Potassium 18-crown-6 polyether

The crowns as model carriers. Many studies involving crown ethers and related ligands have been performed which mimic the ion-transport behaviour of the natural antibiotic carriers (Lamb, Izatt Christensen, 1981). This is not surprising, since clearly the alkali metal chemistry of the cyclic antibiotic molecules parallels in many respects that of the crown ethers towards these metals. As discussed in Chapter 4, complexation of an ion such as sodium or potassium with a crown polyether results in an increase in its lipophilicity (and a concomitant increase in its solubility in non-polar organic solvents). However, even though a ring such as 18-crown-6 binds potassium selectively, this crown is expected to be a less effective ionophore for potassium than the natural systems since the two sides of the crown complex are not as well-protected from the hydro-phobic environment existing in the membrane. 

Impressive applications of the solubilizing effects of crown polyethers and cryp-tands have been described. For example, the dissolution of sodium, potassium, and cesium metal in tetrahydrofurane and diethylether is mediated by certain ligands of this typeS7,78,171 Such solutions have provided new systems for the study of solvated electrons and alkali metal anions. Substances like KMn04, tert-CuYigOYL, or... 

French) or BROMOFORMO (Spanish) (75-25-2) CHBrj Noncombustible liquid. Violent reaction with chemically active metals, acetone, calcium, strong caustics, potassium, potassium hydroxide, sodium hydroxide. Increases the explosive sensitivity of nitromethane. Incompatible with crown polyethers, sodium-potassium alloys. Forms friction- and shock-sensitive compounds with lithium. Aqueous solution is a medium-strong acid. Liquid attacks some plastics, rubber, and coatings. Corrosive to most metals in the presence of moisture. Thermal decon osition products include highly toxic carbonyl bromide and hydrogen bromide fumes. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or COj extinguishers. 

Potassium chloride crown poly ether Crown polyethers as phase transfer catalysts... 

Potassium permanganate/crown polyether Crown polyethers as complexing agents Oxidations with potassium permanganate in benzene... 

Crown polyethers have also been synthesized (Kopolow et al., 1971, 1973) by polymerization of the corresponding vinyl monomer (4 -vinylmonobenzo-15-crown-5) (Scheme 13-4). The polymeric crown ethers were obtained as amorphous solids, softening at 122-128°C and with an average molecular weight of 11,600. The polymeric polyethers, just like the monomeric crown ethers, had the ability to bind alkali metal, particularly potassium, ions. Hence, these have been used for extraction of potassium. The crown polyethers form a complex with KMn04, which is... 

The use of crown polyethers to solubilize potassium permanganate in benzene has been reported. In a study of the oxidation of alkyl toluene-/ -sulphonates with DMSO-sodium bicarbonate, the elements of carbon dioxide are retained in the product (86) as a cyclic carbonate (Scheme 170), inferring that, for this substrate, bicarbonate ion is a more effective nucleophile than DMSO this leads to a revision of the mechanism of such oxidations to that shown in Scheme 170. 

The unsaturation present at the end of the polyether chain acts as a chain terminator ia the polyurethane reaction and reduces some of the desired physical properties. Much work has been done ia iadustry to reduce unsaturation while continuing to use the same reactors and hoi ding down the cost. In a study (102) usiag 18-crown-6 ether with potassium hydroxide to polymerise PO, a rate enhancement of approximately 10 was found at 110°C and slightly higher at lower temperature. The activation energy for this process was found to be 65 kj/mol (mol ratio, r = 1.5 crown ether/KOH) compared to 78 kj/mol for the KOH-catalysed polymerisation of PO. It was also feasible to prepare a PPO with 10, 000 having narrow distribution at 40°C with added crown ether (r = 1.5) (103). The polymerisation rate under these conditions is about the same as that without crown ether at 80°C. 

