Methylmercurie halides

Jensen and Jernelou [52] reported that both mono and dimethylmercury (CH3Hg+ and (CH3)2Hg) can be produced in lake sediments. The gases evolved from incubated sediment samples were analysed for monomethyl mercury by conversion to methylmercury halide by means of gas chromatography, using electron capture and mass spectrometric detection. 

An instructive example is the behavior of methylmercury halides, CHgHgX. Thermochemical calculations (Table VIII) reveal that heterolytic dissociation energies for the reaction... 

Obviously soft acid behavior of methylmercury halides is not an inherent property of the CHgHg ion but actually a function of the solvating properties of the solvent toward the anionic ligands this suggests a more critical interpretation of the basic principles of the Hard and Soft Acids and Bases (HASAB) concept (50). 

Autschbach and co-workers have presented a method for a subsystem-based calculation of indirect nuclear spin-spin coupling tensors. This approach was based on the frozen-density embedding scheme within density-functional theory and was an extension of a previously reported subsystem-based approach for the calculation of nuclear magnetic resonance shielding tensors. The method was particularly useful for the inclusion of environmental effects in the calculation of nuclear spin-spin coupling constants. According to this method, the computationally expensive response calculation had to be performed only for the subsystem of interest. As an example, the authors have demonstrated the results for methylmercury halides which exhibited an exceptionally large shift of the V(Hg,C) upon coordination of dimethylsulfoxide solvent molecules. 

NMR studies in dilute organic solutions indicate that the methylmercuric halides exist in preponderant amounts in equilibrium mixtures with di-methylmercury and mercuric halides (238). The equilibrium constant,... 

Human activities have resulted in the release of a wide variety of both inorganic and organic forms of mercury. The electrical industry, chloro-alkali industry, and the burning of fossil fuels (coal, petroleum, etc.) release elemental mercury into the atmosphere. Metallic mercury has also been released directly to fresh water by chloro-alkali plants, and both phenylmer-cuiy and methylmercury compounds have been released into fresh and sea water -phenylmercury by the wood paper-pulp industry, particularly in Sweden, and methyl-mercury by chemical manufacturers in Japan. Important mercury compounds which also may be released into the environment include mercury(II) oxide, mercury(II) sulfide (cinnabar), mercury chlorides, mer-cury(II) bromide, mercury(II) iodine, mer-cury(II) cyanide, mercury(II) thiocyanate, mercury(II) acetate, mercury nitrates, mercury sulfates, mercury(II) amidochloride monoalkyl- and monoarylmercury(II) halides, borates and nitrates dialkylmercury compounds like dimethylmercury, alkoxyal-kylmercury compounds or diphenylmercury (Simon and Wiihl-Couturier 2002) (for quantities involved, see Section 17.4). 

Detectors Various detectors can be used in combination with GC for the determination of mercury species. An ECD is a sensitive detector with an absolute detection limit of a few picograms. It does not, however, measure mercury directly, but responds to the halide ion attached to the CH3Hg ion. The identification of small methylmercury peaks can sometimes be subject to a positive systematic error owing to coeluting contaminants. The use of a plasma atomic emission detector, a mass spectromet-ric detector, CV-AAS, CV-AFS, or ICP-MS can avoid such problems, since mercury is measured directly. 

IsotopicaUy labelled MeHg was used to investigate artefact formation in water samples during derivatisation with NaBEt4. Halide ions were found to induce different transformation processes. While chloride and bromide converted MeHg into Hg , iodide hindered the ethylation of methylmercury. The effect was shown to occur only during the derivatisation step, and in contrast to ethylation, propylation with NaBPr4 did not cause any transformation. 

---