S(Cl)(Cl)=O.[CH2:5]([O:7][P:8]([CH:13](O)[C:14]1[CH:19]=[CH:18][C:17]([Cl:20])=[CH:16][CH:15]=1)(=[O:12])[O:9][CH2:10][CH3:11])[CH3:6].C(Cl)[Cl:23].N1C=CC=CC=1>O>[CH2:5]([O:7][P:8]([CH:13]([Cl:23])[C:14]1[CH:19]=[CH:18][C:17]([Cl:20])=[CH:16][CH:15]=1)(=[O:12])[O:9][CH2:10][CH3:11])[CH3:6]9.2 g (0.0768 mole) of thionyl chloride were added to a mixture of 20.2 g (0.0725 mole) of 4-chloro-α-hydroxy-benzylphosphonic acid diethyl ester, 65 g of methylene chloride and 5.8 g (0.0725 mole) of pyridine at 20° to 40° C. in the course of about 1 hour, while cooling slightly with water. The reaction mixture was then heated under reflux for 3 hours and was subsequently stirred for 12 hours without further heating. The mixture was poured onto about 100 g of ice-water and the organic phase was separated off and dried. After distilling off the solvent, the residue was concentrated under 6 mm Hg and at 45° C. 21 g (97.7% of theory) of 4-chloro-α-chloro-benzyl-phosphonic acid diethyl ester were obtained as a yellow viscous oil with a purity of 98.6% (gas chromatogram) and a refractive index nD24 of 1.5250.
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