Sodium hydrosulfite reducing agent

Sodium hydrosulfite Sodium metabisulfite Sodium sulfite Sodium thioglycolate reducing agent, phosphors Stannous chloride anhydrous... 

For reductive bleaching of wool the two most popular chemicals are stabilized sodium dithionite (sodium hydrosulfite. Cl Reducing Agent 1) and thiourea dioxide (Cl Reducing agent 11). Most reductive bleaching of wool is carried out using stabilized dithionite (2—5 g/L) at pH 5.5—6 and 45—65°C for 1 h. Thiourea dioxide is more expensive than sodium dithionite, but is an effective bleach when appHed at the rate of 1—3 g/L at 80°C at pH 7 for an hour. 

The reducing agents generally used in bleaching include sulfur dioxide, sulfurous acid, bisulfites, sulfites, hydrosulfites (dithionites), sodium sulfoxylate formaldehyde, and sodium borohydride. These materials are used mainly in pulp and textile bleaching (see Sulfur compounds Boron compounds). 

Hydrosulfite may be purchased as a proprietary formulation containing buffering and stabilizing agents, usually as a dry powder, but sometimes as a solution. The powder is pyrophoric and should be kept dry to avoid the possibiHty of fires. Alternatively, solutions of sodium hydrosulfite may be generated on-site by using a purchased solution of sodium borohydride and sodium hydroxide to reduce sulfur dioxide. 

Chromium Removal System. Chlorate manufacturers must remove chromium from the chlorate solution as a result of environmental regulations. During crystallization of sodium chlorate, essentially all of the sodium dichromate is recycled back to the electrolyzer. Alternatively, hexavalent chromium, Cr, can be reduced and coprecipitated in an agitated reactor using a choice of reducing agents, eg, sodium sulfide, sulfite, thiosulfate, hydrosulfite, hydrazine, etc. The product is chromium(III) oxide [1333-82-0] (98—106). Ion exchange and solvent extraction techniques have also... 

Reduction. Many dyes, particularly azo dyestuffs, are susceptible to destmctive reduction. The reducing agents that can be used are sodium hydrosulfite, thiourea dioxide, sodium borohydtide, zinc sulfoxylate, and ferrous iron. 

Sodium hydrosulfite or sodium dithionate, Na2S204, under alkaline conditions are powerful reducing agents the oxidation potential is +1.12 V. The reduction of -phenylazobenzenesulfonic acid with sodium hydrosulfite in alkaline solutions is first order with respect to -phenylazobenzenesulfonate ion concentration and one-half order with respect to dithionate ion concentration (135). The SO 2 radical ion is a reaction intermediate for the reduction mechanisms. The reaction equation for this reduction is... 

Quinones are reduced to hydroquinones by LiAlH4, SnCl2—HCl, or sodium hydrosulfite (Na2S204), as well as by other reducing agents. 

Other reducing agents that have been reported to afford enamines are sodium hydrosulfite [142], dialkyl aluminohydrides [143], and Grignard reagents [144] for quaternary isoquinoline salts sodium borohydrides [145] and Grignard reagents for 3,5-dicyanopyridines and electroreduction [146, 147] of iV-methylglutarimide. 

Anthraquinone vat dyes are water-insoluble dyes. They arc converted til leuco compounds (anthrahydroquinone.s) by reducing agents such as sodium hydrosulfite in alkaline conditions. These water-soluble leuco compounds have an affinity to cellulose fibers and penetrate them. After reoxidation by means of air or other oxidizing agents, the dye becomes water-insoluble again and fixes firmly on the fiber. 

Water-insoluble vat dyes are converted to soluble anthrahydroquinones by reducing agents, such as sodium dithionite (hydrosulfite) in the presence of sodium hydroxide. The sodium salts of these mostly deep colored leuco compounds penetrate cellulose fibers. The insoluble dye is attached firmly to the fiber after reoxidation (see Section 4.5). Representative of a special form are the water-soluble sulfuric acid esters of the anthrahydroquinone compounds, namely, the leuco esters of vat dyes). 

For a long time, sodium dithionite (hydrosulfite) has been the most important of the reducing agents [5, p. 288-289] for vat dyeing. It is inexpensive and, when produced by modem methods, virtually free of heavy metals (Zn, Hg). Its reduction potential (-970 mV) is high enough to vat all vat dyes quickly and completely-... 

In the two-phase process dyes and chemicals are applied in separate steps first dyes and thickener ( solid phase ) are printed, then chemicals and auxiliaries are added as an aqueous solution by padding. Sodium dithionite (Hydrosulfite) is used as reducing agent, and steaming time is kept short (20-40 s). For stabilized reducing agents, see [5, p. 296-298],... 

Sodium dithionite (hydro sulfite) is a proven reducing agent for sulfur vat dyes, and is used together with alkali. The color yield of some sulfur dyes is remarkably increased by the addition of hydrosulfite. However, as a result of possible overreduction or destruction of the dye chromophore, hydrosulfite and similar reducing agents can be used only with selected dyes. 

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