Dithionite stability

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

Gra.des. There are three primary commercial sodium dithionite products 88 min wt % anhydrous product, 70 wt % dry product (often blended with other stabilizers or additives), and 125 g/L stabilized solution. 

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 stability and efficacy of sodium dithionite can be enhanced by addition of polyacrylamide, a product more frequently used as a migration inhibitor in continuous dyeing processes [227]. This biodegradable polymer allows the amount of dithionite to be... 

Iron-gluconate complexes are sufficiently stable not to cause iron toxicity (in contrast to Fe aq, Fe aq, and complexes of low stability) and are safe and effective in hemodialysis. " There is information on iron transfer between gluconate and transferrin. Dithionite releases Fe + from gluconate. ... 

Sodium dithionite should be fresh. The stability of S2O4 ions in acidic media has not been considered for the formulation of the equation (formulated for the non-defect cluster). It is used as it gives the best results as reducing agent. 

Zinc Dithionite. Zinc dithionite [7779-86-4], ZnS204, is a white, water-soluble powder. Although it exhibits somewhat greater stability in aqueous solution compared to sodium dithionite at a given temperature and pH, it is no longer used in the United States because of regulatory constraints on pollution of water by zinc. 

Prereduced Powders. These are usually made from press cake paste to which a reducing agent has been added, such as sodium sulfide, sodium hydrosulfide, or sodium dithionite, which solubilize the dye in water. Before drying, the dye paste may be mixed with dispersing and stabilizing agents to aid application. 

The properties of the semiquinone from of the ETF isolated from the methylotrophic bacterium resemble those of the bacterial flavodoxins with the exception that flavodoxins form neutral semiquinones whereas this ETF forms an anionic semiquinone. Nearly quantitative anionic semiquinone formation is observed either in the presence of excess dithionite or when excess trimethylamine and a catalytic amount of trimethylamine dehydrogenase are added. Of interest is the apparent stability of the anionic semiquinone towards oxidation by O2 but not to oxidizing agents such as ferricyanide. This appears to be the first example of an air-stable protein-bound anionic flavin semiquinone. Future studies on the factors involved in imparting this resistance to O2 oxidation by the apoprotein are looked forward to with great interest. 

In the case of two flavoenzyme oxidase systems (glucose oxidase (18) and thiamine oxidase s where both oxidation-reduction potential and semiquinone quantitation values are available, semiquinone formation is viewed to be kinetically rather than thermodynamically stabilized. The respective one-electron redox couples (PFl/PFl- and PFI7PFIH2) are similar in value (from essential equality to a 50 mV differential) which would predict only very low levels of semiquinone (32% when both couples are identical) at equilibrium. However, near quantitative yields (90%) of semiquinone are observed either by photochemical reduction or by titration with dithionite which demonstrates a kinetic barrier for the reduction of the semiquinone to the hydroquinone form. The addition of a low potential one-electron oxidoreductant such as methyl viologen generally acts to circumvent this kinetic barrier and facilitate the rapid reduction of the semiquinone to the hydroquinone form. 

The results of this analysis are shown in Table 11.1. It is clear that absorption of nickel in all fibres is reasonably high, but the amount of metallic nickel is considerably higher in PAN fibres and, to a lesser extent, in natural silk. This indicates that the structure of the fibres (pore size and permeability as well as functional groups) plays an important role. Sodium dithionite and rongalite are known as good reducing agents, but their stability is fairly limited. One of their decomposition products (particularly in acidic solutions) is sulphide, which explains why an important fraction of... 

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],... 

The use of sodium or zinc dithionite ("hydrosulfite") represents the most common type of reducing bleaching. Usually 0.5-1% sodium dithionite of the dry pulp weight is added and the bleaching is allowed to proceed at 50°-60°C for 1 -2 hours. Because ions of heavy metals catalyze the decomposition of dithionite solutions, complexing agents, such as EDTA, are added as stabilizers. 

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