Toluene → Diethyl(3-oxo-1,4-dioxaspiro[4.5]dec-2-yl)-phosphonate

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In a reaction vessel with a descending condenser, 50 g (0.236 Mol) (diethoxy-phosphinyl)-hydroxyacetic acid (A) and 240 mL toluene are mixed at ambient temperature and then heated to 110° C. When the boiling temperature of toluene is reached, a mixture of 71.7 mL (0.471 Mol) cyclohexane-dimethylketal (B) and 10 mL toluene are slowly added dropwise, while the azeotrope of toluene and methanol is distilled off. After the addition has ended the reaction mixture is refluxed for 90 minutes. Any solvent distilled off is replaced by the addition of 50 mL toluene. In order to achieve total conversion, a further 10 mL (0.066 Mol) of cyclohexane-dimethylketal (B) are added dropwise. The mixture is heated to a 110° C. for another hour and the solvent distilled off is replaced by the addition of another 100 mL toluene. After the addition of another 120 mL toluene the solvent is distilled off in vacuo. The residue is taken up in 200 mL tert.butyl-methylether and successively extracted twice with 200 mL of 10% potassium carbonate solution, once with 250 mL of 30% sodium bisulphite solution and once with 150 mL of 30% sodium bisulphite solution. After subsequent extraction with 40 mL saturated saline solution the organic phase is dried and evaporated down.

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