Purification temperature-induced

ALR Aired, P.A., Kozlowski, A., Harris, J.M., and Tjemeld, F., Application of temperature-induced phase partitioning at ambient temperature for enzyme purification, J. Chromatogr. A, 659, 289, 1994. 

The postcrystallization treatment sweating is a temperature-induced purification step. After the crystallization process, the temperature of the cooled surface is raised close to the melting point of the pure component (about 1-2 K below). As a consequence, the impurities adhering to the crystal coat and those contained in pores of the crystalline material remelt (partially diluted with pure material). The remolten impure material flows out of the pores and finally drains under the influence of gravity. During the sweating process, a product loss of about 10% is accompanied. 

HF-induced elimination (5). To a solution of aqueous HF (4 drops, 50%) in MeCN (8 ml) was added a solution of the /3-hydroxysilane (lmmol) in MeCN (2ml), and the mixture was stirred at room temperature until t.l.c. analysis indicated completion (5-20min). The reaction mixture was then partitioned between pentane (50 ml) and saturated sodium hydrogen carbonate solution (10ml). The aqueous layer was extracted thoroughly with pentane (3 x 50 ml), and the combined organic extracts were washed with brine and dried. Concentration followed by chromatographic purification gave the product alkenes. 

The assembly of tetrapeptide 19 that contains all possible 0-dipeptide bonds, (03-03)-, (03-02)-, and (02-03), and also a turn inducing 03-(R)-Ala-02-(R)-Val element was achieved employing a Boc-strategy (Scheme 5). A fluorous benzyl group was incorporated in the first amino acid to streamline the purification procedure by fluorous solid phase extraction (LSPE) (Lilippov et al. 2002 de Visser et al. 2003). Thus, the assembly of the fully protected tetrapeptide commenced with the construction of the first 03-03-peptide bond by applying the previously established conditions. A residence time of 3 min at 90°C provided the Boc-protected dipeptide 15 in 91% isolated yield after LSPE. Notably, the product precipitated in the collection flask, which was kept at ambient temperature, indicating the poor solubility of this class of compounds (Hessel et al. 2005). 

Azidoformic esters such as 342 react with Cgg in a [2-tl] addition (Scheme 4.70), if the temperature is high enough to induce the loss of nitrogen prior to addition, otherwise a [3-1-2] addition can be observed (Section 4.3.2) [172, 395, 397]. Typical conditions include heating of the mixture in solvents such as tetrachloroethane [395, 397, 398], chloronaphfhalene [397] or toluene [396] at 110-160 °C. These conditions also afford multiple addition products [172]. To avoid potential hazard during purification of the azido formiates, they were also generated in situ in one pot by the reaction of chloro-formic ester with sodium azide [396]. 

D) Fractional crystallization is a method of refining substances based on differences in solubility. If two or more substances are dissolved in a solvent, they will crystallize out of solution (precipitate) at different rates. Crystallization can be induced by changes in concentration, temperature or other means. Fractional crystallization can be used for purification or analysis. 

Crystallization is often used as a method of product isolation. Crystallization of the reaction product may be induced if, to the reaction medium, in which it is well soluble, a cosolvent is added in which the product is insoluble. Because for the latter purification method the solubility should be high at high temperatures but much lower at low temperatures, the temperature coefficient of the solubility becomes an important criterion for the employment of a solvent. A further guide is the fact that substances tend to dissolve in solvents with similar polarities, so that a solvent and cosolvent for the recrystallization of a given product can be selected according to the polarities. 

N-Phenylhydroxylamine (11 g., 0.10 mole)2 (Note 1) and N-phenylmaleimide (17.4 g., 0.10 mole)3 are suspended in 40 ml. of ethanol contained in a 200-ml. Erlenmeyer flask. To the mixture is added immediately (Note 2) 8.98 g. (11.2 ml., 0.124 mole) of freshly distilled w-butyraldehyde. An exothermic reaction ensues, and the mixture spontaneously heats to the boiling point. A clear slightly yellow solution results which, upon cooling, deposits an almost colorless crystalline cake. The mixture is allowed to stand in the ice box for 1 day it is then filtered through a Buchner funnel, and the crystals are washed twice with 25-ml. portions of ice-cold ethanol. The yield of air-dried product, m.p. 99-101°, is 31-32 g. (92-95%). For further purification the crude material is dissolved in 60 ml. of boiling ethanol on the steam bath, and the resulting solution is allowed to cool slowly to room temperature. If crystallization does not spontaneously begin in 5-10 minutes, it can then be induced by... 

General Procedure for Microwave-Induced Fries Rearrangement. Neat substrate (0.01 mol) was mixed with the support (1 3, w/w) in a beaker and was exposed to microwave irradiation for 7 min. After cooling to room temperature the product was extracted with diethyl ether. Evaporation of the solvent gave almost pure product. Further purification was carried out by recrystallization or column chromatography on silica gel. 

Hexachlorocyclotriphosphazene (3.19) is prepared on an industrial scale by the interaction of phosphorus pentachloride with ammonium chloride in an organic solvent such as chlorobenzene. This compound, after careful purification and protection from moisture, is heated in the molten state at temperatures between 210 and 250 °C to induce polymerization.15-18 The mechanism of this reaction is discussed in a later section. Here it is sufficient to note that the process can also be applied, with minor variations, to cyclic phosphazo-phosphazenes (3.22a, 3.23), to cyclic fluorophosphazenes (3.24,3.25), and to cyclic carbo- (3.26), thio- (3.27), and thionyl (3.28) -phosphazenes. 

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