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, NaBRA, and tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(2-(methylthio)ethyl)resorcin[4]arene, NaSRA) with polluting heavy metals such as Cu, Pb, Cd and Hg 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 NaBRA is able to complex Cu in a 1:1 ratio and Pb in a 1:2 ratio, while NaSRA complexes Hg in a 1:1 ratio. On the contrary, no indications have been observed that either of the resorcin[4]arenes studied complexes the Cd ions. The results suggest that the bonds established between the sulfur atoms located at the lower edge of the SRA and the solvent hydrogens could prevent the entry of the guest into the host cavity. However, in the case of Hg ions, the entry is favoured by the interactions between the sulfur donor atoms present on the lower edge of NaSRA and the Hg ions. Therefore, it can be said that NaBRA is selective for Cu and Pb ions and NaSRA is selective for Hg ions.