Benzo-l,2-quinones

Catechol may be oxidized by peroxidases to the reactive intennediate benzo-1,2-quinone, which readily binds to proteins (Bhat et al., 1988) this process, catalysed by rat or human bone-marrow cells in the presence of H2O2 (0.1 mM), is stimulated by phenol (0.1-10 mM), and decreased by hydroquinone and by glutathione, which conjugates with benzo-l,2-quinone. These phenols (phenol, catechol and hydroquinone) may play a role in benzene toxicity to bone marrow all three are formed as benzene metabolites (Smith et al., 1989) and they interact in several ways as far as their bioactivation by (myelo)peroxidases is concerned (Smith et al., 1989 Subrahmanyam et al., 1990). 

The oxidation of benzene- 1,2-diols to benzo-l,2-quinones is also a process of considerable biological importance, and solutions of copper compounds in organic solvents frequently act as catalysts for the aerial oxidation of such compounds (Fig. 9-5). These reactions almost certainly involve sequential one-electron processes, as indicated in Fig. 9-6. In some cases, the semiquinone forms may be isolated. 

Figure 9-5. The oxidation of benzene-1,2-diols to benzo-l,2-quinones by dioxygen is catalysed by copper salts.

Except under extreme conditions, oxidation of the benzene ring requires the presence of strongly electron-donating groups such as hydroxyl or amino. These groups are simultaneously oxidized. The best known products of this oxidation process are the quinones benzo-l,4-quinone (p-benzoquinone, cyclohexadiene-l,4-dione, 10) and benzo-l,2-quinone (o-benzoquinone, cyclohexadiene-l,2-dione, 11). 

A series of condensed isobenzothiophene derivatives has been synthe-sized144,153,154 from the rhodacyclopentadieno[3. 4 4.5]benzo[l,2-c]thio-phen-4,8-quinone (72) (see Scheme 86 and Section IV,B,5 for details of the preparation of rhodium complexes analogous to 72). 

The BASF route started from hydroquinone, which was converted to 2,5-dihydroterephthalic acid by a Kolbe-Schmitt reaction. One mole of this acid was treated with two moles of an arylamine, both components being in the form of a suspension in aqueous methanol. This was added to a small amount of a solution of vanadium(III) chloride and sodium chlorate. Gentle heating gave a 95% yield of 2,5-bis(arylamino)benzo-l,4-quinone-3,6-dicarboxylic acid. Ring closure to the trans-quinacridonequinone took place in the presence of concentrated sulphuric acid at 60-80 °C. This was then reduced to the required crude pigment by zinc or aluminium powder in caustic soda under pressure,in an aluminium chloride/urea melt or by the use of a sulphuric acid/polyphosphoric acid mixture. 

Synonyms AI3-09068 AIDS-153 B 1266 1,4-Benzoquine Benzoquinone Benzo-l,4-quinone 1,4-Benzoquinone p-Benzoquinone BRN 0773967 Caswell No. 719C CCRIS 933 Chinone Cyclohexadienedione 1,4-Cyclohexadienedione 2,5-Cyclohexadiene-l,4-dione 1,4-Cyclohexa-diene dioxide 1,4-Dioxybenzene EINECS 203-405-2 EPA pesticide chemical code 059805 NCI-C55845 NSC 36324 Quinone 4-Quinone RCRA waste number U197 UN 2587 USAF P-220. 

The isomeric benzo[l,2-A4,3- ]dithiophene-4,5-quinone is prepared in reasonable yields by a one-step Friedel-Crafts reaction of 3,3 -bithienyl with oxalyl chloride in refluxing 1,2-dichloroethane over 7-10 days (Equation 85) <2001JA11899>. 

The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

Benzoquinones reacted with four equivalents of isonitriles to form benzo[c c ]dipyrroles <84LA1003>, and variations of the Nenitzescu reaction, i.e. of quinones with enamines, have been useful synthetic approaches to benzo[l,2-6 4,5-6 ]dipyrroles <71T503J, 73T921). 

The preparation of benzo-l,2-dithiete (264) had been claimed by oxidation of 1,2-benzenedithiol (25JIC318). However, later work has shown that the reaction product was probably a polymeric mixture (61JOC4782). Subsequently, compound 265 was irradiated to give a mixture of CO, sulfur, and dithiin and thiophene derivatives, which could, at least in part, be explained by the formation of 266 (72JHC707). Results of the thermolysis of 267 were also rationalized in terms of the intermediacy of o-dithiobenzo-quinone (the tautomer of 264) (78JOC2084). 

Harriman, A., G. Porter, and A. Wilowska (1983), Photoreduction of Benzo-l,4-quinone Sensitised by Metalloporphyrins, J. Chem. Soc., Faraday Trans. 2 79, 807-816. 

