Purification and drying of organic solvents

The light petroleum of various boiling ranges is generally sufficiently pure for most purposes. Unsaturated hydrocarbons can be removed by treatment with fuming sulfuric acid (oleum). 

Purification of aliphatic hydrocarbons by concentrated sulfuric acid lb The petroleum or hexane to be purified is repeatedly shaken with small portions of weakly fuming sulfuric acid (5 % sulfur trioxide content), until the acid phase remains colorless or at most becomes pale yellow. It is then washed Successively with concentrated sulfuric acid, distilled water, 2% sodium hydroxide solution, and distilled water, dried over sodium sulfate, shaken with fuller s earth, filtered, and distilled. 

Phosphoric oxide or sodium can be used for drying. It is best to use the sodium as a fine wire from a press and to add successive portions at intervals of time as, contrary to its behavior in ether, the metal becomes coated with a tenaciously adhering layer of oxide and thus rapidly becomes ineffective. 

Benzene, toluene, and xylene are sufficiently pure for most purposes as supplied. They can be freed from water by a simple distillation since water passes over with the first portions. They can also be dried by calcium chloride, phosphoric oxide, or sodium. Thiophen-free benzene is obtained as follows  

Removal of thiophen from benzene 2 Benzene (11) is stirred with concentrated sulfuric acid (80 ml) for 1.5 h at room temperature. The sulfuric acid is separated and these operations 

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For determinations of reaction constants, anomeric purity is not necessary, but for the determination of initial rotations, only one anomer can be present. Pure anomers can often be obtained by slow crystallization from a suitable solvent in the presence of nucleating crystals of the desired form and in the absence of crystals of other forms. For measurements in aqueous solution, use of mM potassium hydrogen phthalate as a buffer (pH 4.4) is recommended, to avoid variation in acidity during measurements. Precautions for purification, drying, and use of organic solvents have been described by Lowry and Baker. Anomeric impurities can be removed by lixiviation with a solvent (such as aqueous alcohol) in which both anomers are slightly soluble. 

Methyl (25, 3i )-2-(ferf-Butoxvcarbonylamino)-3-f(methylsulfonyl)oxy]-3-phenylpropanoate (99A) [13°1 To a soln of alcohol 98A (0.94 g, 3.18 mmol) and TEA (0.73 g, 7.18 mmol) at 0°C in CH2C12 was added MsCl (418 mg, 3.65 mmol). The mixture was stirred at 0°C for 45 min, and then quenched with aq dil HC1 and extracted with CH2C12. The organic layer was washed with aq NaHC03, followed by brine, and dried (Na2S04). The solvent was removed under reduced pressure to give the crude mesylate 99A as a foamy white solid that was used in the next step without further purification. 

A mixture of diisopropylethylamine (Hiinig s base, 1.74 ml, 10 mmol), palladium acetate (112 mg, 0.5 mmol, 5 mol%), tetra- -butylammonium bromide (1.61 g, 5 mmol) and 4-bromoanisole (110, 1.87 g, 10 mmol) in DMF (1.25 ml) was stirred under nitrogen at 115 "C for 96 h. After cooling to room temperature, water (50 ml) and diethyl ether (50 ml) were added. The organic phase was separated, washed with water and dried (MgS04). The solvent was evaporated in vacuo. Pure 4,4 -dimethoxy biphenyl (77, 514 mg, 48%) was obtained after purification with preperative chromatography, m.p. 172-173 "C. 

In a fortunate case, distillation aimed at purification may also result in the drying of the solvent. Distillation may be particularly effective in the removal of moisture if azeotropic mixtures with low boiling points are formed. For instance, the first step in the dehydration of ethanol is distillation after the addition of benzene, when water is removed in the volatile ternary azeotrope. Other solvents may also be dehydrated by distillation, e.g., benzene, chloroform, carbon tetrachloride, ethylene dichloride, heptane, hexane, toluene and xylene. In distillations with the aim of dehydration, the apparatus must be fitted with moisture traps (containing calcium chloride, silica gel or some other drying agent). It must be borne in mind that many anhydrous organic solvents are hygroscopic. 

Separation of sulphur compounds from gases has been described widely in literature, cf., e.g., [7-19]. A series of papers is specifically dedicated to the removal of H2S. For this particular purpose, several methods were recommended, e.g., physical gas washing , including absorption/extraction by means of organic solvents, e.g., amines, neutralization of acidic components, oxidation, chemical drying, purification by means of membranes and adsorption by carbonaceous sorbent materials. 

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