Task-Specific Ionic Liquids Incorporating Novel Cations for the Coordination and Extraction of Hg2+ and Cd2+: Synthesis, Characterization, and Extraction Studies

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• 作者：Ann E. Visser ; Richard P. Swatloski ; W. Matthew Reichert ; Rebecca Mayton ; Sean Sheff ; Andrzej Wierzbicki ; James H. Davis ; Jr. ; and Robin D. Rogers
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：June 1, 2002
• 年：2002
• 卷：36
• 期：11
• 页码：2523 - 2529
• 全文大小：108K
• 年卷期：v.36,no.11(June 1, 2002)
• ISSN：1520-5851

文摘

A series of hydrophobic task-specific ionic liquids designedto extract Hg²⁺ and Cd²⁺ from water were prepared byappending urea-, thiourea-, and thioether-substituted alkylgroups to imidazoles and combining the resulting cationicspecies with PF₆^-. The new ionic liquids were characterizedand investigated for their metal ion extraction capabilities.When used in liquid/liquid extraction of Hg²⁺ and Cd²⁺from aqueous solutions, the metal ion distribution ratiosincreased several orders of magnitude, regardless of whetherthe ionic liquids were used as the sole extracting phaseor doped into a series of [1-alkyl-3-methylimidazolium][PF₆](alkyl = n-C₄-C₈) ionic liquids to form a 1:1 solution. Inthe 1:1 mixtures, as the length of the alkyl chain increasedfrom butyl to hexyl to octyl, the metal ion distributionratios increased. Increasing the ratio TSIL/[C₄mim][PF₆]resulted in higher distribution ratios for both Hg²⁺ and Cd²⁺.Overall, the thiourea- and urea-derivatized cationsyielded the highest distribution ratios, and those for Hg²⁺were higher than those for Cd²⁺; however, a change inaqueous-phase pH does not promote the stripping of metalions from the extracting phase. The combination ofthese imidazolium cations and PF₆^- produced ionic liquidswith decreased thermal stability in comparison to [C_nmim][PF₆]. Gaussian98 restricted Hartree-Fock geometryoptimizations for one of the thiourea-appended cationsshows the charge delocalization around the ring and suggeststhat the thiourea group may aid in deprotonating theimidazolium ring and may be responsible for the loweredthermal stability of these cations.