Chelate and intramolecular ion-pair formation: A guiding concept for structure/selectivity relationships in the liquid-liquid extraction of alkali and alkaline earth metal ions by anionic crown ether derivatives
✍ Scribed by Yoshiki Katayama; Ryuji Fukuda; Makoto Takagi
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 840 KB
- Volume
- 185
- Category
- Article
- ISSN
- 0003-2670
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✦ Synopsis
Crown ether dyes with pendent anionic side-arms were synthesized for extractionspectrophotometry of alkali and alkaline earth metal ions. Dramatic changes in metal selectivity were obtained simply by changing the nature of the anionic side-arm on the same crown ether skeleton. A structure/metal selectivity relationship is discussed in detail in terms of "chelate" and "intramolecular ion-pair" formation. Small metal cations (high charge density) are preferred in the extraction by a crown ether reagent with a chargelocalized anionic side-arm through the formation of a "chelate". Large metal cations (low charge density) are preferred in the extraction by reagents with a charge-delocalized anionic side-arm through the formation of an "intramolecular ion-pair". Steric restrictions imposed by the side-arm on the metal ion approaching the crown ether are also an important factor in controlling the selectivity of these reagents.