Bis(spirolactam) 1,3-double-armed calix[4]arene compounds and their application as extractants for the determination of heavy metal ions

A number of double-armed calix[4]arene compounds, with proline-derived spirolactam ligating groups on the lower rim, have been synthesised and investigated as extractants of toxic heavy metal ions from aqueous solution. Pedersen's extraction technique was employed to determine the capability of these new 1,3-distal derived calix[4]arene spiroalactams to extract selected heavy metal ions (e.g. Pb²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺) from an aqueous phase into an organic phase. The percentage extraction was calculated using UV-Vis spectroscopy. All of the compounds synthesised demonstrated good selectivity for the heavy metals selected over the alkali metal and alkaline earth metal ions, in particular for Pb²⁺. The level of selectivity observed was dependent on the N-substituent of the spirolactam moiety attached to alternate phenolic oxygens of the narrow calix[4]arene rim. Interestingly, higher sensitivity and lower selectivity was found when the two remaining -OH groups were replaced by -OCH₃ groups.