Selenious acid

Heat 1 gram of the product in a dry test tube. Smell cautiously. Observations Equations  

Heat a few crystals with 5 cc. of hydrochloric acid. How do you explain the results  

The element selenium exists in several allotropic forms. 

250-cc. beaker, suction filter, spatula, iron or glass, iron ring and ring stand. 

Dissolve 1-2 grams of the crystals in 15 cc. water. Dilute 1 cc. stannous chloride solution with 5 cc. hydrochloric acid add 

---

Selenious acid, H2Se03. Formed water on Se02. More stable than H2SO3, oxidized to H2Se04, reduced to Se by SO2. Gives selen-ates(IV) with oxides, hydroxides or carbonates. 

Selenium dioxide. The compound is conveniently prepared by the oxidation of selenium with nitric acid, followed by dehydration of the selenious acid thus formed by cautious heating ... 

H3PO4 orthophosphoric acid (or H2Se03 selenious acid... 

Selenigsaure, /. selenious acid, -anhydrid, n. selenious anhydride (SeOs). 

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. 

Recendy, ID quantum dots of gallium selenide with average diameter 8-10 nm, connected in the form of chains of average length 50-60 nm, were synthesized on rro substrates by cathodic electrodeposition from acidic aqueous solutions of gallium(III) nitrate and selenious acid [186], The structural analysis from XRD patterns revealed the formation of Ga2Se3/GaSe composition. The films were found to be photoactive in aqueous sodium thiosulfate solution and showed p-type conductivity. 

This concentrate is added to a previously prepared and filtered solution of sodium bisulfite in 40% alcohol (Note 11) contained in a 4-1. beaker provided with a mechanical stirrer (Note 12). The mixture is stirred for 3 hours, and the addition product then is filtered with suction on an 18-cm. Buchner funnel and washed, first with two 150-ml portions of alcohol and then with 150 ml. of ether. The yield of air-dried product is 350-360 g. (72-74%, based on the selenious acid used) (Note 13). 

The selenious acid does not need to be freshly prepared. A larger amount does not increase the yield. The submitters specified selenium dioxide as the oxidizing agent, but the checkers prepared their material by evaporating an aqueous solution to dryness on the water bath. They, therefore, have considered the oxidizing agent to be selenious acid and have calculated the... 

Selenious acid, 24, 61, 62 Selenium, 24, 63 powdered, black, 24, 90 Selenium compounds, ease of oxidation, 24,91... 

In a 2-1. round-bottomed flask, attached to an efficient reflux condenser (Note 1) and set in a hot water bath, are placed 222 g. (1.72 moles) of selenious acid (Note 2), 270 ml. of paraldehyde (Note 3), 540 ml. of dioxane, and 40 ml. of 50% acetic acid (Note 4), and the mixture is refluxed for 6 hours (Note 5). The solution is then decanted from the inorganic material (Note 6),... 

Lead acetate is more satisfactory than sulfur dioxide for the removal of selenious acid, provided that the solution is kept cool and a large excess is avoided. 

Following a report60 that D-fructose, but not D-glucose, is oxidized by selenious acid, Dixon and Harrison61 used this reagent to prepare D-glucosone from D-fructose in aqueous solution isolation and purification were carried out after the manner of Fischer,4 but no yield was given. By this... 

In the preparation of D-glucosone by the direct oxidation of D-glucose, D-fructose, or D-mannose by such reagents as that of Fenton,37 cupric acetate,16- 46- 46 selenious acid,16-61 etc., the degree of oxidation must be carefully controlled if the osone, which is the first product, is to be the main product of the reaction. The nature and mechanism of formation of the products of further oxidation of D-glucosone are discussed on p. 68. 

SELENIUM DIOXIDE Se02 Selenious Acid H2Se03... 

Isoprene, 2,3-dimethylbuta-l,3-diene and other dienes (but not butadiene itself) readily furnish analogous 2,5-dihydroselenophene 1,1-dioxides, e.g. 306, on treatment with selenious acid in chloroform at room temperature (equation 161)153. 

Elemental selenium is not particularly irritating, but various compounds such as selenium oxychloride and selenium dioxide are strong vesicants. Skin contact with the fume of heated selenium dioxide caused an acute, weeping dermatitis, with the development of hypersensitivity in some cases. Selenium dioxide forms selenious acid when in contact with water if allowed to penetrate beneath the fingernails, it causes an especially painful inflammatory reaction. ... 

Reaction with sodium selenate yields lead selenate, PbSe04. Similarly, with sodium selenite or selenious acid, the product is lead selenite, PbSeOs. 

Pale yellow or colorless liquid corrosive refractive index 1.651 at 20°C density 2.42 g/mL at 22°C freezes at 8.5°C boils at 176.4°C decomposes at 176.4°C decomposes in water forming hydrochloric acid and selenious acid soluble in carbon disulfide, carbon tetrachloride, chloroform, benzene, and toluene. 

The pyrazine ring is stable toward permanganate oxidation, and this explains a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines or benzo-fused quinoxalines. In contrast, alkyl side chains on pyrazines are effectively oxidized by permanganate, selenious acid, selenium dioxide, or dichromate to afford the corresponding carboxylic acids (Section 8.03.7.1). Oxidation of pyrazines with hydrogen peroxide or percarboxylic acids gives pyrazine A -oxides and/or A, A -dioxides (Section 8.03.5.2). 

Compound 31, the synthesis of which is described in Section 10.09.9.2.3, undergoes a substantial rearrangement upon oxidation with selenious acid, giving 1,2,4-triazole 32 (Equation 6). A plausible mechanism for this transformation is presented in the original report <2003RCB1740>. 

---