Complexation of Lanthanoid(III) with Substituted Benzoic or Phenylacetic Acids and Extraction of These Acids

Abstract

Abstract The stability constants of lathanoid(III) complexes with several benzoic and phenylacetic acids substituted with –OH, –OCH3, or –NH2 groups as well as the dissociation constants of these acids have been determined potentiometrically in 0.1 mol dm−3 sodium perchlorate solution at 25 °C. The distribution constants of these acids between the perchlorate media and chloroform and the dimerization constants in chloroform were also determined. The distribution constants of ortho-substituted benzoic acids seem to be larger than those of α-substituted phenylacetic acids with the same substituent. There is a trend that the higher the pKa, the larger the dimerization constant. The order of pKa is : o-aminobenzoic>o-methoxybenzoic>β-hydroxy-β-phenylpropanoic>α-hydroxyphenylacetic(mandelic)>α-methoxyphenylacetic>o-hydroxybenzoic acid and the sequence of the stability constants of their complexes for a given lanthanoid is also in a same order except for the mandelate. Mandelic acid forms more stable complexes with the heavier lanthanoid(III) while others are similar to each other regardless of the lanthanoid.