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

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.