Recrystallization, preferential

In a typical procedure61144 the sulfonyl chloride in ether is added to an etheral solution of the diazoalkane and triethylamine. Filtration and evaporation gives the relatively pure thiirane dioxide. Further purification can be easily achieved by recrystallizations preferentially below room temperature in order to avoid fragmentation of the product into sulfur dioxide and the olefin. In general, when the temperature of the above reaction is lowered, the yields are improved without a drastic decrease in reactivity144. Many thiirane dioxides have been successfully synthesized through this method and a detailed list of them can be found elsewhere2. 

Radiolabeled " C-pirlimycin was readily synthesized from sodium cyanide and 4-ethyl-pyridine N-oxide as shown in Figure 2. The final reduction step produced a 2 1 mixture of desired product and a biologically inactive stereoisomer. Recrystallization preferentially produced pirlimycin HCL in >98% radiochemical purity and >99% chemical purity with an overall radiochemical yield of 25%. 

Optically pure (S)-benzyl methyl sulfoxide 139 can be converted to the corresponding a-lithio-derivative, which upon reaction with acetone gave a diastereomeric mixture (15 1) of the /S-hydroxysulfoxide 140. This addition reaction gave preferentially the product in which the configuration of the original carbanion is maintained. By this reaction, an optically active epoxy compound 142 was prepared from the cyclohexanone adduct 141181. Johnson and Schroeck188,189 succeeded in obtaining optically active styrene oxide by recrystallization of the condensation product of (+ )-(S)-n-butyl methyl sulfoxide 143 with benzaldehyde. 

Site of the. acidic surface oxides. The question whether the acidic surface oxides are bound to the periphery of the carbon layei-s or to the basal planes of the crystallites could be resolved by oxidation of a graphitized carbon black (46). The particles of carbon black are, at first approximation, spherical. The graphite-like crystallites show such preferential orientation that their c axis are aligned in a radial direction (64, 65). A schematic representation of this secondary structure is given in Fig. 1. On recrystallization between 2000 and 3000°, many small... 

The reaction of Li2PH in DME leads preferentially to compounds 9 and 10, which appear as a white powder, from which compound 9 can be obtained as cubic crystals by recrystallization with pentane or toluene. The presence of Me2Si(PH2)Cl (1), Me2Si(PH2)2 (2), as well as 3,4,5,6, 7, and 8 can be demonstrated in the liquid products of the reaction (34). 

The chiral, nonracemic, 6-monosubstituted bicyclic lactams 1 are deprotonated by a strong base (usually lithium diisopropyl amide) and then alkylated with an iodoalkane or an allylic or benzylic bromide. Alkylation preferentially takes place from the side opposite to that of the substituent R1, which is usually an alkyl or an aryl group. While the diastereomeric ratios may be as low as 75 25, they are most often >90 10 (see Table 9). The minor diastereomer can in most cases be easily removed by liquid chromatography and/or recrystallization to yield the pure major diastereomer. 

Curing of wetted coal ash results in carbona-tion to form calcite and possibly other metal carbonates. Calcite surfaces have been shown by Zachara et al. (1991) to preferentially sorb certain metals through adsorption followed by recrystallization (Zn, Co, Ni) or surface precipitation (Cd, Mn), but the total adsorption capacity of calcite for these metals is minor compared to their adsorption by other phases. 

If both anomers of the glycoside are obtained in a reaction, it is necessary to separate them. One separation method that has been used is the preferential extraction101 of the anomers with a volatile solvent. After extraction of the individual glycoside, the solvent is removed by evaporation, and the glycoside may be obtained in crystalline form. A second method of separation utilizes fractional recrystallization, and it may be possible by proper selection of the solvent to obtain both anomers in crystalline form. A third method utilizes chromatography for separating the anomers, and the pure anomers may be obtained from appropriate fractions from the column. The anomeric configuration of the anomers which have been obtained in pure form will need to be determined. Such determinations can be made by measurement of physical constants, from the n.m.r. spectra, and from the susceptibility of the anomer to enzymes of known specificity. 

The insoluble Ca(II) salts of weak acids, such as calcium phosphate, carbonate, and oxalate, serve as the hard structural material in bone, dentine, enamel, shells, etc. About 99% of the calcium found in the human body appears in mineral form in the bones and teeth. Calcium accounts for approximately 2% of body weight (18,19). The mineral in bones and teeth is mosdy hydroxyapatite [1306-06-5] having unit cell composition Ca10(PO4)6(OH)2. The mineralization process in bone follows prior protein matrix formation. A calcium pumping mechanism raises the concentrations of Ca(II) and phosphate within bone cells to the level of supersaturation. Granules of amorphous calcium phosphate precipitate and are released to the outside of the bone cell. There the amorphous calcium phosphate, which may make up as much as 30—40% of the mineral in adult bone, is recrystallized to crystallites of hydroxyapatite preferentially at bone collagen sites. These small crystallites do not exceed 10 nm in diameter (20). 

The optical isomers of DOM have been prepared in two ways. The racemic base has been resolved as the ortho-nitrotartranilic acid salt by recrystallization from EtOH. The (+) acid provides the (+) or S isomer of DOM preferentially. Also, the above-mentioned l-(2,5-dimethoxy-4-methylphenyl)-2-propanone can be reductively aminated with optically active alpha-methyl benzylamine with Raney Nickel. This amine is isolated and purified by recrystallization of the hydrochloride salt. When optically pure, the benzyl group was removed by hydrogenolysis with palladium on carbon. The mp of either of the optical isomers, as the hydrochloride salts, was 204-205 °C. 

