Synthesis of α-hydroxyphosphonate cyclotriphosphazene under solvent-free conditions with a basic catalyst

GRAPHICAL ABSTRACT

ABSTRACT

An α-hydroxyphosphonate cyclotriphosphazene compound, hexa-(4-diethylphosphate-hydroxymethyl-phenoxy)-cyclotriphosphazene) (HDHPCP), was synthesized in two steps. First, the intermediate hexa-(4-aldehyde-phenoxy)-cyclotriphosphazene (HAPCP) was synthesized by the elimination reaction of hexachlorocyctriphosphazene (HCCP) with 4-hydroxybenzaldehyde. Then HDHPCP was obtained by the Pudovik reaction under solvent-free condition. In this step, the effects of the type and amount of catalyst on reaction time and yield were investigated, and it was found that triethylamine (TEA) has better activity than KF and K₂CO₃. When the molar ratio of HAPCP to TEA was 1:5, the reaction gave an excellent yield of 95.4% in 70 min. Under these conditions, the reaction was easy to work-up, time-saving, environmentally benign, and with high yield. Fourier transform infrared, Nuclear Magnetic Resonance, and elemental analyses results confirmed that HDHPCP was synthesized successfully, and the thermal gravimetric analysis measurement indicated that it presented good thermal stability and high char residual.

KEYWORDS:

• Cyclotriphosphazene
• α-hydroxyphosphonate
• Pudovik reaction
• solvent-free condition

Funding

This study was supported by the National Science Foundation of Shaanxi Province (2015JM5231), and the Overall Scientific and Technological Innovation Program of Shaanxi Province (2013SZS17-Z01), foundation for the Fundamental Research Funds for Central Universities (201510699201).