MERCURY.138 SELENIUM DIOXIDE

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. ... 

Oxidation of the sulfur- or selenium-bridged azepines (171 X=S or Se) with mercury(II) oxide in methanol yields ultimately the 4f/-azepine (68JCS(C)23ll) with hydrogen peroxide as oxidant, the sulfur compound furnishes the sulfoxide (171 X=SO). Selenium dioxide oxidation of 7,8-dimethyl-lf/-l-benzazepin-2-one affords the 2,3-dioxo derivative (173) that displays no evidence of enol tautomers or heteroaromaticity (7ici(L)1439). 

Extraction.—(1) From Pyrites.—In the oxidation of the pyrites (or other sulphur mineral) for the formation of sulphur dioxide in the manufacture of sulphuric acid, foreign elements like arsenic and selenium also undergo oxidation and pass ofC as vapours with the sulphur dioxide. The selenium dioxide produced in this manner their suffers more or less complete reduction by the sulphur dioxide, when finely divided selenium separates, mainly in the lead chambers, as a red, amorphous powder, accompanied possibly by some of the greyish-black form a portion of the dioxide is also found in the Glover tower acid. The amount of selenium in the chamber mud depends, of course, on the nature of the pyrites relatively large quantities of compounds of arsenic, zinc, tin, lead, iron, copper or mercury are always present, arising almost entirely from impurities in the pyrites. 

Developments in the production of acetaldehyde from acetylene have focussed attention on this reaction. Alcohols may also be formed from olefines. Sulphuric acid (20—4 5%), phosphoric acid 30—35%), or acetic acid (96%), in presence of a mercury salt may be employed. Selenium dioxide has been used for a similar purpose. (J. C. S., 1932, 2342.) See also, A. C. R 1934,123. 

In a further study of routes to steroids with an aromatic ring C, 18-norandrost-13-enes (273) were found to give 7a-hydroxy-18-norandrosta-8,l 1,13-trienes (274) on reaction with selenium dioxide, while the 18-norandrosta-7,13-dienes reacted with mercury(n) acetate to give the 7a-acetate (276), as well as its 7j8-epimer. Mechanisms, including stepwise dehydrogenations, are discussed.226... 

Selenium dioxide oxidations may be accomplished by heating with neat substrates [5f9], but more often, they are carried out in solvents such as water, tert-butyl alcohol, ethanol, dioxane, acetic acid, and acetic anhydride. The solvent used often affects the outcome of the reaction. The use of acetic acid or acetic anhydride favors oxidation to acetates (and thence to alcohols), whereas in water or dioxane, carbonyl compounds are usually formed. An unpleasant feature of oxidations with selenium dioxide is the formation of red colloidal selenium, which cannot always be separated by distillation but can be removed by treatment of the product with potassium cyanide [522], mercury [523], or deactivated Raney nickel [524]. 

Methyl and methylene groups adjacent to carbonyl groups are easily oxidized to carbonyls to yield a-keto aldehydes or a-diketones. The reagent of choice is selenium dioxide or selenious acid. The reaction is catalyzed by acids and by acetate ion and proceeds through transition states involving enols of the carbonyl compounds [518]. The oxidation is carried out by refluxing the ketone with about 1.1 mol of selenium dioxide in water, dilute acetic acid, dioxane, or aqueous dioxane [517]. The byproduct, black selenium, is filtered off, but small amounts of red selenium sometimes remain in a colloidal form and cannot be removed even by distillation of the product. Shaking the product with mercury [523] or Raney nickel [524] takes care of the residual selenium. The a-dicarbonyl compounds are yellow oils that avidly react with water to form white crystalline hydrates (equations 407 and 408). 

Combustion of coal produces many of the same ultimate water pollutants as combustion of petroleum does, that is, PAHs. Coal burning, however, produces greater quantities of metals, sulfur dioxide, and haloacids. Coal combustion stack emissions contain significant quantities of arsenic, mercury, selenium, copper, and tin. I25 Sulfur dioxide is ultimately converted to sulfuric acid in the air. Sulfuric acid and the haloacids (HF, HC1,... 

