Br[CH:2]([CH2:4][CH2:5][CH3:6])[CH3:3].[Mg].[CH3:8][CH:9]([Mg]Br)[CH2:10][CH2:11][CH3:12].[P:15]([O-])(OCCCC)(OCCCC)=[O:16].S(=O)(=O)(O)O>O1CCCC1.C(OCC)C>[CH3:3][CH:2]([PH:15](=[O:16])[CH:9]([CH2:10][CH2:11][CH3:12])[CH3:8])[CH2:4][CH2:5][CH3:6]A Grignard solution prepared from 2-bromopentane (227.3 g, 1.5 moles) and magnesium (39.6 g) in tetrahydrofuran (500 cm3) was estimated by a standard procedure and found to contain 1.05 moles of 2-pentyl magnesium bromide. The solution was diluted with diethyl ether (250 cm3) and cooled to 10° C. in an atmosphere of nitrogen. A solution of dibutyl phosphate (67.9 g, 0.35 moles) in diethyl ether (500 cm3) was added with stirring during 1 hr. whilst the temperature was maintained at 10°-15° C. The solution was then boiled under reflux for ten min. to complete the reaction. The solution was cooled to 10° C. and 25% aqueous sulphuric acid (500 cm3) was added with stirring during 1 hr. The organic layer was separated and successively extracted with water (two 300 cm3 amounts). 10% aqueous sodium bicarbonate (300 cm3), and water (two 300 cm3 amounts). It was then dried (magnesium sulphate) and filtered and distilled yielding di-2-pentylphosphine oxide (35.0 g), b.p. 110° C. at a pressure of 0.8 mm of mercury. All of this compound was stirred in nitrogen atmosphere with phosphorus trichloride (50 cm3) at 22° C. After 1 hr. it was found by gas chromatography that about 20% remained unreacted; a second addition of phosphorus trichloride (10 cm3) was made and stirring was continued for a further 2 hr. when reaction had reached about 95% completion. The solution was distilled yielding volatile phosphorus compounds and finally chloro di-2-pentylphosphine (27.5 g), b.p. 72°-74° C. under a pressure of 1.5 mm of mercury.
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