Into a 500 mL three neck round bottom flask equipped with a mechanical stirrer, thermometer and a Dean-Stark trap equipped with a drying tube was placed 2,4-difluorophenyldiphenylphosphine oxide (12.00 g, 0.0382 mole), 4-aminophenol (8.6673 g, 0.0794 mol), potassium carbonate (13.1682 g, 0.0953 mol), NMP (85 mL) and toluene (25 mL). The mixture was heated to 135° C. while removing water via azeotropic distillation. After 16 hours, the toluene was removed from the reaction and the resulting solution was heated at 165° C. for 4 hours. The reaction mixture was cooled to room temperature and then poured into 1 L of 5% acetic acid (aq) with vigorous stirring. A tan solid formed after stirring for 45 minutes. The crude tan solid was collected via filtration, washed with excess water, and dried in an oven at 110° C. to give 16.76 g (89% crude yield). The solid was recrystallized from a dimethylacetamide/water solution (3:1) and light tan needles were obtained. The solid exhibited a melting point of 271.5-274.7° C. as determined by DSC at a heating rate of 10° C./min. Mass spectroscopic analysis: M+492 [C30H25N2O3P+]
