Calix arene-crown-5-ether with

Calixarene crown-6 compounds, which are neutral extractants like crown ethers, are able to coextract technetium with cesium. Tests carried out with several calix-arene-crown ethers (MC7, MC8, MC14, BC2, BC5, BC8, and BC10) show that the extraction of technetium, present in the aqueous phase at a concentration 10 5 M, is enhanced as the cesium concentration in the aqueous phase increases from 10 5 to 10-2 M. As expected, an increase of nitrate concentration prevents pertechnetate extraction in competition with nitrate anion. The extraction of technetium is only appreciable when the nitric acid does not exceed 1 M. Distribution ratios DCs (close to 8) are comparable for the various calixarenes. However, a decrease of extraction is observed for naphtho derivatives.88 89... 

With the idea that crown ethers based on the p-tert-butylcalix[5]arene platform could provide an interesting extension of our catalytic studies, several calix[5]-crown-ethers were investigated as potential catalysts of ester methanolysis in the presence of a Ba + salt [22]. Of the various structures investigated, the calixcrown-5 derivative 7 gave the... 

Cation Interaction with Calix[4]arene Crown Ethers... 

Although the situation is even more complicated with calix[8]arenes, crown ether derivatives with 1,2- 1,3-, 1,4- and 1,5- bridging have been obtained in good to excellent yields (88% and 78% for l,5-crown-2 and l,5-crown-3) ° . 1,5-Bridged derivatives have been obtained with o- and / -bis(bromomethyl)benzene °, and 1,4-bridged derivatives... 

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. 

J.K. Kim, J.S. Kim, Y.G. Shul, K.W. Lee, and W.Z. Oh. Selective extraction of cesium ion with calix[4]arene crown ether through thin sheet supported liquid membranes. Journal of Membrane Science 187 3-11, 2001. 

By changing the nature of the base and the solvent a certain control of the stereochemical outcome has been achieved in few alkylation [15] and acylation [24] reactions of calix[4]arenes. Recently, in collaboration with the group of Prof. D.N. Reinhoudt, several stereoisomeric calix[4]arene crown ethers have been synthesized and their ionophoric properties toward alkali metal cations determined by the Gam s extraction method [25]. In all cases it was found that these ligands are very selective for potassium cation and that the compounds in the partial cone structure are more efficient and more selective than those in the fixed cone conformation. The highest difference in... 

Various kinds of functionalization methods of the phenol OH groups of calix[n]-arenes have been reported to yield ionophores [6]. Also, turned crown ethers with functional groups on nitrogen have been synthesized and effective recognitions of ions have been reported [7]. 

In water, the introduction of a counteranion (NOy) induces a stronger electrostatic interaction, which tends to draw the cations out of the mean plane of the crown ether loop. Simulations with cesium nitrate and the various calix[4]arene-biscrowns show that the best fit is obtained with BC8 and BC9.59... 

Sachleben et al. observed that for bis(alkoxy)calix[4]arene monocrown ethers, reducing the size of the alkoxy substituent from octyl to allyl increased the cesium extraction by 10%-30% and the cesium-to-potassium selectivity by 20%-40%, with little impact on cesium over sodium selectivity. A standard modeling approach was used to analyze the complementarity of the calix-crown cavity toward potassium and cesium. MM3 optimizations were performed by modifying the K+ and Cs+ complexes, replacing the 1,3-dioxybenzene-substituent with tert-butoxy, methoxy, or hydrogen groups. 

Extraction of tetrahedral pertechnetate anion from aqueous solutions using several crown ethers is well known. The coextraction of cesium (or strontium) and technetium from nuclear waste by calix[4]arene-crown-6 has been reported from alkaline media. Although technetium in its common pertechnetate form does not complex directly with crown ethers, pertechnetate extraction may be facilitated by crown ethers as the coanion of sodium (for alkaline nitrate waste). Pertechnetate at trace levels in the waste may be more than a 1000-fold more extractable than the smaller nitrate anion in ion-pair extraction processes.87... 

The Re(I) bipyridyl unit has been exploited in another series of ion-pair sensors. Molecules 61-64 incorporate crown ether components to act as cation receptors [43,44]. H NMR titrations revealed 61-64 to be selective for acetate over chloride. In all the receptors (except 62 and 64 with acetate) enhanced binding was observed in the presence of K+ cations. The degree of enhancement is lower in the xylyl-spaced molecules 62 and 64 (40-50%) than in 61 and 63 (80-110%). It is also small compared to that seen in the calix[4]arene receptor 60. 

The earliest recognised examples of synthetic supramolecular structures were the complexes formed from crown ethers and metal cations [19]. Since then numerous macrocycles have been synthesised. Representative examples are the cryptands [20], These differ from crown ethers in that the former contains a tridimensional cavity while the latter are characterised by a hole. Similarly, calix[4]arenes are compounds with a cup -like structure that through lower rim functionalisation gives rise to a hydrophilic and a hydrophobic cavity, thus allowing the reception of ionic species in the former and neutral species in the latter. Most of the above mentioned macrocycles are known for their capability to serve as cation receptors. 

Most of the inherently chiral calix[5]arenes described up to now, owe their chirality, however, to the asymmetric substitution pattern at the narrow rim, and due to the lack of other general, selective derivatization reactions are derived from 1,2-or 1,3-crown ethers. Both compounds possess a symmetry plane and can be desymmetrized by a single O-alkyl or O-acyl residue in position 3 (=5) or 4 (=5).151,152,153 In practice, 1,2-crown ethers 79 were prepared from mono-O-alkyl derivatives by reaction with the appropriate ditosylates, while 80 was obtained from the 1,3-crown-ether by subsequent O-alkylation or O-acylation using a weak base to benefit from the fact, that the first deprotonation leads to a hydrogen-bonded (4/5)monoanion. The picolyl derivatives 79 (n = 2) were resolved by HPLC... 

Naphthol may form cyclic tetrameric condensation products with formaldehyde among which 101 has a C4 axis.194 However, since the OH groups are in exo positions in this case (in contrast to the calix[4]arene 97g derived from 2-naphthol) it seems difficult to fix a nonplanar conformation in these cases.195 A possibility would be the connection of two opposite oxygens by a (crown) ether bridge which would lead to a C2-symmetrical derivative. 

Two calix[4](diseleno)crown ethers were synthesized by reaction of the disodium salt of 1,3-propanediselanol 188 with the preorganized l,3-dibromoethoxycalix[4]arenes. These potentially ionophoric calixcrown selenoethers form interesting infinite aggregate sheets via self-inclusion and intermolecular Se- Se interactions in the solid state <2002TL131>. 

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