4-Vinylbenzo-18-crown

We have noted above that benzocrowns may be nitrated quite readily. This approach was used in the formation of a photoresponsive bis-crown (see Sect. 3.8) wherein the nitrobenzo crowns reductively dimerize to the corresponding azobenzene. Kikukawa, Nagira and Matsuda have utilized 4-nitrobenzo-15-crown-5 in a somewhat different way during the synthesis of 4 -vinylbenzo-l 5-crown-5Nitration is effected using nitric acid in a mbcture of chloroform and acetic acid. 

Hydrogenation reduces the nitro group to amino which is then diazotized using sodium nitrite and tetrafluoroboric acid. The diazotized crown was not isolated but the aq. solution was treated directly with sodium acetate and bis(dibenzylideneacetone)-pal-ladium(O) in acetonitrile solution. Ethylene was then introduced to the autoclave and the solution was allowed to stir for 2 days. 4 -Vinylbenzo-15-crown-5 was isolated (30% from 4 -nitrobenzo-15-crown-5) as a colorless solid (mp 43.5—44.2°) °. The synthesis is illustrated in Eq. (3.16). 

Smid and coworkers have developed a straightforward and effective method for the synthesis of 4 -vinylbenzo-15-crown-5. In this method, 3,4-dihydroxybenzaldehyde is converted into the crown in the usual fashion and then the side chain is transformed by successive treatment with methylmagnesium bromide and then toluenesulfonic acid to effect dehydration. The overall yield is about 20%. 

For the purpose of our discussion, a polycrown is here defined as a polymer system arising by polymerization of a crown monomer unit. Extensive work has been done in this field by Kopolow, Hogen Esch and Smid and the examples presented here are taken from a paper by all three of these workers. A typical preparation of vinylbenzo-15-crown-5 is accomplished according to the scheme shown as Eq. (6.25). One might also have utilized a formylation/Wittig sequence on benzo-15-crown-5 to accomplish the same end. 

Poly(vinylbenzo-18-crown-6) [54] dissolved in water also acts as an efficient catalyst for the decarboxylation through transfer of the substrate into the aromatic inner core of the tightly coiled polymer (Shah and Smid, 1978). The bound carboxylate decomposes 2300 times faster than in water, the rate constant (0.042 s-1) being the largest of those observed in aqueous media. 

On the basis of this report, in 2003, Gagne and collaborators described an imprinting system involving the use of the crown ether to improve Cammidge s system [48]. The polymer was prepared by imprinting the polymerisable bis-triphenyl-phosphine-Pd(catecolate) together with a polymerisable 1 1 complex formed by the 4 -vinylbenzo-18-crown-6 ether and n-butylamine (72). 

Poly(carboxylic acid)s Poly(vinylbenzo-18-crown-6) 295... 

Moreover, intermacromolecular complex formation is applied to selective recovery of organic and metallic ions. For example, as shown in Table 27, Cu2+ ion is much more effectively precipitated by the polyelectrolyte complex than by one of its components520. Furthermore, polyelectrolyte complexes including some metal ions have been studied in recent years (see Sect. 3.2.). Crown ethers can bind certain cations they especially exhibit high affinity to K+. Smid et al.S21) synthesized poly(vinylbenzo-[18]-crown-6). Such polymers containing crown ether with K+ behave like polycations in solution and can interact with polyanions such as poly(carboxyHc acid) to generate a kind of polyelectrolyte complexes. Moreover, PAA may interact with the ether oxy-... 

Bunton and his co-workers55 have shown that the decarboxylative ring opening of 6-nitroindoxazene-3-carboxylic acid is strongly catalyzed by cationic micelles and by micelles of zwitterionic surfactants such as N,N-dimethyl-JV-dodecylglycine. Later studies by other workers indicate that the decarboxylation is also catalyzed by polysoaps,56 modified polyethylene-imines,57 cycloheptaamylose,9 and by poly(vinylbenzo-18-crown-6).58 The... 

C-allylation of PhO" Na with H2C=CHCH2C1 in a variety of solvents in the presence of different crown ethers is most effective in each case when using poly(vinylbenzo-15-crown-5)polyether. Only in the presence of the crown ethers 15-crown-5 and 18-crown-6 are the anions in potassium phthalimide and sodium saccharinate, respectively, sufficiently activated to bring about nucleophilic aromatic substitution of the 4-fluorine in pentafluoropyridine. The formation of 2,4-dinitrophenol, in addition to the expected ether, from 2,4-dinitrochlorobenzene and potassium 2-propoxide in 2-propanol-benzene (1 1), in the presence of dicyclohexyl-18-crown-6 polyether, has been accounted for on the basis of a nucleophile-radical reaction (5rn1)/ ... 

Crown ethers with exocyclic multiple bonds and a cavity filled by metal ions would be a potential monomer of this type. The cavity can be considered as a polydentate chelate node. The nature of the cation and the size of athe macrocyclic cavity play an important role (the key-lock principle) [53]. There are reports of the production of such monomers from alkali metals and 4 -vinylmonobenzo-18-crown-6, (81), 4 -vinyldibenzo-18-crown-6 (82), and 4 -vinylbenzo-15-crown-5 (83). 

Polymeric crown ethers may also be bonded chemically to the silica surface. For that purpose, the support material is modified with 3-(N-methacryloylam-ino)-propyl groups, and subsequently co-polymerized with (4-methacryloylam-ino)-benzo-15-crown-5 [55]. Stationary phases, in which the crown ether molecules are chemically bonded to silica via Si-O-C linkages, are obtained with silica treated with thionyl chloride via reaction with 4-hydroxymethylbenzo-18-crown-6 (see Fig. 3-56, upper right). Since Si-O-C-bonds are prone to hydrolysis, water-free methanol is used as eluant for such stationary phases. Much more stable are silicas modified via Si-C-bonds (see Fig. 3-56, bottom left and right) that are prepared by using 4-vinylbenzo-18-crown-6 or 4-butene-18-crown-6 and... 

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