Univalent Mercury

Yang and Zhu [107] have studied, applying several electrochemical methods and mercury electrodes, electrochemical behavior of pharmaceutically important dipeptide captopril. In acidic solution, one-electron transfer led to the formation of a univalent mercury-sulfur compound, which was strongly adsorbed at the electrode surface and gradually transformed into the divalent mercury-sulfur compound. 

The relative density of potassium vapour at 1040° (H unity) is between 40 and 45 very nearly corresponding with monoatomic molecules.59 The vapour densities of the alkali metals are somewhat inaccurate because they attack the containing vessels. The value for sodium, between 15 1 and 25 8, also agrees with a monatomic mol. W. Ramsay s experiments on the effect of potassium on the f.p. of mercury show that the alkali metals are possibly univalent in mercurial soln. C. T. Heycock obtained similar results from the effects of lithium, and potassium on the f.p. of sodium and of sodium on the f.p. of cadmium, tin, lead, and bismuth. 

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) . 

In contrast to the tertiary amines, trialkylphosphines have strong donor properties and form exceedingly stable coordination complexes with a wide variety of metal salts such as those of univalent copper and gold, and bivalent platinum, palladium, and mercury.1 Like phosphine itself, many of these tertiary alkylphosphines are highly flammable, toxic, and extremely susceptible to air oxidation. Ease of oxidation first decreases and then increases as the alkyl group becomes larger.2 3,4 5 The n-butyl compound is thus a convenient member of this group for preparation. 

Apart from antimony, there are other good promoters of the direct synthesis of methylchlorosilanes, which increase the yield of dimethyldichlorosilane, such as arsenic and zinc chloride. If it is necessary to increase the yield of alkylhydridechlorosilanes, one should use univalent copper chloride, cobalt, and titanium. The addition of tin or lead into contact mass increases the yield of dimethyldichlorosilane up to 70% the yield of ethyldi-chlorosilane is increased to 50-80% when contact mass receives 0.5-2% of calcium silicide (Ca2Si). In the synthesis of phenylchlorosilanes effective promoters are zinc, cadmium, mercury or their compounds. In particular, the introduction of zinc oxide (up to 4%) into contact mass may increase the diphenyldichlorosilane content up to 50%, and the introduction of a mixture of zinc oxide and cadmium chloride, even up to 80%. 

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. 

A similar consideration can be applied to the cathodic processes. In a solution of mercuric nitrate bivalent mercury will bo reduced to univalent until the ratio of the respective activity of the mercurous salt formed and tho mercuric salt still remaining reaches the equilibrium value. During the course of further reaction the ratio of activities of both ions in the solution will not change any longer, and metallic mercury will be deposited. Therefrom, it is evident that mercuric nitrate cannot be quantitatively reduced to mercurous salt. Bivalent mercury can be reduced practically completely to univalent in the case of mercuric chloride. As the solubility of the mercurous chloride formed by the reduction and consequently also the concentration of Hg2+ ion is very small the equilibrium between the ions in the solution will be attained only then, when nearly all Hg++ ions will be reduced to univalent ones. On the other hand on reduction of the very slightly dissociated cyanide complex Hg(CN) the equilibrium between mercurous and mercuric ions is reached at the very beginning of electrolysis as soon as a hardly noticeable amount of Hg++ ions has been formed from that moment on metallic mercury will be deposited at the cathode with practically 100 p. o. yield. 

Removal of more than two electrons from the metal atoms practically never occurs, and the +2 oxidation state thus prevails. Although the + 1 oxidation state of mercury (Kg ) is also important, evidence for the existence of univalent zinc or cadmium is not completely convincing. 

The mercurous ion is the only common ionic species having a metal-to-fnetal bond. There are a number of ways of demonstrating that univalent mercury is indeed dimeric the presence of mercury-to-mercury bonds has been revealed by x-ray studies of crystalline mercury(I) chloride and also by spectral studies of aqueous mercury(I) nitrate, whereas magnetic studies of solutions containing univalent mercury show none of the paramagnetism that would be expected if such solutions were to contain Hg+ ions (with an odd number of electrons per ion). Aside from this evidence, a number of studies of equilibrium relations in systems containing the mercurous ion show that the ion is Hg Hg2+ rather than Hg+ (Exercise 5). 

There are important differences between the behaviors of uni- and dipositive mercury in solution. Perhaps the most striking is the very feeble complexing ability of the mercurous ion. Only a handful of com-plexing agents (among them pyrophosphate, succinate, and oxalate) appear to form complexes with univalent mercury. Hg(I) is unstable in basic solutions, in ammoniacal solutions, and in the presence of sulfide or cyanide ions. It decomposes under such conditions to elemental mer-... 

In a solution containing an ionized mercurous salt in equilibrium with mercury metal, the fraction of dissolved mercury in the +2 state is independent of the concentration of univalent mercury. Show that this indicates that the mercurous ion is Hg + and not Hg+. 

The most striking evidence that univalent mercury ion in solution is Hg2+, rather than Hg4, is the diamagnetism of such solutions. Monomeric univalent mercury should have one unpaired electron per ion. 

Argention.—Silver forms a colourless, univalent ion. Its electrochemical equivalent in milligrams per coulomb is given as 1-1172,10 1-1180,11 1-11827,12 1-11829,18 1-1188,14 and 1-1198.18 In the potential series the metal occupies a position intermediate between mercury and platinum. In correspondence with its low electroaffinity it exhibits a strong tendency to form complex ions. The ionic conductivity of silver at 18° C. is 54-0, and at 25° C. 63-4. 

The induced reduction of lead through the reduction of bismuth is due probably to the fact that the reduction Bi —> Bi does not proceed directly. Lower unstable oxides, perhaps BigO, are formed as intermediates Bini By -> Bi . The univalent bismuth may react with the lead Pb i + By Bi + Pb . Thus Bi is regenerated and is again rapidly reduced by stannite to By, which again can act on Pb i, and so on. This assumption is supported by the fact that the bismuth reduction is capable of inducing other reductions accomplished with stannite. The catalytic acceleration of the lead-stannite reaction by bismuth thus makes possible its sensitive detection in the absence of noble metals, copper, and mercury. The interference of the last two may be prevented as described below. 

Lead can be identified easily in the ordinary qualitative scheme, where its chloride may be present along with the chlorides of silver, univalent mercury, and thallium. The mixed chlorides are transferred to a crucible, dried and then carefully heated to redness. Thallous and mercurous chloride volatilize. The cold residue is digested with 4 drops of strong ammonia water to dissolve any silver chloride. The contents of the crucible are then evaporated to dryness. Three drops of the buffer solution and one drop of sodium rhodizonate are added. If the original precipitate contained lead, a red precipitate or coloration will appear. It is necessary to dissolve the silver chloride because it melts and encloses lead chloride, which may thus be shielded from the action of the sodium rhodizonate. 

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