Carboxylate complexes, solvent extraction

Extraction by chemically active solvents. Not infrequently the crude organic product from a reaction may contain a mixture of acidic (phenols and carboxylic acids), basic and neutral components in various combinations. Some of these components may of course be impurities, but none the less, whether as a preliminary purification stage or as a means of separating the mixture, a carefully planned solvent extraction procedure may be adopted using acidic and basic reagents which react chemically with the basic and acidic components of the mixture respectively. The following full account of a typical procedure may be abbreviated in practice according to the complexity of the mixture to be handled. 

Solvent extraction of Fe(III) with calix(6)arene carboxylate derivative followed by spectrophotometric determination with thiocyanate was examined [1]. The developed method was recommended for determination of Fe(III) in samples containing Al, Mn(II), Mo(VI) and V(V). The extraction of Fe(III) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester followed by the determination with thiocyanate was employed to determine Fe in pharmaceuticals, metal and ores [2]. Solvent extraction separation of iron(III) with Cyanex 302 prior to the detection as the thiocyanate complex was applied to determine Fe(III) in multicomponent mixtures and ores, alloys and pharmaceuticals [3]. 

MOR7SEK] Moriya, H., Sekine, T., A solvent-extraction study of zinc(ll) complexes with several divalent anions of carboxylic and inorganic acids, Bull. Chem. Soc. Jpn., 47, (1974), 747-748. Cited on page 264. 

Isolation. Isolation procedures rely primarily on solubility, adsorption, and ionic characteristics of the p-lactam antibiotic to separate it from the large number of other components present in the fermentation mixture. The penicillins are monobasic carboxylic acids which lend themselves to solvent extraction techniques (154). Pencillin V, because of its improved acid stability over other penicillins, can be precipitated direcdy from broth filtrates by addition of dilute sulfuric acid (154,156). The separation process for cephalosporin C is more complex because the amphoteric nature of cephalosporin C precludes direct extraction into organic solvents. This antibiotic is isolated through the use of a combination of ion-exchange and precipitation procedures (157). The use of neutral, macroporous resins such as XAD-2 or XAD-4, allows for a more rapid elimination of impurities in the initial steps of the isolation (158). The isolation procedure for cephamycin C also involves a series of ion exchange treatments (103). 

This three volume series contains equilibrium data on liquid-liquid distribution reactions. The equilibria of concern Include distribution, dissociation and aggregation of the extractant, reactions of the extractant with diluents and with other solvents, extraction of the water, equilibria of the extraction metal Ions, and extraction of metal ions with the extractant as the ligand. Volumes 1 and 2 cover organophosphorous extractions and alkylammonium salt extractants, respectively. Volume 3 deals with distribution reactions of carboxylic and sulfonic acid extractants, and the distribution of Inorganic acids, salts, and complexes between aqueous solutions and both Inert solvents and solvents which have oxygen donor atoms. Each reaction entry Includes the equilibrium constant, the temperature for which the data exists, the conditions, and a reference(s) to the source literature. 

Preston (1985) described the solvent extraction behavior of a large number of metal cations including rare earth nitrates in solutions of Versatic 10 (2-ethyl-2-methylheptanoic acid), naphthenic, 2-bromodecanoic and 3,5-diisopropylsalicylic acids in xylene. The last two acids extract metal cations under more acidic conditions, pH 1-2. For Versatic 10 the order of extraction of yttrium and lanthanides is La < Ce < Nd < Gd < Y < Ho < Yb and for naphthenic acids it is La < Ce < Y < Nd < Gd k Ho Yb. The lanthanides tend to form complexes of predominantly ionic nature. In the case of Versatic 10, the stability of the complexes increases uniformly with atomic number due to the increase in electrostatic energy as a result of the decrease in ionic radius. The primary branched naphthenic acid allows the formation of complexes with high coordination number, nine for La to Nd, eight and eventually six as the metal ionic radius decreases. In general, the extraction of a metal ion by a carboxylic acid H2A2 can be represented by the reaction... 

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