Chlorodifluoromethane → 1,1-Difluoro-4,4-dimethoxybut-2-yne

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Reaction Conditions

Reaction Steps

At −70° C., an n-buthyllithium solution (2.5 M, in hexane, 260 ml, 0.65 mol) was added dropwise to a solution of propargylaldehyde dimethyl acetal (52.8 g, 0.5 mol) in dried tetrahydrofuran (THF, 1000 ml). The reaction mixture was then stirred at −70° C. for 30 min and cooled to −100° C. At this temperature, chlorodifluoromethane (216.6 g, 2.5 mol) was introduced into the reaction mixture (strongly exothermic). The reaction mixture was slowly warmed to −50° C. and stirred at this temperature for 1 h. Aqueous saturated NH4Cl solution (400 ml) was then added, the reaction mixture was warmed to 0° C., a water/MTBE mixture (500 ml) was added and the aqueous phase was removed. The aqueous phase was extracted twice with MTBE (200 ml). The combined organic phases were washed twice with dilute hydrochloric acid (100 ml), dried over magnesium sulfate and filtered, and the solvent was removed under reduced pressure. The residue was separated by fractional distillation. 1,1-Difluoro-4,4-dimethoxybut-2-yne (46.7 g; transition temperature 50-52° C. at 30 mbar) was obtained in a purity of 96% (according to GC analysis). This corresponds to a yield of 65%. More product was found in the cold trap and in the solvent that had been distilled off. Accordingly, the nonisolated yield is 71%.

Provenance & Evidence