The general procedure for the synthesis of bis(4-(trifluoromethyl)phenyl)phosphine oxide by Hays' method using 4-trifluoromethylphenylmagnesium bromide and diethyl phosphite is as follows:
1. in a 100-mL round-bottomed flask fitted with a charging funnel, an evacuation/argon filling operation was performed followed by addition of 33 mL of a 1 M 4-(trifluoromethyl)phenylmagnesium bromide/THF solution (33 mmol, 3.3 eq.), and the solution was cooled to 0°C.
2. 1.38 g of diethyl phosphite (10 mmol, 1.0 eq.) dissolved in 10 mL of THF was added dropwise over 10 min under argon protection.
3. the reaction mixture was kept at 0 °C for 10 min, after which the ice bath was removed and the mixture was allowed to warm up to room temperature and stirred for 2 hours.
4. The reaction mixture was again cooled to 0 °C and 25 mL of 0.1 N HCl (deoxygenated water) was added dropwise over 20 minutes, followed by 25 mL of methyl tertiary butyl ether (MTBE) and stirred thoroughly for 5 minutes.
5. The upper organic phase was separated and retained. To the lower aqueous phase an additional 20 mL of 1 N HCl (deoxygenated water) was added and extracted with dichloromethane (2 x 30 mL).
6. All organic phases were combined and filtered through a diatomaceous earth pad, the pad was washed with dichloromethane and subsequently dried with magnesium sulfate (MgSO4).
7. The solvent was removed under pressure to give the crude product.
8. The crude product was purified by silica gel column chromatography using 2% methanol/dichloromethane as eluent and finally recrystallized from hot ethyl acetate (EtOAc) to give 2.41 g of the target product (92% yield) as a colorless solid.
Product characterization: colorless solid; yield = 92%; 1H NMR (400 MHz, CDCl3) δ: 8.01 (d, 1JHP = 473 Hz, 1H), 7.60 (dd, J = 13.8, 8.2 Hz, 4H), 6.97 (dd, J = 7.8, 2.4 Hz, 4H), 3.83 (s, 6H); 31P NMR (162 MHz, CDCl3) δ: 21.0.
