Application of ionic liquids (ILs) to the extraction of metal ions in aqueous media represents an effective methodology. ILs enter the aqueous phase to maintain charge balance and enable the extraction of metal ions or charged metal-extractant complexes. However, a general limitation is the transfer of the cations and anions into the aqueous phase with the main effects of generating pollutants and loss of the IL. We found that a valid solution to these issues relies in the development of tailored sulfur-containing ILs, inspired by the applications proposed for extraction and separation of soft metals involving sulfur-containing extractants. Our interest in separation and extraction of heavy metals led us to investigate the ability of specific imidazole-2-thiones in the extraction of Hg2+ from aqueous media. Imidazole-2-thiones can be derived from dialkylimidazolium ILs and have partially zwitterionic character, placing them in between ILs and neutral molecules in terms of ionicity. However, 1,3-dialkylimidazole-2-thiones have other interesting properties including redox activity and low melting points which could make them useful as supported liquid phases for removing Hg(0) vapor from flue gas streams. These molecules may supply sulfur atoms for Hg oxidation and coordination in a liquid state, thereby overcoming the limitations of solid sorbents such as elemental sulfur. We present our group’s recent investigations into two thiones, 1,3-diethylimidazole-2-thione (C2C2ImT) and 1-ethyl-3-methylimidazole-2-thione (C2C1ImT), as components of a supported liquid sorbent for Hg(0). Both compounds can be synthesized by simply reacting their respective imidazolium acetates with elemental sulfur and can be purified through crystallization. Their crystal structures, aqueous solubilities, melting points, and mixtures are discussed and compared. Structurally characterized products of thione reactions are shown and discussed in the context of Hg oxidation. The loading of thiones onto silica and its effect on thermal properties such as melting point and volatility are also investigated.

Imidazole-2-thiones as liquid sorbents of Hg(0): Thermal behavior, redox chemistry, and loading on solid supports

251st National Meeting (2016)

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