Melting point drying samples

The final air-dried product is pure except for its moisture content, as is shown by the fact that on drying in vacuo it has a very good melting point. A sample of Kahlbaum s nitroso-/3-naphthol melted at 101-105°. 

A recommended procedure for obtaining accurate melting points on samples tf pentaerythritol Involves adding 7-S mm of the finely powdered product, which las been (fried for 2 hours at 100-110°C, to a dry 16-om tube (1.0-1.6 ram outside li meter) and immersing in a 200°C melting point bath. The temperature of the... 

Before attempting a melting point determination as a check on the purity, care must be taken to ensure a perfectly dry sample of the compound since traces of solvent may lower the melting point appreciably. 

The crude material from one run melted at 125-143°, but the melting point changed to 140-150° upon drying over phosphorus pentoxide at 100° under a pressure of 10 mm. Another crude sample melted at 145-147°. 

Solid sulfonyl cyanides now show a melting point not more than 1-2 below that of recrystallized material. They may be used with t further purification. Analytically pure samples are obtained by r crystallization from dry benzene, diy petroleum ether, or a mixture or the two. 

The acid chloride reacts with the free hydroxylamine with considerable rapidity apparently without dissolving. The reaction is completed when a sample of the suspension shows to become clear on adding aqueous alkali. The crystalline pale-yellow mass of product Is separated by filtering, lavishly washed with water and dried in vacuum. The crude product yield is actually quantitative. The product is purified with excellent yields by repeatedly crystallizing from hot dioxane and washing with ether melting point 181°C to 182°C (dec.). 

The solvents were evaporated in vacuo, and the residue was taken up in 80 ml of 3M hydrochloric acid. After addition of 220 ml of water, the insoluble material was filtered off, washed with 100 ml of water and then dried. The insoluble material weighed 9.5 g and was mainly unreacted bromo compound. The filtrate was reacted with 50 ml of 7 M NaOH, extracted three times with methylene chloride (50 m -t 2 x 25 ml portions), dried over potassium carbonate, and then evaporated. The yield of residue was 26.8 g which corresponds to 71.4% of the theoretical yield. This residue was a colorless solidifying oil and was dissolved in 200 ml chloroform. Hydrogen chloride was bubbled in until a sample of the solution tested acidic to wet pH indicator paper. A precipitate was obtained and recovered by filtration. The precipitate was washed with chloroform and dried. The melting point was determined to be from 246 Cto247.5°C. 

Benzyl cyanide (40 g. = 0 33 mole) is heated in a round-bottomed flask (capacity 0-5 1.), with a mixture of 50 c.c. of concentrated sulphuric acid and 30 c.c. of water. The flask is provided with an upright air condenser, and is placed in a conical (Babo) air bath. The heating is continued until the appearance of small bubbles of vapour indicates that a reaction, which rapidly becomes violent, has set in the liquid boils up, and white fumes are emitted. It is allowed to cool and then two volumes of water are added. After some time the phenylacetic acid which has crystallised out is filtered off with suction. If a sample of the material does not form a clear solution with sodium carbonate in water (presence of phenylacetamide), the whole of the crude material is shaken with sodium carbonate solution and the mixture is filtered. From the clear filtrate phenylacetic acid is reprecipitated with sulphuric acid, and can be recrystallised directly from a rather large volume of hot water or, after drying, from petrol ether. Because of its low melting point (76°) it often separates at first as an oil, but it can also be conveniently purified by distillation in vacuo from a sausage flask.2... 

Freshly distilled benzaldehyde (10 g.) is mixed with 25 c.c. of alcohol and a solution of 2 g. of potassium cyanide in 5 c.c. of water. The mixture is boiled on the water bath under reflux for one hour. Then the product is allowed to cool slowly, and the crystals which form, after being separated by filtration and washed with a little alcohol, are dried on the water bath. In order to obtain some quite pure benzoin a small sample of the crude product is recrystallised from a little alcohol. Melting point 134°. Yield about 90 per cent of the theoretical. 

After the liquid has become clear, filter at the pump, wash the yellowish-brown precipitate with water, and dry thoroughly, first on porous plate and then in a vacuum. Then recrystallise from petrol ether (boiling point. 50°-60°) decolorising with a little animal charcoal. Melting point 98°. Heat a sample with dilute hydrochloric acid in a test tube. 

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