Crown ethers as solvent extraction reagents: Where do we stand
Among the first applications of crown ethers was their use as solvent extraction reagents. In 1962 the compound 2, 3, 11, 12-dibenzo-1, 4, 7, 10, 13, 16-hexaoxacycloocta-2, 11-diene, now called dibenzo-18-crown-6, was identified and found to form alkali-metal-salt adducts soluble in organic solvents. These extraction properties of crown ethers were later used to compare the complex-formation properties of metal ions with crown ethers, and it was observed that salts of organophilic anions were more readily transferred to aprotic solvents. Picrate salts were extensively used in this role. However, analytical or process applications of the complexing abilities of macrocycles needed the aqueous anion to be one of the more common mineral acid anions. In the late 1970's, it was discovered that crown ethers mixed with an organophilic cation exchanger such as alkyl phosphoric, alkyl-aryl sulfonic, or carboxylic acid would produce synergistic extraction systems having excellent and selective affinities for a large number of metal ions. In 1981, macrocyclic compounds with attached carboxylic acid groups were synthesized and found to be excellent extractants. In addition to liquid-liquid extraction, much work has been done using macrocycles as separation agents in membranes and resin beads. Fundamental research, not covered in this paper, is now beginning to provide the stoichiometries and structures of some of the organic-phase complexes produced. Further, some potential uses of these systems are beginning to be identified and applied. 115 refs., 2 figs.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5897067
- Report Number(s):
- CONF-871038-4; ON: DE88002313
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400105* -- Separation Procedures
ALCOHOLS
BIBLIOGRAPHIES
DOCUMENT TYPES
EXTRACTION
GLYCOLS
HYDROXY COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
POLYETHYLENE GLYCOLS
POLYMERS
REAGENTS
REVIEWS
SEPARATION PROCESSES
SOLVENT EXTRACTION
SOLVENTS
USES