The Wittig Reaction Catalyzed by Ethylene Oxide

In the following procedure, use is made of the basic character of epoxides. In the presence of phosphonium salts, ethylene oxide removes hydrogen halide and the alkylidenetriphenylphosphorane is produced. If a suitable carbonyl compound is present in the reaction mixture, its reaction with the in situ generated phosphorane proceeds readily to give the Wittig product. 

Ethylene oxide (2.5 ml, 0.05 mole) is condensed in a 50-ml round-bottom flask containing 5 ml of methylene chloride by introducing the gas via a tube into the ice-cooled flask. To the cooled flask are added triphenylphosphine (6.6 g, 0.025 mole), benzaldehyde (2.6 g, 0.025 mole), and ethyl bromoacetate (4.2 g, 0.025 mole). The flask is closed with a drying tube, brought to room temperature, and allowed to stand overnight. Fractional distillation of the solution then yields 2-bromoethanol, bp 55717 mm followed by the desired ethyl cinnamate, bp 142-144717 mm (27171 atm) in about 90% yield. The residue consists of triphenylphosphine oxide, mp 150°. 

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