Recrystallization from melts

The optical micrographs taken of sample A recrystallized from melt temperatures of 170, 200, and 230°C show that the morphology varied from row to mixed to spherulitic. The line nucleus seemed to break down into shorter lines and finally to a high concentration of points. 

Figure 12 DSC thermogram of poly(e-caprolactone) (a) crystallized from solution (b) native polymer extracted from PEC-urea-inclusion complex (c) recrystallized from melt.

Phenylpropanolamine. - With catalyst prepared as previously described from 0.5g of palladium chloride and 3g of charcoal, it was possible to reduce two portions of 9.8g of isonitrosopropio-phenone (0.06 mol), dissolved in 150 cc. of absolute alcohol containing 7. Og of hydrogen chloride, to phenylpropanolamine in from 145 - 190 minutes with yields of the isolated chloride from 9.4g to 11. Og, or 84 to 98% of the theoretical. After recrystallization from absolute alcohol the salt melted at 191°. The free base was obtained by treating an aqueous solution of the hydrochloride with alkali on cooling, the liberated amino alcohol solidified and after recrystallization from water melted at 103°."... 

Amino-2-hydroxybenZOiC acid. This derivative (18) more commonly known as 4-aminosa1icy1ic acid, forms white crystals from ethanol, melts with effervescence and darkens on exposure to light and air. A reddish-brown crystalline powder is obtained on recrystallization from ethanol —diethyl ether. The compound is soluble ia dilute solutioas of nitric acid and sodium hydroxide, ethanol, and acetone slightly soluble in water and diethyl ether and virtually insoluble in benzene, chloroform or carbon tetrachloride. It is unstable in aqueous solution and decarboxylates to form 3-amiaophenol. Because of the instabihty of the free acid, it is usually prepared as the hydrochloride salt, mp 224 °C (dec), dissociation constant p 3.25. 

When sublimed, anthraquinone forms a pale yeUow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286°C and boils at 379°—381°C. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubiUty in alcohol or benzene and is best recrystallized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the it spectmm, the double aUyflc ketone absorbs at 5.95 p.m (1681 cm ), and the aromatic double bond absorbs at 6.25 p.m (1600 cm ) and 6.30 pm (1587 cm ). 

For further purification the material may be recrystallized from hot water, or dissolved in alkali and reprecipitated, or distilled under reduced pressure or sublimed. Each of these operations involves considerable loss of product, either through solubility or through decomposition by heat. The best-appearing product is obtained by distillation under reduced pressure. The crude acid is distilled from a Claisen flask with a delivery tube set low in order that the acid need not be heated much above the boiling j)oint. The product boiling at i4i-i44°/20 mm. is ])ure wliitc and melts at 125-132° (Note 8). The yield of distilled acid is about 75-85 per cent of the weight of the crude acid. 

The melting point is not appreciably raised by recrystallization from petroleum ether. The highest melting point recorded in the literature is 53.8°. 

The yield is 147-160 g. (68-74 per cent of the theoretical amount). It sinters at 190-191° and melts at 199-200° (corr.). A sample twice recrystallized from glacial acetic acid melted at 200-202° (corr.) (Note 3). The crystal form of this product compares very favorably with that of quinizarin of the highest purity, as observed under the microscope. 

The crude nitrosothymol may be purified by drying and subsequent recrystallization from 2 1. of benzene, from which it sci)arates as a pale yellow solid, melting at 160-164°. A small second crop is obtained on concentrating the mother liquor,... 

Q, lo-Dibromoanthracene (3, 41).—When recrystallized from xylene, samples have been obtained that melt as high as 226° (uncorr.). E. de Barry Barnett (private communication). 

Benzyl-5-(2-hydroxyethyl)-4-inethyl-l,3-thia2ol1iim chloride. The product was isolated by pouring the ethanolic solution into well-stirred, ice-cold water, filtering, and recrystallizing from aqueous ethanol. The solutions should be ice-cold for the isolation of the low-melting acyloins. The products may also be Isolated by extraction as described for butyroin. 

