Anion exchangers ammonium salts, quaternary

Because of their high lipophobic character, compared with other ammonium salts, quaternary ammonium hydroxides are not readily prepared by liquidrliquid anion exchange. Only with quaternary ammonium hydrogen sulphates is it possible to transfer the ammonium hydroxide into the organic phase in any viable degree of concentration [30] and this procedure remains the cheapest and simplest procedure. Other methods include treatment of quaternary ammonium halides with silver oxide [31] and by anion exchange using polymer bound hydroxide [e.g. 32]. 

Most potentiometric anion-selective electrodes are based on anion exchangers such as quaternary ammonium salts. The selectivity pattern of these sensors correlates with anion lipophilicity. Highly hydrated anions such as fluoride, bicarbonate and chloride are difficult to monitor due to significant interference from more lipophilic anions like perchlorate, salicylate and nitrate which may be present in the analyzed sample. The anions can be classified according to their lipophilicity resulting in the classical Hofmeister series (ClOi > SCN > salicylate > I > NOJ > Br >... 

Basic Extractants. Only long-chain quaternary ammonium salts, R3NCH3 X , ia which R represents Cg—0 2 groups and X nitrate or thiocyanate, are effectively used for REE separations (see Quaternary ammonium compounds). The extractant reacts with REE according to an anion-exchange reaction ... 

Last time development of methods of iodine determination, which include preliminary sorption preconcentration of microcomponents and their subsequent determination in phase of concentrate get great practical significance. Silica gel (SG) with adsorptively modified quaternary ammonium salts (QAS) gets properties of anion-exchange resin. The sorbents modified in this way can be used successfully for determination of different anions. 

ANION-EXCHANGE EXTRACTION OF ZINC THIOCYANATE COMPLEXES BY NON-SYMMETRIC QUATERNARY AMMONIUM SALTS... 

High tendency of ZnfSCN) ion to extraction into organic phase is widely used for zinc determination by extraction photometry method. Recently it was shown that when single-chai ged anions ai e exchanged for double-chai ged ones, the selectivity of this process depends on the number of methyl substitutients in quaternary ammonium salt (QAS) cation. 

Strongly basic anion exchange resins, e.g. a cross-linked polystyrene containing quaternary ammonium groups, are largely ionised in both the hydroxide and the salt forms. Some of their typical reactions may be represented as ... 

Quaternary ammonium salts (QAS) are anion exchangers used in solvent polymeric membranes. Variation of substituents at the nitrogen atom is an option for tuning QAS... 

Anion exchange resins are also used frequently for the synthesis of specific quaternary ammonium salts [e.g. 29]. 

Schugerl 115] has recently furnished a detail analysis of the reactive extraction of penicdlin-G and V and precursors like phenyl and phenoxy acetic acids. Thirty different amines have been studied for reactive extraction of penicillins 116] in various solvents such as butyl acetate, chloroform, di-isopropyl ether, kerosene, dioctyl ether, etc. Tertiary amines in n-butyl acetate were found to be advantageous because of their low reactivity with solvent but the distribution coefficients of their complexes are significantly lower than those of secondary amines. While using quaternary ammonium salts for ion-exchange extraction, re-extraction is difficult and very large amounts of anion (e.g.. Cl ) are needed to recover penicillins. The basic relationship for distribution coefficient and extraction kinetics have now been fairly developed for amine-penicillin systems. 

The heterocycles react directly with alkali metals or undergo exchange reactions with, for example, sodium amide and hydride, n-butyllithium and thallium ethoxide, to form the TV-heteroaryl salts. The salts of the alkali metals exist as solvent separated ion-pairs or as contact ion-pairs (71JOC3091), as do the quaternary ammonium salts, whereas the salts of the heavier metals are generally considered to have a high N—metal covalent character. These characteristics, which can be modified by a change in the polarity of the solvent, control the reactions of the heteroaryl anions. 

TEVA-Resin is an extraction-chromatographic material based on Aliquat 336, which is a liquid quaternary ammonium salt, as described previously in connection with "Tc separations.30 It acts as a strongly basic anion-exchange material, retaining tetravalent actinides from 2-4 M HN03 solutions as anionic nitrato complexes (see Figure 9.11). Am(III), Np(V), and U(VI) are much less retained. The extraction... 

Exposure of quaternary ammonium salt 163 to NaOMe gives methyl orthoester 37 and ketene acetal 54 as the consequence of a competing Hofmann-type elimination (Equation 33). Elution of 163 as a methanol solution through an anion-exchange resin (Dowex-550-OH, MeOH) leads exclusively to ketene acetal 54 in 89% yield <2004AGE1117>. 

Basic or anion exchangers, generally quaternary ammonium compounds and alkylamines, extraction is dependent on the ability of the metal ion to form an anionic species in the aqueous phase and then be extracted as an ion-parr by the amine salt. 

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