ELECTRON IONIZATION AND CHEMICAL-IONIZATION MASS-SPECTROMETRIC STUDIES ON 2-BENZOTHIAZOLPHENYLHYDRAZONES AND 1-(2-BENZOTHIAZOLYL)-3,5-DIPHENYLFORMAZANS

The 70 eV electron ionization (EI) and chemical ionization (CI) mass s pectra were recorded for six differently substituted 2-benzothiazolphe nylhydrazones and five related 1-(2-benzothiazolyl)-3,5-di-phenylforma zans, The fragmentation patterns were studied by exact mass measuremen ts, metastable ion analysis and collision-induced dissociation techniq ues. For both hydrazones and formazans the EI spectra were relatively simple, and especially for the formazans the dominance of the C3-N4 bo nd cleavage was striking. The CI spectra of the formazans were recorde d with the use of ammonia, d(3)-ammonia, isobutane or methane as reage nt gas. Only methane was used for the hydrazones because even it was a ble to cause only little fragmentation. In comparison with the hydrazo nes, the protonated formazans were relatively unstable, decomposing th rough several fragmentation pathways. Regardless of the reagent gas, t he decomposition was always of the same degree and the spectra were cl osely similar. The most probable protonation site for the formazans wa s estimated by semiempirical calculations to be the benzothiazole nitr ogen. This result is in agreement with the experimental data under bot h EI and CI, and showed that those tautomeric forms of formazans havin g a single bond between C3 and N4 are dominant in the gas phase. (C) 1 998 John Wiley & Sons, Ltd.