Sodium bichromate

Chrome Tanning. The original chrome tanning was a two-bath process. The unhaired hides, delimed and bated, were treated with a solution of sodium bichromate [10588-01-9]. The amount of bichromate used was about 3—5% based on the weight of the hides. The bichromate was absorbed or adsorbed into the hide, the solution drained, and the hides refloated. Sodium bisulfite was added and two important reactions resulted in the formation of a basic chromium and coUoidal sulfur in the hide. This gave a chrome taimage and also helped to fiH the hide with the soHd sulfur. This cmde system, which continued in the industry in some types of leather for over 50 years, is obsolete. 

Modem chrome-tanning methods are weU controUed and employ an extensive knowledge of the chemistry of the system. The most common chromium-tanning material used is basic chromium sulfate [12336-95-7] Cr(0H)S04, made by the reduction of sodium bichromate with sulfur dioxide or by sulfuric acid and a sugar. 

Lead chromates are prepared by precipitation techniques from soluble salts ia aqueous media. The raw material Hst iacludes a number of different lead compounds, eg, Htharge, lead nitrate, basic lead acetate, basic lead carbonate, as well as acids, alkahes, sodium bichromate, and sodium chromate. The typical reaction can be represented by the foUowiag equation ... 

SODIUM AZIDE SODIUM BICHROMATE SODIUM BIFLUORIDE SODIUM BISULFATE SODIUM BISULFIDE... 

Or an equivalent quantltj of sodium bichromate (75 qrams), which may be dissolved m 3—4 times its weight of water and delivered from a tap funnej... 

Aluminum citrate Chromium sulfate Ferrochromo-lignosulfonate Manganese nitrate Potassium hichromate Sodium bichromate Ferric acetylacetonate Ammonium ferric oxalate... 

The natural product utahin (162), characterized as the 5,7-diisopropyl derivative of 159, presumably has been synthesized for the first time by oxidation (sodium bichromate) or diazotation of 5-aminohinokitiol (160 ... 

Chromate compounds have been considered by many to be the best inhibitors available. They are typically composed of mixtures of sodium bichromate and chromic acid, and art through passivation of the metal surfaces. Passivation involves formation of a tough metal oxide layer or other film on the surfaces. Chromate concentrations of 200 to 1000 ppm in the cooling water are generally required, although for environments where bimetallic influences exist, chromate levels must be much higher. For instance, when steel and copper surfaces are present in the system, chromate levels often exceed 2000 ppm (BETZ 1982, pp. 207, 212). 

Anthraquinone is obtained by oxidation of anthracene using sodium bichromate plus sulfuric add, and is purified by dissolving in concentrated sulfuric acid at 130 Cl and pouring into boiling water, whereupon anthraquinone separates as pure solid, and is recovered by filtration, Further... 

Electrolysis is carried out in series of tanks arranged in cascades. The initial solution is slightly acidified by hydrochloric acid and contains per litre 400 to 500 g sodium chlorate and 3 to 5 g sodium bichromate. The solution after flowing through the cascade is resaturated by chlorate and pumped again into the highest electrolyzer. It is recirculated until it contains per litre some 1 000 g of perchlorate and less than 50 g of chlorate. 

To oxidize some organic compounds, e. g. anthracene to anthraquinone, chromic acid or a solution of sodium bichromate in diluted sulphuric acid are used. During the process the ehromic acid is reduced according to equation ... 

Waste chromium lyes containing chromic sulphate dissolved in sulphuric acid were formerly regenerated by the addition of lime in excess to neutralize the sulphuric acid and precipitate the chromium hydroxide. The precipitate of chromium hydroxide obtained was subject to oxidizing calcination in a rotary fumaee and converted to calcium chromate which in turn was converted to sodium bichromate as follows ... 

Sodium sulfate is produced from natural sources and as byproduct in a variety of processes including ascorbic acid, battery recycling, resorcinol, silica pigment, viscose rayon, and sodium bichromate. Other salt cake production processes are based on the reaction of sulfuric acid (Mannheim process) or S02 and air (Hargreaves process) with sodium chloride. The Mannheim process is no longer in use in the United States. U.S. Hargreaves capacity is very limited. However, both processes are used widely in the rest of the world. 

Lead chromates and lead molybdates are produced by precipitation of soluble salts in aqueous media. Various lead sources include litharge, lead nitrate, basic lead actetate, and lead carbonate. The lead carbonate and basic lead acetate are used primarily to control particle size. Other ingredients include acids, alkalis, sodium bichromate, and sodium chromate. Additionally, molybdate orange manufacture involves the use of sodium molybdate and sodium sulfate as raw materials. 

