Synthesis and Characterization of Large (30-60-Membered) Aliphatic Crown Ethers

Abstract

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 [up to hexa(ethylene glycol)] as starting materials and the ability to optimize the procedure for selective production of either macrocycle, producing yields supe- rior or comparable to previous methods. At higher reaction temperatures the large crown ether is preferentially formed. This approach has been used to produce the crown ethers on 100-g scales. Purification was achi- eved 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 characte- rized by melting points, 1 H- and 13 C-NMR, elemental analysis, and/or MS, GC-MS, and TGA-MS. Melting points were as much as 26°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°C