Synthesis and Isolation of Tropothione: A Comparative Study of Spectral Property with Tropone

Article abstract of DOI:10.1016/0040-4020(94)01001-G

The synthesis, isolation, and spectral characterization of tropothione (1), the sulfur analogue of tropone (2), are described with comparison of those for 2.Direct sulfurization of 2 with tetraphosphorous decasulfide using triethylamine as a catalyst yields the titled compound 1 in high yield.Although 1 is thermally unstable material 1/2(crystalline state, 0 deg C) 56 min>, dilute solutions are found to be sufficiently stable enough for measuring spectral data 1/2(0.01 mol/L, 25 deg C) 10.4 days>.The compound 1 is isolated as a labile material of deep red crystals with the melting range of 20-21 deg C.IR spectrum of 1 exhibits a very strong band of the ν_C=S stretching vibration at 1087 cm^-1 in CCl4.Raman spectrum supports the assignment.UV-visible spectra in six solvents show three transitions at around 225 (log ε ca. 4), 253 (ca. 4), and 380 nm (ca. 4.2), while 1 exhibits an additional weak absorption of n-?* transitions at 610 nm (log ε 1.62). 1H NMR of 1 shows wide signals of symmetrical AA'BB'XX' pattern comprising with a large downfield part of α-protons in the ring due to the magnetic anisotropy of the C=S group greater than that of C=O one in 2. 13C NMR of 1 displays three doublet signals (δ 131.48, 138.36, and 153.80) accompanying with the singlet one at δ 213.83 (C=S). 33S NMR of 1 exhibits δ-287 as the first measurement for thiocarbonyl compounds.These physical properties of 1 are in sharp contrast to those of 2.