In the absence of die polyether, potassium fluoride is insoluble in benzene and unreactive toward alkyl halides. Similar enhancement of solubility and reactivity of other salts is observed in the presence of crown ethers The solubility and reactivity enhancement result because the ionic compound is dissociated to a tightly complexed cation and a naked anion. Figure 4.13 shows the tight coordination that can be achieved with a typical crown ether. The complexed cation, because it is surrounded by the nonpolar crown ether, has high solubility in the nonpolar media. To maintain electroneutrality, the anion is also transported into the solvent. The cation is shielded from interaction with the anion as a... 

In specific applications to phase transfer catalysis, Knbchel and his coworkers compared crown ethers, aminopolyethers, cryptands, octopus molecules ( krakenmole-kiile , see below) and open-chained polyether compounds. They determined yields per unit time for reactions such as that between potassium acetate and benzyl chloride in acetonitrile solution. As expected, the open-chained polyethers were inferior to their cyclic counterparts, although a surprising finding was that certain aminopolyethers were superior to the corresponding crowns. 

Potassium acetate complex with dicyclohexyl-18-crown-6-polyether, 52, 71 Potassium amide, 52, 75 Potassium azide, 50, 10 Potassium tert-butoxide, 52,... 

This residue is a mixture of stereoisomerio dicyclohexyl-18-crown-6 polyethers which may be contaminated with some unchanged dibenzo-18-crown-6 polyether and with alcohols arising from hydrogenolysis of the polyether ring. The submitter reports that this residue is sufficiently pure for many purposes such as the preparation of complexes with potassium hydroxide which are soluble in aromatic hydrocarbons. 

The checkers prepared a crystalline complex of potassium acetate with isomer B of dicyclohexyl-18-crown-6 polyether by the following procedure. To a stirred solution of 15.0 g. (0.0404 mole) of dicyclohexyl-18-crown-6 polyether (mixture of isomers) in 50 ml. of methanol was added a solution of 5.88 g. (0.0600 mole) of anhydrous potassium acetate (dried at 100° under reduced pressure) in 35 ml. of methanol. The resulting solution was concentrated under reduced pressure with a rotary evaporator, and the residual white solid was extracted with 35 ml. of boiling methylene chloride. The resulting mixture was filtered and the filtrate was cooled in a dry ice-acetone bath and slowly diluted with petroleum ether (b.p. 30-60°, approximately 200 ml. was required) to initiate crystallization. The... 

The physical properties of many macrocyclic polyethers and their salt complexes have been already described. - Dibenzo-18-crown-6 polyether is useful for the preparation of sharpmelting salt complexes. Dicyclohexyl-18-crown-6 polyether has the convenient property of solubilizing sodium and potassium salts in aprotic solvents, as exemplified by the formation of a toluene solution of the potassium hydroxide complex (Note 13). Crystals of potassium permanganate, potassium Lbutoxide, and potassium palladium(II) tetrachloride (PdClj + KCl) can be made to dissolve in liquid aromatic hydrocarbons merely by adding dicyclohexyl-18-crown-6 polyether. The solubilizing power of the saturated macrocyclic polyethers permits ionic reactions to occur in aprotic media. It is expected that this [)ropcrty will find practical use in catalysis, enhancement of... 

The reaction sequence outlined in Scheme 12 illustrates how macrocyclic polyether-thiono diesters such as RR)-lfi6 can be prepared (184) from 0,0-dimethyl 2,6-pyridinedicaibothiolate and (RR)-S4, Potassium thiocyanate forms a 1 1 crystalline complex with (RR)-1S6 and presumably the potassium ion serves as a template for the (1 -I-1) cyclization. Raney nickel desulfurization of (/ R)-186 yields the chiral pyridino-18-crown-6 derivative RR)-191. 

More than sixty neutral macrocyclic polyethers containing four to twenty oxygen atoms, each separated from the next by two or more carbon atoms, have been synthesized 40, 41) (see Fig. 8). Many of these compounds form 1 1 complexes in which the cation is encircled by the oxygen atoms of the polyether 44, 71). The potassium complex of di-benzo-30-crown-10 (77) consists of a wrap-around structure, where all the oxygen atoms are approximately equidistant from the central... 

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