Synthesis and Characterization of Thiosemicarbazides

Chemicals for synthesis were purchased from Sigma-Aldrich Srl (Milano, Italy) and used without further purification. The purity of the compounds was determined by elemental analysis and verified to be ≥ 95%. ¹H-NMR spectra were obtained in a 5 mm NMR precision tube at 298 K on a Bruker Avance 400 FT spectrophotometer. Elemental analyses were performed by using a FlashSmartCHNS analyser (Thermo Fisher) with gas-chromatographic separation. The MS spectra were recorded in methanol and acquired in positive EI mode by means of a DEP-probe (Direct Exposure Probe) mounting on the tip of a Re-filament with a DSQII Thermo Fisher apparatus, equipped with a single quadrupole analyser or performing an ESI–MS analysis using a Waters Acquity Ultraperformance ESI–MS spectrometer with Single Quadrupole Detector.
The synthesis of the TSs (Fig. 1) was accomplished following a protocol we have previously reported^{29 (link),31 (link)}. Briefly, the aldehyde was dissolved in hot ethanol and added of few drops of glacial acetic acid. An equimolar amount of the proper thiosemicarbazide was added to the solution and the reaction was heated under reflux for 4–6 h. The solution was cooled r.t. and the TSs were isolated as solids by filtration, washed several times with cold ethanol and ether and then dried under vacuum.