Mercury transformation route

Transformation in water systems There are two main transformation routes for Hg(II) in water systems. The reduction of Hg(II) to Hg° and, most important, the in-situ bacterial conversion of inorganic mercury species to the much more toxic methylmercury, which concentrates in fish muscle (Gilmour and Henry 1991, Rolfhus and Fitzgerald 1995). 

Methylating bacteria transform a small portion of mercury in alluvium into alkyl mercurials which, because of lipotropy, have a long halftime and increased toxicity in animals. The diverse mercury compounds differ in toxicity according to the species involved and route of entry. Selenium seems to be a biogeochemically important element which counteracts toxicity of naturally occurring mercury. 

Reaction of 6-methoxy-l-tetralone (30) with methylmagnesium iodide gave the dihydronaphthalene (31) in high yield (Scheme 4). However, the transformation of 31 to the tetralone 33, via perbenzoic acid epoxidation followed by acid workup, was capricious and resulted in low yields. A better route was developed, involving hydroboration (hydrogen peroxide oxidation) to the alcohol 32, followed by Pfitzner-Moffatt oxidation to the tetralone 33 in an overall yield of 61%. Other oxidation methods were tried but with varied and poor results. Alkylation of the tetralone 33 with 3-bromopropyne yielded 34, which underwent hydration [mercury (II) acetate in acetic acid-formic acid] to the diketone (35). The enone (36) obtained by base catalyzed cyclization was ster-eospecifically reduced with lithium aluminum hydride to the allylic alcohol... 

This procedure introduced by Ferrier, involving the mercury salt-mediated ring transformation of 6-deoxyhex-5-enopyranosides into deoxyinososes, has provided a route of wide practical utilization in the field of aminocyclitols [42 6] and pseudo-sugar chemistry [47, 48]. This procedure has led to the preparation [49] of the B-A ring system of the antibiotic b-rhodomycin and has extended [50] to thioglycoside analogs of hex-5-enopyranosides (Fig. 8.29). 

Mercury also gives the synthetically useful transformation of R—H to R2 in the Mercat reaction (Eqs. 12.37 and 12.39) the weakest C—H bond in the molecule is selectively cleaved. The product shown in Eq. 14.33 is a useful ligand, but very difficult to make by conventional routes. 

Aspects of the rhodium-catalysed hydroformylation of olefins have been reviewed. " Copper(ii) acetate catalyses the highly stereoselective solvolysis of -alkenylpentafluorosilicates to -alkenyl ethers under an atmosphere of air. Since the pentafluorosilicates can be obtained via hydrosilylation of acetylenes, the sequence represents a regio- and stereo-selective transformation of acetylenes into carbonyl precursors in moderate yield. The reaction of vinylmercurials and mercury carboxylates catalysed by palladium(ii) acetate provides a stereospecific route to enol carboxylates, which are valuable precursors of specific enolates. ... 

The chemical transformation of elemental mercury to methylmercury can be performed by bacteria in water and soil. Elemental mercury and methylmercury are both toxic to the central nervous system. Elemental mercury evaporates, aud the toxic vapor is inhaled. The saying mad as a hatter arose from the occupational exposure of hatters to vapors from liquid mercury, which was used for centuries in the manufacture of felt hats. While mercury vapor is very toxic, the liquid metal itself is less so. It does not dissolve well in water, and its poor solubility tends to limit its access to living systems. Methylmercury, on the other hand, dissolves in water and readily enters the body by all exposure routes from the intestinal tract following ingestion, through the skin, and through the lungs. Because exposure to methylmercury can happen quickly and easily, it is considered to be an extremely hazardous chemical. 

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