Benzene, purification method

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

The procedures used for styrene and benzene purification are given elsewhere (15) as is the technique used to study the association states U The viscometric method relies on the fact... 

For many purposes the commercial reagent-grade DMF, dried with molecular sieves, can be used DMF decomposes on distillation at atmospheric pressure. The most convenient way to purify DMF is probably to let it pass through a column [358] of alumina (e.g., ICN Alumina N-Super I). Other methods involve drying (CUSO4 [367], which also removes amines), azeotropic distillation with benzene, or percolation through molecular sieves [368] followed by fractional distillation at reduced pressure. DMF is difficult to obtain in an anhydrous form, but for most purposes a small water content is not critical. An impurity of A-methylformamide may act as a proton donor or otherwise interfere in the follow-up reactions [369]. DMF should be stored in the dark under nitrogen. The different purification methods have been compared and discussed [370]. 

The alkanephosphonic acid dichlorides obtained by these methods are converted with amines, with all reactions carried out in solvents such as acetone, benzene, or diethyl ether at 10°C with triethylamine as HC1 captor. The conversion runs quantitatively followed by a purification with the help of column chromatography with chloroform/methanol in a ratio of 9 1 as mobile phase. The alkanephosphonic acid bisdiethanolamides could be obtained as pure substances with alkane residues of C8, C10, C12, and Ci4. The N-(2-hydroxyethane) alkanephosphonic acid 0,0-diethanolamide esters were also prepared in high purity. The obtained surfactants are generally stable up to 100°C. Only the alkanephosphonic acid bismonomethylamides are decomposed beneath this temperature forming cyclic compounds. 

The steam distillation may be omitted, if desired, by utilising the following method of purification. Allow the reaction mixture to cool, decant the aqueous layer and dissolve the residue in about 150 ml. of benzene. Wash the benzene solution with water, 1 per cent, sodiiun hydroxide solution, and finally with water dry with anhydrous magnesium sulphate, distil off the benzene on a water bath, and distil the residue under diminished pressure. 

The ease with which dissolution of the acetylated products can be achieved is affected by the method of isolation. In the author s experience, drying of the acetate with alcohol and ether results in apparent insolubility (even though the product was soluble at one stage of the purification process), and should be avoided. Drying, under diminished pressure, of the product precipitated by petroleum ether is sufficient. Chloroform is probably the best solvent. Nitroethane, tetrachlorethane, 2,4-pentanedione, pyridine, methyl acetate, ethyl acetate, and benzene, which have also been suggested, have disadvantages in that either they are unstable or they may cause aggregation in solution.44,116 116... 

The crude product can be purified by repeated crystallizations from benzene or water. Greater losses accompany this tedious method of purification than a single distillation. 

Materials and Method. Aqueous solutions of disodium alkyl phosphates were prepared by dissolving the corresponding acids in sodium hydroxide solutions. The alkyl phosphoric acids were synthesized by the reaction of pyrophosphoric acid with the respective alcohol in benzene at room temperature for A days. Details of the purification procedures are given elsewhere(7). 

An alternative method of purification is to wash the silver iodide with 250 ml. of methanol instead of benzene. The ether is evaporated, and the residue is combined with the methanol solution. The product is crystallized at—70°. Recrystallization of this crude product from methanol at —70° gives the same yields as the other method of purification. 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples of p-nitrophenol. Usually, the o-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pKg values. The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers of known pH (see for example Table 19, p. 43) from a solution of the substance in a suitable solvent such as ethyl ether. This method is more satisfactory and less laborious the larger the difference between the pK value of the impurity and the desired compound. Heterocyclic nitro compounds require similar treatment to the nitroanilines. Neutral nitro compounds can be steam distilled. 

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