Cation transport through organic liquid

Cation Transport through Organic Liquid Membranes... 

Kirch and Lehn have studied selective alkali metal transport through a liquid membrane using [2.2.2], [3.2.2], [3.3.3], and [2.2.C8] (146, 150). Various cryptated alkali metal picrates were transported from an in to an out aqueous phase through a bulk liquid chloroform membrane. While carrier cation pairs which form very stable complexes display efficient extraction of the salt into the organic phase, the relative rates of cation transport were not proportional to extraction efficiency and complex stability (in contrast to antibiotic-mediated transport across a bulk liquid membrane). Thus it is [2.2.Ca] which functions as a specific potassium ion carrier, while [2.2.2] is a specific potassium ion receptor (Table VI). 

SELECTIVE SYNTHESIS OF MACROCYCLIC OLIGOESTERS FROM A BICY-CLIC OXALACTONE AND CATION TRANSPORT THROUGH THEIR ORGANIC LIQUID MEMBRANES... 

Light-driven membrane transport. Cations may be transported through liquid membranes using crown ethers. For example, a typical system is of the type water-phase(I)/organic-phase/water-phase(II). The metal ion is added to water-phase(I) and the crown ether to the organic phase (to yield the liquid membrane). The crown acts as carrier for metal ions from water-phase(I) across the liquid membrane phase into water-phase(II). There have now been a very large number of studies of this type reported and a fuller discussion of this topic is given in Chapter 9. 

The performance of calixarenes as cation carriers through H20-organic solvent H20 liquid membranes has also been studied.137 In basic metal hydroxide solutions, the monodeprotonated phenolate anions complex and transport the cations, while [18]crown-6 does not, under the same conditions. Low water solubility, neutral complex formation and potential coupling of cation transport to reverse proton flux have been cited as desirable transport features inherent in these molecules.137... 

Kobuke,Y.,Tabushi, I., Oh, K. Aoki,T. (1988) Transport ofuranyl ion through liquid membrane mediated by macrocyclic polycarboxylate in combination wifli quaternary ammonium cation. Journal of Organic Chemistry, 53 (25), 5933-5940. 

Metal extraction by carboxylic acids is a stepwise process in which the acid partitions between the organic phase and the aqueous phase and ionizes in the latter. Then the anion reacts with the metal cation and the neutral salt partitions between the organic and aqueous phases. Although this description is well-known in extraction, an ysis of transport through liquid membranes with the same chemistry is usually based for the sake of simplicity, on the assumption that metal ions in the aqueous phases are present in well-stirred reservoirs and the ion-exchange itself takes place only at the membrane surface. The carrier in this case is able to move only inside the membrane from one of its surfaces to the other. These mechanisms where the carrier is or is not able to leave the membrane could be called, a " big and small carrouser, respectively (6). 

Bulk Liquid Membranes (BLM). This is the simplest type of liquid membrane (2-8) and is utilized for fundamental studies of certain aspects of liquid membrane transport processes. In one such process, a beaker-in-a-beaker cell (Figure 1) consists of inner and outer compartments which contain the aqueous feed (F) and strip (S) solutions, respectively. The inner beaker contains the stripping solution and is surroimded by the feed solution. Both aqueous solutions contact the upper organic layer, which is the liquid membrane. Mass transfer takes place from the feed solution through the liquid membrane and into the strip solution. Bartsch et aL studied the transport of alkali metal cations across bulk liquid membranes in which a crown ether carboxylic acid in the organic layer served as the carrier (2,3). 

The ditopic crown ether-amide caging hgand 256, prepared in [180], co-encapsulates cationic and anionic species by Scheme 2.159. This hgand transports NaCl, KCl, NaBr, and KBr salts from their aqueous solutions through a liquid organic membrane with the selectivity changing in a row K > Na > Li. The selectivity order is reversed when this covalent capsule extracts solid alkah metal chlorides and bromides into organic phases [180],... 

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