The checkers found that 4-hydroxy-3,5-diiodobenzoic acid may be made from 4-hydroxybcnzoic acid using the above directions with the exception that the product is not recrystallized from acetone, in which it is only slightly soluble. The yield of 4-hydroxy-3,5-diiodobenzoic acid melting at 278-279° with decomposition is 59 g. (84 per cent of the theoretical amount). 

About two-thirds of the carbon tetrachloride is distilled. The solution is cooled, and the crystals of />-nitrophenyl isocyanate are filtered as quickly as possible in order to avoid prolonged exposure of the compound to the moisture of the air. By concentration of the mother liquor a further crop is obtained. The product is recrystallized from dry carbon tetrachloride and is obtained in the form of light yellow needles melting at 56-57° (Note 6). The yield after one recrystallization is 152-170 g. (85-95 P r cent of the theoretical amount) (Note 7). 

Since the pure material melts at 144°, the product needs no further purification for ordinary purposes. It has a faint odor, which can be removed by recrystallization from aqueous ethanol (suitably by solution in 8-10 ml. of ethanol per gram of material and the addition of water just short of precipitation from the hot solution). The loss in rccrystallization is only about 5% the melting point is unchanged. 

The product, D i-612, solidifies on chilling. Recrystallization from ethanol gives solid of melting point 34-35°. 

In a 500-ml. round-bottomed flask fitted with a reflux condenser are placed 16.2 g. (0.08 mole) of dry a-naphthylthiourea (Note 1) and 180 ml. of redistilled chlorobenzene. The flask is heated at the reflux temperature by means of an electric heating mantle. Evolution of ammonia begins almost at once, and all of the solid dissolves after 30-45 minutes. The solution is maintained at reflux for 8 hours (Note 2) and then evaporated on a steam bath at water-pump pressure to remove all of the chlorobenzene. The residue crystallizes on cooling and is extracted with four 30-ml. portions of boUing hexane (Note 3). Removal of solvent from the combined hexane extracts affords pale yellow crystals of naphthyl isothiocyanate, m.p. 58-59°. The yield is 12.7-13.0 g. (86-88%). Recrystallization from hexane (9 ml. of hexane for 1 g. of solute) gives colorless needles, melting point unchanged (Note 4). 

The product may be recrystallized from 1 2 acetic acid-water (about 8 ml./g.), but this process effects little improvement in melting point or color, even when activated carbon is used. 

Witt and Kopetschni report a melting point of 295-296° (dec.). This compound may be recrystallized from glacial acetic acid or ethanol. 

The pure nitrile melts at 81-83° after further recrystallization from hexane. ... 

Fig. 7.8. High temperature conversion of a-silicon nitride with an MgO additive to the p-pha.se is thought to be a consequence of dissolution of the a phase in a magnesium silicate with subsequent recrystallization from the melt. Enhanced dissolution rate should then strongly influence a. p conversion [84B01].

Cyano-3 -hydroxy-5a-pregnan-20-one A suspension of 5a-pregnane-3, 20-dione (2 g) in ethanol (90 ml) is treated with acetone cyanohydrin (4 ml) and three drops of triethylamine and stirred at room temperature until complete dissolution. After 3 hr, the solution is diluted with 200 ml of water, acidified with acetic acid and the crystalline precipitate is thoroughly washed with water and dried under vacuum to give 2.1 g (97%) of product mp 172-178° (dec). A sample recrystallized from ethyl acetate melts at 176-179° (dec) [a]p 86° (ethyl acetate). 

The total yield is 134.5 g (66%). Recrystallization from methanol-benzene of material (mp 202-205°) obtained from a pilot preparation gives yellow crystals melting at 208-212° 240 mp (e 11,500), 320-352 m ... 

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