Synthesis and spectroscopic characterization of 2-furancarbothioamide: N-(4-fluorophenyl)furan-2-carbothioamide

This investigation deals with an alternative thionation synthetic strategy for the preparation of N-(4-fluorophenyl)furan-2-carbothioamide using elemental sulphur and applying the Willgerodt-Kindler reaction. The carbothioamide was obtained with ca 30 % yield assessing the purity (higher than 90 %) with GC/MS spectrometry, and the compound was fully characterised by NMR (¹H, ¹³C), FTIR and UV–visible spectroscopies. Indeed, ¹H NMR spectroscopic analysis demonstrated that a single conformer with anti-anti geometry was formed attributed to the observation of only one N-H signal (9.37 ppm) of the NH-C=S group and, FTIR spectroscopy (N-H stretching at 3372 cm⁻¹) also reinforces this observation. UV-visible absorption and fluorescence emission spectra were recorded in different polar and nonpolar solvents (acetonitrile, ethanol and n-heptane) and the λ^0,0 cross point displays a bathochromic shift of 11 nm with the increasing solvent polarity. The fluorescence quantum yield (ϕ_f) has been measured at room temperature concluding that this carbothioamide derivative is not a fluorescent compound showing a ϕ_f value of 0.0002. Finally, theoretical calculations have been carried out to estimate the NMR chemical shifts as well as vibrational frequencies values of the anti-anti isomer and these values were compared with the experimental data obtaining satisfactorily correlations.