1.4- Dihydroxybenzene, from reactions

This process has been widely studied and led to the constmction of new and original industrial units. Interest in the reaction stems from the simplicity of the process as well as the absence of undesirable by-products. However, in order to be economically rehable, such a process has to give high yield of dihydroxybenzenes (based on hydrogen peroxide as well as phenol) and a great flexibiUty for the isomeric ratio of hydroquinone to catechol. This last point generated more research and led to original and commercial processes. 

The enzymes catalyzing the Kolbe-Schmitt carboxylation seem to occur ubiquitously. Some of them, such as 2,6-dihydroxybenzoate decarboxylase and pyrrole-2-carboxylate decarboxylase, catalyze efficiently the reverse carboxylation reaction and accumulate high concentration of 2,6-dihydroxybenzoate from 1,3-dihydroxybenzene and pyrrole-2-carboxylate from pyrrole, respectively, in the... 

As we presented above, the presence of quartz in the temperature range studied had no effects on the decomposition of dihyroxybenzenes. To further investigate this point and show the different effects of iron oxide and quartz on the product distribution, we present the product distribution for two cases of nanoparticle iron-oxide mixed with quartz chips and only quartz chips. Comparison in product distribution over nanoparticle iron oxide/quartz mixture and quartz was carried out with 3% of oxygen andl8 x 10 mmol/min of feedrate for starting materials, and at reaction temperatures that resulted in a comparable conversion of dihydroxybenzenes (e.g., 80%). Figure 12.6 shows the average spectra of the products obtained from MBMS for two cases with about 80% catechol conversion that was achieved at 300°C in the presence of iron oxide... 

Anticipated products from the reaction of phenol with ozone or OH radicals in the atmosphere are dihydroxybenzenes, nitrophenols, and ring cleavage products (Cupitt, 1980). Reported rate constants for the reaction of phenol and OH radicals in the atmosphere 2.8 x 10 " cmVmolecule-sec at room temperature (Atkinson, 1985) and with NO3 in the atmosphere 2.1 x lO" cmVmolecule-sec at 296 K (Atkinson et al., 1984). 

Benzotrithiole 2-oxide (41) was obtained in 76% yield from the reaction of benzene-1,2-dithiol with thionyl chloride <93TL673>. Similarly, 1,3,2-benzodioxathiole 2-oxide was prepared from 1,2-dihydroxybenzene and thionyl chloride <66HC(2i-i)i>, and 1,2,3-benzoxadithiole 2-oxide was obtained from 2-mercaptophenol and thionyl chloride <81AG(E)570>. Reaction of the monosodium salt of 1,2-dihydroxybenzene with sulfuryl chloride afforded an intermediate chlorosulfate ester, which was dehydrochlorinated to 1,3,2-benzodioxathiole 2,2-dioxide by the action of pyridine <66HC(21-l)l>. The substituted 1,3,2-benzodioxathiole 2,2-dioxide (121) was isolated from the photolysis of pyrenedione in the presence of sulfur dioxide <87TL2057>. 

The two major routes to 3,4-dihydro-2JT-l,5-benzodioxepins (274) from (273) and (275) are applicable to a wide range of substituted derivatives. The 3-oxo derivative, important as a perfume odorant, can be prepared via the reaction of 1,2-dihydroxybenzene with chloroacetonitrile (75CJC2279) or via a Dieckmann cyclization (74USP3799892). 

Diazotization in the presence of boron trifluoride enables diazonium tetrafluoroborates to be isolated from the reaction mixture and purified. Subsequent controlled decomposition produces the required fluoroaromatic. Although explosion hazards and the toxicity of the isolated salts are significant concerns with this process, known as the Balz-Schiemann process, 4,4 -di-fluorobenzophenone (BDF. 6) has been prepared by this route as a monomer for the production of the engineering plastic poly(ether ether ketone) , or PEEK , by condensation with 1,4-dihydroxybenzene in the presence of potassium carbonate. BDF 6 is superior to its chlorine analog because in aromatic systems the nucleophilic displacement of fluorine is more facile than that of chlorine, leading to a shorter polymerization time and a better quality product containing less degradation impurities. 

In all the aprotic solvents (with no proton donor admixtures), the superoxide ion generally cannot act as an oxidant, taking into account a wide range of functionally substituted compounds. For example, in dry pyridine, 07 does not oxidize 1,2-dimethoxybenzene (Sawyer Gibian 1979). This ion, however, reacts with 1,2-dihydroxybenzene. For the OH form, the first step consists of proton transfer from the hydroxyl group to the superoxide ion. Next, reactions proceed with the participation of HOO. The latter is formed according to the disproportionation of Scheme 1-70. 

