Toluene → Triethyl(methoxymethyl)phosphonium bromide

62 g (0.5 moles) of bromomethylmethyl ether (a reagent available from Tokyo Chemical Industry Co., Ltd.) was added dropwise in 236 g (0.5 moles) of a 25% toluene solution of triethylphosphine (HISHICOLIN (registered trademark) P-2, a trade name of Nippon Chemical Industrial Co., Ltd.), and the mixture was allowed to react at 70 to 80° C. for 6 hours. After completion of the reaction, hexane was added for crystallization, thereby obtaining 97 g (percent yield: 80%) of a crystal of triethyl(methoxymethyl)phosphonium bromide. 86 g (0.3 moles) of lithium bis(trifluoromethylsulfonyl)imide (a reagent available from Kanto Chemical Co., Inc.) was added to 73 g (0.3 moles) of this triethyl(methoxymethyl)phosphonium bromide, and the mixture was allowed to react in an aqueous system. Subsequently, the reaction mixture was stirred for aging at room temperature for 3 hours. After completion of stirring, a lower layer (product) was separated. The separated product was washed with pure water four times and then washed with hexane four times. After completion of washing, the product was dried in vacuo at 100° C. and at a degree of vacuum of 0.5 kPa for 5 hours. Confirmation of the obtained product was carried out by means of 1H-NMR, 13C-NMR, 31P-NMR and 19F-NMR. A yield of the product (colorless transparent liquid) was 104 g (percent yield: 78%), and it was confirmed by 3P-NMR that its purity was 98% or more.