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1-Oxo-2-methoxy-2-(2-diethylphosphonoethyl)-1,2-diphenylethane (100 g, prepared from benzoin methyl ether and diethyl vinyl phosphonate as described in Example 1 of U.S. Pat. No. 4,082,821) is dissolved in methanol (400 ml). Sodium hydroxide (40 g) is added to the solution and the mixture is heated under reflux for 2 hours. The methanol is removed by rotary evaporation, water (300 ml) is added and the mixture is washed with diethyl ether (4×100 ml). The resulting aqueous mixture is cooled to 0° C., and concentrated hydrochloric acid is added until the pH is zero, when a solid is precipitated. This is washed with water and then stirred together with acetone (300 ml), when sodium chloride remains as undissolved solid. The sodium chloride is filtered off and acetone is removed by evaporation to give a solid which is recrystallised from a mixture of acetone and ether to give 90 g of product, a compound of formula XVIII where R1 is methoxy, R3 and Ar1 are each phenyl, R7 is --CH2CH2 -- and R8 is --CH2CH3.

1. temperaturethe mixture is heated
2. temperatureunder reflux for 2 hours
3. customThe methanol is removed by rotary evaporation, water (300 ml)
4. additionis added
5. washthe mixture is washed with diethyl ether (4×100 ml)
6. additionconcentrated hydrochloric acid is added until the pH is zero, when a solid
7. customis precipitated
8. washThis is washed with water
9. filtrationThe sodium chloride is filtered off
10. customacetone is removed by evaporation
11. customto give a solid which
12. customis recrystallised from a mixture of acetone and ether