Fractional crystallization and

A fourth ahoy separation technique is fractional crystallization. If shica is co-reduced with alumina, nearly pure shicon and an aluminum shicon eutectic can be obtained by fractional crystallization. Tin can be removed to low levels in aluminum by fractional crystallization and a carbothermic reduction process using tin to ahoy the aluminum produced, fohowed by fractional crystallization and sodium treatment to obtain pure aluminum, has been developed (25). This method looked very promising in the laboratory, but has not been tested on an industrial scale. 

Pyridine, and its monomethyl and 3,5-dimethyl derivatives " combine exothermically with dimethyl acetylenedicarboxylate in ether yielding some ether soluble materials, including trimethyl pyrrocoline-1,2,3-tricarboxylate (Section III,F,3) and deep red ether-insoluble gums. A number of crystalline compounds have been isolated from these gums by fractional crystallizations and will now be considered in detail. In the case of pyridine, Diels et al. ° isolated a red labile 1 2 molar adduct, which they formulated as (75), which isomerized rapidly on standing to a yellow stable adduct (76). These formulations are no longer accepted. Diels and Alder also suggested that the acetylenic ester first dimerized to the diradical (74) which then combined with the pyridine. 

Besides discovering this method of resolution, Pasteur also discovered the method of conversion to diastereomers and separation by fractional crystallization and the method of biochemical separation (and, by extension, kinetic resolution). 

This model of liquid extraction is symmetrical to fractional crystallization and has attracted renewed interest after the demonstration by Johnson et al. (1990) that REE distributions in abyssal peridotite clinopyroxene cannot be accounted for by equilibrium melting processes. The solid is supposed to maintain its chemical homogeneity while liquid is continuously extracted. Only the last drop of liquid is supposed to be in equilibrium with the residue. 

As for fractional crystallization and fractional melting, element-element plots with a logarithmic scale should show straight lines for the solid as well as for the liquid, since both differ by a constant coefficient. Contrary to fractional crystallization but similar to fractional melting, discussed above, and to percolation, to be presented below, zone-melting is a very powerful process to separate incompatible elements. 

The diastereoisomers have different physical properties. They have different melting and boiling points, solubilities, densities, refractive indices or adsorption coefficients. They can be easily separated, most often by fractional crystallization and adsorption. The enantiomers are not separated by these techniques. 

Morse S. A. (1976). The lever rule with fractional crystallization and fusion. Amer. Jour. Scl, 276 330-346. 

X-Ray studies on Na[(-)5 g-Co(ox)(aa)2],2H20 [aa = trans-iV-methyl-(S)-alaninate] confirm the RS configuration of the aa ligands and show the absolute configuration of the anion to be A. Fractional crystallization and column chromatography on D-lactose has been used to separate diastereoisomers of [Co(acac)2(L-Phe)] and [Co(acac)2(L-Val)]. The method was, however, unsuccessful for the corresponding L-Ala complex. ... 

Chromatographic methods seem to offer the only possibility to provide pure stoichiometric selenium sulfides as fractional crystallization and sublimation result in more or less complicated mixtures. Conventional column chromatography has turned out to be unsuccessful, but recently it has been shown that high-pressure liquid... 

A key problem in the present natural analogue study is the distinction between chemical variations related to trace element migration during basalt alteration and variations due to magmatic fractionation and other syn-intrusive processes. The detailed evaluation of the available data has shown that the chemical and isotopic composition of the HC1 residues is largely controlled by fractional crystallization and syn-intrusive assimilation of salt. In contrast, the chemical composition of the leachates is strongly modified by post-intrusive alteration (Steinmann et al. 1999). 

The reaction of a racemic form with a chiral reagent, for example, a racemic ( ) acid with a (-) base, yields two diastereomeric salts ( + )(-) and (-)(-) with different solubilities. These salts can be separated by fractional crystallization, and then each salt is treated with a strong acid (HCI) which liberates the enantiomeric organic acid. This is shown schematically ... 

A mixture of l,cw-3-dibromo-/ram-l,/ran.v-3-dinitro-dM-2,rran,s-4-diphenylcyclobutane (4 7,6 g, 17 mmol) and pyridine (1.6 g, 20 mmol) in benzene at 20 nC within a few seconds became yellow and deposited a white precipitate. After 10 min, the mixture was filtered and concentrated to dryness in a stream of air. Fractional crystallization and chromatography gave fine yellow needles of 5 yield 4.47 g (73%) mp 129-131 C. 

Treatment of chromium (III) acetylacetonate with acetic anhydride and boron trifluoride etherate yielded a complex mixture of acetylated chelates but very little starting material. Fractional crystallization and chromatographic purification of this mixture afforded the triacetylated chromium chelate (XVI), which was also prepared from pure triacetylmethane by a nonaqueous chelation reaction (8, 11). The enolic triacetylmethane was prepared by treating acetylacetone with ketene. The sharp contrast between the chemical properties of the coordinated and uncoordinated ligand is illustrated by the fact that chromium acetylacetonate does not react with ketene. 

The synthetic route to R(+)-MPTSO is outlined in Reaction 6. The experimental detail followed that of Boucher and Bosnich (39) and is a modification of literature methods (46, 41). Chlorination of the para-toluene sulfinate gives the sulfinyl chloride that was converted to the (—)menthyl sulfinates. This di-astereomer mixture was resolved by fractional crystallization, and the subsequent Grignard reaction, that is known to proceed by direct inversion at the sulfur (42),... 

The linear trinuclear cation (100) and the tetranuclear cations (101) to (103)448-450 (Table 52) exist with mononuclear complexes in aqueous ethylenediamine buffer solutions in which equilibrium has been established by the catalytic effect of Cr2+ and charcoal under well-specified conditions.358 The cations were separated by ion exchange chromatography and fractional crystallization, and isolated as various salts (Table 52). The tetranuclear (rhodoso) compound (104)4S1 has been reprepared448 by a modification of Pfeiffer s method. 

Froth Flotation. Froth flotation (qv) of potassium chloride from sylvinite ores accounts for ca 80% of the potassium chloride produced in North America and about 50% of the potassium chloride in Europe and the CIS. Fractional crystallization and heavy-media processing account for the remaining amounts produced. Froth flotation has been described (6,16,17). 

Analyses of the purified compound by G. Lemoine, G. Ramme, H. Schulze, J. Mai and F. Schaffer, L. Wolter, and A. Stock and co-workers are in agreement with the formula P4S3. G. Lemoine found that the fractional crystallization and fractional sublimation of the tetritatrisulphide gave no evidence of a heterogeneity. The vap. density determinations of G. Ramme, G. Lemoine, F. Isambert, A. Helff, and A. Stock and H. von Bezold are in agreement with this formula, so also is the mol. wt. calculated from the effect of this sulphide on the b.p. of carbon disulphide by A. Helff, and A. Stock and H. von Bezold. The fused product appears as a... 

Resolution of bromohydrifts.2 Diastereoisomeric esters of bromohydrins with MTPA are readily separated by fractional crystallization and characterized by NMR. The optically pure bromo MTPA esters are convertible by known methods into chiral alcohols, diols, and epoxides, including arene oxides. 

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