Catechol dibenzoate

Pedersen s preparation of dibenzo-18-crown-6 involves catechol and bis(2-chloroethyl) ether. In this procedure, sodium hydroxide is used as base and M-butanol as solvent. The reactants are heated overnight and the crude crown is obtained by precipitation from acetone in which it is almost completely insoluble. The yield range specified is 39—48% and is readily realized. The overall preparation is illustrated in Eq. (3.11). 

The preparation of dibenzo-18-crown-6 polyether directly from catechol and bis(2-chloroethyl) ether has been reported previously. The present procedure is an improvement of this method. Although dibenzo-18-crown-6 polyether can be obtained in 80% yield from bis-[2-(o-hydroxyphenoxy)-ethyl] ether and bis(2-chloroethyl) ether, the former intermediate has to be synthesized by a method involving several steps. One of the hydroxyl groups of catechol must be protected against alkali by reaction with a molecule of dihydropyran or chloromethylm ethyl ether. Then the intermediate is treated with bis(2-chloroethyl) ether in the presence of alkali and, finally, converted into the desired intermediate by acid hydrolysis. The yield of bis[2-(o-hydroxyphenoxy)-ethyl] ether was less than 40% so that the overall yield of dibenzo-18-crown-6 polyether never approached 39-48%, the yield of the present direct method. 

The reaction of a dichloro and dihydroxy component can lead to crown ethers via route (b) or (c), and frequently mixtures of products must be separated. However, the presence of rigid benzo groups in the reactants limits the conformational freedom of uncyclized intermediates and an increase in product selectivity results. For example, the condensation of catechol and bis(2-chloroethyl) ether (33) in equimolar amounts leads almost exclusively to dibenzo[18]crown-6 (2) in 45% yield (B-78MI52101). 

The yield of crown ether can be increased to more than 80% by using a longer stepwise route in which the initial catechol is partially protected. Reaction of the phenol (34) with bis(2-chloroethyl) ether (33) forms intermediate (35) which after deprotection can react with a further molecule of bis(2-chloroethyl) ether to give dibenzo[18]crown-6. 

As noted in Chapter 3, Pedersen synthesized dibenzo-18-crown-6 44 which marked the beginning of inclusion (or host-guest) chemistry as a minor product obtained as a result of the presence of catechol as an impurity in the reaction... 

Dibenzo[/ ][ 1,4]dioxin (oxanthrene) 85 (Z, Z = 0) is prepared by heating 2-chlorophenol, potassium carbonate, and copper <1957JA1439>. Cyanooxanthrenes 88 were quantitatively prepared from catechols 86 by nucleophilic displacement of fluoride from 2,3- and 3,4-difluorobenzonitriles 87 (Scheme 47) <1999CL479, 2001NJC379, CHEC-III (8.12.9.1.1)882>. 

Reactions such as the one that gave Pedersen the first crown can produce additional products. Thus, catechol (1,2-dihydroxybenzene) reacts with 0(CH2CH2)2C1 in the presence of base to give dibenzo-18-crown-6. Tribenzo-27-crown-9 and benzo-9-crown-3 have also been identified as resulting from this process. For this reason, such crown preparations are sometimes referred to as shotgun reactions. Attempts have been made to direct the cyclization to the correct receptor size by including a K+ template ion to direct formation of 18-membered ring. 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

In 1967 Charles J. Pedersen, then 2 years away from retirement as a research chemist with Du Pont, published an extensive paper detailing the preparation of 33 cyclic polyethers [1], His thorough investigation of these macrocycles was the culmination of several years work initiated by the accidental preparation of dibenzo[18]crown-6 [2], The compound formed as a result of trace amounts of catechol that had contaminated 2-(hydroxyphenoxy)tetrahydropyran used in the synthesis of the original target compound, bis[2-(hydroxyphenoxy)ethyl]ether. The dibenzocrown ether thus became the first of the crown ethers, as Pedersen called them, to be isolated. 

Polycyclic aromatic hydrocarbons Alkylated aromatic hydrocarbons Chlorinated aromatic compounds Chlorobenzenes Polychlorinated biphenyls Polychlorinated dibenzo[l,4]dioxins Chlorinated guaiacols and catechols Nitrogen-containing aromatic compounds Azaarenes and aromatic nitriles Oxygenated aromatic compounds 2,4-Dipentyl phenol Polycyclic quinones and ketones Aliphatic carboxylic acids Cs and C, dicarboxylic acids... 

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