Selenous acid chloride

Tellurium trioxide, TeOa, is an orange yellow powder made by thermal decomposition of telluric(VI) acid Te(OH)g. It is a strong oxidising agent which will, like H2Se04, oxidise hydrogen chloride to chlorine. It dissolves in hot water to give telluric(VI) acid. This is a weak acid and quite different from sulphuric and selenic acids. Two series of salts are known. 

Discussion. This gravimetric determination depends upon the separation and weighing as elementary selenium or tellurium (or as tellurium dioxide). Alkali selenites and selenious acid are reduced in hydrochloric acid solution with sulphur dioxide, hydroxylammonium chloride, hydrazinium sulphate or hydrazine hydrate. Alkali selenates and selenic acid are not reduced by sulphur dioxide alone, but are readily reduced by a saturated solution of sulphur dioxide in concentrated hydrochloric acid. In working with selenium it must be remembered that appreciable amounts of the element may be lost on warming strong hydrochloric acid solutions of its compounds if dilute acid solutions (concentration <6M) are heated at temperatures below 100 °C the loss is negligible. 

The white basic selenate, 2Po02Se03, is obtained by treating polonium V) hydroxide or chloride with selenic acid (0.015 iV-5.0 N) the salt is yellow above 250°C and is stable to over 400°C. It is rather less soluble than the basic sulfate, but the solubility increases a hundredfold in passing from 0.05 N to 5 N selenic acid (10), indicating complex ion formation. 

Selenates, on distillation -with sulphuric acid and sodium chloride, yield a mixture of selenium tetrachloride and chlorine anhydrous selenic acid also gives an excellent yield of selenium tetrachloride on treatment -with acetyl chloride at 0° C.1... 

Selenic Acid, HaSe04.—This acid was first prepared by Mitscher-lich in 1827, who suspended lead selenate in water and precipitated the lead by means of hydrogen sulphide. By the oxidation of aqueous solutions of selenious acid with suitable reagents, e.g. chlorine or bromine, selenic acid may also be obtained.6 When chlorine is used, any hydrogen chloride must be removed as soon as it is formed, for selenic acid is reduced by hot hydrogen chloride to selenious acid, with liberation of chlorine the process is best carried out6 by passing a... 

On crystallisation, copper selenate separates, contaminated with about 1 per cent, of cupric chloride. The latter may be removed by extraction with acetone, in which it is readily soluble, whereas the selenate is only very slightly soluble after this operation the copper selenate is finally purified by recrystallisation from water. The copper may then be removed by electrolysis,1 using low current density, when selenic acid free from selenious acid and chlorine remains in the electrolyte. The solution may be concentrated until it contains about 82 per cent, of the acid by evaporating at 95° C. under reduced pressure. 

Pure selenic acid may be prepared from the solutions obtained in the foregoing processes by first neutralising with ammonia, precipitating barium selenate by the addition of barium chloride, and heating the separated precipitate with a solution containing the correct quantity of sulphuric acid. After removing the barium sulphate, a solution of pure selenic acid remains, and if this is concentrated as far as possible (see... 

By the action of hydrazine hydrate on a dilute solution of selenic acid, hydrazine hydrogen selenate may be obtained as a colourless compound which is not decomposed by boiling water, but which, when dry, explodes with great readiness when subjected to heat, to shock, or to fumes of hydrogen chloride. For this reason, before hydrazine hydrate is used in the analysis of selenium compounds (see p. 307), it is essential that selenic acid and selenates should be reduced to selenites by means of hydrochloric acid.3... 