It is well known that benzophenone generates a biradical through n-ir electronic transition under irradiation ( 340 nm). Irradiation of a mixture of 1,4-benzoquinone (34) and aromatic aldehydes in the presence of benzophenone generates 2-aroyl-l,4-dihydroxybenzene (35) [47-49]. This reaction comprises of the abstraction of a formyl hydrogen atom of an aromatic aldehyde by the oxygen-centered radical of the benzophenone biradical to form an aroyl radical and a 1,1-diphenylhydroxymethyl radical, and addition of the nucleophilic aroyl radical to 1,4-benzoquinone (34) to form a phenoxyl radical derivative, which finally abstracts a hydrogen atom from an aromatic... 

Zymalkowski and Strippel hydrogenated dihydroxybenzenes with only slight hydrogenolysis over rhodium-platinum oxide in acetic acid at room temperature and 10 MPa H2 and obtained the corresponding cyclohexanediols in 92-96% yields (eq. 11.17).97 The hydrogenations at atmospheric pressure required much longer reaction times, and the yield of cyclohexanediol decreased to 86% with resorcinol. The proportions of cis isomer in the cyclohexanediols obtained at 10 MPa H2 were 81% from catechol, 68% from resorcinol, and 68% from hydroquinone and always greater than those obtained at atmospheric pressure (75,49, and 52%, respectively). 

Phenazines can be obtained from o-nitrodiphenylamines by reduction or from o-aminodiphenylamines by oxidative techniques. Phenazine 5,10-dioxides are prepared by the Beirut reaction (see Section 4.4.6.4) using hydroquinone , and they can also be synthesized by treatment of o-nitroanilines with dihydroxybenzenes (e.g., Scheme 37) <1995M1217>. 

Reaction between phenol and hydroxyl yields the dihydroxybenzenes, which can then undergo further oxidation (hydroquinone to benzoquinone, further hydroxylated to hydroxybenzoquinone, catechol and resorcinol to trihydroxybenzenes [79,100]). The condensation products, phenoxyphenols and dihydroxybiphenyls, most likely originate from the reaction between phenol and the phenoxyl radical [101]. Their presence indicates that some phenoxyl forms in the system, due to the reaction of phenol with OH or NO2. The possibility for NO2 to oxidise phenol to phenoxyl has been the object of a literature debate [102,103] in the context of nitration processes. The problem can be tackled upon consideration of the reduction potentials of the various species. The reduction potential of phenoxyl to undissociated phenol is E = 1.34 V - 0.059 pH [104], while for the reduction of nitrogen dioxide to nitrite it is E = 0.90 V [105]. Accordingly oxidation of phenol to phenoxyl would be possible above pH 7.5, and of course in the presence of phenolate (pH > 10 [106]). 

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. 

Dihydroxybenzene may be prepared from 2-hydroxybenzaldehyde by the Dakin reaction, which involves oxidation in alkaline solution by hydrogen peroxide (Scheme 4.15). The reaction involves a 1,2-shift to an electron-deficient oxygen and is similar to the cumene process used to synthesize phenol (Section 4.2). 

The naphthylamines may be prepared by reduction of the corresponding nitro compound, but they are readily accessible from naphthois by the Bucherer reaction The naphthol is heated, preferably under pressure in an autoclave, with ammonia and aqueous sodium hydrogen sulfite solution, when an addition-elimination sequence occurs. The detailed mechanism is not completely elucidated, but the Bucherer reaction is restricted to those phenols that show a tendency to tautomerize to the keto form, such as the naphthois and 1,3-dihydroxybenzene (resorcinol). Using 1-naphthol for illustration, the first step is addition of the hydrosulfite across the 3,4-double bond of either the enol or keto tautomer (Scheme 12.9). Nucleophilic attack by ammonia at the carbonyl group... 

Stirring diorgano tellurium diethoxides in a diethyl ether/pentane medium with the stoichiometrically required amounts of 1,2-dihydroxyethane, 1,3-dihydroxypropane, 2-hydroxyphenylmethanol, 1,2-dihydroxybenzene, 2,2 -dihydroxybiphenyl, 2,3-dihydroxy-naphthalene, or 4-methylphenol produced diorgano tellurium alkoxides and phenoxides. These compounds precipitated as white solids from the reaction mixtures or separated as oils that crystallized during storage at low temperatures. The products of the transesterification with diols could be oligomeric. The low solubility of these compounds prevented the determination of their molecular masses . 

Diaryl carbonates are made from the reaction of phosgene with two molar equivalents of the particular sodium phenolate [3]. However, the direct conversion of phenols can be achieved by reaction of phosgene in the presence of quaternary ammonium salts, or acid acceptors (such as pyridine), at ambient temperatures [2016]. The three dihydroxybenzenes... 

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