Fundamental chemistry of iodine. The reaction of di-iodine towards thiourea and its methyl-derivative: formation of aminothiazoles and aminothiadiazoles through dicationic disulfides?

Dalton Transactions Pub Date: 2014-01-06 DOI: 10.1039/C3DT53302F

Abstract

The reactivity of di-iodine towards thiourea (TU) and its derivative methylthiourea (MeTU) was studied. A diversity of products was obtained from these reactions. TU reacted with di-iodine in the absence or presence of hydroiodic or hydrochloric acids in a 1?:?1, 1?:?1?:?1 or 1?:?1?:?2 (TU?:?I2?:?HX (X = I, Cl)) molar ratio to form the ionic compounds [(TU2)2+2(I?)·H2O] (1), [2(TU2) 2+·(Cl?)·2(I?)·(I3?)] (2) and [(TUH)+ (I3?)] (3). The compounds [(TU2)2+(Br?)(I3?)] (4) and [(TU2)2+2(Br?)·H2O] (5) were derived from the reactions of TU with di-iodine in the presence of hydrobromic acid in a 1?:?1?:?1 or 1?:?2?:?1 (TU?:?I2?:?HBr) molar ratio. However, when the product of the reaction between TU and di-iodine in a 2?:?1 (TU?:?I2) molar ratio was crystallized in acetone–ethylether media the ionic salt of formula [(DAThdH+)(I?)] (6) (DAThd = 3,5-diamino-1,2,4-thiadiazole) was obtained. Methylthiourea (MeTU) reacted with di-iodine in the presence of hydrobromic acid (1?:?1?:?1, MeTU?:?I2?:?HBr) in dichloromethane to form a solid product which gives [2(MeTU2) 2+·(2Br?)(I42?)] (7). Moreover, MeTU reacted with I2 in 2?:?1 (MeTU?:?I2) to form an intermediate powder product which was crystallized in acetone to give the 2-amino-3,4-dimethylthiazolium cation in [(DMeAThH+)(I?)(H2O)] (8). Upon changing the crystallization medium to ethanol, instead of acetone, the cationic 5-amino-3-methylamino-4-methyl-1,2,4-thiadiazolium (AMeAThdH)+ in [(AMeAThdH+)(I3?)] (9) was formed. The compounds were characterized by m.p., FT-IR, UV-Vis, 1H-NMR spectroscopy and mass spectrometry. The crystal structures of compounds 1–9 were determined by X-ray crystallography.

Graphical abstract: Fundamental chemistry of iodine. The reaction of di-iodine towards thiourea and its methyl-derivative: formation of aminothiazoles and aminothiadiazoles through dicationic disulfides
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