Arenes picrates

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... 

Recently, Deligoz and Yilmaz [24,25] described the preparation of two polymeric calix[4]arene tetra esters (Scheme 4) and their Na -complexation. Based on phase-transfer experiments with these compounds using alkali picrates in water-dichloromethane, they confirmed that polymers are as Na selective as monomers. 

In the tetra-bridged phosphocavitands containing four donor P(0)R groups, the P=0 bonds can adopt the inward (f) or outward (o) orientations relatively to the molecular cavity. Only the ini isomer with the four P=0 groups oriented inwards can benefit from both cooperativity of P=0 binding and r-in-teractions with the aromatic cavity of the resorc[4]arene framework [19, 63]. The complexation properties of new iiii tetra-phosphonatocavitands 12b-12d and 12g towards metal ions were characterized by extraction of the metal picrate from water to chloroform solution containing the host compound (Fig. 4). 

The first studies performed at Strasbourg University by the picrate extraction method developed by Pedersen reveals a high preference of calix-crowns fixed in the 1,3-alternate conformation for cesium. In contrast to its conformational isomer, di-isopropoxy-calix[4]arene-crown-6 in the cone conformation does not extract cesium (Table 4.4). 

It was calculated that the 1,3-alternate form of calix[4]arene-crown-6 will selectively extract, with or without picrate counterion, Cs+ over Na+. However, it was shown that the counterion reduces somewhat the preference for Cs+. 

Dialkoxy Calix[4]arene Substituted Benzocrown-6 Extraction Percentages (% ) of Alkali Picrates from Water into Dichloromethane... 

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). 

The X-ray structure of the L-Sr(Picrate)2 (L = p-tert-butyl-calix[4]arene-tetra(diethylamide)) is reported, as well as MD simulations on the L M2+ complexes in vacuo, in water, and in acetonitrile solutions for alkaline earth cations with a comparison of converging and diverging conformers.130 In the simulated and solid-state structures of the L M2+ complex, the ligand wraps around the complexed cations M2+ (more than it does with alkaline cations), which are completely encapsulated within the polar pseudo-cavity of L, without coordination to its counterion in the crystal or to solvent molecules in solution. In contrast to alkali cation complexes, which display conformational flexibility in solution, computations show that the alkaline earth cation complexes are of the converging type in water and in acetonitrile. Subtle structural changes from Mg2+ to Ba2+ are observed in the gas phase and in solution. Based on FBP calculations, a binding sequence of alkaline earth cations was determined Mg2+ displays the weakest affinity for L, while Ca2+ and Sr2+ are the most stable complexes, which is in agreement with the experiment. 

The corresponding dependence of cation complex stability on the anion differs profoundly from that of most other cation receptors such as cyclophanes or calix-arenes [16]. For these cation complex stability decreases on changing the anion from picrate through iodide to tosylate, a dependence that has been attributed to ion-pair aggregation in non-polar solvents. Because the interaction of quaternary ammonium ions with tosylate or iodide in chloroform is considerably stronger than with picrate, cation complexes in the presence of the latter anion are usually more stable. Only when iodide or tosylate cooperatively contributes to cation binding, as in 3 or in some recently described calixarene derivatives [17], is reversal of this order observed. 

Two dioxa-trithia- and two trioxa-dithiacrown ethers connected to one calix[4]arene unit have been prepared by Sim et al. <2002BKC879>. Macrocycles 165 and 166 have an Ag+ selectivity in metal picrate extraction, but the percentage extractability was lower than those of corresponding monocrown derivatives 155 and 156 due not only to electrostatic repulsion between the two metal ions, but also to an induced conformation change that does not favor binding of the second metal. The extractability is consistent with the result of silver ion-induced chemical shift change upon the complexation. 

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%,... 

Cleavage of hydrocarbon pierates. Picrates of dimethyinaphthalenes are usually cleaved by absorption of the picrate on a column of basic alumina and elution of the hydrocarbon with benzene. Eisenbraun et al. report that petroleum ether dissolves the arene but essentially no picric acid the method reduces the amount of solvent and alumina required. In addition the picric acid can be recovered for reuse. The method is less suitable for picrates of more complex arenes which are not readily cleaved (fluoranthene picrate and pyrene picrate). 

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. 

Reinhoudt DN, Dijkstra PJ, in t Veld PJA, Bugge KE, Harkema S, Ungaro R, Ghidini E, Kinetically stable complexes of alkali cations with rigidifiedcalix[4]arenes- X-ray structure ofa calixspherand sodium picrate complex. J. Am. Chem. Soc. 1987 109, 4761. 

In a previous work, the same group synthesized an adaptable heteroditopic cavitand by using a flexible cone conformer of calix[4]arene, bearing four 4-hydroxybenzyl groups, 39." The derivative was able to bind cooperatively to a series of tetramethylammonium (TMA) salts (tosylate, chloride, acetate, trifluoroacetate, and picrate). 

The homoazacalix[3]arenes 72 showed (Mily low afhnity for alkali and alkaline-earth metal cations as shown already in 1992 by Takemura [47] and later confirmed by Hampton [52], using picrate extractiOTi experiments. 

Preliminary binding properties of Schiff base-p-te/t-butylcalix[4]arenes 17-20 were tested by solvent extraction of alkaline, alkaline earth metal, Mn, Fe, Co, Ni, Cu, Cd, Pb, Y, Pr, Nd, Eu, Gd, Yb picrates into dichloromethane under neutral... 

Fig. 11 Partial H NMR spectra of azacalix[4]arene 13b (0.50 mM) in the presence of potassium picrate (0.50 mM) in CDCI3/CD3OD (4 1, v/v). Open and solid circles represent the NMR resonances of free 13b and those of potassium complex [K 13b], respectively. Peaks marked with an asterisk are due to solvent impurities [33]...

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