ION-PAIR EXTRACTION OF LANTHANOID(III) WITH CROWN ETHERS AND PICRATE ION

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Abstract
The extraction of lanthanoid(III) with 15-crown-5, 18-crown-6, or dibenzo-18-crown-6, and picrate ions into chloroform was measured at 25°C. The stoichiometry of the dominant species extracted was found to be 1:2:3 with respect to lanthanbid(III), crown ether, and picrate ions. The extraction constants decrease through the lanthanoid series (except lanthanum). The constants for praseodymium or neodymium are larger than that for ytterbium or lutetium by an order of magnitude. The pattern of the plot of the extraction constants for the crown ethers vs. the lanthanoid atomic number is similar for all crown ethers tested, although the sizes of all the cations are close to the cavity size of 15C5. The present result suggests that lanthanoid(III) would not be trapped in the center of the cavity of the crown ether.