Arylthio- and Arylseleno-Substituted s-Heptazines.

In contrast to numerous thio- and selenocyanuric acid derivatives, sulfur- or selenium-containing s-heptazines have not been reported so far. Thio- and selenocyameluric acid esters were obtained by substitution reactions of s-heptazine chloride C6 N7 Cl3 with aromatic thiols and selenophenol; the resultant white or yellow solids were stable in air. They were comprehensively characterized by elemental analysis, 1 H, 13 C NMR, and IR spectroscopy. The thiocyameluric acid phenyl ester (1, C6 N7 (S(C6 H5 ))3 ) and the corresponding selenium compound (7) formed co-crystals with mesitylene, which were analyzed by single-crystal X-ray diffraction. Both structures showed unusually large channels of ≈12 Å diameter. The thermal stability was measured by TGA (thermogravimetric analysis), and the flame retardancy of compound 1 was tested in PP by carrying out limiting oxygen index (LOI) measurements, which gave promising results. Quantum chemical calculations of the title compounds were performed to explain the observed properties and structural characteristics.