Recognition of Heavy Metals by Using Resorcin[4]arenes Soluble in Water

The complexing properties of two water-soluble resorcin[4]arenes (tetrasodium 5,11,17,23-tetrakissulfonatemethylen 2,8,14,20-tetra(butyl)resorcin[4]arene, Na(4)BRA, and tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(2-(methylthio)ethyl)resorcin[4]arene, Na(4)SRA) with polluting heavy metals such as Cu(2+), Pb(2+), Cd(2+) and Hg(2+) were studied by conductivity, and the findings were confirmed by using other techniques to try to apply this knowledge to removing them. The results indicate that Na(4)BRA is able to complex Cu(2+) in a 1:1 ratio and Pb(2+) in a 1:2 ratio, while Na(4)SRA complexes Hg(2+) in a 1:1 ratio. On the contrary, no indications have been observed that either of the resorcin[4]arenes studied complexes the Cd(2+) ions. The results suggest that the bonds established between the sulfur atoms located at the lower edge of the SRA(4−) and the solvent hydrogens could prevent the entry of the guest into the host cavity. However, in the case of Hg(2+) ions, the entry is favoured by the interactions between the sulfur donor atoms present on the lower edge of Na(4)SRA and the Hg(2+) ions. Therefore, it can be said that Na(4)BRA is selective for Cu(2+) and Pb(2+) ions and Na(4)SRA is selective for Hg(2+) ions.