SYNTHESIS AND CHARACTERIZATION OF LARGE (30-60-MEMBERED) ALIPHATIC CROWN-ETHERS

We report a new synthetic approach to large. (30-72-membered) crown ethers based on isolation of the small and large Cyclic polyethers made by combination of 1 mol or 2 mol each, respectively, of oligo(ethylene glycol)s and oligo(ethylene glycol) ditosylates. The advantages of this approach are the use of readily available glycols Cup to hexa(ethylene glycol)l as starting materials and the ability to optimize the procedure for selective production of either macrocycle, producing yields superior or comparable to previous methods. At higher reaction temperatures the lai ge crown ether is preferentially formed. This approach has been used to produce the crown ethers on 100-g scales. Purification was achieved by a combination of filtration through silica gel, treatment with a polymeric acid chloride, and recrystallization techniques, avoiding standard column chromatography. The pure crown ethers, 60-crown-20, 48-crown-16, 42-crown-14, 36-crown-12, and 30-crown-10, were characterized by melting points, H-1- and C-13-NMR, elemental analysis, and/or MS, GC-MS, and TGA-MSI Melting points were as much as 26 degrees C higher than previously reported for these crown ethers. All the aliphatic crown ethers larger than 18-crown-6 decompose upon heating in air at ca. 200 degrees C.