Synthesis, Crystal Structure and Thermal Properties of N,N′-Bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl) Ethylene Diamine

The title compound N,N′-bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl) ethylene diamine (DPTDEDA, C12H26N2O4P2S2) was synthesized by the reaction of neopentyl glycol, phosphorus thio-chloride and 1,2-ethylenediamine, 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 analyzed by TG analysis. The crystal structure belongs to monoclinic, space group P21/c, with a = 14.557(16), b = 11.299(12), c = 12.163(13) , β = 98.707(19)°, Dc = 1.305 g/cm3, Z = 4, λ = 0.71073 , μ(MoKα) = 0.447 mm-1, Mr = 388.41, V = 1977(4) 3, F(000) = 824, S = 1.107, the final R = 0.0478 and wR = 0.0810 for 1738 observed reflections (I > 2σ(I)). X-ray analysis reveals that the crystal structure is centrosymmetrically distributed through 1,2-ethylenediamine to join two distorted six-membered rings. The weak N–H···S interactions are observed and link the molecules into sheets. TG analysis shows that the title compound has good thermal stability and char-forming capability, which are required for an excellent intumescent fire retardant.