Mercury/ions/salts

A. Mercury(II) chloranilate method Discussion. The mercury(II) salt of chloranilic acid (2,5-dichloro-3,6-dihydroxy-p-benzoquinone) may be used for the determination of small amounts of chloride ion. The reaction is ... 

The first product of the oxidation of alcohol is acetaldehyde and an important end-product is fulminic add, which latter can, however, only be isolated if silver or mercury ions are present. With these ions it forms salts—fulminates—which are stable towards nitric add in them, it must be presumed, the linkage with the metal is homopolar and non-ionogenic, as in mercuric cyanide. The formation of fulminic acid takes place because the carbonyl group of the aldehyde confers reactivity on the adjacent methyl group which then forms a point of attack for the nitrous acid. The various stages in the process are indicated by the following formulae ... 

The mercury ion is capable of causing local or systemic toxicity. For local irritation, they are combined with theophylline in an attempt to diminish the irritative toxicity at the site of injection. IV administration may lead to ventricular arrhythmias. They cause hepatocellular damage and even precipitate hepatic failure. They can also lead to low salt syndrome, hypochloraemic alkalosis and potassium depletion. 

The above reactions in this section have been examples of addition alone or addition followed by elimination. Ligand reactions involving nucleophilic substitution are also known and these are of the dealkylation type. Lewis acids such as aluminum chloride or tin(IV) chloride have been used for many years in the selective demethylation of aromatic methyl ethers, where chelation is involved (Scheme 27). Similar cleavage of thioethers, specially using mercury(II) salts, is commonly used to remove thioacetal functions masking ketones (equation 27).104 In some cases, reactions of metal ions with thioether ligands result in isolation of complexes of the dealkylated organic moiety (equations 28 and 29).105-107... 

The apparent anomaly between mercury and the lighter elements of transition group 2. in that mercury regularly forms both univalent and divalent compounds, while zinc and cadmium do so very rarely, is partly under mm id from the observation that mercury III salts ionize even in the gaseous late to Hg.. rather than Hg Evidence for this double ion is provided by its Hainan spectral line, by the lineal CI-Hg-Hg-CI units in crystals or mercury It chloride, and by the cml of incrciirytll nitrate concentration cells The anomaly is fuitlicr removed by the obsetv.ttioii that cadmium also forms a (much less stable) diatomic ton Cdj T eg., ill Cd.-lAICL) . 

The use of soft metal ions to direct the course of reactions of sulfur compounds has been utilised in the preparation of nitriles from thioamides. The first step involves the alkylation of the thioamide to give the iminothioester, which is then converted to the nitrile on treatment with mercury(n) salts (Fig. 4-41). 

Mercury(II) salts add to C=C double bonds (Figure 3.48) in nucleophilic solvents via the the onium mechanism of Figure 3.42. However, the heterocyclic primary product is not called an onium, but rather a mercurinium ion. Its ring opening in an H20-containing solvent gives a... 

In anodic dissolution of mercury in a solution of nitric acid, where both mercurous and mercuric salts are asumed to be completely dissociated, both the formed ions enter the solution in the ratio of their respective activities hKo+/ h1 ++ = 76. When alkali cyanide is used as electrolyte the bivalent ions formed on dissolution are predominantly consumed for the formation of the complex Hg(CN). As a result of the formation of this complex the concentration of free Hg++ jpns decreases considerably in accordance with the neghgible degree of dissociation of the above-mentioned complex, and consequently the dissolution potential of the system Hg/Hgt+ also decreases. For this reason, mercuric ions converted to mercuricyanide complex can be considered to be practically the sole product of the anodic process while the amount of univalent mercury ions is quite negligible. Contrary to this, on dissolving mercury in a solution of hydrochloric acid mercurous ions are predominantly formed due to the slight dissociation of mercurous chloride, the main product of the reaction. 

Mercury salts have a number of important uses in industry and in chemical analysis. Because mercury compounds are poisonous, however, the mercury ions must be removed from the waste water. Suppose that 25.00 mL of 0.085 mol/L aqueous sodium sulfide is added to 56.5 mL of 0.10 mol/L mercury(II) nitrate. What mass of mercury(II) sulfide, HgS(s), precipitates ... 

Manganese ions interfere (oxidized to permanganate) as do also mercury(II) salts, molybdates, and vanadates, which give blue to violet compounds with the reagent in acid solution. The influence of molybdates can be eliminated by the addition of saturated oxalic acid solution thereby forming the complex H2[Mo03(C204)]. 

If the solution contains chloride ions, it is evident that no silver or mercury(I) salt is present. When lead is present, the solution may be clear while hot, but PbCl2 is deposited upon cooling the solution, due to the slight solubility of the salt in cold water. Lead may be found in Group II, even if it is not precipitated in Group I. 

A detailed procedure for the synthesis of a free imBT ligand by the slow addition of aqueous glyoxal to tren solution in iso-propanol is described in Ref. 200. The free ligand obtained readily reacted with lanthanum and gadolinium (III) ions in an acetonitrile-chloroform mixture [201] and with lead, cadmium, and mercury(II) salts in acetonitrile-ethanol medium [202]. 

Zinc and cadmium form simple bipositive cations only. Mercury displays in addition the cation Hg + in mercury(I) salts. The evidence for the form of this ion is ... 

The Hg + ion involves an electron-pair bond. This type of metal-metal bonding is rare, but probably occurs in [W2Cl9] and in [Ni2(CN)J . The Hg + ion is but little more stable than the Hg + ion hence the reduction of a mercury (II) salt normally yields the metal. 

At very negative potentials neither the tetraalkylammonium ions nor the metallic electrode are inert they combine to form reduced TAA-metals [7]. Tetraalkylammonium (TAA) metals are composed of quaternary ammonium ions, electrons, and a post-transistion metal such as Hg, Pb, Sn, Sb, Bi [5-18] or Pt [19] most of them have the composition R4N" MeJ [13] or R4N" Mc4 [20] and have been described as Zintl ion salts or Zintl phases [21,22]. They have been shown to be useful intermediates in the electrochemical reduction of certain substrates that are reducible with difficulty. On reduction of the quaternary ammonium salt, the initial layer of the metal compound is controlled by a two-dimensional nucleation, whereas the bulk phase is initiated by a three-dimensional nucleation and a growth controlled by the diffusion of R4N from the solution. In some cases (A-methylquinuclidinium (MQ" ) mercury) the catalytic efficiency of the initial layer is greater than that of the bulk phase [18], whereas in other cases (A, A-dimethylpyrrolidinium (DMP" ) lead) the opposite is found [16]. 

Many other variations of the stripping technique have been developed. For example, a number of cations have been determined by electrodeposition on a platinum cathode. The quantity of electricity required to remove the deposit is then measured coulometrically. Here again, the method is particularly advantageous for trace analyses. Cathodic stripping methods for the halides have also been developed in which the halide ions are first deposited as mercury(I) salts on a mercury anode. Stripping is then performed by a cathodic current. 

Precautions have always been practiced to contain the mercury (Table 8.3) of the operating mercury cells, primarily for the value of the metal itself. The steel flasks of the metal are also covered with a layer of water to reduce mercury vapor loss during shipping and storage. However, in 1970, it was demonstrated that mercury ions and the free metal could be converted by natural processes to the far more toxic forms of mercury, methylmercury salts and dimethyl mercury even under water [23, 24]. Industrialists, toxicologists, and legislators alike were alarmed by this discovery, which led to the rapid installation of control measures to drastically reduce mercury loss rates in Europe, Japan, and North America [25] (Table 8.4). 

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