Cellulose is insol in w, ale, eth all known simple org solvs. The best solv for it is cuprammonium hydroxide, [Cu(NH3)4(OH)2], also called Schweitzer s Reagent. It is also sol in a coned soln of Ca thiocyanate alone or in combination with formaldehyde. Other solvs gelatinizers for cellulose include zinc chloride (in 40% soln on heating), basic beryllium perchlorate, 84% phosphoric acid, selenic acid, arsenic acid, sulfurous acid, 66% HBr, 70-75% HF, coned HI, chloral with pyridine, chloral hydrate in H2S04, and inorg salts(such as NaCl) in coned solns at high temps. Coned solns of NaOH at ca -10° only partially dissolve cellulose while the remainder is swelled "mercerized . 

Selenic Acid.—Selenic Acid, H2Se04, is also a il colourless syrupy liquid it can be produced by direct oxidation of selenium by chlorine water, but on concentra-I tion the resulting hydrochloric acid reduces the selenic acid I to selenious acid, as hydriodic acid reduces sulphuric acid. It is best prepared by addition of copper carbonate to the mixture of selenic and hydrochloric acids obtained in that way selenate and chloride of copper are formed the 1 mixture is evaporated to dryness, and the copper chloride is dissolved out with alcohol, leaving the insoluble selenate 1 behind. The selenate is dissolved in water, and on treatment with sulphuretted hydrogen, copper sulphide is precipitated, and removed by filtration the selenic acid is then concentrated if it contains a trace of water, it is a heavy liquid 5 but if quite anhydrous, it forms a solid, melting at 58°. 

Selenium is a steel gray or purplish powder, also fabricated into pellets, sticks, or plates. Selenium dioxide, selenous acid, and the alkali-metal selenites and selenates are colorless powders or crystals. Selenium chloride (reddish yellow), selenyl chloride (colorless or yellow) (bp, 176°C), and selenic acid (colorless) are liquids, whereas selenium tetrachloride is a cream-colored crystalline solid.1... 

Wear nitrile rubber gloves, laboratory coat, and eye protection. Selenium powder may be mixed with sand and treated as normal refuse, as may the disulfide. Soluble selenites and selenates can be dissolved in water and run to waste, diluting with at least 50 times its volume of running water. Soda ash should be applied liberally to spills of selenium dioxide, selenic and selenous acids, and selenyl and selenium chlorides, which may then be mopped up cautiously with plenty of water wash down the drain, diluting greatly with at least 50 times its volume of water.16... 

Samarium (III) nitrate, analysis of anhydrous, 6 41 Selenic acid, crystalline, 3 137 Selenides, precipitation of pure metallic, from solutions of hydrogen selenide, 2 185 Selenium, red and gray, 1 119 Selenium (II) chloride, formation of, by selenium(IV) chloride, 6 127... 

Aryl chloride Aryl iodide Aryl selenic acid Aryl sulfonic acid Azide... 

Compounds (195-197) are prepared starting with o-aminothiophenols or o-aminoselenophenols and thionyl chloride. Mono- and di-selenium compounds (196-197) are synthesized by reaction of selenous acid and the corresponding sulfur derivatives (Scheme 86) (75KGS275, 76KGS1361). 

Iron Selenites.—Although metallic iron does not appear to be soluble in selenous acid, yet selenites of iron are readily obtained in a variety of ways. When sodium selenite is added to ferrous sulphate solution, a white precipitate of ferrous selenite, FeSe03, is obtained.4 This becomes darker on exposure to air in consequence of oxidation. If the white precipitate is dissolved in hydrochloric acid, a portion of the selenium separates out, whilst ferric chloride and selenous acid remain in solution. Thus —... 

Cl 64.24%. SeCI4. Prepd by the action of an excess of chlorine on selenium Berzelius, cited in Meltor s vol X, 898 (1930) by the action of thionyl chloride or phosphorus trichloride on selenium oxychloride and by the action of phosphorus pentachloride on selenium oxide Michael is. Z Chem. [2) 6, 460 (1870) by the action of anhydr selenic acid on acetyl chloride at 0 Lamb, Am, Chem. J. 30,209 (1903). Crystal structure Shoemaker, Abrahams, Acta Cryst. 18,... 

---