Dichloro hydroquinone

In the degradation of 2,4,6-trichlorophenol by a strain of Azotobacter sp. (Li et al. 1991), the monooxygenase that produces 2,6-dichloro-hydroquinone as the initial metabolite has been purified and characterized (Wieser et al. 1997). 

Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) and DDQ (2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone). The latter is more reactive and can be used in cases where the substrate is difficult to dehydrogenate. It is likely that the mechanism involves a transfer of hydride to the quinone oxygen, followed by the transfer of a proton to the phenolate ion °... 

Lee J-Y, L Xun (1997) Purification and characterization of 2,6-dichloro-p-hydroquinone chlorohydrolase from Flavobacterium sp. strain ATCC 39723. J Bacterial 179 1521-1524. 

Xun L, J Bohuslavek, M Vai (1999) Characterization of 2,6-dichloro-p-hydroquinone 1,2-dioxygenase (PcpA) of Sphingomonas chlorophenolica ATCC 39723. Biochem Biophys Res Commun 266 322-325. 

Dichloro-5,6-dicyano-l,4-benzoquinone is readily regenerated in good yield from the hydroquinone by oxidation with nitric acid.4... 

A solution of 100 mg. (0.41 mmole) of 4,4 -dimethoxybibenzyl (Note 1) in 1.5 ml. of anhydrous dioxane (Note 2) was placed in a 10-ml. round-bottomed flask. To this was added 103 mg. (0.45 mmole) of 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ Note 3) dissolved in 1.5 ml. of anhydrous dioxane. The flask was fitted with a reflux condenser and heated in an oil bath at 105° for 18 hours. The solution, which was initially deep green, became pale yellow as the hydroquinone crystallized out. The mixture was cooled, and the solid was filtered off. It was washed with 1 ml. of warm benzene followed by 6 ml. of warm chloro-... 

In an aqueous solution, 4-nitrophenol (100 pM) reacted with Fenton s reagent (35 pM). After 15 min into the reaction, the following products were identified 1,2,4-trihydrottybenzene, hydroquinone, hydroxy-p-benzoquinone, p-benzoquinone, and 4-nitrocatechol. After 3.5 h, 90% of the 4-nitrophenol was destroyed. After 7 h, no aromatic oxidation products were detected. The pH of the solution decreased due to the formation of nitric acid (Lipczynska-Kochany, 1991). In a dilute aqueous solution at pH 6.0, 4-nitrophenol reacted with excess hypochlorous acid forming 2,6-dichlorobenzoquinone, 2,6-dichloro-4-nitrophenol, and 2,3,4,6-tetrachlorophenol at yields of 20, 1, and 0.3%, respectively (Smith et al., 1976). 

The photolytic process of p-quinone diazides are of great interest since they establish a synthetic route for the preparation of a large number of phenolic compounds. CCXXII and CCXXIV are obtained on irradiation of p-quinone diazide (CCXXI) and imino-p-quinone diazide (CCXXIII) in the presence of primary alcohols,279 respectively photolysis of CCXXI in water produces hydroquinone.137 Another well-authenticated example of this reaction, is the photodecomposition of CCXXI and CCXXIII in the presence of benzene, and 2,6-dichloro-quinoneimine diazide-4 in the presence of pyridine to CCXXV, CCXXVI, and CCXXVII, respectively. 

To a mixture of 1-methoxy-l,3-butadiene (1 55.3 g, 0.66 mol) [43] and n-butyl glyoxylate (86.0 g, 0.66mol) [44], 0.1 g hydroquinone was added and the solution was refluxed at 100°C for 6 h under argon. Distillation at 88°-90°C/0.5 tonr gave 2 (R = Bu) (91.6 g, 65%) as a pale-yellow liquid with a faint odor. By gas chromatography this product is a mixture of cis and trans (ca. 7 3) isomers. Treatment of the isomer mixture in dichloro-methane solution with p-toluenesulfonic acid or zinc chloride for 2 h leads to an almost pure trans-isomer (ca. 95%). 

Dithioacetic acid derivatives add to 1,4-benzo- or 1,4-naphthoquinones to give, after oxidation of the adduct with silver oxide or chloranil, the quinones 217 and 218 (69LA103). Quinones 218 were prepared also from 2,3-dichloro-1,4-naphthoquinone and salts of dithiocarbamic acids (51JA3459) and those of type 219 by oxidation of the corresponding hydroquinones. From reduction potentials and the semiquinone formation constants, it was concluded that their anion radicals are thermodynamically stable (86CC1489). 

Dehydrogenation of pyrocatechol by silver oxide gives 0-benzoquinone.469 For preparation of amino-0-benzoquinones see Homer and Lang.470 Hydro-quinones are also dehydrogenated with success by lead tetraacetate.222 Further, 2,3-dichloro-5,6-dicyano-l,2-benzoquinone is obtained from the hydroquinone in 83% yield when a solution of the latter in 5% ethanolic hydrogen chloride is shaken with a mixture of Pb02 and benzene.471... 

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