Reduction with Mercury

A bulk reduction of Cjq in solution is also possible with less electropositive metals. This was demonstrated by the reduction of Cjq with mercury, leading to Cjq or 55 [141]. The addition of a drop of mercury to a 1 mM solution of tetra- 

The reaction behavior of towards the Hg2X2/Hg couple strongly depends on the solvent. In a solution of 1 mM (THA)I in benzonitrile, for example, no reaction was observed. This is because the formal potential of the Hg2l2/Hg couple imder these conditions is not sufficiently negative to allow the reduction of Cgg. An increase of the (THA)I concentration to 0.1 M, however, leads to the reduction of Cgg to the monoanion and only traces (0.3%) of the dianion. 

This early success in forming CT-salts with interesting properties led to the preparation of various donor-Cgg complexes ]1,26,150]. Amongst others, complexes withtetrathiafulvalene-derivatives (TTE) [150-153], tetraphenylporphyrin-derivatives (TPP) [143,150,154,155] or metallocenes [74,102,149,156-160] were crystallized 

A metal-free reductant that is strong enough to produce the Cgg -anion was found with the crystal violet radical 7 [161,162] 7 is a non-dimerizing, persistent radical that can be readily prepared by treatment of crystal violet iodide with zinc. It does not, as expected for a radical, add to Cgg but reduces it to give Cgg as the brovm 

Similarly, treatment of [Cr (TPP) ]C5Q in toluene reverses the redox reaction [143]. The addition of a few drops oftetrahydrofuran to the toluene solution promotes the electron transfer again. This is consistent with the lower first reduction potential of CgQ reported in tetrahydrofuran compared with other solvents [10]. 

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ISO 11489 1995 Determination of platinum in platinum jewelry alloys - gravimetric determination by reduction with mercury(l)... 

Other volatile compounds of elements can be used to transport samples into the plasma flame. For example, hydride reduction of mercury compounds gives the element (Hg), which is very volatile. Osmium can be oxidized to its volatile tetroxide (OSO4), and some elements can be measured as their volatile acetylacetonate (acac) derivatives, as with Zn(acac)2. 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

Electrolytic reduction with a mercury or platinum electrode produces equimolar amounts of sulfide and sulfite ... 

Finally, secondary arsines can be obtained by the reductive cleavage of diarsines with mercury and hydrogen iodide (49) or with hthium aluminum hydride... 

Dithiols, like diols, have been protected as 5,5 -methylene, 5,5 -isopropylidene, and 5,5 -benzylidene derivatives, formed by reaction of the dithiol with formaldehyde, acetone, or benzaldehyde, respectively. The methylene and benzylidene derivatives are cleaved by reduction with sodium/ammonia. The isopropylidene and benzylidene derivatives are cleaved by mercury(II) chloride with sodium/ ammonia the isopropylidene derivative is converted to a monothio ether, HSCHR-CHRSCHMe2- ... 

To determine the purity of a sample of a mercury(II) salt, the following procedure in which the compound is reduced with phosphorous (phosphonic) acid may be used to assay a sample of a mercury(I) salt, the reduction with phosphorous acid is omitted. 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Monoalkylthallium(III) compounds can be prepared easily and rapidly by treatment of olefins with thallium(III) salts, i.e., oxythallation (66). In marked contrast to the analogous oxymercuration reaction (66), however, where treatment of olefins with mercury(II) salts results in formation of stable organomercurials, the monoalkylthallium(III) derivatives obtained from oxythallation are in the vast majority of cases spontaneously unstable, and cannot be isolated under the reaction conditions employed. Oxythallation adducts have been isolated on a number of occasions (61, 71,104,128), but the predominant reaction pathway which has been observed in oxythallation reactions is initial formation of an alkylthallium(III) derivative and subsequent rapid decomposition of this intermediate to give products derived by oxidation of the organic substrate and simultaneous reduction of the thallium from thallium(III) to thallium(I). The ease and rapidity with which these reactions occur have stimulated interest not only in the preparation and properties of monoalkylthallium(III) derivatives, but in the mechanism and stereochemistry of oxythallation, and in the development of specific synthetic organic transformations based on oxidation of unsaturated systems by thallium(III) salts. 

