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Dithionites

Dithionites are obtained by the action of reducing agents, such as zinc, upon hydrogen sulphites [Pg.247]

Sulphur dioxide may also be passed into a cooled suspension of zinc dust in water  [Pg.247]

Zinc ions, which are produced in both processes, can be removed from the solution with sodium carbonate, when zinc carbonate is precipitated. By saturating the solution with sodium chloride, sodium dithionite, Na2S204 2H2O, is precipitated. [Pg.247]

Sodium dithionite is a powerful reducing agent. A solution of the salt, containing an excess of sodium hydroxide, is used as an absorbent for oxygen in gas analysis. [Pg.247]

To study these reactions use a freshly prepared 0.5m solution of sodium dithionite, Na2S204. [Pg.247]


Fieser s solution An aqueous alkaline solution of sodium anthraquinone -sulphonale (silver salt) reduced with sodium dithionite, Na2S204, and used as a scrubbing solution for partially removing O2 from, e.g., N2. [Pg.174]

Sodium hyposulphite (dithionite) NajS O, may also bo employed for the reduction see under Methyl Orange, Section IV,78. [Pg.623]

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LIAIH, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjHj, NjHJ, phosphorus (e.g. triethyl phosphite, triphenyiphosphine), and sulfur (e.g. HO-CHj-SOjNa = SFS, sodium dithionite = Na S O. ... [Pg.96]

The most common chemical bleaching procedures are hypochlorite bleach for cotton hydrogen peroxide bleach for wool and cotton sodium chlorite bleach for cotton, polyamide, polyester, and polyacrylonitrile and reductive bleaching with dithionite for wool and polyamide. [Pg.119]

The reaction of formate salts with mineral acids such as sulfuric acid is the oldest iadustrial process for the production of formic acid, and it stiU has importance ia the 1990s. Sodium formate [141-53-7] and calcium formate [544-17-2] are available iadustriaHy from the production of pentaerythritol and other polyhydric alcohols and of disodium dithionite (23). The acidolysis is technically straightforward, but the unavoidable production of sodium sulfate is a clear disadvantage of this route. [Pg.504]

The inorganic reductions of NaBH are numerous and varied (Table 7). Comparatively few anions are reduced, yet the reduction of bisulfite to dithionite (hydrosulfite) (25), which is used in the pulp (qv) and paper (qv), clay (see Clays), and vat dyeing industries, is an important inorganic appHcation ofNaBH,. [Pg.302]

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. [Pg.441]

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). [Pg.470]

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. [Pg.311]

With hot metals, sulfur dioxide usually forms both metal sulfides as well as metal oxides. In aqueous solution, sulfur dioxide is reduced by certain metals or by borohydrides to dithionites. [Pg.144]

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. [Pg.148]

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. [Pg.150]

Chemical Properties. Anhydrous sodium dithionite is combustible and can decompose exothermically if subjected to moisture. Sulfur dioxide is given off violentiy if the dry salt is heated above 190°C. At room temperature, in the absence of oxygen, alkaline (pH 9—12) aqueous solutions of dithionite decompose slowly over a matter of days. Increased temperature dramatically increases the decomposition rate. A representation of the decomposition chemistry is as follows ... [Pg.150]

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). [Pg.150]

Sodium dithionite is most stable and effective as a reducing agent in alkaline solutions, although with excess strong alkaH the following reaction... [Pg.150]

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. [Pg.150]

Addition of sodium dithionite to formaldehyde yields the sodium salt of hydroxymethanesulfinic acid [79-25-4] H0CH2S02Na, which retains the useful reducing character of the sodium dithionite although somewhat attenuated in reactivity. The most important organic chemistry of sodium dithionite involves its use in reducing dyes, eg, anthraquinone vat dyes, sulfur dyes, and indigo, to their soluble leuco forms (see Dyes, anthraquinone). Dithionite can reduce various chromophores that are not reduced by sulfite. Dithionite can be used for the reduction of aldehydes and ketones to alcohols (348). Quantitative studies have been made of the reduction potential of dithionite as a function of pH and the concentration of other salts (349,350). [Pg.150]

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). [Pg.150]

