Molecular Design of Crown Ethers. 3. Extraction of Alkaline Earth and Heavy Metal Picrates with 14- to 17-Crown-5 and 17- to 22-Crown-6

Article abstract of DOI:10.1246/bcsj.58.525

The solvents extraction of alkaline earth and heavy metal picrates with a series of ring-contracted and ring-enlarged crown ethers has been carried out in order to reveal the effects of methylene-chain lenght upon cation-binding ability.Compared with the parent 3m-crown-m, the ring contracted crown ethers and their sila analogues possess limited extractabilities, often as low as those for the corresponding glymes.On the other hand, the ring-enlarged crown ethers, in general, show gradual, but not drastic, decreases in extractability for most cations with increasing methylene-chain lenght.Interestingly, the extractabilities for Ag+, Tl+, and Ba2+ do not decreases monotonously with ring expansion; in particilar 16-crown-5 is a better extractants for Ag+ than 15-crown-5 and even than 18-crown-6.Effects of cation hydration upon extractability and the limitations of solvent extraction technique are also discussed.