Anion exchangers Amberlyst

Many borohydrides are highly unstable and have to be used as freshly prepared ethereal solutions. However there are instances where the polymer-supported versions are more stable e. g. an Amberlyst anion exchange resin supported borohydride and cyanoborohydride [61], polyvinylpyridine supported zinc borohydride [62] and the corresponding zirconium borohydride [63]. Such compounds, in their labeled forms, should turn out to be very useful. 

A 20-g sample of the bitumen was dissolved in cyclohexane and charged to a column containing 50 g of Amberlyst A-29 anion exchange resin (OH form) on top of 50 g of Amberlyst 15 cation exchange resin (H+ form) (Rohm and Haas). The column was exhaustively eluted with... 

Preparation of Resins and Adsorbents. A volume of Amberlyst A-29 anion-exchange resin was added to a liquid-chromatographic... 

Amberlyst-15 cation-exchange resin was activated in the manner described for the anion-exchange resin except that the sequence of acid/base washings were reversed. Also, the rate of addition of both the acidic and basic methanolic solutions were governed by the heat generated. 

Thus, the choice of method depends on the application. For routine analyses of FFAs, the BDI method or modifications of it, and methods based on the Dole extraction procedure appear to be most popular (IDF, 1983), while for accurate determination of all FFAs in a product, the capillary GC (Chilliard et al., 1983 de Jong and Badings, 1990 Anderson et al., 1991) or the HPLC methods (Garcia et al., 1990) are the methods of choice. Solvent extraction using acidified ether (Salih et al., 1977) followed by separation of the free acids from fat on an anion exchange resin, [e.g., Amberlyst 26 (Needs et al., 1983)], and capillary gas chromatography of the acids or their methyl esters has been suggested by the IDF as a reference method (Anderson et al., 1991). 

Bills et al. (1963) used pre-treated Amberlite resin dispersed in hexane to isolate FFAs from milk. Fat was removed from the resin using hexane, absolute ethanol and methanol and the FFAs were esterified prior to analysis by GC. Needs et al. (1983) extracted lipids from milk by using ether and the FFAs were isolated using a strong basic anion exchange resin (Amberlyst 26, BDH Ltd, Poole Dorset, UK). The FFAs were methylated and resolved by GC. McNeill et al. (1986) also used Amberlyst resin to isolate FFAs in conjunction with silicic acid to remove phospholipids. Extracted FFAs were then analyzed by GC. This method was used by McNeill and Connolly (1989) to quantify FFAs in a number of semi-hard cheeses. 

Chromic acid also becomes a selective oxidant for the preparation of aldehydes and ketones when it is supported on an anion exchange resin (Amberlyst A-26 Table 16). The reaction appears to be general and highly tolerant of a wide range of solvents, unlike many resin-based oxidations where the availability of the oxidant is critically dependent upon the nature of the solvent. 

The anion exchange resin was Amberlite IRA-904, and the cation exchange resin was Amberlyst 15. Preparation of the resins was similar to that described by Jewell et al. (7). 

Nitrogen and phosphor functionalized adsorbents for the adsorption of Co(II). Hereby, Amberlyst A2I was selected for its nitrogen functionality. It is a macroreticular polystyrene - crosslinked by divinylbenzene - anion exchange resin functionalized with an alkylamine group. As a phosphorous functionalized adsorbent, polymerbounded PPhj has been selected. It is a gel-type polystyrene - crosslinked by 2 [%] divinylbenzene - resin functionalized with a PPh2 group. 

A solution of chromium trioxide in dilute sulfuric acid used in aqueous acetone is called Jones reagent [572]. Other solvents of chromium trioxide are ether [535] and hexamethylphosphoric triamide (HMPA) [543. Oxidations are also carried out with chromium trioxide adsorbed on Celite (diatomaceous earth) [53S], silica gel [537], or an ion exchanger such as Amberlyst A26 (a macroreticular quaternary ammonium salt anion exchanger) [571, 617]. Such oxidations often take place at room temperature and can be used not only for saturated alcohols but also for unsaturated and aromatic alcohols (equations 208 and 209). 

