Sulfides and Disulfides of s-Triazine: Potential Thermal Thiyl Radical Generators

A series of aliphatic and aromatic thioethers and dithioethers of s-triazine were synthesised to study their thermal properties, in particular the thermally induced thiyl radical generation ability. Four symmetric s-triazine sulfides of the type (RS)₃ C₃ N₃ , namely 2,4,6-tris(phenylthio)- (1), 2,4,6-tris(para-tolylthio)- (3), 2,4,6-tris(ethylthio)- (5) and 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7), as well as four symmetric s-triazine disulfides of the type (RSS)₃ C₃ N₃ , namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(ethyldithio)- (6) and 2,4,6-tris(tert-butyldithio)-1,3,5-triazine (8) were synthesised. All compounds were comprehensively characterised by ¹ H and ¹³ C NMR, infrared and Raman spectroscopy as well as elemental analyses. Single-crystal X-ray diffraction analyses of 1, 2 and 5 are discussed. The thermal behaviour was studied by thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and quantum chemical calculations. Limiting oxygen index (LOI) flammability tests showed that the disulfides are the most promising radical generators, and are most likely suitable flame retardants for selected polymers.