Topochemical Polymerization The chiral crystalline environment of a monomer itself can be a source of asymmetric induction in solid-state polymerization [69-72], Prochiral monomers such as 37 give enantiomorphic crystals, one of which can be preferentially formed by recrystallization with a trace amount of optically active compounds. Photoir-... 

Preferential Enrichment was found in the middle of the development of a certain antiallergic drug, suplatast tosilate (ST).9 Whenever the racemic sample of ST was synthesized, the ee value of the solid sample obtained after recrystallization differed, i.e., it was not 0%, but was always distributed in the... 

Figure 4. Enantiomeric resolution of a racemic mixed crystal using Preferential Enrichment a case of an enrichment of the R enantiomer in solution after the first recrystallization of the racemic sample. Actually, the probability for either the R or the S enantiomer to be enriched in solution after recrystallization of an exactly racemic sample was 50% (see ref 9a).

Usual standard recrystallization conditions have been applied to the Preferential Enrichment experiment, except that highly supersaturated solutions are employed, because the supersolubility (a solubility obtained by dissolving the sample in a solvent on heating followed by being cooled) of the compounds showing Preferential Enrichment is considerably higher than that of the usual solubility at 25°C. 

These are all unusual. Thus, by collecting the enantiomerically enriched mother liquors with the same handedness, very efficient separation of the two enantiomers (>96% ee) has been easily achieved. Therefore, to probe if Preferential Enrichment occurs or not for a given compound, one only have to repeat recrystallization of the racemic sample several times at 25, 0, or -20°C and measure the ee value of the supernatant solution after each crystallization. 

Experimental-2] Example of resolution by preferential crystallization To a few 100 mL Erlenmyer Flask was added 0.6-0.8g of ( )-2 and 30 mL of water, and the mixture was heated up to give a clear solution. The solution was then gradually cooled and inoculated with a needle crystal obtained from Experimental-1, and allowed to crystallize. When about 15-30 mg of crystals were deposited, they were filtered off and dried. Yield and optical rotation were measured. Crystals with the same chirality were combined and recrystallized from water (10 20 parts (v/w) versus crystals) to afford enantiomerically pure salt 2 mp 104-105°C, [a]D25 + and - 24.5°C (c 1, EtOH). 

Finely divided calcium for laboratory purposes can also be prepared by recrystallizing bulk calcium from a sodium solution. The bulk calcium dissolves in sodium at elevated temperatures and, upon cooling, crystallizes out in small dendritic platelets that become trapped in a sodium matrix when the sodium solidifies. As in the previous synthesis, the sodium matrix may be removed by preferential reaction with a hydrous lower alcohol. 

Pentadienyltricarbonyliron cations are readily attacked by nucleophiles. They are more reactive in this respect than the corresponding cyclic complexes (160). Cyclohexadienyltricarbonyliron tetrafluoroborate can be recrystallized from water, while the 1-methylpentadienyl derivative is rapidly converted to the alcohol. In reactions of 1-alkylpentadienyltricarbonyliron cations with water or methanol the nucleophile adds preferentially to the carbon atom bearing the substituent, even when this is bulky. It is suggested that the alkyl substituent stabilizes the S-ion intermediate. Some authors consider that this intermediate could have an f/3-pentadienyl structure, the 18-electron configuration at the metal center being maintained by coordination of a molecule of water or of solvent (173). 

Pellizzari and Roncagliolo2 prepared this compound by reaction of carbohydrazide in dilute acetic acid with 2 mols of potassium cyanate and also by condensation of carbohydrazide- A-carboxamide hydrochloride with 1 mol of cyanate. The former procedure does not give a pure product, probably because of the preferential formation of the less soluble carbohydrazide-A-carboxamide. The latter reacts wjth hydrochloric acid to form the hydrochloride, which is water-soluble. Prior condensation of carbohydrazide to form the A-carboxamide is advantageous, since the hydrochloride of this compound will undergo further reaction with cyanate to give the desired product by precipitation from water. When the procedure outlined below is followed, it is not necessary to recrystallize the carbohydrazide-A, A -dicarboxamide unless an extremely pure material is desired. 

Another thermal separation unit often used for the laboratory scale purification of ionic liquids is recrystallization [125]. It is an attractive option for those ionic liquids that can form solids with a high degree of crystallinity. Crystals of ionic liquids are expected to be pure because each molecule or ion must fit perfectly into the lattice as it leaves the solution. Impurities preferentially remain in solution as they do not fit as well in the lattice. The level of purity of the crystal product finally depends on the extent to which the impurities are incorporated into the lattice or how much solvent is entrapped within the crystal formed. 

Anderson, Goodman, and Baker employed an O-(methoxycarbonyl) protecting group in an analogous manner for their synthesis of methyl 2,3-anhydro-D-ribofuranoside (XLV). Treatment of 1,2-0-isopropylidene-D-xylofuranose (XLI) with methyl chloroformate in pyridine gave, by preferential esterification of the least-hindered alcohol group (at C5), predominantly 1,2-0-isopropylidene-5-0-(methoxycarbonyl)-D-xylofuranose (XLII) a small proportion of the 3,5-di-0-(methoxycarbonyl) derivative was separated by fractional recrystallization. Subsequently, the C3-hydroxyl was esterified with tosyl chloride, and the resulting 3-0-tosyl ester XLIII... 

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