Twenty-five methylthio- and 28 methylsulfonylpolychlorobiphenyls have been synthesized and characterized by chromatographic and 1H nuclear magnetic resonance data. The influence of the position of the sulfur-containing group on the mass spectrometric fragmentation has been studied. The 2-methylthiopolychlorobiphenyls gave intense ions due to loss of CH3Cl from the molecular ion, probably with formation of a dibenzothiophene structure. 3-Methylthiopolychlorobiphenyls could be recognized by loss of an SH radical, while the expulsion of CH3 characterized the mass spectra of the biphenyls with the methylthio group in the 4-position. In the mass spectra of the methylsulfonylpolychlorobiphenyls, the ions [CH3SO]+ and [CH3SO2]+ were dominant. After rearrangement of the sulfone group, biphenyls containing the methylsulfonyl group in the 2-position gave a dibenzofuran ion through loss of CH3SO + Cl. However, 3- and 4-methylsulfonylpolychlorobiphenyls seem to be difficult to differentiate by their mass spectra.
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Bergman et al. (1980) studied this question.