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-)·(I 3-)] (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. © 2014 The Royal Society of Chemistry.