Alkali metal picrates, extraction

Calestani et al. [8] prepared dietylamide of the tetra-carboxymethyl ether of p-tert-h W.y calix[4]arene and reported alkali metal picrate extraction constants of 1.9... 

Marchand, A.P. Chong, H.-S. Synthesis and alkali metal picrate extraction capabilities of novel, cage-functionalized diaza(17-crown-5) ethers. Tetrahedron 1999. 55. 9697-9706. 

In Pedersen s early experiments, the relative binding of cations by crown ethers was assessed by extraction of alkali metal picrates into an organic phase. In these experiments, the crown ether served to draw into the organic phase a colored molecule which was ordinarily insoluble in this medium. An extension and elaboration of this notion has been developed by Dix and Vdgtle and Nakamura, Takagi, and Ueno In efforts by both of these groups, crown ether molecules were appended to chromophoric or colored residues. Ion-selective extraction and interaction with the crown and/or chromophore could produce changes in the absorption spectrum. Examples of molecules so constructed are illustrated below as 7 7 and 18 from refs. 32 and 131, respectively. 

Table 1. Extraction (%) of alkali metal picrates from the aqueous into the organic phase by 3a-d 3a-d 10 2 M (in dichloromethane), alkaline metal picrates 10 1 M (in water), picric acid 7xl0 5 M (in water).

MCAm is the ion-pair formed between the crown (C) complex containing the metal ion (Mm+) and A- is the counter ion. It needs to be noted that the degree of extraction is anion-dependent. For example, the extraction of an alkali metal into an organic phase is enhanced when the counter ion is a large anion such as picrate. Alkali metal picrates undergo extraction into benzene in the presence of 18-crown-6 in the order K+ > Rb+ > Cs+ > Na+ (Iwachido, Sadakane Toei, 1978). Divalent ions may also be extracted. For 15-crown-5 in benzene, the picrate extraction coefficients (from water) fall in the order Pb2+ > Sr2+ > Ba2+ > Ca2+... 

Table 7. Photostationary cis/trans Percentages and Extractabilities of Alkali Metal Picrates with lonophores 88, 89, and 90 under Visible and UV Light Irradiation ...

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). 

The preorganization of the receptor molecule by introduction of an ethyleneoxy bridge imit at the upper rim was also described [131]. The cavities of these bridged calixarenes (27) were larger than the lower rim bridged calixarenes and extraction experiments were done with both solid alkali metal and ammonium picrates into chloroform. The measurements showed that these calixarenes have a lower affinity for alkali metal ions (extraction <3%) than the lower rim bridged calix[4]arenes. However, primary ammonium ions were efficiently extracted with efficiencies of 27-57%,... 

The distribution of alkali-metal picrate 1 1 complexes of dibenzo-18-crown-6 between water and benzene has been investigated. The formation of 2 1 complexes was recognized for Rb and Cs ions in a large excess of polyether. The extractability of complex cation-picrate ion pairs decreased in the order K > Rb > Cs>Na>Li. This order was confirmed in a parallel investigation, and bis-(3,5-di-t-butylbenzo)-18-crown-6 also has good extraction ability for alkali-metal ions. ... 

The stability constants of the 1 1 alkali metal picrate complexes of diketone 18. heptacyclic terpyridyl 27 and flexible terpyridine 28 were estimated by hquid-liquid extraction, and the resulting log fj values for Na" " and are also given in Fig. 4. The affinities of 18 and 27 for these alkali metals are remarkably high for hosts containing only five or three ligand atoms, respectively. In water-saturated chloroform, pentadentate host 18 binds Na" and K more strongly than do most crown ethers. Compared to naphtho-18-crown-6 (26), 18 binds Na " 4000 times better, and K 40 times better. Even tridentate host 27 extracts alkali metal picrates into chloroform, whereas flexible model system 28 is ineffective under the same experimental conditions. The potent complexation... 

In the recent past liquid membranes were employed for the separation and extraction of materials, and they can be conveniently employed for separating biological materials [129-137], Microemulsions of Winsor I (o/w) and Winsor II (w/o) types are considered dispersed liquid membranes that can augment the transfer of oil-soluble and water-soluble compounds, respectively, across them by trapping them in microdroplets for convenient uptake and subsequent release. The microemulsions (Winsor I and II) are called bulk liquid membranes. They are recent additions in the field of separation science and technology. This field has been fundamentally explored and advanced by Tondre and coworkers [138-147], who worked out the fundamentals of the transport process by studying the transfer of alkali metal picrates and other compounds across the w/o microemulsions [140-142], They also studied the transport of lipophilic compounds (pyrene, perylene, and anthracene) across o/w liquid membranes [138,139],... 

In this equation, n — 1 and 2 for neutral solute and alkali metal picrate, respectively, the subscript s stands for the operating concentration of S in the source phase at steady-state conditions Cq is the droplet (carrier) concentration, D the diffusion coefficient of the droplets, and L the cumulative thickness of the diffusion layer and K is either the extraction constant or the product of a partition constant times the equilibrium constant for solubilization inside the droplets. 

