Repeated extractions

Soxhlet Extraction. Occasionally a crude product (often of natural occurrence) is obtained, from which a particular component may be isolated by repeated extraction with a hot soK-ent. For this purpose, Soxhlet s Extraction Apparatus (Fig. 19) is usually employed. 

Many antioxidants ia these classes are volatile to some extent at elevated temperatures and almost all antioxidants are readily extracted from their vulcanizates by the proper solvent. These disadvantages have become more pronounced as performance requirements for mbber products have been iacreased. Higher operating temperatures and the need for improved oxidation resistance under conditions of repeated extraction have accelerated the search for new techniques for polymer stabilization. Carpet backiag, seals, gaskets, and hose are some examples where high temperatures and/or solvent extraction can combine to deplete a mbber product of its antioxidant and thus lead to its oxidative deterioration faster (38,40). 

Used alumina can be regenerated by repeated extraction, first with boiling methanol, then with boiling water, followed by drying and heating. The degree of activity of the material can be expressed conveniently in terms of the scale due to Brockmann and Schodder (Chem Ber B 74 73 1941). 

Diatomaceous earth (Celite 535 or 545, Hyflo Super-cel, Dicalite, Kieselguhr) is purified before use by washing with 3M hydrochloric acid, then water, or it is made into a slurry with hot water, filtered at the pump and washed with water at 50° until the filtrate is no longer alkaline to litmus. Organic materials can be removed by repeated extraction at 50° with methanol or chloroform, followed by washing with methanol, filtering and drying at 90-100°. 

Naphthol [135-19-3] M 144.2, m 122.5-123.5°, pK 9.57. Crystd from aqueous 25% EtOH (charcoal), water, benzene, toluene or CCI4, e.g. by repeated extraction with small amounts of EtOH, followed by dissolution in a minimum amount of EtOH and pptn with distilled water, then drying over P2O5 under vacuum. Has also been dissolved in aqueous NaOH, and ppted by adding acid (repeated several times), then ppted from benzene by addition of heptane. Final purification can be by zone melting or sublimation in vacuo. [Bardez et al. J Phys Chem 89 5031 7955 Kikuchi et al. J Phys Chem 91 574 1987.]... 

Anthraquinone Blue B (Acid Blue 45, l,5-diamino-4,8-dihydroxy-9,10-anthraquinone-3,7-disulfonic acid di-Na salt) [2861-02-1] M 474.3, m >300°, Cl 63010, X.max 595nm, pKesi(1) <0, pKEst(2) 2, pKEst(3) 9. Purified by salting out three times with sodium acetate, followed by repeated extraction with EtOH [McGrew and Schneider 7 Am Chem Soc 72 2547 1950]. 

Metanil Yellow (3[ 4-phenylamino phenylazo]-benzenesulfonic acid) [587-98-4] M 375.4, pKes, <0. Salted out from water three times with sodium acetate, then repeatedly extracted with EtOH [McGrew and Schneider, J Am Chem Soc 72 2547 7950]. 

Orange RO acid orange 8, l,8-[bis(4-n-propyl-3-sulfopbenyl-l-amino)]antbra-9,10-quinone di-Na salt] [5850-86-2] M 364.4, Cl 15575, Xmax 490nm. Salted out three times with sodium acetate, then repeatedly extracted with EtOH. 

Sodium deoxycholate (H2O) [302-95-4] M 432.6, [aJu +48° (c 1, EtOH). Crystd from EtOH and dried in an oven at 100°. The solution is freed from soluble components by repeated extraction with acid-washed charcoal. 

It is interesting to note that thymol, as well as its isomer carvacrol can be removed from its alkaline solution either by distillation by steam, or by repeated extraction by ether... 

The methanol is evaporated with agitation. The residue is dissolved in 1.5 liters water and is repeatedly extracted with chloroform. The combined chloroform extracts are evaporated to dryness, and the residue is recrystalllzed from carbon tetrachloride. 80 g of 2-amlno-5-methoxyethoxypyrimidine of MP 80°C to 81 °C are obtained. 

C = CM/CAo, where product is shown in the lower phase and Sc = CAu/CAo, where product partitions to the upper phase. When single-stage extraction does not give sufficient recovery, repeated extraction can be carried out in a chain or cascade of contacting and separation units. 

