Thermal mercury compounds

Regulations. In order to decrease the amount of anthropogenic release of mercury in the United States, the EPA has limited both use and disposal of mercury. In 1992, the EPA banned land disposal of high mercury content wastes generated from the electrolytic production of chlorine—caustic soda (14), accompanied by a one-year variance owing to a lack of available waste treatment faciUties in the United States. A thermal treatment process meeting EPA standards for these wastes was developed by 1993. The use of mercury and mercury compounds as biocides in agricultural products and paints has also been banned by the EPA. 

Successful thermal decarboxylation of metal arenoates other than poly-halogenoarenoates are restricted to mercury compounds and fall into three categories, namely (i) those where electron-withdrawing substituents other than halogens are present in the organic groups, (ii) those where substituents and/or conditions are used which favor a different mechanism, e.g., classic electrophilic aromatic substitution, or (iii) those where the conditions are sufficiently forcing for both mercuration and decarboxylation to occur. 

S S342 Alkyl mercury compounds 0.01 (TWA) Carbosieve Thermal desorption Flame-. 004-.017 (TWA)... 

Suitable candidates for a-elimination reactions are silylmethyl halides (— base-induced elimination of H-Hal), silylmethyl dihalides (— halide/metal exchange followed by elimination of a metal halide) and stable carbenoid-type compounds such as (a-halo-a-silylalkyl)mercury compounds (— thermal elimination of mercury(II) halide). Bis(phenylthio)(trimethylsilyl)methyl lithium (— elimination of LiSPh) represents a borderline case (see Section III.E.8). 

One of the very important traditional uses for alkyl mercury compounds has been their use as reagents in preparations of more reactive organometallic compounds. The trifluoromethyl mercurial is also beginning to demonstrate a similar utility as a precursor, for example, in the synthesis of the more reactive reagent (CF3)2Cd glyme. The latter material is clearly a superior agent for the formation of products of only limited thermal stability, since it is active at ambient temperatures and the reactions generally require only a few minutes, or at most a few hours. 

The thermal decomposition of phenyl(trihalomethyl)-mercury compounds, C6H5.Hg.CX3, in the presence of olefins yields the dihalo-cyclopropane virtually quantitatively. A typical example is expressed in equation (15). The initial rate of disappearance of the organometallic... 

Both cadmium and mercury compounds M[SnR3]2 (R = Me, Et, Pr, f-Bu, Ph) are oxidized by air to the related stannoxanes and MO (M = Cd) or M (M = Hg)239,241. Peroxides, e.g. Bz202, also perform similar oxidations to form M(OBz)2(M = Cd) and BzOSnR3365. Even the thermally stable complexes with bulky ligands (R = Me3SiCH2) are also oxidized333. 

Depending on the mode of generation, a carbene may be initially formed in either the singlet or triplet state, irrespective of its stability. Common methods used for the generation of carbenes include photolytic, thermal, or metal catalyzed decomposition of diazocompounds, elimination of halogenfrom gem-dihalides, elimination of Hx from CHX3, decomposition of ketenes, thermolysis of a-halo-mercury compounds and cycloelimination of shelf stable substrates such as cyclopropanes, epoxides, aziridines and diazirines. 

DOT CLASSIFICATION 6.1 Label Poison SAFETY PROFILE A poison by ingestion and intraperitoneal routes. Moderately toxic by skin contact. Thermally unstable and decomposition may be vigorous. When heated to decomposition it emits very toxic fumes of Hg, NOx, SOx, and CN". See also MERCURY COMPOUNDS and CYANATES. 

The thermal decomposition of equimolar amounts of bis[dichloro(or dibromo)trimethylsilyl-methyljmercury and diphenylmercury, carried out in the presence of an excess of alkene in chloro- or bromobenzene, gave l-chloro-" (or l-bromo )-l-trimethylsilylcyclopropanes 1, in poor to good yield. Diphenylmercury is used to effect the utilization of both dihalot-rimethylsilylmethyl groups present in the starting mercury compounds. 

To be detectable, mercury must be present in elemental form. Thus for gaseous samples a thermal conditioner unit converts, in the presence of a catalyst, all mercury species present in the sample into elemental form. For liquid samples as polluted water, a first treatment by an acidic oxidizing mixture exchanges mercury compounds into Hg(II) ions that are then reduced to elemental mercury with a tin salt. 

At irradiation with thermal neutrons, stable isotopes of mercury and many other elements are converted into radioactive daughter isotopes, that can be identified and quantified by high resolution gamma spectrometry. The irradiation is usually carried out in a nuclear reactor with thermal neutron flux densities of lO -IO cm s NAA is well established as a multi-element technique, and has a reputation of good accuracy. Separation and specification of mercury compounds is, however, not possible, since organic mercury turns into inorganic at irradiation (Rottsohafer et al., 1971). 

Ethylated mercury species are volatile and can therefore be purged from solution at room temperature and then collected on adsorbent materials such as Carbotrap or Tenax. After thermal release, individual mercury compounds are separated by cryogenic or isothermal GC. As the species are eluted they are thermally decomposed (pyrolized) at 900°C and measured as Hg° using a CV-AFS detector, which achieves very low detection limits (< 10 g). A CV-... 

In the period when pneumatic chemistry was gaining ground, the French chemist P. Bayen wrote a paper (1774) in which he discussed the causes for an increase in the mass of metals during calcination. He believed that a peculiar variety of air—an expansible fluid, heavier than ordinary air—was added to a metal in the process of calcination. Bayen obtained this fluid by thermal decomposition of mercury compounds. And, conversely, acting on metallic mercury, the fluid transformed it into a red compound. 

Table tr.1-175 Linear thermal expansion coefficient a of mercury compounds ... 

By combining the cold-vapor technique with HPLC, a very sensitive method for the determination of Hg spedes at the sub-ng level becomes possible [322]. When applying cold-vapor AAS to the detection of mercury subsequent to the separation of the species by HPLC, which also enables thermally labile compounds to be separated, the organomercury compounds have to be destroyed to allow for the AAS determination. They can be destroyed by wet chemical oxidation with H2S04-Ct207 or by photochemical oxidation. It is then possible to perform spe-ciation of mercury in gas condensates easily, where the species can be separated by reversed phase HPLC [323]. 

The oxymercuration of 1-substituted (i,e, H, Me, and C02Me) tricyclo[4,l,0,0 ]-heptanes with mercuric acetate affords norcaranyi- and norpinyl-mercury compounds. A synthesis of 3,4-benzotricyclo[4,l,0,0 ]heptene (692) has been reported in which the usual cyclopropylcarbene C—H insertion process is employed. Isomerization of (692) with silver perchlorate gave benzocycloheptatriene which is also formed in the thermal isomerization of (692). Reaction of (692) with n-ally 1 palladium(ii) chloride dimer yielded 2-methylene-l T-naphthalene which rearranged readily to 2-methylnaphthalene at room temperature a carbenoid mechanism appears to be involved. 

Mercury compounds of all varieties when heated to dull red heat leave no residue or this contains no mercury. This behavior, which is unique among metal compounds, is due to the sublimation of mercury salts and to thermal decomposition with production of mercury vapor. The latter can be detected by the sensitive test with palladium chloride in which the reaction PdCla + HgO Pdo -f- HgCl ... 

When organic mercury compounds are heated, mercury vapor is formed mostly through thermal dissociation. To detect this mercury vapor by means... 

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