Recovery Recrystallisation

The potential for crystal growth by SSE lies in the fact that, not only impurity atoms but also crystalline defects tend to migrate under the influence of an electric field (Fieri et al. 1973). This effect is reinforced by the Joule heating of the metal by the current flow which increases the electromigration rate and enhances the process of recovery, recrystallisation and grain growth essential to the production of large crystals. 

Phenyl acridinium 9-carboxylate (1 g) ist refluxed with zinc dust (0.3 g) in acetic acid solution (10 ml) until the intermediate purple colour vanishes. Any unreacted zinc dust is removed by filtration, and the product precipitated by addition of water. If the precipitate is difficult to filter, extraction with ether followed by drying over MgSo4 and evaporation gives good recovery. Recrystallisation from ethanol gives white needles m.p. 116-118 in 60% yield. 

The inflammable solvents most frequently used for reaction media, extraction or recrystallisation are diethyl ether, petroleum ether (b.p. 40-60° and higher ranges), carbon disulphide, acetone, methyl and ethyl alcohols, di-Mo-propyl ether, benzene, and toluene. Special precautions must be taken in handling these (and other equivalent) solvents if the danger of Are is to be more or less completely eliminated. It is advisable to have, if possible, a special bench in the laboratory devoted entirely to the recovery or distillation of these solvents no flames are permitted on this bench. 

Frequently the recrystallized azobenzeno has m.p. 61°, which is unaffected by recrystallisation from alcohol. Upon distillation from a. 50 ml. distilling flask fitted with a short air condenser, the m.p. is raised to 67-5° and the recovery is about 90 per cent. one recrystallisation from diluted alcohol (as above) then gives perfectly pure azobenzene of m.p. 68-5°. 

In a 500 ml. wide-mouthed reagent bottle place a cold solution of 25 g. of sodium hydroxide in 250 ml. of water and 200 ml. of alcohol (1) equip the bottle with a mechanical stirrer and surround it with a bath of water. Maintain the temperature of the solution at 20-25°, stir vigorously and add one-half of a previously prepared mixture of 26-5 g. (25 -5 ml.) of purebenzaldehyde (Section IV,115) and 7 -3 g. (9-3 ml.) of A.R. acetone. A flocculent precipitate forms in 2-3 minutes. After 15 minutes add the remainder of the benzaldehyde - acetone mixture. Continue the stirring for a further 30 minutes. Filter at the pump and wash with cold water to eliminate the alkali as completely as possible. Dry the solid at room temperature upon filter paper to constant weight 27 g. of crude dibenzalacetone, m.p. 105-107°, are obtained. Recrystallise from hot ethyl acetate (2-5 ml. per gram) or from hot rectified spirit. The recovery of pure dibenzalacetone, m.p. 112°, is about 80 per cent. 

To obtain the pure dibromo ester, recrystallise from light petroleum, b.p. (60-80°) the recovery of the pure ester, m.p. 75°, is 85 per cent. 

If a-nitroso-p-naphthol is required in the crystalline condition, recrystallise it from light petroleum, b.p. 60-80° (7 -5 ml. per gram) the recovery is almost quantitative, m.p. 106°. 

The mother liquors from the washings and recrystallisations are saved for the recovery of the 4-nitrophthalic acid. The combined mother liquors ore concentrated to a small bulk and the acid is extracted with ether. Upon esterification by the Fischer - Speier method, the 3-nitro acid forms only the acid ester and may be removed by shaking the product with sodium carbonate solution, whilst the neutral ester of 4-iiitrophthalic acid remains unaffected. Hydrolysis of the neutral ester gives the pure 4-nltrophthalio acid, m.p. 165°. 

Benzyl phthalimide. Grind together 53 g. of finely-powdered, anhydrous potassium carbonate and 147 g. of phthalimide (Section IV,169) in a glass mortar, transfer the mixture to a 750 ml. round-bottomed flask, and treat it with 252 g. (230 ml.) of redistilled benzyl chloride. Heat in an oil bath at 190° under a reflux condenser for 3 hours. Whilst the mixture is still hot, remove the excess of benzyl chloride by steam distillation. The benzyl phthalimide commences to crystallise near the end of the steam distillation. At this point, cool the mixture rapidly with vigorous stirring so that the solid is obtained in a fine state of division. Filter the solid with suction on a Buchner funnel, wash well with water and drain as completely as possible then wash once with 200 ml. of 60 per cent, ethanol and drain again. The yield of crude product, m.p. 100-110°, is 180 g. Recrystallise from glacial acetic acid to obtain pure benzyl phthalimide, m.p. 116° the recovery is about 80 per cent. 

Hydrolyse the acetyl-sulphapyridine by boiling it with 10 parts of 2N sodium hydroxide for 1 hour, and allow to cool. Precipitate the base by the addition of 50 per cent, acetic acid until the mixture is just acid to litmus (pH about 6 5) avoid a large excess of acid. Filter off the crude sulphapyridine, wash well with water, and dry at 90° to constant weight (about 12 hours any acetate formed will bo decomposed). The yield is 35 g. Recrystallise from 90 per cent, acetone (5) the recovery of the pure compound, m.p. 190-191°, is about 80 per cent. 

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