Thioethers heavy metals

AgN03, EtOH, Pyr, 90°, 1.5 h H2S, 47% yield. An 5-triphenylmethyl thioether can be selectively cleaved in the presence of an 5-diphenylmethyl thioether by acidic hydrolysis or by heavy-metal ions. As a result of the structure of the substrate, the relative yields of cleavage by AgN03 and Hg(OAc)2 can be reversed. 

Replacement of ethers by thioethers in crown compounds [see, for example (178)] also reduces their affinity for the alkali metals and again leads to a tendency to complex heavy metals such as Ag(i) more strongly (Pedersen, 1971 Frensdorff, 1971). 

Botta and coworkers recently developed an Oxone cleavage methodology for the solid-phase synthesis of substituted uracUs (equation 57) . Whereas some common methods of thioether cleavage, such as reduction with Na/NHs, acid catalyzed hydrolysis, heavy metal ions followed by treatment with hydrogen sulfide and iodofrimethylsilane proved to be unsuccessful for this reduction, Oxone was shown to be an efficient and selective reagent for cleavage of polymer bound thiouracUs. 

The interaction of amine-modified silica with Cu2+ ion is the most documented.23,24,25 However, the retention of other transition metals as well as precious metals with dedicated modification layers has also been reported. The separation of Pd and Pt from base metals, Ir(III) and Rh(III) was effectuated by using silica-bound thioether sulfur and primary amine groups.26 A review on polymeric as well as modified silica supports for separation and preconcentration of trace metals is presented by Kantipuly.27 This metal immobilization also allows other applications such as metalion chromatography28 and heavy metal catalysis.29... 

To improve the solubility of metal ion, the commonly used method is including a metal ion-ligating functional group in structure of one of the ions named task-specific ionic liquids, which play dual role as hydrophobic solvent and as extractant. Visser et al. [191,192] presented new thiourea, urea, and thioether derivatives of ILs designed to extract heavy metal ions (e.g., Hg + and Cd ), and the same methods have been used to the extraction and separation of rare earth metals by Chen et al. [210,211]. 

Crown thioethers have found a number of uses as ligands, related particularly to their affinity for late- and post-transition elements. Attention has focused on the coordination chemistry of silver, with relevance to photography, silver-selective electrodes, and ligands for chromogenic analysis and recovery of silver. Biomedical applications include the removal of toxic heavy metals such as Cd, Hg, Pb, and T1 and delivery of radioisotopes such as ""Tc, Re, and Re to specific sites in the body. Finally, some crown thioethers have been found to promote novel reactivity in their transition metal complexes, including activation of small molecules such as N2, CO and C2H4. 

The interest in functionalized ionic liquids is growing because ionic liquids bearing ether, amino or alcohol functionalities have been shown to display special properties, including the ability to dissolve a larger amoimt of metal halide salts and to extract heavy metal ions from aqueous solutions. Imidazolium-based ionic liquids with ether and hydroxyl (see Section 2.2.1), thiourea, thioether and urea (see Section 2.2.8) " have been prepared following the standard quatemization procedure. A straightforward approach has been described for the preparation of imidazolium (as well as pyridinium) cations with ester, ketone or cyanide functionalities 1-methylimidazole reacts with methanesulfonic acid to provide the imidazolium salt 11, which undergoes a Michael-type reaction with methyl vinyl ketone as a ,j8-unsaturated compound to produce the ionic liquid 12 (Scheme 5). ... 

The affinity of crown thioethers for heavy metals - and their antipathy to the biologically important ions, such as Na, Ca, and Mg -suits crown thioethers particularly well for decorporation of toxic metal ions. Similarly, crown thioethers may find potential use in the hydrometallurgical winning of precious metals such as silver, gold, and platinum, or as the basis for ion-selective electrodes [219]. Other potential applications [220] may arise from use of crown thioethers as structural building blocks or capping members (e.g. (M(9S3) ) for synthesis of metal cluster compounds. 

Cooper SL (2001) Optical Spectroscopic Studies of Metal-Insulator Transitions in Perovskite-Related Oxides. 98 161-220 Cooper SR, Rawle SC (1990) Crown Thioether Chemistry. 72 1-72 Corbett JD (1997) Diverse Naked Clusters of the Heavy Main-Group Elements. Electronic Regularities and Analogies. 87 157-194 Corbin PS, see Zimmerman SC (2000) 96 63-94... 

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