CCH, CCCH3, COCH3, COC2H5 and COC6H5) has been studied by comparison of normal and daughter-ion mass spectra. Among several characteristic pathways, formation of [MOR]+, C12H8NS+ ions (m/z 198) was found to result in a common and abundant fragment peak for both N-alkyl and N-acyl derivatives. Appearance energy measurements as well as thermochemical considerations revealed this ˙OR loss, to be a single-step dissciation process and to correspond to the energetically most favoured primary decomposition of M+˙; it seems to involve a transannular rearrangement. The ˙OR elimination also occurred from [MH]+ ions, produced by fast-atom bombardment.