Ion exchanger Dowex

Isopropylidene acetals are cleaved under acidic conditions, with the acid strength and reaction time varying considerably as a function of the substrate. In this case a 1M solution of the acetonide in THF was treated with an equal volume of 6N hydrochloric acid at room temperature Final chromatographic purification was accomplished with an ion exchanger (Dowex 1 x8 200 OH ). 

Figure 14 Determination of stability constants for the CoSCN complex in cat-ion-exchanger Dowex 30W phase and in the aqueous solution at 25°C with the spectrophotometric method. (From Ref. 14.)...

We compared various chromatographic materials employed in the separation and immobilization of biopolymers, such as loosely cross-linked gels based on natural polysaccharide polymers (Sephadex, Sepharose, etc.), moderately cross-linked polystyrene ion exchanger (Dowex 1-X2), highly cross-lined hydrophilic maeroporous heterc eneous gel with each of 3 - 4 monomeric units cross-linked (Spheron P-300) and porous glass coated with a hydrophilic monolayer. ... 

Fig. 3. The elution of tnpositive actinide and lanthanide ions. Dowex-50 ion-exchange resin was used with ammonium a-hydroxyisobutyrate as the eluant.

Ion-exchange separations can also be made by the use of a polymer with exchangeable anions in this case, the lanthanide or actinide elements must be initially present as complex ions (11,12). The anion-exchange resins Dowex-1 (a copolymer of styrene and divinylben2ene with quaternary ammonium groups) and Amherlite IRA-400 (a quaternary ammonium polystyrene) have been used successfully. The order of elution is often the reverse of that from cationic-exchange resins. 

Sulfonated styrene—divinylbensene cross-linked polymers have been appHed in many of the previously mentioned reactions and also in the acylation of thiophene with acetic anhydride and acetyl chloride (209). Resins of this type (Dowex 50, Amherljte IR-112, and Permutit Q) are particularly effective catalysts in the alkylation of phenols with olefins (such as propylene, isobutylene, diisobutylene), alkyl haUdes, and alcohols (210) (see Ion exchange). Superacids. 

Recovery and Purification. The dalbaheptides are present in both the fermentation broth and the mycelial mass, from which they can be extracted with acetone or methanol, or by raising the pH of the harvested material, eg, to a pH of 10.5—11 for A47934 (16) (44) and A41030 (41) and actaplanin (Table 2) (28). A detailed review on the isolation of dalbaheptides has been written (14). Recovery from aqueous solution is made by ion pair (avoparcin) or butanol (teicoplanin) extraction. The described isolation schemes use ion-exchange matrices such as Dowex and Amberlite IR, acidic alumina, cross-linked polymeric adsorbents such as Diaion HP and Amberlite XAD, cation-exchange dextran gel (Sephadex), and polyamides in various sequences. Reverse-phase hplc, ion-exchange, or affinity resins may be used for further purification (14,89). 

The residue is leached to give cesium sulfate solution, which can be converted to cesium chloride by ion exchange on Dowex 50 resin and elution with 10% HCl, treatment using ammonia or lime, to precipitate the alurninum, or by solvent extraction, followed by purification at neutral pH using hydrogen peroxide or ammonia. 

One important factor to consider in the preparation of the organic phase is the presence of inhibitors in the monomers. Some formulae call for the removal of inhibitors, primarily TCB, from the monomers. The TCB inhibitor forms highly colored complexes with metallic salts rendering the final product colored. Styrene has about 50 ppm of TCB. DVB, being more reactive, contains about 1000 ppm of TCB. There are several options for the removal of inhibitors. Columns packed with DOWEX MSA-1 or DOWEX 11 ion-exchange resins (Dow Chemical Company) can be used. White drierite or activated alumina also works well. 

Aromatization of 8-(cyano or ethoxycarbonyl)-2-oxo-2,3,4,4a,7,8-hexa-hydropyrido[l,2-A][l,2]oxazine-8-carbonitriles 12 by treatment with CS2CO3 resulted the formation of (2-pyridyl)propionic acids 13 (00OL4007). Application of other bases, e.g. DBU, NEt3, Dowex 1X8-400 ion-exchange resin afforded (2-pyridyl)propionic acids in irreproducible or considerably lower yields. 

Finally,Captopril is produced. Thethioester (0.85g) isdissolved in5.5N methanolicammonia and the solution is kept at room temperature for 2 hours. The solvent is removed in vacuo and the residue Is dissolved in water, applied to an ion exchange column on the H cycle (Dowex 50, analytical grade) and eluted with water. The fractions that give positive thiol reaction are pooled and freeze dried. The residue Is crystallized from ethyl acetate-hexane, yield 0.3 g. The 1 -(3-mercapto-2-D-methylpropanoyl)-L-proline has a melting point of 103°C to 104°C. 

Deoxy-D-ribo-hexono-l,4-lactone. To 286 mg. of 2-deoxy-D-ribo-hexose in 4 ml. of water is added 0.3 ml. of bromine. The solution is kept overnight at 37°C. and is then aerated to remove the excess bromine. Silver carbonate (1.5 grams) is added and the mixture is filtered. The clear filtrate is stirred with 5.4 grams of Dowex-50W X8 (H+) ion-exchange resin, decolorized, and filtered, and the filtrate is evaporated... 

Hydrolysis 10 mmol of the phosphate salt are dissolved by swirling with Dowex AG50W-X8 (H ) in 200 mL of water. After filtration, the pH is adjusted to 6.0, acid phosphatase (150 U EC 3.1.3.2) is added and the mixture is incubated at 25 CC until complete conversion, as monitored by TLC (48 h). The solution is desalted by ion exchange, concentrated in vacuo, and the residue is crystallized from ethanol to give colorless crystals of D-sorbosc yield 1.6g (89%). 

Place 200 g of ion exchange resin Dowex 50W-X8, 100-200 mesh, hydrogen form into a 1-L beaker and add 600 ml of 1 M hydrochloric acid solution. Allow to stand for 24 h with occasional swirling. Decant off the liquid and filter off the resin using filter funnel and paper. Place the resin in a beaker and add 600 ml of distilled water. Stand for 24 h with occasional swirling. Decant off the liquid and repeat the washing procedure until the wash water is neutral to pH paper. 

Gardell, S. Separation on Dowex 50 Ion Exchange Resin of Glucosamine... 

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