Hydroquinone dihydroxybenzene

Quinones are an interesting and valuable class of compounds because of their oxidation-reduction, or redox, properties. They can be easily reduced to hydroquinones (/>dihydroxybenzenes) by reagents such as NaBFQ and. SnCQ, and hydroquinones can be easily reoxidized hack to ejuinones by Fremy s salt. 

Phenol is oxidised by H2O2 to hydroquinone (/ -dihydroxybenzene) and catechol (o-dihydroxybenzene) over TS-1 in aqueous or mixed aqueous/organic solutions (Scheme 9.1). Both isomers are formed, with an o-jp-raXio of 0.5 to 1.3, depending on the conditions. No hydroxylation occurs at the meto-position (Scheme 9.3). 

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. 

Biochemical Routes. Enzymatic oxidation of benzene or phenol leading to dilute solution of dihydroxybenzenes is known (62). Glucose can be converted into quinic acid [77-95-2] by fermentation. The quinic acid is subsequently oxidized to hydroquinone and -benzoquinone with manganese dioxide (63). 

Starting from Benzene. In the direct oxidation of benzene [71-43-2] to phenol, formation of hydroquinone and catechol is observed (64). Ways to favor the formation of dihydroxybenzenes have been explored, hence CuCl in aqueous sulfuric acid medium catalyzes the hydroxylation of benzene to phenol (24%) and hydroquinone (8%) (65). The same effect can also be observed with Cu(II)—Cu(0) as a catalytic system (66). Efforts are now directed toward the use of Pd° on a support and Cu in aqueous acid and in the presence of a reducing agent such as CO, H2, or ethylene (67). Aromatic... 

Other Methods. A variety of other methods have been studied, including phenol hydroxylation by N2O with HZSM-5 as catalyst (69), selective access to resorcinol from 5-methyloxohexanoate in the presence of Pd/C (70), cyclotrimerization of carbon monoxide and ethylene to form hydroquinone in the presence of rhodium catalysts (71), the electrochemical oxidation of benzene to hydroquinone and -benzoquinone (72), the air oxidation of phenol to catechol in the presence of a stoichiometric CuCl and Cu(0) catalyst (73), and the isomerization of dihydroxybenzenes on HZSM-5 catalysts (74). 

Polycarbonates were first prepared by Einhom in 1898 by reacting the dihydroxybenzenes, hydroquinone and resorcinol, separately with phosgene in solution in pyridine. The hydroquinone polycarbonate was an infusible and insoluble crystalline power whereas the resorcinol polymer was an amorphous material melting at about 200°C. The third dihydroxybenzene, catechol, yields a cyclic carbonate only, which is not surprising bearing in mind the proximity of... 

Dihydroxybenzene, see Hydroquinone Diisobutyl ketone Diisoctyl phthalate Diisodecyl phthalate Diisononyl phthalate Diisopropylamine... 

The main product of the Elbs reaction is the 1,4-dihydroxybenzene (hydro-quinone). If the para position is already occupied by a substituent, the reaction occurs at an ortho position, leading to a catechol derivative although the yields are not as good as for a hydroquinone. Better yields of catechols 7 can be obtained by a copper-catalyzed oxidation of phenols with molecular oxygen ... 

Dihydroxybenzene (hydroquinone), and probably also the 1,2-isomer, act as reducing agents for arenediazonium ions arylhydrazines are formed, but not in good yields. The azo coupling of 2-hydroxy-l,4-benzoquinone is discussed in Section 10.10 (Scheme 10-71). 

S-Hydroperoxylanostenyl acetate 62 Hydroquinone see Dihydroxybenzene n-Hydroxy acids 71 Hydroxyanthraquinones 148,288... 

Diethyl ketone Diethyl phthalate Difluorodibromomethane Diglycidyl ether (DGE) dl Dihydroxybenzene, see Hydroquinone Diisobutyl ketone Diisoctyl phthalate Diisodecyl phthalate Diisononyl phthalate Diisopropyl ether Diisopropylamine Di-linear 79 phthalate Dimethoxymethane, see Methylal Dimethyl acetamide Dimethylamine... 

