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.