Chromium trioxide in water

Addition of acetic anhydride to a solution of chromium trioxide in water caused violent boiling [1], due to the acid-catalysed exothermic hydrolysis of the anhydride [2],... 

Quantitative Determination. — Dissolve 5 gm. of chromium trioxide in water and dilute to 500 cc. Introduce 10 cc. of this solution into a stoppered flask of about 400 cc. capacity, dilute with 100 cc. of water, and add 5 gm. of potassium iodide and 2 cc. of hydrochloric acid. Allow the mixture to stand for about ten minutes with frequent shaking, then dilute with 200 cc. of water, and titrate with decinormal sodium thiosulphate solution. 

When pyridine is added to a solution of chromium trioxide in water, it is possible to obtain a precipitate of the pyridinium salt of dichromic acid, that is pyridinium dichromate (PDC).11... 

Instead of dichromates, chromic acid obtained by dissolving chromium trioxide in water and sulfuric acid and acetic acid is used [184, 573],... 

A common way to change reaction conditions for the oxidation of alcohols is to modify the acid that is added to the medium. Indeed, chromium trioxide will have different oxidizing abilities in different acids. Since most organic compounds are insoluble in water, a cosolvent is usually required to dissolve not only the chromium reagent but also the alcohol substrate. This solvent must be resistant to oxidation, and acetic acid or acetone are commonly used. For the alcohol - carbonyl conversion several Cr(VI) reagents can be used, including chromium trioxide in water or aqueous acetic acid catalyzed by mineral acid, sodium dichromate in aqueous acetone catalyzed by mineral acid, sodium dichromate in acetic acid, the Cr03 pyridine complex, and err-butyl chromate.Both primary and secondary alcohols can be oxidized to the aldehyde or ketone, respectively. Aldehydes may be oxidized to the carboxylic acid under some conditions. 

The crystals are chromium trioxide, CrOs, not chromic acid, H2Cr04. The Shlubility of chromium trioxide in water was measured by R. Kremann who found that sat. soln. at d° contained S grms. of CrOs per 100 grms. of soln. 

Dissolve 1 g. of anthracene in 10 ml. of glacial acetic acid and place in 50 ml. bolt head flask fitted with a reflux water-condenser. Dissolve 2 g. of chromium trioxide in 2 ml. of water and add 5 ml. of glacial acetic acid. Pour this solution down the condenser, shake the contents of the flask and boil gently for 10 minutes. Cool and pour the contents of the flask into about 20 ml. of cold water. Filter off the crude anthraquinone at the pump, wash with water, drain well and dry. Yield, 1 g. Purify by re crystallisation from glacial acetic acid or by sublimation using the semi-micro sublimation apparatus (Fig. 35, p. 62, or Fig. 50, p. 70). 

A 8 A solution of chromic acid is prepared by dissolving 26.72 g of chromium trioxide in a mixture of 23 ml of concentrated sulfuric acid and enough water to make the total volume of the solution 100 ml. Rapid dropwise addition of a slight excess of this reagent to an acetone solution (2 % or less) of the hydroxy steroid at room temperature or below with stirring usually results in complete conversion to ketone in less than 10 min. The product is isolated by dilution with water followed by filtration or extraction. 

Acid (69)." To a well-stirred mixture of 108 g (0.232 mole) of cholesterol acetate and 1.2 liters of glacial acetic acid is added over a period of 2 hr, a solution of 70 g of chromium trioxide in 200 ml of 50 % glacial acetic acid. The reaction mixture is maintained at a temperature of 55°. Upon completion of the addition, the mixture is stirred for an additional 2 hr at 55°. Excess chromic acid is destroyed by addition of 60 ml of methanol, and then 800 ml of acetic acid is removed by distillation under reduced pressure at a bath temperature of 40°. The remaining liquid is diluted with 50 ml of water and allowed to stand for 12 hr. The crystalline 7-ketocholesterol acetate which separates is removed by filtration and washed with 80 % acetic acid to yield 33.3 g (35%) of (68) mp 149-152°. 

The chromic acid oxidizing reagent is prepared by dissolving 13.4 g of chromium trioxide in 25 ml of water. To this solution is added 12 ml of concentrated sulfuric acid. An additional minimum quantity of water is added if necessary to dissolve any precipitated salts. 

It has been claimed that chromium trioxide reacts with tetra-n-butylammonium chloride in water to produce tetra-n-butylammonium chromate, n-Bu4N+HCr04- [7], whereas benzyltriethylammonium dichromate is obtained from the closely analogous reaction of benzyltriethylammonium chloride with chromium trioxide in dilute hydrochloric acid [8]. 

Jones reagent was prepared by the method in Fieser and Fieser Dissolve 13.36 g of chromium trioxide in 11.5 nt of coned sulfuric acid, and carefully dilute this cooled solution (0 C) with water to 50 ml. 

Fusion of polonium dioxide with a potassium chlorate/hydroxide mixture gives a bluish solid (colorless when hot) which is more soluble in water than the corresponding polonite (Po032 ) this presumably contains some potassium polonate. The trioxide may possibly be formed by strongly heating polonium dioxide and chromium trioxide in air (12). 

Potassium Sulphate and Potassium Chromate. — Ignite 0.2 gm. of chromium trioxide in a porcelain crucible, triturate the residue with about 20 cc. of water, and filter. Evaporate the filtrate to dryness on a water-bath, dry the residue at 100° C., and weigh. The residue must not weigh more than 0.002 gm. 

P,5a-Dihydroxyandrostane-6, l-dione 3-Acetate (76)53a The foregoing mixture of epoxides (75) (18 g) is dissolved in 180 ml of hot, reagent-grade methyl ethyl ketone. The solution is cooled to room temperature and the crystalline mass is stirred with a paddle stirrer while 18 ml of a solution prepared from 15 g of chromium trioxide in 20 ml of water is added in portions over a period of about 10 min. During this time the temperature rises to about 58°. After an additional 10 min, 1 liter of water is added with stirring... 

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