Crown ethers carboxylic acids

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

Table 7. Selectivity orders for transport of alkali metal ions into toluene by crown ether carboxylic acids for several separation techniques...

In related work,20 these same authors evaluated a fluorinated crown ether carboxylic acid,. rym-difluorobenzo-16-cniwn-5 oxyacetic acid, for use in the SCF extraction of uranyl ion and lanthanides, again from a cellulose matrix. Although this compound... 

Barium 0.01 N BaClz, MgClz, CaClz, S1CI2, pH 8.5 0.01 M crown ether carboxylic acid... 

Bartsch RA, Charewicz WA, and Kang SI. Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids. J Membr Sci 1984 17 97-107. 

Strezelbicki, J. and Bartsch, R.A., Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids. J. Membr. ScL, 1982, 10 35 7. 

Crown ether carboxylic acids and alkyl esters are novel reagents port of alkali metal cations membranes. Metal Ion transport transport of protons. The in variation within the ionizabl molecule upon the selectivity petitive alkali metal transport liquid surfactant (emulsion) liquid membranes is assessed. 

In the present paper, we examine the influence of structural variation within series of crown ether carboxylic acid and crown ether phosphonic acid monoalkyl ester carriers upon the selectivity and efficiency of alkali metal transport across three types of liquid organic membranes. Structural variations within the carriers include the polyether ring size, the lipophilic group attachment site and the basicity of ethereal oxygens. The three membrane types are bulk liquid membranes, liquid surfactant (emulsion) membranes and polymer-supported liquid membranes. 

The ionizable crown ethers which were utilized in the metal ion transport studies include a series of dibenzo crown ether carboxylic acids 1-6 and a series of crown ether phosphonic acid monoethyl esters"2, (Figure 2). Within the first series, the crown ether ring sizeTs systematically varied from 14-crown-4 to 16-crown-5 to 19-crown-6 in compounds 1, 2 and 2 respectively. For compounds 2, 4 and 5, the crown etfier ring size is held constant but tTie attachment site of the lipophilic alkyl group is altered. Finally, for compounds 2 and 6, the crown ether ring size and lipophilic... 

The influence of lipophilic group attachment site variation was examined for competitive alkali metal cation transport through the chloroform membrane by the series of isomeric crown ether carboxylic acids 2, 4 and 5. All three carriers exhibited the transport selectivity of Na K >Li, Rb, Cs and for which showed the... 

For both crown ether carboxylic acid carriers 2 and 6, the transport selectiyities are Na >K >Rb >Li. Somewhat Tiigher selectivity for Na transport and transport efficiency were noted for 6 which has the more basic ether oxygens (13). 

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). 

Crown ether carboxylic acid was dissolved in a 80 20 chloroform-heptanol mixture and was contacted with the aqueous solution of the lanthanides. The solubility of sym-dibenzo-16-crown-5-oxyacetic acid in water at different pH was measured by its ultraviolet absorption. 

Heimann and Vogtle [38] synthesized triesters of glycerol with different ether carboxylic acids with a short alkyl chain. They have found that these hydrophilic lipids, in contrast with the fatty acid glycerol triesters, give complex-ation with alkali and alkali earth metal cations in an analogy of crown ethers. 

Critical micelle concentration (Section 19 5) Concentration above which substances such as salts of fatty acids aggre gate to form micelles in aqueous solution Crown ether (Section 16 4) A cyclic polyether that via lon-dipole attractive forces forms stable complexes with metal 10ns Such complexes along with their accompany mg anion are soluble in nonpolar solvents C terminus (Section 27 7) The amino acid at the end of a pep tide or protein chain that has its carboxyl group intact—that IS in which the carboxyl group is not part of a peptide bond Cumulated diene (Section 10 5) Diene of the type C=C=C in which a single carbon atom participates in double bonds with two others... 

The six-position may be functionalized by electrophilic aromatic substitution. Either bromination (Br2/CH2Cl2/-5°) acetylation (acetyl chloride, aluminum chloride, nitrobenzene) " or chloromethylation (chloromethyl methyl ether, stannic chloride, -60°) " affords the 6,6 -disubstituted product. It should also be noted that treatment of the acetyl derivative with KOBr in THF affords the carboxylic acid in 84% yield. The brominated crown may then be metallated (n-BuLi) and treated with an electrophile to form a chain-extender. To this end, Cram has utilized both ethylene oxide " and dichlorodimethyl-silane in the conversion of bis-binaphthyl crowns into polymer-bound resolving agents. The acetylation/oxidation sequence is illustrated in Eq. (3.54). 

A completely different dipolar cycloaddition model has been proposed39 in order to rationalize the stereochemical outcome of the addition of doubly deprotonated carboxylic acids to aldehydes, which is known as the Ivanov reaction. In the irreversible reaction of phenylacetic acid with 2,2-dimethylpropanal, metal chelation is completely unfavorable. Thus simple diastereoselectivity in favor of u f/-adducts is extremely low when chelating cations, e.g., Zn2 + or Mg- +, are used. Amazingly, the most naked dianions provide the highest anti/syn ratios as indicated by the results obtained with the potassium salt in the presence of a crown ether. 

Carboxylic esters can be treated with ketones to give p-diketones in a reaction that is essentially the same as 10-118. The reaction is so similar that it is sometimes also called the Claisen condensation, though this usage is unfortunate. A fairly strong base, such as sodium amide or sodium hydride, is required. Yields can be increased by the catalytic addition of crown ethers. Esters of formic acid (R H) give P-keto aldehydes. Ethyl carbonate gives P-keto esters. 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

The chemistry of a-haloketones, a-haloaldehydes and a-haloimines Nitrones, nitronates and nitroxides Crown ethers and analogs Cyclopropane derived reactive intermediates Synthesis of carboxylic acids, esters and their derivatives The silicon-heteroatom bond Syntheses of lactones and lactams The syntheses of sulphones, sulphoxides and cyclic sulphides... 

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