Our standard incorporation assays contained resuspended particulate enzyme, labelled UDP-Gal (0.1 mM) and (10 mM) in resuspension buffer (Tris, pH 7.5). After incubation, reaction mixtures were heated briefly to 100°C and soluble lupin galactan was added, to ensure the precipitation of small amounts of galactan formed in the en me reaction and dissolved during the heating step. Precipitation of macromolecular products was achieved by adding methanol to a final concentration of 70%. The pellet was freed of soluble labelled products, including residual UDP-Gal, by repeated extraction with hot 70% methanol and was then analysed for labelled (l- )-P-D-galactan. The supernatant was analysed for soluble labelled products. 

Because the protein analyte is endogenous to the plant, it can be difficult to demonstrate the efficiency of the extraction procedure. Ideally, an alternative detection method (e.g., Western blotting) is used for comparison with the immunoassay results. Another approach to addressing extraction efficiency is to demonstrate the recovery of each type of protein analyte from each type of food fraction by exhaustive extraction, i.e., repeatedly extracting the sample until no more of the protein is detected. " ... 

Weigh 50 g of the potato sample into a 250-mL centrifuge vial and homogenize with 100 mL of acetone. After centrifugation at 1500-2000 rpm for 5 min, decant the supernatant over filter paper filled with Celite and collect in a 500-mL evaporation flask. Repeat extraction with 80 mL of acetone, centrifuge, filter and combine the extracts. Rinse Celite with 20 mL of acetone into the combined filtrates. 

A mixture of 2.65 g. of freshly distilled 2,3-O-isopropylidene-D-glycerose, 1.5 ml. of ethyl acetoacetate, 0.7 g. of zinc chloride, 20 ml. of N sulfuric acid, and 20 ml. of 96% ethyl alcohol is kept at room temperature for twenty-four hours. After addition of 3 g. of crystalline sodium acetate and keeping for a further 48 hours at room temperature, the mixture is heated for 15 minutes at 90°. It is then repeatedly extracted with ether, and the united extracts are successively washed with water, an aqueous solution of sodium bisulfite, and a small quantity of aqueous sodium hydroxide solution. The ether layer is dried with anhydrous sodium sulfate and the solvent is evaporated, yielding an oil which is saponified with aqueous sodium hydroxide solution (4 ml. of 10%) by heating on a steam bath for one hour. The aqueous solution is extracted with ether, acidified (to Congo Red) with phosphoric acid, and then repeatedly extracted with ether the united extracts are dried with anhydrous sodium sulfate and the solvent is evaporated, giving a residue which crystallizes from water yield, 0.2 g. of the product (X) m. p., 153-155°. 

D-ara tno-Tetrahydroxybutylquinoxaline (15 g.) plus 50 ml. of concentrated sulfuric acid is heated on a steam bath for two hours, with occasional stirring. The resulting red solution is poured onto 500 g. of ice, and the black, spongy precipitate formed is removed by filtration. The filtrate is repeatedly extracted with ether, the united ethereal extracts are shaken several times with 10% sodium hydroxide (until the aqueous layer is colorless), and the yellow ethereal layer is dried with anhydrous sodium sulfate and decolorized with activated carbon. On evaporating the solvent, glucazidone remains as a yellow residue which is purified by recrystallization from alcohol or aqueous alcohol yield, 4.5 g. m. p., 102-104°. 

Alternatively, add 100 ml petroleum ether to 100 g finely ground seeds and let soak about two days. Filter, discard petroleum ether and let seeds dry. Add 100 ml methanol to the seeds and let soak about two days. Filter, repeat extraction with another 100 ml methanol and evaporate in vacuum the combined methanol extracts. The residual yellow oil contains the alkaloids. 

The methanolic solution is poured into a separatory funnel containing salt water solution and ethylene dichloride. The salt water layer is repeatedly extracted with ethylene dichloride to separate the LSD base from the w ater-base mixture. The ethylene dichloride extracts are combined, dried with MgS04, decolorized and filtered. The ethylene dichloride solution is then evaporated to dryness under reduced pressure. 

Unfortunately, the appeal of solid phase extractions on small scale fades as the scale increases due to the cost and inconvenience of using large amounts of fluorous silica gel. Here, modified techniques to reduce the tedium of repeated extractions are attractive. For example, Crich has recently introduced the minimally fluorous selenide C6Fi3CH2CH2C6H4SeH[171. This selenol is added in catalytic quantities to tin hydride reductions of reactive aryl and vinyl radicals. The high reducing capacity of the aryl selenide suppresses undesired reactions of product radicals without suppressing the reactions of the aryl and vinyl radicals themselves. After the reaction is complete, the selenol can be recovered by a modified continuous extraction procedure. 

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