Influence of the structure of organophosphorus substituents on the extraction ability of diphosphorylated crown ethers

Abstract

Extraction properties of lariat crown ethers were studied. Dibenzo-substituted crown ethers of a new class, with electron-donor side phosphoryl groups -P(O)R₂ (R = iso-C₃H₇O, n-C₄H₉O, C₆H₅), were proposed as extracting agents. The oxygen atoms of the phosphoryl groups form additional bonds with metal ions in the extractable complexes. Extraction of 31 metals from 0.01–7 M HNO₃ with five diphosphorylated derivatives of 18-crown-6 and 21-crown-7 was studied. Diphosphorylated endoreceptors were prepared by introduction of organophosphorus fragments into the structure of dibenzo crown ethers. The extraction properties of these compounds depend on the electron-donor properties of the phosphoryl oxygen. If the sum of the reaction constants of the substituents at the phosphorus atom of these groups is −1.77 or more negative, the phosphoryl oxygen is coordinated with the metal of the extracted metal salts and the endoreceptos are effective and selective extracting agents for the following metals (the maximal distribution ratio is given): Tl (1.1) ≈ Rb (1.1) < Bi (5.7) < Re (26) < Mo (36) < Sc (>103). In this case, the extraction ability of diphosphorylated dibenzo crown ether increases by a factor of 10²–10³ as compared to that of the unsubstituted analogs. The resulting compounds can be used as endoreceptors of new generation with unique extraction properties.