triethyloxonium hexachl~roantimonate~~ (350 mg, 0.8 mmol) in dichloromethane (5 ml), and the mixture was stirred at room temperature for 2 hr. The reaction mixture was then added to a solution of silver nitrate (0.76 g, 0.0045 mol) in methanol (50 ml), causing immediate formation of a white precipitate. This heterogeneous mixture was stirred for 10 min and was filtered. Removal of solvent under reduced pressure afforded the crude (-)-(S)-phosphonium nitrate (7) as a yellow oil, [ a ]~ -15 =! = 3 O, which had been purified by extracting three times with 50-ml portions of ether, to remove (by decantation) any phosphine oxide (8) which was produced by treatment with methanolic silver nitrate.3z The pmr spectrum of 735 exhibited PCH3, d, T 7.28, JPCH = 13 Hz; POCHt-CHI, apparent quintet, T 5.62,Jpoc~ = 7 Hz, JHCCH = 7 Hz; POCHZ-A solution (10 ml) of 0.5 M sodium hydroxide in 50% v/v aqueous dioxane, containing 5.11 i 0.10 atom % 180/mole in the water, was added to freshly prepared35 (-)-(S)-7, and the mixture was stirred at room temperature for 5 min. The reaction mixture was extracted three times with 50" portions of dichloromethane and the combined organic layers were dried (magnesium sulfate). Removal of solvent under reduced pressure afforded the phosphine oxide, 8, as a white crystalline solid, which was purified by sublimation (130", 0.1 mm) to yield (150 mg, 7573 optically pure CH,, t, T 8 . 4 8 , J~c c~ = 7 H Z ; PC6Hs, m, T Ca.