Hydrosulphite sodium

Reductive bleaching with non-stabilised sodium hydrosulphite [98], sodium hydrosulphite-based sulphoxylate formaldehyde [99] and sodium and zinc hydroxymethanesulphinate [100] have been shown to provide wool excellent whiteness, with a lower cystine content than in the case of bleaching wool with other reducing agents. The result obtained is permanent, in contrast to the unstable peroxide white. 

The goods are treated with a solution containing sodium hydrosulphite (4-8 g/1) or stabilised sodium hydrosulphite (5-10 g/1) and pyrophosphate or buffer (3-4 g/1) at 50-55°C for 1-2 h. Sodium hydrosulphite in aqueous solution is converted into sodium bisulphite when applied at 50 C at pH around 7.0. After bleaching the 

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Reduction to hydroquinone. Dissolve, or suspend, 0-5 g. of the quinone in 5 ml. of ether or benzene and shake vigorously with a solution of 1 0 g. of sodium hydrosulphite (Na2S204) in 10 ml. of N sodium hydroxide until the colour of the quinone has disappeared. Separate the alkaline solution of the hydroquinone, cool it in ice, and acidify with concentrated hydrochloric acid. Collect the product (extract with ether, if necessary) and recrystalhse it from alcohol or water. 

Sodium hydrosulphite is unstable. It decomposes violently at 190°C. The interaction with water is particularly dangerous and can cause its ignition. 

The sodium chlorite/sodium hydrosulphite mixture combusts spontaneously. This is explained by the fact that sulphur-containing salts catalyse the decomposition of chlorite. 

Reducing substances which may combine with atmospheric oxygen, thus removing the ingredient necessary for the explosion of methane, e.g. sodium hydrosulphite. 

On pouring the solution into alcohol a double sulphite of sodium and zinc is rapidly precipitated, whilst needles of sodium hydrosulphite, Na9S204.2H20, separate slowly afterwards. Another procedure for the removal of the zinc from the solution is to add milk of lime cautiously, when a solution of sodium hydrosulphite remains.1... 

Titanous chloride also reduces sulphurous acid or sodium hydrogen sulphite solution with formation of an orange-yellow solution of hydro-sulphurous acid,5 from which sodium hydrosulphite is obtainable by further treatment with sodium hydroxide solution ... 

Indigo and many other colouring matters are bleached by sodium hydrosulphite.9 Organic nitro-compounds are reduced to amino-compounds, the group — NOa being converted into —NHa.10... 

Considering sodium hydrosulphite instead of the unisolated free acid, the constitution is probably to be represented by one of the... 

Selenium is soluble in sulphuric acid, forming a green solution which, in the case of the metallic form, probably contains a compound of composition S03Se (p. 338), and in the case of the red amorphous variety, a polymeric form of this compound.8 The presence of selenium does not affect the electrical conductivity of sulphuric aeicl. Dilute aqueous potassium hydroxide dissolves the red variety, producing a solution which probably contains polyselenides in the presence of sodium hydrosulphite, however, only sodium selenide, Na2Se, is obtained.9... 

Still another method for the detection of small quantities of selenious acid consists in adding sodium hydrosulphite, NaaS jO, to the solution,2 which is then neutralised with solid sodium carbonate. The presence of the least trace of selenium causes a red coloration due to the colloidal element. 

A small quantity of arsenic is precipitated in each case. Sodium dihydrogen arsenite yields a considerable precipitate of arsenic and also of the red disulphide. The polythionates react similarly to thiosulphates, yielding sulphite, thioarsenate and arsenate.5 The per- 1 ites also cause oxidation to arsenate. Sodium hydrosulphite... 

In cold aqueous solution, sodium orthoarsenate reacts with sodium hydrosulphite to form sodium arsenohydrosulphite,6 NagAs(S204)3, a creamy white granular powder. In the presence of sodium sulphite this compound decomposes, forming sodium arsenothiosulphate, an unstable intermediate product, and finally arsenious sulphide.7 If the reduction by sodium hydrosulphite takes place in the presence of hydrochloric acid, some arsenic subsulphide, As3S, is also precipitated,8 and this product is also obtained when the orthoarsenate in aqueous solution is treated with phosphorus trichloride and the mixture saturated with sulphur dioxide.9... 

Sodium hydrosulphite reduces arsenates and arsenites, yielding precipitates containing sulphides the composition of which varies with conditions. In strongly acid solutions arsenic trisulphide is the main product.2 Sodium thiosulphate also precipitates arsenic as the trisulphide from acid solutions,3 but the amount of precipitation depends on the nature and concentration of the acid present. Thus, with hydrochloric, perchloric or sulphuric acid, the precipitation reaches a maximum of 50 to 80 per cent, for 0-1N acid,4 and above this concentration the amount of precipitation falls to zero with hydrochloric acid but passes through a minimum with perchloric acid at N concentration and with sulphuric acid at 2 to 3N concentration. At still higher acid concentrations precipitation becomes almost quantitative. 

The anthraquinones may be reduced to the corresponding anthra-quinols (hydroxyanthranols) with alkaline sodium hydrosulphite this reaction has a wide application in the dye industry. These compounds are difficult to isolate pure, for they rapidly oxidise in air. The anthranols —y-monohydroxyanthracenes—however, are stable, and may be obtained by reducing anthraquinone with acid-reducing agents—tin and hydrochloric acid, zinc and glacial acetic acid, copper or aluminium, and sulphuric acid, etc. For the complete reduction of anthraquinone, see Reaction LYIII. (a). 

Various hyposulphite compounds are used for industrial purposes including stable aldehyde compounds. Of these the formaldehyde compound (Formosul) is tie most important, since it is the reducing agent almost universally employed in applying vat dyes by printing methods to textile materials. The less stable sodium hydrosulphite is used in dyeing with vat dyes. Stable zinc compounds (Rongalite) are also on the market. 

Reagents. 1. Hydrosulphite solution prepared by dissolving 3-4 grams of pure powdered sodium hydrosulphite in water with addition of 3 grams of sodium hydroxide and making the volume up to a litre. This solution should be kept away from the light and air (it is convenient to cover it with a layer of petroleum) and as it is unstable, its titre should be determined immediately before it is used. 

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