Chromic acid mixture

Oxidation of farnesol with chromic acid mixture gives rise to the aldehyde farnesal, which has the following characters —... 

Beckmann has examined the characters of the optically active men-thones. The oxidation of natural Z-menthol by chromic acid mixture yielded Z-menthone [a]n = - 28 5° which when treated with 90 per cent, sulphuric acid is converted into a d-menthone [ajn = 4- 28 1°, which, however, is not the optical antipode of the first it behaves as a mixture of d- and Z-menthone, but is more strongly dextro-rotatory than it would be if it were only a mixture of the two optical antipodes. 

By heating carvacrol with alkalis, it is converted into isocuminic-acid, C(jH3(C3Hy)(OH)(COOH), melting at 93°. By oxidation with chromic acid mixture, thymoquinone results. This compound forms-crystalline tables melting at 45° to 46°. 

ChromsMure, /. chromic acid, -anhydrid, n. chromic anhydride, chromium(VI) oxide, emisch, n. chromic acid mixture. -Ibsung. /. chromic acid solution, -salz, n. salt of chromic add, chromate. 

Nitrotoluene may be oxidized by means of strong nitric acid,2 chromic acid mixture,3 or permanganates.4 Electrolytic oxidation 5 has also been proposed. The procedure given above involves the use of chromic acid mixture, but, owing to a change in the concentration of sulfuric acid, the time of reaction is greatly shortened and the preparation is thus considerably improved. 

Procedure Weigh 200 g sodium dichromate and transfer to a 2 Litre hard-boroslicate glass beaker. Dissolve it in 100 ml of water and cool in an ice-bath to about 10-15°C. Now, add to it 1500 ml of sulphuric acid (3 6 N) in small bits at intervals with constant stirring. Chromic acid mixture is extremely corrosive and hygroscopic and must be stored in closed glass-stoppered bottles. 

Mercapto-l,2,4-thiadiazoles are oxidized, by 2N nitric acid at 50-60°, by chromic acid mixture, chlorine, or potassium permanganate to the disulfides, which are reconvertible to the thiols by reduction with sodium amalgam and alcohol.71,72,91 168 Use of excess chlorine in aqueous acetic acid results in replacement of the mercapto group by the halogen.168... 

Iodobenzoic acid has been prepared by the oxidation of -iodotoluene with chromic acid mixture 1 and with nitric acid 2 from the nitrile obtained from -iodonitrobenzene and potassium cyanide 3 and from / -aminobenzoic acid by diazotization.4... 

It should also be borne in mind that other substances, which often accompany ethyl alcohol, e g., certain higher alcohols, acetone, higher ketones, various essences, etc., are Oxidised by chromic acid mixture with formation of carbon dioxide. These substances are, however, almost completely eliminated by the procedure indicated above. 

Trinitrobenzoic acid is sparingly soluble in water, and soluble in alcohol and ether. It is prepared by oxidation of TNT with nitric acid, or with a solution of KCI03 in nitric acid, or with a chromic acid mixture. 

The Ostwald viscometer used for measuring viscosity by the above method is shown in the figure given above. It is first thoroughly cleaned with chromic acid mixture and dried. A known volume of water, usually 10 to 25 ml depending upon the capacity of the bulb A, is pipetted into the bulb B (bulb B is bigger than... 

It must be emphasized that all glass and porcelain apparatus, including spot plates and crucibles, must be kept scrupulously clean. It is a good plan to wash all apparatus (particularly spot plates) immediately after use. Glassware and porcelain crucibles are best cleaned by immersion in a chromic acid-sulphuric acid mixture or in a mixture of concentrated sulphuric acid and hydrogen peroxide, followed by washing with a liberal quantity of distilled water, and drying. The use of chromic acid mixture is not recommended for spot plates. 

The silver mirror test is best performed as follows. The solution of the tartrate is acidified with dilute nitric acid, excess of silver nitrate solution added and any precipitate present filtered off. Very dilute ammonia solution (approximately 0-02m) is then added to the solution until the precipitate at first formed is nearly redissolved, the solution is filtered, and the filtrate collected in a clean test-tube the latter is then placed in a beaker of boiling water. A brilliant mirror is formed on the sides of the tube after a few minutes. The test-tube may be cleaned either by boiling with chromic acid mixture or by boiling it with a little sodium hydroxide solution, and then rinsing it well with distilled water. 

---