Chlorite, sodium

The sodium salt of chlorous acid HC102 was introduced onto the market as a modem bleaching article in 1940. Decomposition of this salt by hydrochloric acid proceeds according to the following equation  

From this it can be seen that 100 g of chlorite are equivalent to 156.99 g of active chlorine. The commercial product which has some 80 per cent NaCKX therefore contains 125 per cent active chlorine. 

Chlorite is known in two forms NaC102 and NaC102.3 HzO. The powder is completely stable, if stored in a dry place and at a normal temperature. When heated up to 150 to 200 °C, it decomposes mainly into chlorate and chloride and to a lesser extent into oxygen and chloride. Chlorite is more stable than hypochlorite, but less stable than chlorate. Its reaction with sulphur is spontaneous. It is, therefore, imperative to prevent chlorite from coming into contact with rubber which had been vulcanized with sulphur. 

Chlorine dioxide is also set free, if chlorine is introduced into a concentrated chlorite solution  

The manufacture of sodium chlorite starts from chlorine dioxide C102. It can easily be prepared in a laboratory by heating a mixture of powdered potassium chlorate and oxalic acid to 70 °C. The gas escaping will contain carbon dioxide and chlorine dioxide. 

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Oxalic acid Furfuryl alcohol, silver, mercury, sodium chlorate, sodium chlorite, sodium hypochlorite... 

Sodium chlorite [sodium chlorate (IV)] Sodium peroxide ... 

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. 

NaClO sodium hypochlorite NaC102 sodium chlorite NaClO sodium chlorate NaClO sodium perchlorate... 

Sodium chlorite oxidation of com and rice starches is recommended for the production of textile sizes (101) and oxidized starch is recommended as a hardening agent in the immobilization of microbial cells within gelatin (102). 

Chlorine dioxide, CIO2, is another chlorine derivative. This unstable, potentially explosive gas must be generated at the point of appHcation. The most common method of generating CIO2 is through the reaction of chlorine gas with a solution of sodium chlorite. 

The refining process most commonly used involves treatment with hot aqueous alkaH to convert free fatty acids to soaps, followed by bleaching, usually with hydrogen peroxide, although sodium chlorite, sodium hypochlorite, and ozone have also been used. Other techniques include distillation, steam stripping, neutralization by alkaH, Hquid thermal diffusion, and the use of active adsorbents, eg, charcoal and bentonite, and solvent fractionation... 

After World War I, other chlohne-based bleaches were developed. In 1921 the use of chlorine dioxide for bleaching fibers was reported followed by the development of the commercial process for large-scale production of sodium chlorite. In 1928 the first dry calcium hypochlorite containing 70% available chlorine was produced in the United States. This material largely replaced bleaching powder as a commercial bleaching agent. 

Hypochlorous acid can also be used, but the reaction is slower. Chlorine dioxide is also made by adding acid to sodium chlorite solutions by the overall reaction in equation 11 ... 

Some chlorine and chlorate also form through competing reactions. Chlorine dioxide is also evolved from mixtures of powdered sodium chlorite and acidic clays or alumina. 

Other Cellulosics. Rayon is bleached similarly to cotton but under milder conditions since the fibers are more easily damaged and since there is less colored material to bleach. Cellulose acetate and triacetate are not usually bleached. They can be bleached like rayon, except a slightly lower pH is used to prevent hydrolysis. The above fibers are most commonly bleached with hydrogen peroxide. Linen, dax, and jute requite more bleaching and mil der conditions than cotton, so multiple steps are usually used. Commonly an acidic or neutral hypochlorite solution is followed by alkaline hypochlorite, peroxide, chlorite, or permanganate, or a chlorite step is done between two peroxide steps. A one-step process with sodium chlorite and hydrogen peroxide is also used. 

Synthetic Fibers. Most synthetic fibers are sufficientiy white and do not requite bleaching. For white fabrics, unbleached synthetic fibers with duorescent whitening agents are usually used. When needed, synthetic fibers and many of theit blends are bleached with sodium chlorite solutions at pH 2.5—4.5 for 30—90 min at concentrations and temperatures that depend on the type of fiber. Solutions of 0.1% peracetic acid are also used at pH 6—7 for 1 h at 80—85°C to bleach nylon. 

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. 

Chlorine dioxide produced from the methanol reductant processes contains carbon dioxide and small amounts of formic acid. For this reason, sulfur dioxide and chloride-based chlorine dioxide processes are stih used for sodium chlorite production. This problem has been addressed by recycling a portion of the vapor from methanol-based generators so that formic acid further reacts to carbon dioxide ... 

In all cases, chlorine dioxide is produced at the point of use either from sodium chlorite or sodium chlorate. Production volume can be accurately estimated from total sodium chlorate consumption for chemical pulp bleaching because this use accounts for greater than 95% of all chlorine dioxide production. 

Sodium Chlorite. The standard enthalpy, Gibbs free energy of formation, and standard entropy for aqueous chlorite ions ate AH° = —66.5 kJ/mol ( — 15.9 kcal/mol), AG = 17.2 kJ/mol (4.1 kcal/mol), and S° = 0.1883 kJ/(molK) (0.045 kcal/(molK)), respectively (107). The thermal decomposition products of NaClO, in the 175—200°C temperature range ate sodium chlorate and sodium chloride (102,109) ... 

Many of the metal chlorites are not particularly stable and will explode or detonate when stmck or heated. These include the salts of Hg", Tl", Pb ", Cu", and Ag". Extremely fast decomposition with high heat evolution has been noted for barium chlorite [14674-74-9] Ba(Cl02)2, at 190°C, silver chlorite [7783-91-7] AgC102, at 120°C, and lead chlorite [13453-57-17, at 103°C (109). Sodium chlorite can be oxidized by ozone to form chlorine dioxide under acidic conditions (110) ... 

Sodium chlorite is used to produce chlorine dioxide by chemical oxidation, electrochemical oxidation methods, or by acidification with acids. Most of the commercial methods employ chlorine or sodium hypochlorite. 

Acid—Sodium Chlorite System. The addition of a strong inorganic acid into an aqueous sodium chlorite solution produces chlorous acid, which rapidly disproportionates into chlorine dioxide. One proposed set of reactions using hydrochloric acid is (110) ... 

Hypochlorous Acid—Sodium Chlorite System. In this method, chlorine gas is educted into water forming a hypochlorous acid solution which then reacts with aqueous sodium chlorite to produce chlorine dioxide (114—116). Hypochlorous acid, formed from the disproportionation of chlorine gas in water ... 

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