Selenium sulphite

The gas is used in various chemical industries. For example, it forms an intermediate stage in the production of sulphuric acid and of sulphites it is also applied in the preparation of chemical substances such as selenium, tellurium, quinol, etc. To some extent sulphur dioxide finds application for fire-prevention and -extinguishing, and much is used in the form of alkali sulphite in the production of wood pulp for paper and artificial silk manufacture. 

Reinders and Vies, Bee. Tran, chim., 1925,44,249. For changes occurring in solutions of various hydrogen sulphites m the presence of selenium as catalyst, see Sandonnini, Atti B. Aecad, Idncei, 1923, [v.], 32, ii., 84. 

Alkali sulphites in boiling aqueous solution dissolve selenium with formation of a selenotrithionate, which subsequently decomposes giving the alkali dithionate 8... 

Chlorine also converts the selenium and sulphur of dried chamber mud into the volatile chlorides, from which the selenium can be liberated by decomposition with water followed by reduction with an alkali sulphite.4... 

Selenium prepared by the reduction of selenious acid with sodium or ammonium hydrogen sulphite forms colloidal solutions, that precipitated... 

In 1847 Sacc determined the atomic weight by several methods, of which only two proved of value, namely (i) pure selenium dioxide was reduced with ammonium hydrogen sulphite and the resulting selenium weighed (ii) barium selenite was calcined with sulphuric acid and the resulting barium sulphate weighed. The results were as follows 5... 

Estimation of Selenium in Organic Compounds.—A trustworthy method consists in oxidising the substance with fuming nitric acid, refluxing with concentrated hydrochloric acid until the nitrous fumes disappear and then precipitating the selenium with sodium sulphite.7... 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

The detection and estimation of selenium in the mother-liquors from the preparation of sulphite-cellulose is rendered difficult by the colour of these liquors, due to the organic substances present. The presence of the element is indicated by the fact that a red deposit is formed on the sides of the combustion tube when the organic matter is being burnt off. Estimation may be carried out by evaporating the liquor until all the free sulphur dioxide has been evolved, acidifying with hydrochloric acid and boiling to remove the last traces of sulphur dioxide. After allowing to stand in a warm place for a few days the selenium settles to the bottom of the container and may be estimated as described.4... 

Selenosulphuric Acid or Thioselenic Acid, H2SSeOa.—Salts of this acid are obtained when finely divided selenium is dissolved by warming with an aqueous solution of an alkali sulphite, potassium sulphite being the most satisfactory 4... 

Selenotrithionic Acid, H2SeS20B.—In the preparation of potassium selenosulphate as just described, a certain small amount of a potassium selenotrithionate, K2SeS2O0, is obtained, which generally crystallises first on evaporation of the solution at the ordinary temperature. The yield is much better if potassium hydrogen sulphite is also present with the selenium and normal potassium sulphite.2... 

Selenium. — On overlaying 2 cc. of sulphuric acid with 2 cc. of hydrochloric acid, in which a granule of sodium sulphite has been dissolved, a reddish zone must not form at the contact-surfaces of the two liquids nor should a red precipitate form on warming. 

Reduction by zinc dust yields an oil iodine in chloroform has no action, but chlorine in the same solvent gives selenium tetrachloride and chloroacetylacetone, and bromine yields lachrymatory products and a colourless crystalline substance of melting-point 180° C. Aqueous hydrogen sulphide causes slow decomposition, with liberation of sulphur and selenium. Potassium metabisulphite and sodium hydrogen sulphite transform selenium acetylacetone quantitatively into alkali selenodithionates, a reaction which affords the best known means of preparing these salts. 

The silver salt is a sulphonate, while the potassium salt is a sulphite. This peculiarity is not shown by selenium or It appears certain that they are represented by. OH. OH... 

Sodium selenate can be produced by electrolytic oxidation of neutral selenite solution.1 On evaporation of the solution, crystals of selenate can be obtained together with a small amount of selenium. The addition of a small quantity of chromate to the bath prevents the cathodic deposition of selenium. F. Foerster2 had previously shown that neutral sulphites give, by electrolytic oxidation, both sulphate and dithionate. No dithion-ate analogue was found by Muller when oxidising the selenites, and in attempting to oxidise sodium tellurite a considerable amount of free tellurium was obtained. 

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... 

Selenites are likewise reduced to selenium. If, however, the solution of the selenite in concentrated sulphuric acid is treated with sodium sulphite, selenium separates but the tellurite is unaffected the latter can be detected in the solution after eliminating the sulphur dioxide. Salts of silver, copper, gold, and platinum must be absent for they are reduced to the metal by the reagent. 

Selenium also dissolves in sulphite solutions to give selenosulphates ... 

The reaction products obtained when dissolving elemental selenium in aqueous sulphite solution were found to be ScSC), and some reactions using similar sulphur or selenium reagents afforded the ScfSOi) isomers with O- and with S-bonded Se as well as other related species, as determined by Se NMR and Raman spectroscopy. Selenium dioxide, ScC)2. is the... 

Kullberg [74KUL] found it impossible to study the aqueous Cu -SeCN system since a brown precipitate was immediately formed upon addition of selenocyanate ions to a copper(ll) solution. Toropova [56TOR] prepared CuSeCN(s) by adding KSeCN to a solution of copper(l) sulphite or thiosulphate complexes, and tried to study the complex formation by measuring the solubility of CuSeCN in selenocyanate solutions. The experiment failed since the complexes initially formed were found to decompose into elementary selenium and copper(l) cyanide compounds. 

The reaction of [O3S—Se—Se—SOJ " with [CN]- is more complex, the stoicheio-metry varying with reaction conditions. Second-order rate constants (1 mol s" ) at 25 °C are [O3S—Se-Se-SOJ -, 2500 [OgS-SeCN]- 0.2 and [O3SMS—S-SO3] -, 0.0029. For [O3S—SCN] at 30 °C the rate constant is 0.02951 mol s. Another system that has been investigated is [O3S—S—Se—S—S03] nucleophilic attack by [CN]- occurs at selenium, and is about two orders of magnitude faster than on the central sulphur in [O3S—S—S—S—SO3] -. Related species appear to be involved in the selenium-catalysed disproportionation of sulphite to sulphate + sulphur. Nucleophilic substitution at u-nitrobenzeneseleneyl halides has also been studied. ... 

The reproducibility of the method is 1 pg/g at the 10 Mg/g level and 4 iq/g at the 120 Mg/g level. As tests show, the method is not interfered even by a tenfold excess of selenium, tellurium, arsenic and antimony, which can cause complications with the titrimetric determination. The calibration curve is plotted using a sodium sulphite solution. 

---