The title compound N,N'-di(diethoxythiophosphoryl)-1,4-phenylenediamine was synthesized by the reaction of diethoxythiophosphoryl chloride and p-phenylenediamine and characterized by elemental analysis, IR and ¹H NMR spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis and the thermal property was studied by TG analysis. The relative molecular weight of the title compound is 412.42, the crystal structure belongs to orthorhombic, Pbca space group, with a＝0.86936(16) nm, b＝1.2787(2) nm, c＝1.8897(3) nm, β＝90°, V＝2.1006(7) nm³, Z＝8, D_c＝1.304 g/cm³, μ(Mo Kα)＝0.425 mm^－1, F(000)＝872, S＝1.052, the final R＝0.0628 and wR＝0.1860 for 1852 observed reflections with I＞2σ(I). The X-ray single crystal diffraction analysis demonstrates that the crystal structure is centrosymmetric. The weak N—H…S intramolecular hydrogen bonds were observed to link the molecules into sheets. The TG analysis shows that the title compound has good thermal stability and char forming capability, and its retarding the fire by polyacrylonitrile reveals that the compound is an excellent intumescent fire retardant.

Key words: diethoxythiophosphoryl chloride, p-phenylenediamine, N,N'-di(diethoxythiophosphoryl)-1,4- phenylenediamine, crystal structure, thermal property, intumescent fire retardant