Synthesis and Crystal Structures of New 1,4-Disubstituted 1,2,4-Triazoline-5-thiones

Introduction of sulfur into the 5-position of 1,4-disubstituted quaternary 1,2,4-triazolium salts (1-9; Cl, Br, I, BF4, PF6, CH3OSO3 were used as anions) by two methods was investigated. The syntheses of nine 1,4-disubstituted 1,2,4-triazoline-5-thiones 10-18 are reported (1, 10: R-1 = CH3, R-2 = CH3; 2,11: R-1 = NH2, R-2 = CH3; 3,12: R-1 = NH2, R-2 = CH(CH3)(2); 4,13: R-1 = N(CH3)(2), R-2 = CH3; 5, 14: R-1 = N(CH3)(2), R-2 = CH(CH3)2; 6, 15: R-1 = CH3, R-2 = NH2; 7, 16: R-1 = OCH2Ph, R-2 = CH3; 8, 17: R-1 = OCH2Ph, = CH2CH3; 9, 18: R-1 = CH3, R-2 = CH2Ph). Compounds 11-17 represent 1-amino, 4-amino, 4-dimethylamino, and 4-benzyloxy-1,2,4-triazoline-5thiones, whereas 10 served as a reference compound. Thione 18 was identified as an unexpected by-product in the synthesis of 16 and was also prepared independently. Thermolysis of 10 in air gave 1,4-dimethyl-1,2,4-triazolium hydrogensulfate. Crystal structures of eight 1,4-disubstituted 1,2,4-triazoline-5-thiones were determined by single-crystal X-ray diffraction. Intermolecular hydrogen bonds (C-H center dot center dot center dot S, C-H center dot center dot center dot N, N-H center dot center dot center dot N, N-H center dot center dot center dot S) were observed in the solid state. The solvent-dependent H-1 NMR chemical shifts of signals of 10 and 13 were satisfactorily correlated with the Kamlet-Abboud-Taft pi* and beta parameters in ten solvents. From the lack of correlation with the alpha parameter and from the C=S bond length (average 1.67 angstrom) a significant contribution of a mesoionic imidazolium-2-thiolate resonance structure seems unlikely.