A mixed solution of magnesium (2.94 g, 1.0 eq.), a small amount of iodine and a small amount of 1,2-dibromoethane in THF (30 mL) was stirred at room temperature for 1 hour under argon protection. Warmed to 35 °C, a solution of 2-bromonaphthalene (25 g, 0.121 mol) in THF (20 mL) was slowly added, followed by stirring the reaction mixture at 40 °C for 30 min. Cooled to 5 °C, a solution of diethyl phosphite (9.77 g, 0.5 eq.) in THF (10 mL) was added dropwise and stirring was continued for 3 h at 5 °C maintaining the temperature. Upon completion of the reaction, water (20 mL) was added at 3 °C, followed by toluene (60 mL) and 6 M hydrochloric acid (20 mL) and stirred at room temperature for 30 min. The organic phase was separated and washed sequentially with water (10 mL), 5% aqueous sodium bicarbonate (10 mL) and 5% aqueous sodium chloride (10 mL). The organic layer was dried over anhydrous magnesium sulfate, gravity filtered and the filtrate was concentrated under reduced pressure. The resulting residue was recrystallized with diisopropyl ether-heptane mixed solvent to afford white crystals of 2,2'-bis-(2-naphthalenyl)phosphine oxide (9.62 g, 53.0% yield) with a melting point of 98.3 °C. The product was purified by NMR hydrogen spectroscopy. The structure of the product was confirmed by nuclear magnetic resonance hydrogen (1H-NMR, 300 MHz, CDCl3, TMS), carbon (13C-NMR, 75 MHz, CDCl3) and phosphorus (31P-NMR, 121 MHz, CDCl3, 85% H3PO4) spectra.
