Solvents for Recrystallization

The ethanol not only converts the excess thionyl chloride to gaseous by-products (sulfur dioxide, hydrogen chloride, and ethyl chloride) but also serves as the recrystallizing solvent for the desired product. The checkers found that about 80% of this thick product can be poured directly into 800 ml. of ethanol. Two hundred milliliters of warm ethanol should be used to decompose the product remaining in the reaction flask. This is combined with the main portion. 

The acid is analytically pure. There is no satisfactory solvent for the recrystallization of large amounts of terephthalic acid. Small quantities may be recrystaUized from acetic acid, but the purity of a properly precipitated and washed sample is not thereby improved. 

Until one develops a feel for recrystallization, the best procedure for known compounds is to duplicate a selection in the literature. For new compounds, a literature citation of a solvent for an analogous structure is often a good beginning point. To assist in the search, Table A3.4 lists several of the common recrystallizing solvents with useful data. The dielectric constant can be taken to be a rough measure of solvent polarity. 

The caprolactam obtained must meet die specifications of permanganate number, volatile bases, hazen color, UV transmittance, solidification point, and turbidity in order to be used for repolymerization alone or in combination witii virgin CL.5 Reported CL purification methods include recrystallization, solvent extraction, and fractional distillation. One solvent extraction technique involves membrane solvent extraction. Ion exchange resins have been shown to be effective in the purification of aqueous caprolactam solutions. In one such process,... 

The crystal of 2 OPr recrystallized from EtOH/H20 solution, and the mixed crystal of the same ethyl and propyl cinnamate derivatives (2 OEt and 2 OPr), on photoirradiation for 2h at room temperature with a 500 W super-high-pressure Hg lamp, afforded the highly strained tricyclic [2.2] paracyclophane (2 OEt-2 OPr-cyclo) crystal quantitatively (Maekawa et ai, 1991b). A crystal structure analysis was carried out of a single crystal of the complex of 2 OEt-2 OPr-cyclo with HFIP (recrystallization solvent) in a 1 2 molar ratio. Fig. 13 shows the molecular structure of 2 OEt-2 OPr-cyclo viewed along the phenylene planes. The short non-bonded distances and deformation of the benzene rings, as seen in Fig. 13, are common to those of [2.2] paracyclophanes, as previously reported (Hope et ai, 1972a,b). 

The synthetic procedures for isolation of the salt appear to be rather simple. First, one prepares a solution in which the carbocation and carbanion coexist free from any combination reactions. Then, the hydrocarbon cation-anion salt is isolated after separation of the concomitant inorganic salt and evaporation of the solvent. For the purification of the crude salt recrystallization or reprecipitation with proper solvents is used. 

The enantioselective inclusion complexation of the reaction product with lOa-c in aqueous medium is more efficient than that by the recrystallization method. For example, inclusion complexation of rac-65e with 10a,b did not occur by recrystallization from an organic solvent however, enantioselective complexation occurred efficiently in aqueous medium to give finally optically active 65e [12]. 

Some fluoran compounds in Table 6 are found to form adducts with solvent. For example, when 6 -diethylamino-2 -(2,4-dimethylanilino)-3 -methylfluoran (77e) is recrystallized from toluene, it forms an adduct, mp 137-139°C, having 0.5mol of toluene of crystallization per mol of the fluoran the toluene of crystallization liberates on treatment with boiling n-hexane or isopropanol or on heating in vacuo. 2 -Anilino-6 -(N-cyclo-hexyl-N-methylaminoj-3 -methyl fluoran (77c) forms an adduct with... 

Turanose Phenylosazone. A mixture of 4 g. of turanose, 2 ec. of water, and 1 co. of phenylhydrazine was warmed on the steam-bath until solution was complete. To the cooled solution was added 3.5 cc. of phenylhydrazine and 4 cc. of glacial acetic acid, and the mixture returned to the steam-bath for one hour. At the expiration of this time, 40 cc. of warm 60% alcohol was added and, upon cooling, a rapid crystallization of the osazone occurred. The osazone was recovered by filtration and washed with absolute alcohol followed by ether to yield 4.2 g. (69%) of lemon-yellow needles. The osazone is soluble in hot water and separates on cooling as jelly-like particles, but water is not a satisfactory solvent for its purification. It was recrystallized from 15 parts of 95% alcohol with good recovery, as needles which melted with decomposition at 200-205° and rotated [ ]d +24.5° - +33.0° (24 hours, constant value c, 0.82) in a mixture of 4 parts of pyridine, by volume, and 6 parts of absolute ethyl alcohol. In methyl cellosolve (ethylene glycol monomethyl ether) solution it rotated C< 3d" + 44.3°— + 48.5° (24 hours, constant value c, 0.80). 

This product is sufficiently pure for most purposes. It may be crystallized from a mixture of alcohol and benzene using 155— 160 cc. solvent for 5 g. of tetraphenylcyclopentadienone the melting point of the recrystallized material is 219-220°. 

The checkers used methylene chloride alone as the solvent for recrystallization sublimation gave a product, m.p. 178-180°. 

Information in the notebook (which came from a handbook) for your compound might say, for alcohol (meaning ethyl alcohol), s.h. Since this means soluble in hot alcohol, it implies insoluble in cold alcohol (and you wondered what the i meant). Then alcohol is probably a good solvent for recrystallization of that compound. Also, check on the color or crystalline form. This is important since... 

The Buchner funnel (Fig. 46) is used primarily for separating crystals of product from the liquid above them. If you have been boiling your recrystallization solvents dry, you should be horsewhipped and forced to reread these sections on recrystallization ... 

Gafarov, et al.1 2 3 reported that heating neat tris(chloromethyl)acetic acid to a higher temperature cleanly affords the final product, 3-chloro-2-(chloromethyl)-1-propene. The present procedure allows for the pyrolysis of the crude material obtained in Step B to be used in Step C, thus eliminating the use of large amounts of solvents for recrystallization. 

In principle, separation of resonances of diastereomeric compounds (such as dl and meso isomers) may be increased simply through use of an appropriate achiral solvent. Chiral solvents may in some cases be especially effective in producing a separation, particularly if the diastereomers differ in configuration about a center that is amenable to analysis by the CSA method. Kaehler and Rehse (89) give a detailed account of conditions necessary for measurement of the ratio of meso- and dZ-tartaric acid employing A,N-dimethyl PEA. Bomyl acetate used as solvent for l,2-difluoro-l,2-dichloroethane (90) allows measurement of the diastereomeric composition. Paquette and co-workers (91,92), using TFAE, were able to determine the diastereomeric purity of the recrystallized adducts 47 of... 

This procedure may be used for the preparation of a variety of a-amino ketones as is indicated in Table I, which summarizes most of the submitters experience with this reaction. Principal deviations from the procedure wifi be in the time required for a negative starch-iodide test and the nature and amount of extraction and recrystallization solvent. It is strongly recommended that any one using the reaction for the first time carry out the preparation on a-phenylethylamine before attempting to use it on other more valuable amines. 

The cyclohexane in the recrystallization solvent reduces the tendency for the product to come out of solution as an oil. 

The application of supercritical fluids as anti-solvents is an alternative recrystallization technique for processing solids that are insoluble in SCF. This method exploits the ability of gases to dissolve in organic liquids and to lower the solvent power of the liquid for the compounds in solution, thus causing the solids to precipitate. 

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