Synthesis and isolation of butylene crown ethers

The synthesis of the butylene crown ethers was accomplished by acid catalyzed ring opening of tetrahydrofuran. Trifluoromethanesulfonic acid is an effective and convenient catalyst for initiating the polymerization of tetrahydrofuran and other cyclic ethers. Its use as an initiator for the formation of cyclic oligomers was thus investigated. The highest concentration of crown ethers was generated from a 43.7/1.00/39.3 molar ratio of tetrahydrofuran to trifluoromethanesulfonic acid in nitromethane. This system produced a mixture of butylene crown ethers ranging from 15-crown-3 to 100-crown-20 ((C4H8O)(n) for n = 3-20) as observed by ESI+/MS. isolation and separation of the macrocyclic oligomers, from a 1 L tetrahydrofuran reaction lasting 22 days, was achieved by liquid/liquid extraction followed by column chromatography on silica gel. Crowns larger than 55-crown-11 were isolated by a combination of LC on silica gel and preparative HPLC with a polymeric column. Crowns ranging from 15-crown-3 to 70-crown-14 were individually isolated and characterized.