Fractional crystallisation under reduced pressure

Methylnaphthalene [91-57-6] M 142.2, m 34.7-34.9 , b 129-130 /25mm. Fractionally crystallise repeatedly from its melt, then fractionally distil under reduced pressure. It has been crystallised from benzene and dried under vacuum in an Abderhalden pistol. It can be purified via its picrate (m 114-115°) or better via the 1,3,5-trinitrobenzene complex as for 1-methylnaphthalene (above). [Beilstein 5IV 1693.]... 

Methyl oleate (methyl cis-9-octadecenoate) ]112-62-9] M 2%.5, f -19.9 , b 217°/16mm, d4 0.874, up 1.4522. Purify the oleate by fractional distillation under reduced pressure, and by low temperature crystallisation from acetone. Store it in the dark tmder N2. [Beilstein 2IV 1649.]... 

VinyInaphthalene [827-54-3] M 154.2, m 66 , 65-68 , b 76-81 /2.5mm, 135-137 /18mm. Commercial material can containup to 5% of MeOH. The flammable solid can be fractionally distilled under reduced pressure using a spinning-band column dry it with CaH2 and again distil it under vacuum. It crystallises from aqueous MeOH, EtOH (m 66 ) or petroleum ether (m 66-66.5 ). Store it in sealed ampoules in a freezer. The picrate has m 91-92 (from EtOH). [Beilstein 5 IE 1775,5IV 1833.] It is an irritant. 

The common methods of purification, discussed below, comprise distillation (including fractional distillation, distillation under reduced pressure, sublimation and steam distillation), crystallisation, extraction, chromatographic and other methods. In some cases, volatile and other impurities can be removed simply by heating. Impurities can also sometimes be eliminated by tbe formation of derivatives from which the purified material is regenerated (see Chapter 2). 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

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