Mass Spectra of New Heterocycles: XXVI. Electron Impact Ionization Study of N-(5-Amino-thiophen-2-yl)- and N-[2-(Methylsulfanyl)-1,3-thiazol-5-yl]-isothioureas.

The behavior of a series of previously unknown N-(5-aminothiophen-2-yl)- and N-[2-(methyl-sulfanyl)-1,3-thiazol-5-yl]isothioureas under electron impact ionization (70 eV) has been studied for the first time. 2-Thienylisothioureas give rise to a fairly stable molecular ion (Irel 11–25%), whereas no molecular ion peak is present in the mass spectra of 1,3-thiazolylisothioureas. A common fragmentation pathway of the molecular ions of 2-thienyl- and 1,3-thiazolylisothioureas involves cleavage of the C–N bond in the isothiourea fragment with charge localization on the imino nitrogen atom to give [R3SC≡NR2]+ ion (Irel 34–100%); furthermore, [M – R3SC=NR2]+ ion with charge localization on the amino nitrogen atom is formed from thienyl derivatives and is the most abundant (Irel 91–100%). The mass spectra of 1,3-thiazolylisothioureas also showed [M – MeSCN]+· and [MeSCS]+ ion peaks resulting from decomposition of the thiazole ring in the molecular ion. In addition, unlike 2-thienylisothioureas, the molecular ions of 1,3-thiazolyl analogs underwent Chet–N bond cleavage with charge localization on the thiazole fragment. [ABSTRACT FROM AUTHOR]