Since the rate does not display an inverse dependence on Hg(II) concentration, the oxidation of Hg atoms, in equilibrium with mercury(l) and mercury(II), can be discounted, although Hg atoms are kinetically important in the reduction of thallium(IIl) by mercury(I) . It seems likely that the acid-dependent path (A ) involves CoOH. Anion effects were not investigated. 

Following this preparation of 39 it is subjected to oxymercuration with mercury acetate and sodium chloride to give 4,8-bischloromercury-substi-tuted 2-oxaadamantane (107). Subsequent reduction with sodium borohy-dride yields 104.134,136... 

Following reduction of mercury with stannous chloride the mercury vapour is flushed from the system. 

A method described by Florence and Farrer [584] separated tin from its associated lead by distillation from an aqueous sulfuric acid medium into which the vapour from boiling 50% hydrobromic acid is passed. The distillate provides an ideal supporting electrolyte for the determination of tin (II) (produced by reduction with hydrazinium hydroxide) by anodic stripping at a rotating vitreous-carbon electrode in the presence of codeposited mercury [585,586]. The tin is deposited at -0.70 V versus the SCE for 5 minutes, and then stripped at -0.50 V during a sweep from -0.70 V to -0.45 V at 5 V per minute. Tin in seawater is coprecipitated on ferric hydroxide, and the precipitate is then dissolved in the aqueous sulfuric acid, and subjected to the above procedure. The average content for Pacific coastal waters was found to be 0.58 xg/l. 

Reductions are also discussed under the section on analysis. The reduction on Hg has been extensively studied in connection with analytical applications (see Section VI), and is complicated by adsorption, transmetallation with mercury and reoxidations of transient products. Some disagreement as to the details is apparent in the primary literature76. Comparisons between different experimental settings should be made with critical appraisal. 

Polarography of Ph3PbAc, 1.084 x 10 4 M in the same electrolyte solution gave, at pH 7.0, E /2 values of —0.425 and —1.075 V (SCE) which, too, show cathodic shifts with increasing pH. Unlike Bu2PbAc2, Ph3PbAc undergoes a SET reduction to radicals, which adsorb on the DME and react with mercury ... 

A half-life of about 40 days was reported for hexachloroethane in an unconfined sand aquifer (Criddle et al. 1986). Laboratory studies with wastewater microflora cultures and aquifer material provided evidence for microbial reduction of hexachloroethane to tetrachloroethylene under aerobic conditions in this aquifer system (Criddle et al. 1986). In anaerobic groundwater, hexachloroethane reduction to pentachloroethane and tetrachloroethylene was found to occur only when the water was not poisoned with mercury chloride (Roberts et al. 1994). Pentachloroethane reduction to tetrachloroethylene occurred at a similar rate in both poisoned and unpoisoned water. From these results, Roberts et al. (1994) suggested that the reduction of hexachloroethane to tetrachloroethylene occurred via pentachloroethane. The first step, the production of pentachloroethane, was microbially mediated, while the production of tetrachloroethylene from pentachloroethane was an abiotic process. 

Reduction potentials also depend greatly on the nature of the cathode material as shown in Table 2 [8], For example, primary perfluoroalkyl iodides are ca. 0.3 V easier to reduce at mercury than at platinum due to the strong interaction of Rfl with mercury. In fact, cathodic reduction of Rfl at a mercury cathode provides RfHgl [9]. 

Earlier work on the determination of total mercury in river sediments also include that of Iskander et al. [41], Iskander applied flameless atomic absorption to a sulphuric acid nitric acid digest of the sample following reduction with potassium permanganate, potassium persulphate and stannous chloride. A detection limit of one part in 109 is claimed for this somewhat laborious method. 

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