Diglycolamide derivatives for separation and recovery of rare earth elements from aqueous solutions

A liquid solution useful for extracting rare earth elements from aqueous solutions, the solution comprising a rare earth extractant compound dissolved in an aqueous-insoluble hydrophobic solvent, wherein the rare earth extractant compound has the following structure:

• wherein:
• R1, R2, R3, and R4 are independently selected from alkyl groups containing 1-30 carbon atoms and optionally containing an ether or thioether linkage connecting between carbon atoms, provided that the total carbon atoms in R1, R2, R3, and R4 is at least 12;
• and R5 and R6 are independently selected from hydrogen atom and alkyl groups containing 1-3 carbon atoms;
• and provided that of the following condition applies:
• at least one of R1, R2, R3, and R4 is a distal branched alkyl group constructed of a linear alkyl backbone having at least four carbon atoms with an alpha carbon atom of the linear alkyl backbone attached to a nitrogen atom shown in Formula (1), and the linear alkyl backbone contains a substituting hydrocarbon group at a gamma carbon or higher positioned carbon on the linear alkyl backbone, wherein the substituting hydrocarbon group contains at least two carbon atoms, provided that the distal branched alkyl group contains a total of up to 30 carbon atoms.