Partition Coefficients and Equilibrium Constants of Crown Ethers between Water and Organic Solvents Determined by Proton Nuclear Magnetic Resonance

• Published in: Journal of chemical and engineering data 2004-05, Vol.49 (3), p.594-598
• Main Authors: Cheng, Han-Wen, Rustenholtz, Anne, Porter, Richard A, Ye, Xiang R, Wai, Chien M
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Liquid-liquid extraction
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/je034195c

The extraction of water by several crown ethers into chloroform + carbon tetrachloride mixtures has been investigated using a proton NMR technique. The equilibrium is well described by formation of a 1:1 water−crown complex in rapid exchange with uncomplexed ligand and water. The fraction (k) of crown ether complexed with water increases with crown cavity size, varying from (15 ±1)% for 12-crown-4 to (97 ± 5)% for 18-crown-6. Addition of carbon tetrachloride to chloroform lowers the k value for all crown ethers in equilibrium with water, and the value is close to zero in pure CCl4. The partition coefficient follows the opposite trend:  the amount of crown ether in the organic phase increases with the percentage of CCl4 in this phase. The chemical shifts of free and complexed water also vary with solvent composition. Interaction of water with crown ether depends on solvation environment and may play a significant role in liquid−liquid extraction of metal ions using macrocyclic polyethers as extractants.