Fragmentation patterns of protonated benzothiazole sulfenamides by atmospheric pressure chemical ionization

Benzothiazole sulfenamides of N-t-butylbenzothiazole-2-sulfenamide (TBBS), N-cyclohexylbenzothiazole-2-sulfenamide (CZ), and N,N'-dicyclohexylbenzothiazole-2-sulfenamide (DZ) are most popular sulfur cure accelerators. In this study, the benzothiazole sulfenamides were ionized by atmospheric pressure chemical ionization (APCI) method, the product ions were directly analyzed using a single quadrupole mass spectrometer, and their fragmentation patterns were characterized. Structures and energies of the fragment ions and the precursor ions were calculated, an appropriate precursor ion was determined, and the fragmentation mechanisms were suggested. Protonated benzothiazole sulfenamides had ammonium structures, and they were rearranged through 5- and 7-membered cyclic structures to produce the fragment ions of m/z 166 and 183, respectively. DZ had the other fragment ion of m/z 265. Relative abundances of the fragment ions for TBBS were much greater than those for CZ and DZ. It was found that the steric hindrance and the number of hydrogen atoms participating in the rearrangements influenced on efficiency of the fragmentations. Relative abundances of the fragment ions increased as the source fragmentor voltage increased. The intensity ratios of the (m/z 166)/(m/z 183) were also increased by increasing the source fragmentor voltage. The (m/z 166)/(m/z 183) ratios of TBBS were smaller than those of CZ and DZ. The benzothiazole sulfenamides could be directly identified by comparing kinds and relative abundance ratios of the fragment ions as well as their protonated molecules. And difference in the fragmentation behaviors according to the benzothiazole sulfenamides might be related to their cure characteristics.