Reducing agents bleaches

Dithionite is a stronger reducing agent than sulfite. Many metal ions, eg, Cu", Ag", Pb ", Sb ", and Bi ", are reduced to the metal, whereas TiO " is reduced to (346). Dithionite readily reduces iodine, peroxides, ferric salts, and oxygen. Some of the decolorizing appHcations of dithionite, eg, in clay bleaching, are based on the reduction of ferric iron. 

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. 

Zinc hydrosulfite (zinc dithionite) is a powerhil reducing agent used in bleaching paper and textiles it is prepared from zinc dust and sulfur dioxide ... 

Another hydrosulfite reducing agent is zinc formaldehyde sulfoxylate, Zn(HS02-CH20)2 (see Bleaching agents). 

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). 

Wool may also be bleached with reducing agents, usually after bleaching with hydrogen peroxide. This is the normal practice with wool blends. In the reducing step, 0.2—0.5% sodium dithionite solutions are often used at pH 5.5—7 for 1—2 h at 45—65°C. Faster bleaching is obtained with 2inc hydroxymethane-sulfinate [24887-06-7] below pH 3 and above 80°C. 

Large-Scale Industrial Production. Large amounts of chlorine dioxide ate used in pulp bleaching and smaller quantities ate used for the manufacture of sodium chlorite. In these appHcations, sodium chlorate is the only commercially available taw material. Chlorine dioxide production from sodium chlorate is achieved by the reduction of the chlorate ion in the presence of strong acid. The reaction consumes acid, so that acid and reducing agents must be constantly added to maintain the reaction. 

The final step after peroxide bleaching is to ensure that the goods do not contain residual peroxide. Reducing agents have been used traditionally for this purpose. However, the possibility of using environmentally friendly catalase enzymes should not be overlooked [87-89]. 

In solution, NaOCl dissociates into sodium ions (Na+) and hypochlorite ions (OC1). Bleaching involves an oxidation-reduction reaction in which the Cl in the OC1 ion (oxidizing agent) is reduced to the chloride ion (Cl ). The reducing agent is either a dye, which fades, or the stain being removed. 

Hydroprocessing, in petroleum refining, 18 654-657 Hydropulping, 10 535 Hydropyrolysis, coal liquefaction, 6 854 Hydroquinolines, 21 198-199 Hydroquinone (HQ) from benzene, 3 620 as a black-and-white chemical reducing agent, 19 205-206 in bleaching preparations, 7 847 clathrates, 14 160 dye releaser, 19 291-292 inclusion compounds in, 14 172, 174 intermediate used in oxidation hair dyes, 7 858t... 

Reduced sulfur fuel, 18 667 Reducing agents, 9 687, 688-689 Reducing atmospheres, reaction of photoholes with, 19 84-85 Reducing bleaches, 4 63-64 bleaching mechanism, 4 47 Reducing chemistry, in water treatment, 23 222-226... 

Sulfur dioxide serves as a reducing agent in many preparative reactions. It reduces sodium chlorate in sulfuric acid solution to form chlorine dioxide. The reaction is used to produce chlorine dioxide in situ, a bleaching agent in the pulp and paper industry ... 

All the positive oxidation states of the Group 17 elements are powerful oxidants. In alkaline conditions the positive oxidation states are still reasonably powerful oxidants, e.g. HOC1 is the basis of some household bleach solutions which allegedly kill all known germs. Dilute chloric(VII) acid has a high reduction potential, but reacts very slowly with most reducing agents. 

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