Chromic acid wash

Chromic acid-washed molybdenum-glass vessels and boric acid coated surfaces also appear to encourage peroxide formation [34—36], and the hydrogen peroxide so produced must be important in these oxidations since addition of H2 O2 increases the oxidation rate. 

Chromic acid washed molybdemum glass vessel ... 

In some cases, the removal of organic residues from glassware requires the use of a chromic acid wash (prepared by adding 100 ml of concentrated sulfuric acid slowly and with constant stirring to a solution of 5 g of sodium dichromate in 5 ml of water). In this situation, it is important to thoroughly rinse the glassware in deionized water so as to remove any trace of chromium, particularly if the latter species is part of the analytical scheme. 

The rods are effectively regenerated and can be reused. If necessary, they can be decontaminated by dipping in chromic acid, washing thoroughly with water and then fully reactivated by passing the rod through the flame of the FID. 

Chromatographic Separation of a Mixture of o- and p-Nitroaniline. Prepare a glass tube A (Fig. 24) in which the wider portion has a diameter of 3 cm. and a length of ca. 30 cm. the narrow portion at the base has a diameter of 5-7 mm. Wash the tube thoroughly (if necessary, with chromic acid, followed by distilled water and ethanol) and then dry. Insert a small plug of cotton-wool P as shown just within the narrow neck of the tube it is essential that this plug does not project into the wider portion of the tube. Clamp the tube in a vertical position. 

While keeping the collected deuterioammonia at dry ice-isopropyl alcohol temperature, lithium wire (10 mg) is added, followed by a solution of 3/3-hydroxy-5a-cholest-7-en-6-one (161 50 mg) in anhydrous tetrahydrofuran (4 ml). The reaction mixture is stirred for 20 min, the cooling bath is then removed and the ammonia is allowed to boil under reflux for 40 min. A saturated solution of ammonium chloride in tetrahydrofuran is added dropwise until the deep blue color disappears and then the ammonia is allowed to evaporate. The residue is extracted with ether and the organic layer washed with dilute hydrochloric acid and sodium bicarbonate solution and then with water. Drying and evaporation of the solvent gives a semicrystalline residue which is dissolved in acetone and oxidized with 8 N chromic acid solution. After the usual workup the residue is dissolved in methanol containing sodium hydroxide (0.2 g) and heated under reflux for 1 hr to remove any deuterium introduced at C-5 or C-7. (For workup, see section II-B). 

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°. 

A solution of 2.7 grams of chromic acid in 20 cc of water and 50 cc of acetic acid was added to the stirred solution of the above oil in 100 cc of acetic acid, maintaining the temperature below 20°C. After 90 minutes standing, 50 cc of methanol were added and the mixture concentrated under vacuum (20 mm). The residue was extracted with ether, washed to neutral and evaporated to dryness. The residual semicrystalline product (7 grams) was chromatographed over alumina and the fractions eluted with ether yielded 3.2 grams of A -19-norandrosten-3,17-dione having a MP of 163° to 167°C. 

Note in making up the chromic acid solution it is advisable to dissolve the silver nitrate separately and add it to the boiling chromic acid to prevent excessive crystallisation of the silver chromate. The chromic acid must be free from sulphate to avoid attack on the zinc. Immerse each specimen for 15 s in a 6% solution of hydriodic acid at room temperature to remove the remaining corrosion products. Immediately after immersion in the acid bath, wash the samples first in tap water and then in absolute methanol, and dry in air. This procedure removes a little of the zinc and a correction may be necessary. 

This procedure, coupled with the procedure described on p. 41, illustrates the Barbier-Wieland method for systematically degrading carboxylic acids. foxwor-Desoxycholic acid may be prepared from wor-desoxycholic acid by repetition of this procedure. If the chromic acid oxidation product is not sufficiently solid to filter after dilution with water, the mixture must be extracted with ether and washed with dilute hydrochloric acid before the alkaline extraction. Wxwor-Desoxycholic acid may be crystallized from ethyl alcohol. It melts at 239-241°. 

D. 3-Trimethylsilyl-3-buten-2-one (4). A solution of 55 g. of crude butenol 3 in 100 ml. of acetone is placed in a 500-ml., three-necked, round-bottomed flask equipped with a mechanical stirrer and a 250-ml. dropping funnel. The reaction vessel is immersed in an ice-water bath, and 95 ml. of an aqueous solution containing chromic acid and sulfuric acid (Note 13) is added to the stirred acetone solution. After completion of the addition, isopropyl alcohol is added to the reaction mixture until a green endpoint is reached, indicating consumption of the excess oxidant. The contents are poured into 450 ml. of ethyl ether, 300 ml. of water are added, and the aqueous layer is saturated with sodium chloride. The layers are separated, and the aqueous solution is extracted with five 150-ml. portions of ethyl ether. The combined ether solutions are washed with two 150-ml. portions of saturated aqueous sodium... 

Norprogesterone. A solution of 2.2 g of 19-hydroxyprogesterone in 110 ml acetone is treated with 11 ml of an 8 N chromic acid solution in dilute sulfuric acid 18a at 0° for 40 min. Then 110 g crystalline sodium acetate in 170 g water is added and the mixture extracted 3 times with benzene. The combined extracts are washed 5 times with saturated sodium chloride solution, dried and evaporated. The crystalline residue is washed with a small amount of benzene to give 2 g of the corresponding 19- acid mp 138° (dec). 

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