2.5- Dichlorobenzoquinone

The degradation of 2,4,6-trichlorophenol has been examined in a number of bacteria. Monooxygenation plays a key role, and 2,6-dichlorobenzoquinone and 6-chlorohydroxy-quinol have been recognized as intermediates ... 

Fig. 1 Charge-transfer absorption spectra of enol silyl ethers complexes with re-acceptors. (a) Spectral changes accompanying the incremental additions of cyclohexanone enol silyl ether [2] to chloranil in dichloromethane. Inset Benesi-Hildebrand plot, (b) Charge-transfer absorption spectra of chloranil complexes showing the red shift in the absorption maxima with decreasing IP of the enol silyl ethers, (c) Comparative charge-transfer spectra of EDA complexes of a-tetralone enol silyl ether [6] showing the red shift in the absorption maxima with increasing EAs of the acceptors tetracyanoben-zene (TCNB), 2,6-dichlorobenzoquinone (DCBQ), chloranil (CA), and tetracyanoqui-nodimethane (TCNQ). Reproduced with permission from Ref. 37.

Azidoacetaldehyde, 0772 Azidoacetic acid, 0774 Azidoacetone, 1190 Azidoacetone oxime, 1215 2,5-Diazido-3,6-dichlorobenzoquinone, 2054 Ethyl -azido-A-cyanophenylacetim idatc. 3397 Ethyl 2-azido-2-propenoate, 1890 Ethyl 2,3-diazidopropionate, 1903 Tetraazido-l,4-benzoquinone, 2633 See 2-AZIDO-2-FLUOROCARBOXYLATES... 

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). 

In a dilute aqueous solution at pH 6.0, 2,4,6-trichlorophenol reacted with an excess of hypochlorous acid forming 2,6-dichlorobenzoquinone (18% yield) and other chlorinated compounds (Smith et al., 1976). Based on an assumed 5% disappearance after 330 h at 85 °C, the hydrolysis half-life was estimated to be >40 yr (Ellington et al., 1988). 

Keywords diarylacetylene, dichlorobenzoquinone, donor-acceptor complex, photoirradiation... 

Dichlorobenzoquinone 2,2,-Dichlorobiphenyl 4,4 -Dichlorobiphenyl Dichlorodifluoromethane 1,1 -Diehl or oethane 1.881 6.97... 

Dichlorobenzoquinone-4-chloroimide, 2071 c/.v-Dichlorobis(2,2 -bipyridyl)cobalt(III) chloride, 3793a fraws-Dichlorobis [ 1,2-phenylenebis(dimethylarsine)]palladium(IV)... 

Dichlorobenzoquinone-4-chloroimide, 2071 N,N -dichlorobis(2,4,6-trichlorophenyl)urea, 3590 Dichlorofluoramine, 4053... 

A solution of 1.04 g of 6-chloro-9p,10a-pregna-4,6-diene-3,20-dione and 0.95 g of 2,3-dichlorobenzoquinone in 50 ml of dry benzene was heated to reflux for 10 hours. The reaction mixture was diluted with 70 ml of benzene and extracted three times with 50 ml of 2 N sodium hydroxide solution. The benzene layer was washed with water to neutral, dried with sodium sulfate and evaporated to dryness. The residue (0.7 g) was chromatographed on 20 g Of aluminum oxide (activity II). The fraction eluted with benzene-petroleum ether were combined and recrystallized from acetone. The 6-chloro-9p,10a-pregna-l,4,6-triene-3,20-dione melted at 208-209°C(decomposition), Xmax 229 nm. 

Dichlorobenzoquinones react with 1,3-di thiol-2-ylphosphonate esters to give 1,4-dithiin-fused quinones rather than the Wittig-Homer product (95TL7153). 2,5-Diaryl-1,4-dithiins are rearranged to 2,6-diaryl-l,4-dithiafulvenes on treatment with BU4NOH (95ACS503). 

Among the early synthetic works, we wish to mention here the synthesis of polyporic acid (3) [115] and thelephoric acid (82) [78]. As summarised in Scheme 3a, several terphenylquinones have been synthesized with moderate yields starting from 2,5-dichlorobenzoquinone by arylation with V-nitrosoacetanilides or diazonium salts and subsequent alkaline hydrolysis. This method allowed preparation of symmetrical and unsymmetrical terphenylquinones, this latters with low yields. 

Figure 9. Step height versus activity. The data are for the samples shown in Figures 7 and 8. Step heights were calculated from unnormalized data ratioed to the incident X-ray intensity. Percent activity is relative to the control (ca. 1200 pM O mg chlorophyll/h) using 2,6-dichlorobenzoquinone as an acceptor.

Three successive [2+4] cycloadditions were used in the synthesis of the pentacyclic methyl ether of G-2N by Kraus and Zhao [92] and later, by a slightly modified procedure, also of the natural product G-2N (118) [93] (Scheme 31). Thermal reaction of the cyclobutanol 112 with acrylic ester gave the dihydronaphthalene 113 which was demethylated by treatment with boron tribromide and converted into the exocyclic ketene acetal 114. This unstable diene was reacted in a second cycloaddition with 2,6-dichlorobenzoquinone (115) to afford the tetracyclic chloroquinone 116. In a last Diels-Alder reaction, ring E was anella-ted by treatment of 116 with l-methoxy-l,3-bis[(trimethylsilyl)oxy]-l,3-buta-diene (117) to yield the pentacyclic natural product G-2N (118) [93]. 

Figure 2. Dependence of rate constant on -AG° for electron transfer from B to A in A-Sp-B " generated pulse radiolytically in 2-methyltetrahy-drofuran. B = 4-biphenylyl, A = 2-naphthyl (1), 9-phenanthryl (2), 1-pyr-enyl (3), hexahydronaphthoquinon-2-yl (4), 2-naphthoquinonyl (5), 2-benzoqui-nonyl (6), 5-chlorobenzoquinon-2-yl (7), 5,6-dichlorobenzoquinon-2-yl (8). (Adapted from Ref. [31]).

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