Add time:08/02/2019         Source:sciencedirect.com

The mass spectra of twenty-four 3-phenylisothiazoles and three 3-(halophenyl)isothiazoles are reported and discussed. Their common features are the prominent molecular ions and the diagnostic fragment ions arising from cleavages of the NS or SC(5) bonds, eliminations of the side chains and fragments from the phenyl ring. The production of M-1 ions is not common in the 5-Me derivatives in contrast with the reported cases of methyl-thiophenes, furans and pyrroles. Several characteristic fragmentation patterns are noted depending upon the nature of substituents at the 4-position: (1) 4-acetoxy-isothiazoles preferentially decompose to give molecular ions of 4-hydroxy derivatives, (2)-4-nonsubstituted and 4-cyano-isothiazoles, though not all, produce the M minus S or M minus SH ions, (3) rearrangements of 4-bromo and 4-cyano groups take place to the phenyl-containing fragment ions, (4) the hydrogen of 4-hydroxy derivatives and the Me group of 4-MeO derivatives migrate to the phenyl containing ions, (5) migration of a hydrogen from the 3-phenyl ring takes place in 4-cyano and 4-hydroxyisothiazoles and (6) methyl esters of 4-carboxylic acids produce M-15 ions regardless of the presence of an adjacent Me group at the 5-position.

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