Dihydro-1,2-dihydroxybenzene (10.13) is oxidized by dihydrodiol dehydrogenase (EC 1.3.1.20) to catechol (10.15) (Chapt. 4 in [la]) [76], In a typical experiment in which 10.13 is incubated with phenobarbital-induced rabbit liver microsomes, phenol (10.14), catechol (10.15), and hydroquinone (10.16) represent 54, 39, and 1%, respectively, of the total metabolites detected [75]. In other words, neither benzene oxide (10.1) nor its hydration product l,2-dihydro-l,2-dihydroxybenzene (10.13) was detected. 

The total conversions of catechol, 3-methylcatechol, hydroquinone, 2-methyl-hydroquinone, and 2,3-dimethyldhydroquinone were compared in the presence and absence of the nanoparticle iron oxide in quartz chips beds. It is evident that the presence of nanoparticle iron oxide lowered the temperature for a given conversion by about 180°C for all starting materials. In Fig. 12.4, representative results of the comparison are shown for catechol and hydroquinone over nanoparticle iron oxide/quartz mixture and quartz only, as a function of temperature. Each data point in Fig. 12.4 represents the averaged result of more than two experiments under the same conditions and a fresh catalyst was used for each new experiment. Catechol showed lower reactivity (50% conversion) than hydroquinone (100% conversion) at 260°C in the presence of the catalyst. This could be attributed to two phenomena. When the dihydroxybenzenes approach the catalyst surface in a co-planar fashion, intermolecular hydrogen bonding will lower the adsorption of catechol onto the catalyst surface and its interaction... 

It is necessary to point out that our off-line pyrolysis data with GC/MS analysis of the resultant pyrolysates showed no interconversion between catechol and hydroquinone, and each dihydroxybenzene gave the corresponding benzoquinone. In addition, the analysis confirmed that the peak found at m/z 132 was indeed indanone (CgHs O). Nevertheless, the identities of other products should be confirmed by off-line experiments. This should be applied also to the following discussion. 

Synonyms AI3-00072 Arctuvin p-Benzenediol 1,4-Benzenediol Benzohydroquinone Benzoquinol Black and white bleaching cream BRN 0605970 CCRIS 714 Dihydroxybenzene jO-Dlhydroxybenzene 1,4-Dihydroxybenzene p-Dioxobenzene EINECS 204-617-8 Eldopaque Eldoquin HQ Hydroquinol Hydroquinole a-Hydroquinone p-Hydroquinone 4-Hydroxy-phenol p-Hydroxyphenol NC1-C55834 NSC 9247 Quinol p-Quinol Quinone Tecquinol Tenox HQ Tequinol UN 2662 USAF EK-356. 

Amorphous elastomers are obtained when phosphazene is refluxed with nucleophiles, such as sodium trifluoroethoxide or sodium cresylate, and secondary amines. Difunctional reactants such as dihydroxybenzenes (hydroquinone) produce cross-linked phosphazenes. 

Many quinoxaline 1,4-dioxides have been prepared by the Beirut reaction (Section 8.03.10). Phenazine 5,10-dioxides are prepared by the Beirut reaction using hydroquinone (Section 8.03.10), and they can be also synthesized by treatment of o-nitroanilines with dihydroxybenzenes (Equation 32) <1995M1217>. 

Hydroquinone, Hydroquinol, 1,4-Benzenediol or p-Dihydroxybenzene (Hydrochinon in Ger). See 1,4-Dihydroxybenzene in Vol 5 of Encycl, p D1270-R... 

The standard compounds considered to be of interest and/or likely to be found were 2,U-, 2,5- and 2,6-diaminotoluene, 2,U-diaminoanisole, resorcinol (l,3-dihydroxybenzene), hydroquinone (l,U-dihydroxybenzene) and a-naphthol. 

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