The 5-(isopropylidene)-2-thiobarbituric acid: Preparation, crystal structure, thermal stability and IR-characterization

5-(Isopropylidene)-2-thiobarbituric acid (1), C7H8N2O2S, has been crystallized by reacting 2-thiobarbituric acid with excessing acetone for 5–6 days under ambient conditions. The pale yellow crystals have been investigated using X-ray single crystal and powder techniques and characterized by differential scanning calorimetry, thermogravimetry and infrared spectroscopy. The compound crystallizes in the monoclinic system with a = 8.8268(19) Å, b = 12.044(3) Å, c = 8.0998(19) Å, β = 105.388(6)°, Z = 4, V = 830.2(3) Å3, space group P21/c. The geometric parameters of the heterocycle of the molecule 1 are similar to those found previously for the molecule of thionedicarbonyl tautomer in polymorphic modifications of 2-thiobarbituric acid. Infrared spectroscopy also evidences the thionedicarbonyl structure of the 1 heterocyclic ring. Intermolecular NH⋯O hydrogen bonds join the molecules in the chains along b axis. The 1 compound is thermally stable up to 230.0 °С and melts with decomposition at 261.4 °C. The results of mass spectrometric analysis are consistent with the structural parameters found by X-ray diffraction methods.