There are several methods available for the extraction of bile salts from serum or plasma. The most convenient methods utilize some form of liquid-solid extraction. An early procedure involved the anion-exchange resin, Amberlyst A-26 (S8), but considerable time and effort was required to perform column chromatography and to concentrate the eluate from the column. The introduction in 1972 of the neutral resin, Amberlite XAD-2, improved the ease of extracting bile acids and their conjugates from serum samples (M6). Further improvement occurred in 1977 with the description of a batch extraction technique using the related neutral resin, Amberlite XAD-7 (B5). With this technique, serum is diluted in 0.1 M sodium hydroxide to release bile acids from albumin and mixed with resin for 1 hour. After washing the resin in dilute alkali, bile acids are eluted with methanol, which cdn be removed on a rotary evaporator (B5). 

We evaluated both gel and macroreticular types of styrene-divinyl-benzene (DVB) and acrylate-DVB strong base anion-exchange resins, all having quaternary ammonium groups attached to the polymer backbone. We used commercially available resins, specifically those of Rohm and Haas Amberlyst A-26, Amberlite IRA-400, Amberlyst XE-279, and Amberlite IRA-458 (all in the chloride form). The A-26 and IRA-400 resins contain styrene-DVB skeletal structures, with IRA-400 being a gel-type resin and A-26 the macroreticular resin. Resins IRA-458 and XE-279 contain acrylate-DVB skeletal structures, where IRA-458 is a gel-type resin and XE-279 a macroreticular resin. These studies compare the properties of the borohydride form of these resins with sodium and tetraethylammonium borohydride. 

A catalyst prepared by attaching W(CO)6 to a strong anion-exchange resin (Amberlyst A-27) to form [resin]-Me3N[WCl(CO)5] polymerizes oct-l-ene after addition of EtAlCl2, but isomerization (to oct-2-ene) and cross-metathesis are also observed (du Plessis 1982). The combined metathesis and isomerization of oct-1 -ene in the pesence of RMe3N[WCl(CO)5]/EtAlCl2 (R = Me or Amberlyst) takes place at a molar ratio of AlAV > 2 for R — Me, and AlAV > 7 for R = resin, while the presence of small amounts of HCl or H2O is necessary to activate the system (Pienaar 1985 du Plessis 1988). 

F -Anion exchange resins. Fluoride ion immobilized on strongly basic anion exchange resins, particularly Amberlyst A27 and Dowex MSA-1, promote the various reactions that have been found to be promoted by alkali metal or tetraalkylammonium fluorides, such as C- and O-alkylation, sulfenylation, and Michael additions. 

Aikyl fluorides by exchange from alkyl halides or methanesulfonates. The resin used for the reaction is the F form of Amberlyst-A26 (Rohm and Haas), a macroreticular anion-exchange resin containing ammonium groups. When this material and primary alkyl halides or sulfonates are refluxed in a solvent (pentane, hexane, ether), alkyl fluorides are formed, usually in satisfactory yields. Alkenes accompany fluorides in the reaction of secondary substrates. This reaction has been conducted previously under phase-transfer catalysis (5, 322). ... 

Polymer-supported /eagent. Italian chemists have prepared a supported form of this oxidant by reaction of the Cl" form of an anion exchange resin (Anibcriyst A-26, Amberlyst A-29, Amberlite IRA 400, or Ainberlite 904) in llaO with chromium trioxide to obtain a CrOaH" form of the resin. This polymeric reagent oxidizes primary and secondary alcohols in high yield (usually 85-957o). The chloride form of the resin is regenerated by wash with NaOH and HCI solutions. 

With the procedure of Okishio et al. (24,124) freeze-dried rat liver homogenates are exhaustively extracted with 95% ethanol containing 0.1% ammonium hydroxide, and the extract is taken to dryness. The residue is dissolved in aqueous NaOH, pH 11, and applied to an Amberlyst A-26 anion exchanger. After alkaline or enzymatic hydrolysis the free bile acids are extracted with diethyl ether after acidification. The bile acids are methylated and then purified on aluminum oxide. The bile acid methyl ester fraction eluted from this column is taken to dryness and the residue is trifluoroacet-ylated and analyzed on a triple-component column (QF-1-SE-30-NGS) for quantitative determination. 

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