Dibenzo-24-crown-8 ether

Slomkowski, S., and Penczek, S., Influence of dibenzo-18-crown-6 ether on the kinetics of anionic polymerization of p-propiolactone, Macromolecules, 9, 367-369, 1976. 

In our recently published paper on kinetics of elementary reactions in polymerization of BPL, initiated with acetate anion with potassium crowned with dibenzo--18-crown-6 ether (DBCK+) counterion in methylene... 

The introduction of substituent groups into the benzo rings on dibenzo-18-crown-6 ethers leads to marked effects on their selectivity. A reversal of the usual selectivity sequences occurs when strong, electron-withdrawing substituents are present.490 Similar effects are found for benzo-15-crown-5, and a good correlation is found with the Hammett functions of the substituents.491 In contrast for substituted benzo-18-crown-6 systems, no such correlation was found, indicating that caution must be exercised on extrapolating from one crown ether system to another. 

As far back as 1984, Wolfbeis described the quenching of fluorescence of dibenzo-18-crown-6 ether in the presence of K+ and I" ions [S71 this can now be viewed as NAND logic behavior. It is likely that the oxidizable I" is ion-paired to the crown-bound K+ in much the same way as in the system involving 14, Ba, and SCN . 

Samples of mesoporous titanium dioxide were synthesized via sol-gel hydrolysis of Ti(IV) tetrabutoxide in 1-butanol by atmospheric moisture in the presence of a structure-directing template dibenzo-18-crown-6 ether. After completion of the sol-gel transformation and ageing of the precipitate, the mother liquor with the precipitate was exposed to hydrothermal treatment (HTT) at 100 - 175 °C for 24 h. Then, the precipitate was separated, dried, and calcinated on air at 350 - 500 °C for 4 hours. 

Synthesis of mesoporous TiO/M composites and their photocatalytic activity in hydrogen evolution. Hydrolysis of Ti(TV) tetrabutoxide with subsequent sol-gel transformation in the presence of dibenzo-18-crown-6 ether as a template yields amorphous titanium dioxide (Fig. 1). Calcination of the parental amorphous sample at 500 °C causes crystallization of Ti02 and formation of a porous material with high specific surface area and a narrow pore size distribution with the average pore diameter 5.0 nm (Table 1, sample No. 2). Combination of the hydrothermal treatment (HTT) of Ti02 samples at 100 - 175 °C with their subsequent calcination... 

C. Chuit, R. J. P. Corriu, G. Dubois, and C. Reye, Hybrid organic-inorganic materials. Preparation and properties of dibenzo-18-crown-6 ether-bridged polysilsesquioxanes, Chem. Commun. 723-724 (1999). 

Fig. 4.6. (Top) Reaction that eventually led to the serendipitous synthesis of dibenzo-18-crown-6 ether. (Middle) common crown ethers with their usual denomination. (Bottom) some cryptands with their denomination.

A functionalized carbon multi-walled nanotube, MWNT, was prepared in 2 steps by initially oxidizing the unfunctionalized nanotube with mixed acids followed by amida-tion with guanidine. When reacted with polystyrene-g-dibenzo-18-crown-6-ether, the polymer, polystyrene-g-dibenzo-18-crown-6-ether-g-(nanotube-g-guanidine), was formed having the nanotube component aligned perpendicular to the polystyrene backbone. 

Polystyrene-g-carboxylic acid (5g) and hydroxylmethyl dibenzo-18-crown-6-ether (Ig) were dissolved in 500 ml of pyridine and reacted at ambient temperature for 5 hours. The mixture was then treated with water, and the layers were separated. The organic phase was concentrated, and the product was isolated. 

Preparation of Polystyrene-g-Dibenzo-18-Crown-6-Ether-g-(Nanotube-g-Guanidine)... 

Molybdenum and tungsten have been separated on a chelating resin with thioglycolate groups. A mixture of these metals is sorbed from an acetate solution of pH 4.3, then Mo and W are eluted successively with 2 M HCl and a mixture of 0.1 M NaOH and 0.1 M NaCl [36]. The sorption of Mo and W on silicate sorbents, modified with hydroxamic acids, was also studied [37,38]. Mo was also preconcentrated on dibenzo-18-crown-6 ether columns from HCl [39] and HBr [40] media. 

The thiocyanate complex of niobium may be extracted in the presence of ethylenebis(triphenylphosphonium) cation [38], promazine [39], triphenylguanidine [40], and dibenzo-18-crown-6 ether [41]. Chloroform, trichloroethylene, toluene and benzene are used as the solvents. 

Complexation of dibenzo-18-crown-6 ether with 3,6-dimethylthieno[3,2-Z)] thiophene-2,5-dione 293 (77JCS(P2)1327), homolytic aromatic silylation of 2-cyanothieno[2,3-Z)]- and -[3,2-Z ]thiophenes (79G395), addition of silyl radicals to 3,6-dimethylthieno[3,2-Z)]thiophene-2,5-dione and 5-benzylidene-3,6-dimethylthie-no[3,2-Z)]thiophen-2-one (86JA4993) and the conformational behaviour of the dithieno[3,2-Z 2, 3 -< -thiophene-2,6-dicarbaldehyde radical anions (78JCS(P2)212) were studied by ESR spectroscopy. 

Ohira. A. Sakata, M. Hirayama, C. Kunitake, M. 2-D supramolecular arrangements of dibenzo-18-crown-6-ether and its inclusion complex with potassium ion by potential controlled adsorption. Org. Biomol. Chem. 2003, 1,251-253. 

Ratio of trans-trans to cis-trans conformers given as a function of the counter-ion for 223 K. Coupling constants unchanged after addition of dibenzo-18-crown-6 ether. 

Determination of barrier to internal rotation to cis-trans conformer. Determination of barrier to internal rotation for dibenzo-18-crown-6 ether complex of Na-ketyl. Assignment based on MO calculation. Stereochemistry not discussed. Determination of barrier to internal rotation to cis-trans conformer from temperature dependence. ) Determination of activation and thermodynamic parameters for the cis-transtrans-trans forward isomerization. Determination of barrier to internal rotation to cis-trans conformer. ... 

Dibenzo-l,4,7,10,13,16-hexaoxacyclooctadeca-2,ll diene (dibenzo-18-crown 6-"ether)... 

Dibenzocrown ethers, namely dibenzo-18-crown-6 and -24-crown-8 by similar treatment with a larger excess of the reagent (20 equivalents) gave the corresponding disulfonyl chlorides. For example, dibenzo-18-crown-6 ether 500 afforded the disulfonyl chloride 501 as a mixture of stereoisomers, showing that chlorosulfonation of the dibenzocrown ethers does not occur regioselectively. The chlorosulfonyl and dichlorosulfonyl derivatives were converted into sulfonamides by reaction with ammonia and amines. 

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