[Cl:1][C:2]([Cl:19])([P:11](=[O:18])([O:15]CC)[O:12]CC)[P:3](=[O:10])([O:7]CC)[O:4][CH2:5][CH3:6].[Na+:20].[I-].C[Si](Cl)(C)C.ClC(Cl)(P(=O)(O[Si](C)(C)C)OCC)P(=O)(O[Si](C)(C)C)O[Si](C)(C)C.[OH-].[Na+]>CC#N.CO.O>[Na+:20].[Na+:20].[Na+:20].[CH2:5]([O:4][P:3]([C:2]([Cl:1])([Cl:19])[P:11](=[O:12])([O-:18])[O-:15])(=[O:7])[O-:10])[CH3:6]5.0 g (0.014 moles) of tetraethyl (dichloromethylene)bisphosphonate and 6.7 g (0.045 moles) of NaI are dissolved in 50 ml of anhydrous CH3CN and while stirring 12.2 g (0.112 moles) of trimethylsilyl chloride are added. After the addition stirring is continued at room temperature, protected from moisture, for appr. 4 days and is evaporated under a vacuum. To the mixture obtained as a residue (contains as the major component monoethyl tris(trimethylsilyl) (dichloromethylene)bisphosphonate) 10 ml of water are added and the mixture is made alkaline with a 10% NaOH solution. The mixture is diluted with 50 ml of CH3OH and is left standing at +4° C. for 2 h and is filtered (the precipitate is (dichloromethylene)bisphosphonic acid sodium salt). To the filtrate 25 ml of ethanol are added and it is left standing for 1 day at +4° C. and is filtered. The filtrate is evaporated under a vacuum and the residue is washed with acetone and filtered. The precipitate is dried to constant weight whereby appr. 2.0 g (50% of the theor.) of colourless crystalline (dichloromethylene)bisphosphonic acid monoethyl ester trisodium salt are obtained (31P-NMR (D2O): δ 6 11.86 (P), 9.40 (P') 2JPP =15.4 Hz) at a concentration of >90% and wherefrom the corresponding acid may be liberated with acid treatment.
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