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

• Published in: Russian journal of organic chemistry Vol. 59; no. 7; pp. 1136 - 1143
• Main Authors: Klyba, L. V., Sanzheeva, E. R., Nedolya, N. A., Tarasova, O. A.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-07-2023; Springer Nature B.V
• Subjects: Chemistry; Chemistry and Materials Science; Cleavage; Electron impact; Ion charge; Ionization; Localization; Mass spectra; Mass spectroscopy; Molecular ions; Nitrogen; Organic Chemistry; [2-(methylsulfanyl)-1,3-thiazol-5-yl]isothioureas; mass spectra; molecular ions; (5-aminothiophen-2-yl)- and; electron impact ionization; fragmentation
• ISSN: 1070-4280; 1608-3393
• DOI: 10.1134/S1070428023070035

The behavior of a series of previously unknown
N
-(5-aminothiophen-2-yl)- and
N
-[2-(methyl­sulfanyl)-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 (
I
rel
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 [R
3
SC≡NR
2
]
+
ion (
I
rel
34–100%); furthermore, [
M
– R
3
SC=NR
2
]
+
ion with charge localization on the amino nitrogen atom is formed from thienyl derivatives and is the most abundant (
I
rel
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 C
het
–N bond cleavage with charge localization on the thiazole fragment.