As previously noted, the high temperature of the combustion process causes the nitrogen and oxygen in the air to react to produce nitrogen oxides. The non-carbon (elements) impurities in the fuels react to form oxides sulfur dioxide is the primary hazardous product, but others such as selenium dioxide and arsenic trioxide are also produced. Mercury is released as vapor. When vented from the combustion zones this complex mixture of compounds blends with the air. Under the influence of sunlight, it continues to react to produce the complex product, smog. "... 

Selenium dioxide oxidation of cyclobutanone may lead to y-btityrolactone or cyclopropanecarboxylic acid, depending on the reaction conditions, but thallium(iii) oxidation gives only ring-contraction. Thallium(iii) or mercury(ii) oxidation of methyl-enecyclopropane gives rise to butan-2-one or its derivatives by ring-cleavage. °... 

Carbonate formation from an alcohol and carbon monoxide is known to take place in the presence of a number of metal and non-metal redox couples, e.g. palladium, platinum, cobalt, copper, nickel, rhodium, mercury, selenium, and bromine. Most of these are also active in the oxidation of CO to CO2 in water, due to the similarity of the reaction pathways for CO2 and carbonate formation, which involve intermediate hydroxy carbonyl and alkoxy carbonyl species, respectively. Competition between carbon dioxide and carbonate formation is a major factor that has to be considered when catalyst re-oxidation is carried out by oxygen, as in most technical developments, since in this case water is co-produced in the reaction system. 

A PS-peroxyselenic acid (29) was prepared by treatment of PS-mercury(II) chloride (30) with selenium dioxide followed by 30% hydrogen peroxide (Scheme 10). In a triphase system, consi ting of (29) (1.5 mol %), 1.5-1.8 equivalents of 30% aqueous hydrogen peroxide and dichloromethane, alkenes were oxidized to 1,2-diols, and ketones to esters or lactones. The polymeric seleninic acid (31) could be reoxidized to the PS-peroxyseleninic acid (29) and recycled with no apparent loss of activity. 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

Selenium and tellurium are converted into their respective tetrachlorides by thionyl chloride, whilst gold, mercury, bismuth, arsenic, antimony, tin and iron give a mixture of the metallic chloride with sulphur dioxide and sulphur monochloride,2 for example ... 

Aqueous solutions of osmium tetroxide are readily reduced by the introduction of practically any metal except those known as the precious metals.3 Thus zinc, silver, mercury, etc., effect the precipitation of metallic osmium from acidulated solutions in a very pure form. In the last-named ease an amalgam is produced from which the osmium is obtained by distilling off the mercury. Ferrous sulphate and stannous chloride4 also reduce the tetroxide solutions, but hydrogen,5 sulphur and selenium 6 appear to have no action under ordinary conditions. Sulphur dioxide reduces the solution to osmium sulphite, whilst potassium iodide reduces it to dioxide with liberation of iodine—a reaction that may be utilised in the volumetric determination of osmium.7... 

The volcanoes of Hawaii emit large quantities of fumarolic sulfur dioxide which causes widespread damage to human health and vegetation downwind. These emissions often take the appearance of widespread hazes and are locally known as vogs. The primarily component is of sulfuric acid and sulfate formed through oxidation of the sulfur dioxide. The vog particles also contain trace elements selenium, mercury, arsenic. 

Volcanic smog (known as vog) is a mixture of atmospheric gases and suspended liquid and solid particles. It forms by the reaction of sulfur dioxide and other volcanic gases with atmospheric moisture, gases, dust, and sunlight (Sutton et al, 1997). Vog consists primarily of sulfuric acid and other sulfate compounds, and can contain a variety of heavy metals, including selenium, mercury, and arsenic (Sutton et al, 1997). Laze, a volcanic haze, forms when molten lava flows into the sea and vaporizes seawater (Sutton et al, 1997). It has many of the same characteristics as vog, with the exception that it probably contains higher levels of chloride and hydrochloric acid derived from seawater. 

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