Sodium dichromate.dihydrate

Methyl ethyl ketone. Use the apparatus of Fig. Ill, 61, 1 but with a 500 ml. round-bottomed flask. Place 40 g. (50 ml.) of see. butyl alcohol, 100 ml. of water and a few fragments of porous porcelain in the flask. Dissolve 100 g. of sodium dichromate dihydrate in 125 ml. of water in a beaker and add very slowly and with constant sturing 80 ml. of concentrated sulphuric acid allow to cool, and transfer the resulting solution to the dropping funnel. Heat the flask on a wire gauze or in an air bath until the alcohol mixture commences to boil. Remove the flame and run in the dichromate solution slowly and at such a rate that the temperature... 

Dissolve 15-0 g. of A.R. barium nitrate and 130 g. of A.R. cupric nitrate trihydrate in 450 ml. of water at 80°. Prepare a solution of sodium chromate by dissolving 89 g. of recrystallised sodium dichromate dihydrate in 200 ml. of water and adding 112 5 ml. of cone, ammonia solution (sp. gr. 0-90). Add the warm solution (80°) of nitrates in a thin stream, with stirring, to the sodium chromate solution (at 25°). Collect the orange precipitate by suction Bltration, wash it with two 50 ml. portions of 5fiter, drain well, and dry at 75-80° for 12 hours powder finely. 

Traditionally, sodium dichromate dihydrate is mixed with 66° Bh (specific gravity = 1.84) sulfuric acid in a heavy-walled cast-iron or steel reactor. The mixture is heated externally, and the reactor is provided with a sweep agitator. Water is driven off and the hydrous bisulfate melts at about 160°C. As the temperature is slowly increased, the molten bisulfate provides an excellent heat-transfer medium for melting the chromic acid at 197°C without appreciable decomposition. As soon as the chromic acid melts, the agitator is stopped and the mixture separates into a heavy layer of molten chromic acid and a light layer of molten bisulfate. The chromic acid is tapped and flaked on water cooled roUs to produce the customary commercial form. The bisulfate contains dissolved CrO and soluble and insoluble chromic sulfates. Environmental considerations dictate purification and return of the bisulfate to the treating operation. 

The classification as a carcinogen need not apply to fibres with a length weighted geometric mean diameter less two standard errors greater than 6 pm Sodium dichromate Sodium dichromate dihydrate... 

An autoclave (Note 1) is charged with 200 g. (1.28 moles) of 2,3-dimethylnaphthalene (Note 2), 940 g. (3.14 moles, 23% excess) of sodium dichromate dihydrate, and 1.8 1. of water. The autoclave is closed, heated to 250°, and shaken continuously at this temperature for 18 hours. The autoclave is cooled with continued agitation (Note 3), the pressure is released, and the autoclave is opened. The contents are transferred to a large vessel (Note 4). To effect complete transfer, the autoclave is rinsed with several 500-ml. portions of hot water. Green hydrated chromium oxide in the reaction mixture is separated on a large Buchner funnel and washed with warm water until the filtrate is colorless. The combined filtrates (7-8 1.) are acidified with 1.3 1. of 6N hydrochloric acid. The acidified mixture is allowed to... 

Propionaldehyde. Use 34 g. (42-6 ml.) of n-propyl alcohol, and a solution containing 56 g. of sodium dichromate dihydrate, 300 ml. of water and 40 ml. of concentrated sulphuric acid. The experimental details are identical with those for n-butyraldehyde, except that the addition of the dichromate solution occupies 20 minutes, the temperature at the top of the column is not allowed to rise above 70-76°, and during the subsequent heating for 15 minutes the liquid passing over below 80° is collected the receiver must be cooled in ice. The yield of propionaldehyde, b.p. 47-50°, is 12 g. 

The mixture of alcohols is placed in a 1000-mL round-bottomed flask, dissolved in 300 mL of ether, and cooled to 0°C. To this solution is added via an addition funnel over a 30-min period a mixture of sodium dichromate dihydrate (27.5 g, 0.092 mol), 100 mL of water, and 10.2 mL of coned sulfuric acid. The mixture is stirred at 0°C for 1 hr, warmed to room temperature where stirring is maintained overnight, diluted with 200 mL of water, and poured into a separatory funnel. The layers are separated and the aqueous phase is extracted with ether (3 x 200 mL). The combined organic layers are washed with saturated sodium bicarbonate solution (200 mL) and brine (200 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated by rotary evaporation to give 16.8-17.8 g (61-65%) of verbenone (Note 7). Final purification is achieved by distillation of the oil through a 5-in Vigreux column at reduced pressure (dry ice-acetone cooled receiver) 13.1 g (47%), bp 108-110°C (5 mm) (Note 8). 

Chromium(VI) oxide is prepared by heating sodium dichromate dihydrate with a slight excess of sulfuric acid in a steel tank or cast iron container ... 

Finely divided sodium dichromate (dihydrate or anhydrous) is mixed homogeneously with sulfur. This mixture is then reacted in a furnace lined with refractory bricks at 750-900 °C. An excess of sulfur is used to ensure completion of the reaction. The reaction mass is leached with water to remove water-soluble components such as sodium sulfate. The solid residue is then separated, dried, and ground. 

To this cold solution or suspension of /3-phenylhydroxylamine, a cold solution of sulfuric acid (750 ml. of concentrated acid and sufficient ice to bring the temperature down to —5°) is added with stirring. An ice-cold solution of 170 g. of sodium dichromate dihydrate in 500-750 ml. of water is added as rapidly as it can be poured into the mixture, which is stirred or swirled (Note 8). After 2 to 3 minutes, the straw-colored precipitate of nitrosoben-zene is collected on a Buchner funnel and washed with 1 1. of water (Note 9). 

At room temperature there is added in one portion a solution of 11 g. (0.037 mole, 50% excess over the theoretical amount) of sodium dichromate dihydrate in 20 ml. of water. A rise in temperature of some 6-7° will be observed it is desirable to moderate the temperature by external cooling if it should rise above 35°. 

Notes. (1) The chromic acid solution may be prepared as follows. Dissolve lOOg (0.33 mol) of sodium dichromate dihydrate in 300 ml of water and slowly add 134g (73 ml, 1.34 mol) of concentrated sulphuric acid (98%, d 1.84). Cool the solution and dilute to 500 ml with water in a graduated flask. 

Hydroxylamine. Violent reaction between sodium dichromate dihydrate and aqueous hydroxylamine may accelerate to explosion. Anhydrous hydroxylamine explodes violently on contact with sodium dichromate.5... 

Information regarding gastrointestinal effects in animals after inhalation exposure to chromium or its compounds is limited. Histological examination of the stomachs of rats exposed to sodium dichromate dihydrate at 0.2 mg chromium(VI)/m3 for 28 or 90 days revealed no abnormalities (Glaser et al. 1985). In mice exposed intermittently to 4.3 mg chromium(VI)/m3 as calcium chromate for 18 months, small ulcerations in the stomach and intestinal mucosa were reported to occur occasionally, but the incidence in the treated mice, in controls, or other details regarding these lesions were not reported (Nettesheim et al. 1971). No treatment-related histopathological lesions were found in the stomach, large intestine, duodenum, jejunum, or ileum of rats chronically exposed to chromium dioxide at 15.5 mg chromium(IV)/m3 (Lee et al. 1989). 

Characteristic Potassium dichromate (Chromium(VI)) Sodium chromate (Chromium(VI)) Sodium dichromate, dihydrate (Chromium(VI))... 

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