Mixing fractional crystallization

A computer- There are a number of computer programs which can be used to interpret trends on based approach variation diagrams and to solve mixing problems of the type described above. to mixing Fractional crystallization, for instance, may be expressed as ... 

Ciyst lliz tion. Low temperature fractional crystallization was the first and for many years the only commercial technique for separating PX from mixed xylenes. As shown in Table 2, PX has a much higher freezing point than the other xylene isomers. Thus, upon cooling, a pure soHd phase of PX crystallizes first. Eventually, upon further cooling, a temperature is reached where soHd crystals of another isomer also form. This is called the eutectic point. PX crystals usually form at about —4° C and the PX-MX eutectic is reached at about —68° C. In commercial practice, PX crystallization is carried out at a temperature just above the eutectic point. At all temperatures above the eutectic point, PX is stiU soluble in the remaining Cg aromatics Hquid solution,... 

Elution with a petroleum ether-benzene (1 1) mixture (2.2 liters) affords 5.8 g of starting material. Further elution with petroleum ether-benzene (1 1) (400 ml) gives initially 0.57 g of a mixed fraction, followed by 0.47 g of a crude product (eluted with another 400 ml of the same solvent mixture). Crystallization of the latter fraction from methylene dichloride-petroleum ether gives (20 R)-18,20-cyclo-5a-pregnane-3/5,20-diol 3-acetate mp 164-166.5° [ ]q 9°. Elution with benzene (400 ml) gives 1.57 g of an oil. Continued elution with benzene (600 ml) and benzene-ether (9 1) (800 ml) provides 1.81 g of crude (20 S)-18,20-cyclo-5a-pregnane-3j9,20-diol 3-acetate mp 139-140° [a]o 15°. 

As expected, similar treatment of 3-nitroarenes furnishes mixtures of 4- and 6-substituted 3H-azepines, 54 and 55, respectively.176 Comparable yields of mixed azepines were also obtained by deoxygenation of 3-nitroarenes with alkylphophorous triamides, formed in situ from hexa-methylphosphorous triamide and excess of a secondary amine.66 In a few cases the 3//-azepines were separated by fractional crystallization of their oxalate salts66 but, in general, pure isomers were not isolated and the yields cited in the table were determined by HNMR spectroscopy. 

The melt mixed 80/20 PS/iPP blend displays a set of exotherms, where the amount of the iPP component that was heterogeneously nucleated is substantially reduced as indicated by the decrease of the crystallization enthalpy in the temperature region where the iPP crystallizes in bulk, i.e., at 109-111 °C (exotherm labeled A). This effect is due to the confinement of iPP into a large number of droplets. If the number of droplets of iPP as a dispersed phase is greater than the number of heterogeneities present in the system, fractionated crystallization occurs. The number of droplets for this composition is known (by scanning electron microscopy observations) to be of the order of 1011 particles cm-3 and polarized optical microscopy (POM) experiments have shown that this iPP contains approximately 9 x 106 heterogeneities cm-3. In fact, it can be seen in Fig. 1 that the fractionated crystallization of the iPP compon-... 

Because of the large demand for p-xylene, another method is now being used by Amoco to increase the percentage of the para isomer in mixed xylenes. They are heated at 300°C with an acidic zeolite catalyst, which equilibrates the three xylenes to an o,m,p ratio of 10 72 18%. The para isomer is separated by fractional crystallization, whereas the o,m mixture is reisomerized with the catalyst to produce more para product. Theoretically, all the xylenes could be transformed into the desired para isomer. The zeolite catalyst has the following structure. 

In one run (5.0-mmol scale), the checkers obtained a crude product that contained ca. 40% of recovered 1. Attempts to purify the aldol product from this mixture by using the described crystallization procedure was unsuccessful. Accordingly, the crude product (2.36 g) was purified by flash chromatography on 170 g of silica gel using 1000 ml of a 9 1 1 mixture of hexane, ethyl acetate and methylene chloride. This provided 0.72 g of starting ester 1, 1.39 g of pure aldol 2, and 0.259 g of mixed fractions containing 2 and the minor aldol diastereoisomer (4 1 by H NMR analysis). 

The mixed alum solution, on treatment with ammonia or potassium carbonate, forms carbonates of potassium, rubidium and cesium. Rubidium carbonate is separated from other alkab metal carbonates by fractional crystal-bzation (see Rubidium)... 

Substance A is a solid and is mixed with Y which is also a solid. A student wishes to separate the two substances through fractional crystallization. Which property allows the two substances to be separated through this procedure ... 

The vinasse of sugar beet.—Sugar beet contains about 0 5 per cent, of potash, K20, largely in combination with organic acids. The potash accumulates in the molasses of the best sugar factories. The molasses are fermented and distilled for alcohol. The residue which remains in the retort—called vinasse—may be used as a manure, or it may be mixed with lime and ignited to form what was once called vinasse cinder, and used in the manufacture of soft-soap. It is, however, more profitably refined for potash by fractional crystallization.6 The product has approximately the composition ... 