Analytical procedures for hydroxyl radicals noted in Section 2.3 and have been used to demonstrate the role of the anticancer drug 2,5-bis(l-azacyclo-propyl)-3,6-bis(carboethoxyamino)benzo-l,4-quinone in mediating the production of hydroxyl radicals in JB6 mouse epidermal cells (Li et al. 1997). 

Pentachlorophenol produces a wide variety of transformation products including chloranilic acid (2,5-dichloro-3,6-dihydroxy-benzo-l,4-quinone) by hydrolysis and oxidation, a dichlorocyclo-pentanedione by ring contraction, and dichloromaleic acid by cleavage of the aromatic ring (Figure 4.4) (Wong and Crosby 1981). 

Remberger, M., P.-A. Hynning, and A.H. Neilson. 1991. 2,5-Dichloro-3,6-dihydroxy-benzo-l,4-quinone identification of a new organochlorine compound in kraft mill bleachery effluents. Environ. Sci. Technol. 25 1903-1907. 

N,N-dibenzylamino)ethyl 2-, 3-, and 4-benzoylbenzoate. The first fluorescence and fluorescence quantum yield measurements from the excited state of the radical anion of benzo-l,4-quinone have appeared, and since these species are powerful reducing agents generally, such parameters are of considerable impor-... 

Quinones. - Goerner has demonstrated that the yield of semiquinone radicals is low in the absence of hydrogen donating solvents. He notes that the quantum yield for decomposition is substantial in aqueous solution. A detailed account of the photohydroxylation reactions of 1,4-benzoquinone in aqueous solution has been published.The photochemical cyclization of some Diels-Alder adducts of benzo-l,4-quinones has been described. This has provided a path to complex molecules such as 3-bromotetracyclo[5.3.1.0 . 0 ]undec-10(12)-ene-9,l 1-dione. A biradical has been identified as the key intermediate in the photocyclization of phenylbenzoquinone. " A charge-transfer complex is formed initially on irradiation of 2-chloro-5-methoxybenzo-l,4-quinone in the presence of triethylamine and various solvents.2-Chloro-5-methoxyben-zo-l,4-quinone also undergoes addition to arylalkynes to afford oxetenes. The mechanism of this addition reaction was studied.A hydrogen abstraction is involved in the photochemical reactions of chloranil with 3-diketones. ... 

Hydroxy-2-methyl-5-(3 methyl-2-butenyl)benzo-l, 4-quinone CHCI3 [118]... 

Hydrogen chloride Benzo[l,2-d 4,5-d]diimidazoles Quinols from quinones... 

The detail preparation method is described elsewhere [71]. In brief, before adding quinone solution, the reaction mixmre of n-butyllithium and acetylene in THF solution was kept at 0 °C under argon atmosphere and stirred for a day until room temperature. The reaction mixmre was quenched by HCl and further stanous chloride dehydrate in acetic acid was added to obtained the product. The yield of obtained product 2, 6-dioctyl-4,8-bis(trimethylsilylethynyl)-benzo[l,2-b 4,5-b ] dithiophene as a white colour solid was 32 %. 

Benzo[l,2-c 3,4-c 5,6-c ]tris[l,2,5]thiadiazole.—Four related condensed tetracyclic ring systems incorporating 1,2,5-thiadiazole (202 X = S, Se, CH, or CH=CH) are accessible from a common starting material, benzo[l,2-c 3,4-c ]-bis[l,2,5]thiadiazole (200), which is converted into the diamine (201) and variously cyclized to (202). The condensation of (201) and 9,10-phenanthrene-quinone in boiling acetic acid similarly yields the heptacyclic ring system dibenzo-[a,c]bis[l,2,5]thiadiazolo[3,4-/r.3, 4V]phenazine. 2... 

The photochemical transformation of phenanthrene sorbed on silica gel (Barbas et al. 1996) resulted in a variety of products including c -9,10-dihydrodihydroxyphenanthrene, phenanthrene-9,10-quinone, and a number of ring fission products including biphenyl-2,2 -dicarboxaldehyde, naphthalene-l,2-dicarboxylic acid, and benzo[c]coumarin. 

The oxidation behavior of 3-oxa-chromanols was mainly studied by means of the 2,4-dimethyl-substituted compound 2,4,5,7,8-pentamethylM /-benzo[ 1,3]dioxin-6-ol (59) applied as mixture of isomers 27a it showed an extreme dependence on the amount of coreacting water present. In aqueous media, 59 was oxidized by one oxidation equivalent to 2,5-dihydroxy-3,4,6-trimethyl-acetophenone (61) via 2-(l-hydroxyethyl)-3,5,6-trimethylbenzo-l,4-quinone (60) that could be isolated at low temperatures (Fig. 6.41). This detour explained why the seemingly quite inert benzyl ether position was oxidized while the labile hydroquinone structure remained intact. Two oxidation equivalents gave directly the corresponding para-quinone 62. Upon oxidation, C-2 of the 3-oxa-chroman system carrying the methyl substituent was always lost in the form of acetaldehyde. 

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