Phosphorus-containing podands 4. Effect of polyether chain length of oligoethylene glycol bis(ortho-diphenylphosphinylmethyl)phenyl ethers on their complex-forming and selective properties with respect to alkali metal cations

Alkylation of o-(diphenylphosphinylmethyl)phenol by oligoethylene glycol ditosylates leads to a series of acyclic polyether complexing agents (podands) with phosphinylmethylphenyl terminal groups. A conductometric method in tetrahydrofuranchloroform (4∶1 by volume) has been used to determine the stability constants of the podands with alkali metal 2,4-dinitrophenoxides. Several of the prepared ligands exhibited a high Li/Na, Na/K, and Li/K selectivity. For lithium and sodium cations, the curve of complex-forming ability against the overall number of donor centers in the structure of the podand has a maximum for the case of tetraethylene glycol bis(o-diphenylphosphinylmethyl)phenyl ether. For lithium cations, this compound surpasses the crown ethers in terms of its effectiveness and is the most powerful of the phosphoryl-containing complexing agents. For potassium, rubidium, and cesium cations, the complex-forming ability increases with increase in the number of oxygen donor centers in the polyether chain of the ligand.