Potassium iodide can also be obtained from the aq. extract of kelp or from the mother liquid remaining after the separation of sodium chloride and potassium sulphate from sea-water by evaporation. In E. Allary and J. Pellieux process,8 the liquid is evaporated to dryness and roasted in a special furnace so as to avoid a loss of iodine. The product is fractionally extracted with cold water, when a soln. is obtained which on evaporation gives a residue with 50 per cent, of alkali iodide. This product is extracted.in a special digester with 50 per cent, alcohol. The solvent dissolves little more than the iodides. The alcohol is distilled off, and on evaporation a residue containing about 34 per cent, of potassium iodide, and 66 per cent, of sodium iodide is obtained. To convert the latter into potassium iodide, the proper quantity of a soln. of potassium carbonate is added and carbon dioxide passed into the liquid whereby sodium bicarbonate is precipitated. The precipitate is separated by a filter press, and the small amount of sodium bicarbonate remaining in the soln. is separated by the addition of a little hydrochloric acid and the sodium chloride and potassium iodide separated by fractional crystallization. In E. Sonstadt s process, the mother liquid is treated with chlorine mixed with potassium chlorate or permanganate so as to convert the iodine into iodate. A soln. of a barium salt is added, and the barium iodate treated with potassium sulphate. Barium sulphate is precipitated, and the soln. of potassium iodate is evaporated to dryness and calcined to convert the iodate to iodide. The latter is purified by crystallization. 

The overall process, illustrated in Scheme 10.4, intercepts the racemate (2) by crystallization from heptane. After separation of the enantiomers using the MCC process, the radafaxine free base is converted to the desired salt directly on treatment with anhydrous HCl. Any mixed fractions from the MCC separation are combined with the epimerized R,R)-enantiomer and fresh racemate for processing, hence generating further radafaxine free base for conversion to the hydrochloride salt. These results were subsequently confirmed in a Proof of Concept study performed on the medium- to large-scale in-house MCC equipment prior to scale-up. 

Gordon and Spinks [19] also isolated the same product from the precipitate formed by mixing anhydrous nitric and perchloric add, by fractional crystallization from methanol. 

The Z-protected derivative, again prepared by standard methods using benzyl chloroformate,t208 may serve in the case of racemic pipecolic acid for resolution into the pure enantiomers by fractional crystallization with L-tyrosine hydrazide/208 Acylation with N-protected pipecolic acid or of pipecolyl peptides is performed by standard procedures via the active ester methods, e.g. A-hydroxysuccinimide ester/121 by the mixed anhydride method, e.g. with isobutyl chloro-formate 95-114 or pivalic acid chloride/121 as well as by DCC/HOBt/118 In the synthesis on solid support, longer coupling times are required when compared to N-protected proline.1[235 ... 

The biscarbene complexes were found (142) from their H-NMR spectra to be mixtures of geometrical isomers, due to hindered rotation about the C—N or C—O bonds, and the isomers have been separated by fractional crystallization in the case of [Au C(0Et)NHC6H4Me 2]+C10. Treatment of these species with triphenylphosphine gave mixed ligand complexes and formamidines [Eq. (39)]. They also underwent oxidative addition of iodine to yield the first gold(III) carbene complexes. 

Palmitic acid is present as cetyl ester in spermaceti from which, by hydrolysis, the acid may be obtained it is present in bee s wax as the mehssic ester and in most vegetable and animal oils and fats, in greater or lesser amounts, as glyceryl tripalmitate or as mixed esters, along with stearic and oleic adds, Palmitic acid is separated from stearic and oleic acids by fractional vacuum distillation and by fractional crystallization. With NaOH, palmitic add forms sodium palmitate, a soap, Most soaps are mixtures of sodium stearate, palmitate, and oleate. 

When naphtha or naphthenic gasoline fractions are catalytically reformed, they usually yield a Cx aromatics stream that is comprised of mixed xylenes and ethylbenzene. It is possible to separate the ethylbenzene and o-xylene by fractionation. It is uneconomic to separate the m- and p-xylenes in this manner because of the closeness of their boiling points. To accomplish the separation, a Werner-type complex for selective absoiption of p-xylene from the feed mixture may be used. Or, because of the widely different freezing points of the two xylene isomers, a process of fractional crystallization may be used. To boost the p-xylene yield, die filtrate from the crystallization step can be catalytically isomerized. 

Of the procedures cited in Section 3, procedures (1), (3), and (4) have been examined by the submitters for comparison with the present procedure. Of these, the present procedure and that based on the Delepine reaction (1) appeared to be the most satisfactory for preparative purposes. Yields by the two procedures were comparable however, the Delepine reaction could be run somewhat more conveniently on a larger scale (provided that one was willing to accept a tedious extraction of the product from the copious quantity of ammonium salts with which it is mixed). The Delepine reaction also makes a lesser demand on the skill and technique of the operator. On the other hand, attempts in the submitters laboratory to extend the Delepine reaction to sec-bromides have been unsuccessful therefore the Delepine reaction appears to lack the generality of the present procedure, which shares such generality, apparently, with procedures (2), (3), (7). and (8). Furthermore, the Delepine reaction gives a mixture of phenacylamine hydrochloride and hydrobromide M0 (although the submitters have found that by careful fractional crystallization from isopropyl alcohol-hydrochloric acid solution about 50% of the pure hydrochloride can be obtained). 

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