Trivalent chromium pigments include chromium oxide (Cr203) and hydrated chromium oxide (Cr203 xH20). Chromium oxide is prepared by calcination, either by reduction of sodium bichromate (Na2Cr207) with sulfur or carbon at 750-900°C or by reduction of sodium bichromate with ammonium chloride or ammonium sulfate at 700°C. Hydrated chromium oxide is manufactured by hydrolyzing a complex chromium borate, which in turn has been produced by heating sodium bichromate with boric acid in a furnace. 

Iron blues, or cyanide iron blues, are complex ferriferrocyanide, generally with ammonium, potassium, or sodium cations. They are most commonly produced by a two-step process. First, ammonium, potassium, or sodium ferrocyanide, M4[Fe(CN)6], is reacted with ferrous sulfate, FeS04, to yield M2Fe[Fe(CN)]6. The latter is digested with hot sulfuric acid and oxidized with sodium chlorate or sodium bichromate to yield the ferric ferrocyanide M(Fe[Fe(CN)6]. ... 

In a large lead-lined vessel, 300 grams of sublimed, still moist, anthracene (calculated on the basis of 100 per cent product) is stirred with 6 liters of water and 600 grams of sodium bichromate. The mixture is heated to 80°C. over a Fletcher burner, and 1800 grams of 50 per cent sulfuric acid is added over a period of 10 hours. Chromic-acid should always be present, and the mixture should be stirred with a wooden or glass rod. Finally, the mixture is boiled for 2 hours, replacing the water lost by evaporation. The precipitate is then filtered off and washed thoroughly. The mother liquor can be worked up to recover chrome alum or chromic sulfate. 

For dyeing wool, the water-insoluble material is dissolved in ammonia and the solution is made distinctly acid with acetic acid. The dye is after-chromed with sodium bichromate, making the shade fuller and completely fast to boiling. 

The leuco compound (7.9 grams, 0.01 mole) is dissolved in 100 cc. 50 per cent acetic acid, and to the well stirred solution are added, simultaneously, 30 cc. 10 per cent oxalic acid solution and 12.5 cc. 10 per cent sodium bichromate solution. The mixture turns blue immediately and the oxidation is complete in 10 minutes. The solution is mixed with an equal volume of saturated salt solution and the acetic acid is neutralized with ammonia. The dye precipitates as a reddish, bronzy slime which soon becomes glass-hard. The product is dissolved in hot water, the solution is filtered, and the dye is then salted out by adding an equal volume of saturated salt solution. In this way, 7.8 grams of pure dye is obtained. It gives bright blue tints on wool from neutral or weakly acid solution. The dye is not very fast to light. 

This oxidation must be carried out in the presence of a zinc chloride solution which has no reducing action. A suitable solution can be prepared by dissolving sheet zinc in concentrated hydrochloric acid. (In the industry, the technical zinc chloride liquor is treated with enough sodium bichromate to destroy the reducing action. Frequently, this requires 100 to 250 grams of bichromate for 100 kilograms of the liquor.) The thiosulfuric acid is supplied by aluminum thiosulfate which is so highly dissociated that it reacts as free thiosulfuric acid. 

The beaker is placed on a felt pad, and a tube is arranged for blowing in steam. With thorough stirring, Solution I is added at room temperature, followed by Solution II, and 2 seconds later by one-third of Solution III (equivalent to 19 grams of sodium bichromate). The temperature of the mixture is raised to 40°C. in the course of 1 minute by the introduction of dry steam, and then Solution IV is added followed by the remainder of Solution III. The mixture is then heated rapidly to 70°. The solution becomes dark greenish blue in color due to the formation of the thiosulfonic acid of Bindsehedler green. When the temperature reaches 70°, the slurry (V) is added and the temperature is raised to 85°. 

Oxidation dyes. These dyes are produced on the substrate by oxidation of colorless compounds such as aromatic amines and phenols. For example, anihne may be oxidized in cotton with sodium bichromate to produce aniline black. The color produced by aniline black is characterized by a full bluish black shade and excellent fastness. However, oxidation dyes are rapidly decreasing in importance because aniline, other aromatic amines, and bichromate that are used for oxidation, are toxic [7]. 

Manufacture Finely powdered chromate, FeO.Cr Oj, is mixed with sodium carbonate and slake lime. It is heated and melted in a rotary kiln to 10001300 0, Water is poured into the product and sodium chromate is extracted as a solution. Sulphuric acid is added to the solution until the pH value becomes about 3i thus producing sodium bichromate, Ua r Orj 0 Insoluble matter is removed and the solution is concentrated by vacuum evaporation. A theoretical amount of potassium chloride is added to the solution and it is cooled to obtain raw crystals of potassium bichromate, Kj>Cra07, which are purified further by recrystallization. 

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