Extraction of Heavy Metal Ions by Alkylated Anthranilic Acids

Abstract

Anthranilic acid is one of the most strong chelating agents. In order to lower the solubility of anthranilic acid in water, an alkyl group was introduced to its benzene ring i. e., 6-alkylated [4] and 5-alkylated anthranilic acid [8] were prepared by the Schmidt rearrangement of corresponding phthalic anhydrides and by the reduction of corresponding nitrobenzoic acids, respectively.5-Alkylated anthranilic acids [8] turned out to be good chelating agents for metal ions such as Cu²⁺, Co²⁺, pb²⁺, Cd²⁺, Ni²⁺ and Hg²⁺, whereas 6alkylated anthranilic acids [4] did not react with any metal ions, probably because of the strongly hydrophobic alkyl chain at the vicinity of the weak hydrophilic β-amino acid moiety as well as the steric hindrance for the chelation.
Cu²⁺ ion was extracted from aqueous solution of pH >2 to heptane solution of chelating agents [8] in 99% yield within 2 h shaking. The insoluble chelate thus formed was easily decomposed by shaking with 12% aqueous HNO₃ and released ca.95% of the metal ion back into acieous phase. Moreover, the chelating agents recovered were reusable,
The extraction of Hg²⁺ ion was carried by using a large excess of compound [8c]. After shaking for 22 h, almost, 98% of Hg²⁺- ion was bound to the agent. Unless it is highly acidic (pH <3), the Hg²⁺ ion release into aqueous phase from the organic phase was almost negligible.