Synthesis and mass spectrometry of some methoxylated PCB

Abstract

The syntheses of 46 methoxy-polychlorobiphenyls (MeOCBs), containing 3 to 7 chlorine atoms, are described. The MeOCBs were synthesized via the Cadogan diaryl coupling reaction of the appropriate polychloroaniline and polychloroanisole, or via the Ullmann coupling of a polychloroiodobenzene and 4-iodoanisole with subsequent chlorination of the isolated 4-MeOCB product. The synthesized MeOCBs were characterized by electron ionization (EI) mass spectrometry (MS) on an ion trap MS instrument and by EI and negative ion chemical ionization (NICI) on a quadrupole mass spectrometer. Both instruments gave similar El spectra but the fragments were in general more abundant relative to the molecular ion, in the spectra obtained from the ion trap instrument. Characteristic fragmentation patterns were obtained by El for ortho-, meta- and para-MeOCBs, respectively, depending on the position of the MeO-group, with the exception of three meta-substituted MeO-heptaCBs, with a 3-MeO-2,4,6-trichloro-substitution pattern, that gave an abundant [M-15] +-fragment, similar to para-substituted MeOCBs. MS(NICI) of ortho-, meta- and para-MeOCBs did not give any characteristic fragmentation patterns depending on the position of the MeO-group, except for ortho-substituted MeOCBs that showed abundant fragments at [M-36] −. The MS(NICI) gave approximately 10–50 times higher response for MeO-tetraCBs - MeO-heptaCBs than the MS(EI). The ion trap instrument (ITS40) has a somewhat lower detection-limit than the quadrupole MS when operated in the EI-mode.