Fragmentation mechanisms of some prazoles and their related substances were newly investigated in this paper via positive mode ESI-TOF HRMS1 and HRMS2. Some novel fragmentation rules or ions were found or detected in the research. The pyridine and the benzoimidazole ring remained in most cases during the ionization, and heterolytic fragmentations often occurred near the -S(O)nCH2- linker to give the [1,3]-H migration ion or [1,7]-H migration ion rearranging across the benzoimdazole ring. Smiles rearrangement ionizations also frequently occurred, initiated by the attack of the lone pair electrons from the pyridine ring, and the sulfones gave special N-(2-benzoimdazolyl) pyridine ions (11b and 12c) by a direct extraction from SO2, and the thioethers gave similar framework ions (8c, 9c and 10c) via the rearrangement and a further homolytic cleavage of SH radicals. However, the sulfoxides were seldom detected in the corresponding Smiles rearrangement ions during our measurement, and the N′-oxides of the pyridines did not undergo the Smiles rearrangement ionization due to the absence of the lone pair electrons. The 5/6-membered chelating ions with Na+ or K+ were frequently detected as the molecular and further fragment ions. Some novel and interesting fragment ions containing bivalent (8b and 9b), tetravalent (4b, 5c and 6c) or hexavalent (15b and 16b) sulfurs were first reported here.
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