[Mg].Br[C:3]1[CH:8]=[CH:7][C:6]([O:9][CH3:10])=[CH:5][CH:4]=1.[O:11]=[P:12](Cl)(Cl)Cl>BrCCBr.C1COCC1>[CH3:10][O:9][C:6]1[CH:7]=[CH:8][C:3]([P:12](=[O:11])([C:3]2[CH:8]=[CH:7][C:6]([O:9][CH3:10])=[CH:5][CH:4]=2)[C:3]2[CH:8]=[CH:7][C:6]([O:9][CH3:10])=[CH:5][CH:4]=2)=[CH:4][CH:5]=1A reaction flask under nitrogen containing magnesium turnings (223.9 g, 9.21 mol) and 1950 mL THF was charged with 1 drop of 1,2-dibromoethane and heated to reflux for 1 h. Heating was removed and p-bromoanisole (1683 g, 9.00 mol) was added dropwise at a rate to maintain reflux. After holding the reaction mixture overnight, POCl3 (460.0 g, 3.00 mol) was added slowly over 2 h at 50–79° C. and the resulting mixture was held overnight at 50° C. The product was isolated by aqueous workup to give 984.5 g of tris(4-methoxyphenyl)phosphine oxide (89.0% yield). Recrystallized analytical specimen (from ethyl acetate): mp 145.2° C. (DSC), lit. 143–144° C. (J. Org. Chem. 1960, 25, 2001).
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