Economic Aspects. U.S. capacity for production of merchant sodium dithionite (soHds basis) was estimated at 93,000 metric tons in 1994. There are three North American producers of sodium dithionite. Hoechst Celanese is the largest producer (68,000 tons capacity) with two formate production locations and one zinc process location. Olin (25,000 t capacity) produces solution product only at two locations using both the amalgam and electrochemical processes. In 1994, Vulcan started a small solution plant in Wisconsin using the Olin electrochemical process. In addition, it is estimated that 13,000 t/yr is produced at U.S. pulp mills using the Borol process from sulfur dioxide and sodium borohydride. Growth is estimated at 2—3%/yr. The... [Pg.150]

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. [Pg.151]

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). [Pg.151]

Sodium dithionite is considered only moderately toxic. The solution is reported to have an LD q (rat, oral) of about 5 g/kg. As with sulfites, fairly large doses of sodium dithionite can probably be tolerated because oxidation to sulfate occurs. However, irritation of the stomach by the Hberated sulfurous acid is expected. As a food additive, sodium dithionite is generally recognized as safe (GRAS) (367). [Pg.151]

Zinc Dithionite. Zinc dithionite [7779-86-4] is a white, water-soluble powder. Although it exhibits somewhat greater stabiHty in... [Pg.151]


See other pages where Dithionites is mentioned: [Pg.145]    [Pg.215]    [Pg.363]    [Pg.363]    [Pg.364]    [Pg.433]    [Pg.121]    [Pg.112]    [Pg.219]    [Pg.846]    [Pg.1213]    [Pg.87]    [Pg.89]    [Pg.89]    [Pg.1]    [Pg.420]    [Pg.257]    [Pg.276]    [Pg.150]    [Pg.150]    [Pg.150]    [Pg.150]    [Pg.151]    [Pg.151]    [Pg.151]    [Pg.151]    [Pg.151]   
See also in sourсe #XX -- [ Pg.2 , Pg.42 , Pg.705 , Pg.720 ]

See also in sourсe #XX -- [ Pg.539 , Pg.540 ]

See also in sourсe #XX -- [ Pg.364 ]

See also in sourсe #XX -- [ Pg.2 , Pg.720 ]

See also in sourсe #XX -- [ Pg.457 ]

See also in sourсe #XX -- [ Pg.128 ]

See also in sourсe #XX -- [ Pg.128 ]




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Alkenes Sodium dithionite

Basic electrochemical reactions of dithionite and sulphite

Citrate-bicarbonate-dithionite extraction

Detection of sodium dithionite

Diazo bonds dithionite

Dithionite

Dithionite

Dithionite bleaching

Dithionite detection

Dithionite disulfide

Dithionite ion

Dithionite ions, reactions

Dithionite oxidation

Dithionite oxidation kinetic limitations

Dithionite redox chemistry

Dithionite redox potential

Dithionite reductions

Dithionite reductive activation

Dithionite reductive activation products

Dithionite salts

Dithionite stability

Dithionite, Sulphite and Thiosulphate

Dithionite-citrate-bicarbonate

Dithionite-difference spectra

Dithionite-reduced proteins, Mossbauer

Dithionites compounds

Dithionites in antibody labelling with technetium

Dithionous Acid and Dithionites

Electrocatalysis with modified gold electrodes towards sodium dithionite

H Decomposition of Sodium Dithionite

Hydrogen dithionite

Hydrosulfite s. Dithionite

Hyposulfite s. Dithionite

Kinetic limitations in oxidation of dithionite and sulphite

Photochromism of Rhodium Dithionite Complexes

Photochromism rhodium dithionite complexes

Preparation and Analysis of Zinc Dithionite

Products of Dithionite Reductive Activation

Pyridinium salts dithionite reduction

Pyridinium salts reduction with dithionite

Reactions of Dithionite and Thiosulfate

Reagents dithionite

Reducing agents dithionites

Reduction sodium dithionite reactions

Reduction with sodium dithionite

Simultaneous detection of sodium dithionite, sulphite and indigo at a wall-jet electrode

Sodium dithionite

Sodium dithionite cleaving diazo bonds

Sodium dithionite compounds

Sodium dithionite detection

Sodium dithionite dienoic carboxylic acids

Sodium dithionite imines

Sodium dithionite manufacture

Sodium dithionite oxidation

Sodium dithionite pyridines

Sodium dithionite reduction

Sodium hydrosulfite dithionite

Sodium hydrosulfite s. Dithionite

Vatting with sodium dithionite

With dithionite

With sodium dithionite

Zinc dithionite

Zinc hydride dithionite

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