Figure 7 Values of extraction constant from water to dichloromethane at 25 °C (log Xextr) found for the podands shown for a range of alkali metal picrates. (Reproduced from Ref. 20. Springer, 2010.)...

In extraction experiments with chloroform and aqueous alkali metal picrate solutions, no picrate anion was detected in the organic phase. Within the limits of detection of the spectrophotometer (4 X 10 M), the picrate anion was insoluble in chloroform. All of the picrate solutions obeyed Beer s law over the absorbance range (0.15 to 0.65) used in the spectral measurements. 

In the absence of polymer, none of the picrates are extracted into the chloroform phase. In the presence of either polyester or polyamide a portion of the alkali metal picrate is extracted into the organic phase. It is reasonable to assume that the alkali metal picrate that is extracted into the organic phase in the presence of pol3mier is being bound to the pol3mier in some way. It is assumed that only polymer-bound alkali metal picrate will exist in... 

With the object to obtain an effective and selective extracting material and also to investigate the dependence of the selectivity in the cation binding on the copolymer composition, we have prepared the methacrylamide derivatives of 15-crown-5 Q) and 18-crown-6 U) and their homopol3nners and copolymers with methyl methacrylate (MMA) with various crown monomer compositions. Cation binding properties of these polymers were evaluated by the extraction of alkali metal picrates into methylene chloride. 

Table 4.1.12. Extraction of alkali metal picrates by different crown ethers into methylene chloride"...

In the case of clathrates and adducts described earlier, the so-called compounds formed are separated by crystallization. Although handling of slurry/soUd in an industrial context is sometimes not desired, the solid phase conclusively demonstrates the nature of the non-stoichiometric dissociable host-guest compound formed. That macrocyclic ethers form reasonably stable complexes has also been demonstrated by the isolation of the complexes as crystals (Pedersen, 1988). That a particular crown ether having a certain cavity diameter will prefer a certain alkali metal cation having a certain diameter is illustrated in Table 4.1.12 for the extraction of a particular alkali metal picrate salt from water into methylene chloride containing the crown ether. From the table it appears that potassium picrate is most effl-ciently extracted by 18-crown-6 compared to other crown ethers, since the cavity size of 18-crown-6 is quite close to that of (see Table 4.1.11). 

Fig. 2. Plots of extraction ratios (%) of alkali metal picrates from aqueous to organic phase.

Fig. 3. Extraction (%) of alkali metal picrates by ionophores 3 and 4 in CH2CI2. Extraction conditions 2.5 x 10 M of ionophore in CH2CI2 2.5 x lO " M of picric acid in 0.1 M of alkaline hydroxide at 25°C. Ionophore solution (5.0 mL) was shaken for 2 h with picrate solution (5.0 mL) and % extraction was measured by the absorbance of picrate in CH2CI2. Experimental error was 2%.

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

Fig. 4.8. Extraction of a) alkali metal nitrates and b) cesium picrate and nitrate with dibenzo-18-crown-6 (2) in CHCI3.

Macrocycllc compounds (some crown ethers and cryptands) are selective reagents for extractive separation of alkali metals [22-27]. These ligands form cationic complexes with alkali metal ions, and these can be extracted as ion-pairs with suitable counter-ions e.g., picrate) [28], most often into chloroform. For potassium, p-nitrophenoxide was used as counter-ion [29]. In cases, where a coloured anionic complex is a counter-ion [30], the extract may serve as a basis for determining the alkali metal. The effect of the structure of the dibenzo-crown ether rings upon the selectivity and effectiveness of isolation of alkali metals has been studied in detail [31]. Chromogenic macrocyclic reagents applied for the isolation and separation of alkali metals have been discussed [32]. 

Macrocyclic reagents, such as chromogenic crown ethers of the type 14-crown-4 (extraction to 1,2-dichloroethane in the presence of picrate) were used for determination of Li [53]. The 14-crown-4 type derivatives have been applied for determination of Li in blood by a continuous FIA method [54,55]. The use of chromogenic reagents aza-12 (-13 or -14)-crown-4 has also been proposed [56,57]. The effect of substituents on the selectivity of separation of Li (and Na) by means of benzo-14-crown-4 and 13-crown-4 ethers was studied [58]. A review of chromogenic macrocyclic reagents used for determination of lithium (and other alkali metals) has been published [32]. 

The use of macrocyclic compounds for extraction of various analyte cations in the presence of suitable anions is still growing. Extraction-spectrophotometric methods for the determination of alkali metals (with picrate counter ion) using 18-crown-6 and its derivatives [12-15] and calix[4]arene crown ethers [16] have recently been developed. The application of hexa-acetatocalix[6]arene for extraction of Fe [17] and Pb [18] have been described. 

The extraction of alkali-metal ions from H2O into 18-crown-6 solutions in different organic solvents in the presence of picrate [1] and into dibenzo-18-crown-6 solution in 1,2-... 

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