Sodium hydrosulfite dithionite

Because of this low oxidation-reduction potential, the number of methods available for reducing ferredoxin is limited. Apart from hydrogen gas, ferredoxin may be reduced with organic reductants, such as pyruvate or hypoxanthine in the presence of the appropriate enzymes. Ferredoxin can be reduced nonenzymically with sodium hydrosulfite (dithionite) (Tagawa and Arnon (99) Fry et al. (45)), potassium borohydride (D Eustachio and Hardy (40)), and formamidine sulfinic acid (Shashoua (90)). It can be reduced also by illuminated chloroplasts (Whatley, Tagawa, and Arnon (114)) and, under these conditions, the reduction of ferredoxin is most complete (Bachofen and Arnon (12)). 

Amino-5-chloromethyl-3-cyanopyrazine 1-oxide was also deoxygenated by sodium hydrosulfite (dithionite) in boiling water to give a poor yield of 2-amino-5-chloromethyl-3-cyanopyrazine, but 2-amino-6-chloromethyl-3-cyanopyrazine 1-oxide under the same conditions underwent both deoxygenation and reductive dehalogenation to 2-amino-3-cyano-6-methylpyrazine (529,534). 

Reduction of 2-hydroxy-3,6-dimethyl-5-phenylazopyrazine (8) with sodium hydrosulfite (dithionite) gave 2-amino-5-hydroxy-3,6-dimethylpyrazine (872), and vigorous reduction of the disodium salt of 2-(p-sulfophenylazo)-3-methyI-5-hydroxypyrazine with stannous chloride and hydrochloric acid gave 2-amino-5-hydroxy-3-methylpyrazine (434). 2-Hydroxy-5,6-diphenyl-3-phenylazopyrazine in methanol was reduced with hydrogen over Raney nickel to 2-amino-3-hydroxy-5,6-... 

Fio. 4. Difference spectrum of cytochrome P-4S0 in hepatic microsomes. The dotted line is a base-line difference between two cuvettes containing aliquots of the same microsomal suspension. One cuvette is then bubbled with carbon monoxide for a few minutes, the reducing agent sodium hydrosulfite (dithionite) added to both cuvettes and the difference spectrum (solid line) recorded. (Omura and Sato, J. BioL Chem ... 

Another method employed is the treatment of aqueous solutions of aminophenols with activated carbon (81,82). During this procedure, sodium sulfite, sodium dithionite, or disodium ethylenediaminotetraacetate (82) is added to increase the quaUty and stabiUty of the products and to chelate heavy-metal ions that would catalyze oxidation. Addition of sodium dithionite, hydrazine (82), or sodium hydrosulfite (83) also is recommended during precipitation or crystallization of aminophenols. 

Uses. The dominant use of sulfur dioxide is as a captive intermediate for production of sulfuric acid. There is also substantial captive production in the pulp and paper industry for sulfite pulping, and it is used as an intermediate for on-site production of bleaches, eg, chlorine dioxide or sodium hydrosulfite (see Bleaching agents). There is a substantial merchant market for sulfur dioxide in the paper and pulp industry. Sulfur dioxide is used for the production of chlorine dioxide at the paper (qv) mill site by reduction of sodium chlorate in sulfuric acid solution and also for production of sodium dithionite by the reaction of sodium borohydride with sulfur dioxide (315). This last appHcation was growing rapidly in North America as of the late 1990s. 

Physical Properties. Sodium dithionite (sodium hydrosulfite, sodium sulfoxylate), Na2S204, is a colorless soHd and is soluble in water to the extent of 22 g/100 g of water at 20°C. 

Sodium dithionite solution can be produced on-site utilizing a mixed sodium borohydride—sodium hydroxide solution to reduce sodium bisulfite. This process has developed, in part, because of the availabiHty of low cost sulfur dioxide or bisulfite at some paper mills. Improved yields, above 90% dithionite based on borohydride, can be obtained by the use of a specific mixing sequence and an optimized pH profile (360,361). Electrochemical technology is also being offered for on-site production of sodium hydrosulfite solution (362). 

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). 

Production of Sodium Borohydride. In the pulp and paper industry, sodium borohydride is used to generate sodium hydrosulfite (sodium dithionite), a bleaching agent, from sodium bisulfite. Methyl borate is used as an intermediate in the production of sodium borohydride (33). 

Iodo-7-nitrofluorene gave 2-iodo-7-aminofluorene in 85% yield by reduction with hydrazine in the presence of Raney nickel [277], and 2-iodo-6-nitronaphthalene and 3-iodo-6-nitronaphthalene afforded the corresponding iodoaminonaphthalenes in almost quantitative yields on treatment with aqueous-alcoholic solutions of sodium hydrosulfite (hyposulfite, dithionite) [257]. 

Sodium hydrosulfite (i.e. sodium dithionite, Na2S2Ot) has been used extensively for reduction of the aminochromes.5, 65,70,74,102,104, 109,118-120,128,148.151-155 Heacock and Scott showed by paper... 

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