Extraction of Anionic Metal Complexes through High Molecular Weight Amines:

In Sec.2.3, we have discussed that one of the best examples of extraction by ion pair formation comes from extraction of anionic metal complexes through high molecular weight amines. That was also pointed out that some phosphonium and arsonium compounds also find extensive use as extractants of this category. As an example, we have already discussed the equilibria involved in the extraction of MnO₄^-   by (C₆H₅)4 As⁺.Cl^-. We now discuss the mechanism of extraction by high molecular weight amines. Those involve primary, secondary and tertiary amines as well as quaternary ammonium salt.

While the organic solution of the amine is equilibrated along with aqueous solution of the acid, the amine is converted to its corresponding salt.

R₃N_o + HCl_a   ↔ R₃NH⁺Cl ^-

While the amine salt is equilibrated with an anion (A^-) , the (Cl^-) will be exchanged.

 R₃NH+Cl^-   + A^-_a ↔ R₃NH+ A_o^-   + Cl^-_a                                                                  

A -  can be a simple anion like NO^-₃ , a complex anion like CrO ^2-₄  or an anionic metal complex such as FeCl^-₄ , CdCl^2- ₄ or ZnCl^2-₄ .