- Cycloacylation of chloro-substituted hydroquinone dimethyl ethers with dichloromaleic anhydride
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Under the drastic conditions of Zahn—Ochwat cycloacylation of 2-chloroand 2,3-dichlorohydroquinones with dichloromaleic anhydride (a melt of anhydrous AlCl3 and NaCl, 185—195 °C), the substrates undergo various degrees of disproportionation, which reduces the yields of the target triand tetrachloronaphthazarins. Quantum chemical calculations showed that the cycloacylation in question proceeds as a double aromatic electrophilic substitution of the vicinal protons with the corresponding oxocarbenium ions (acylium cations).
- Novikov,Balaneva,Shestak,Anufriev, V. Ph.,Glazunov
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p. 993 - 1003
(2017/01/11)
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- Chlorine atom substitution influences radical scavenging activity of 6-chromanol
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Synthetic 6-chromanol derivatives were prepared with several chlorine substitutions, which conferred both electron-withdrawing inductive effects and electron-donating resonance effects. A trichlorinated compound (2), a dichlorinated compound (3), and three monochlorinated compounds (4, 5, and 6) were synthesized; compounds 2, 3, and 6 were novel. The antioxidant activities of the compounds, evaluated in terms of their capacities to scavenge galvinoxyl radical, were associated with the number and positioning of chlorine atoms in the aromatic ring of 6-chromanol. The activity of compound 1 (2,2-dimethyl-6-chromanol) was slightly higher than the activities of compounds 2 (2,2-dimethyl-5,7-dichloro-6-chromanol) or 3 (2,2-dimethyl-5,7,8-trichloro-6- chromanol), in which the chlorine atoms were ortho to the phenolic hydroxyl group of 6-chromanol. The scavenging activity of compound 3 was slightly higher than that of 2, which contained an additional chlorine substituted in the 8 position. The activities of polychlorinated compounds 2 and 3 were higher than the activities of any of the monochlorinated compounds (4-6). Compound 6, in which a chlorine was substituted in the 8 position, exhibited the lowest activity. Substitution of a chlorine atom meta to the hydroxyl group of 6-chromanol (compounds 2 and 6) decreased galvinoxyl radical scavenging activity, owing to the electron-withdrawing inductive effect of chlorine. Positioning the chloro group ortho to the hydroxyl group (compounds 4 and 5) retained antioxidant activity because the intermediate radical was stabilized by the electron-donating resonance effect of chlorine in spite of the electron-withdrawing inductive effect of chlorine. Antioxidant activities of the synthesized compounds were evaluated for correlations with the O-H bond dissociation energies (BDEs) and the ionization potentials. The BDEs correlated with the second-order rate constants (k) in the reaction between galvinoxyl radical and the chlorinated 6-chromanol derivatives in acetonitrile. This indicated that the antioxidant mechanism of the synthesized compounds consisted of a one-step hydrogen atom transfer from the phenolic OH group rather than an electron transfer followed by a proton transfer. The synthesized compounds also exhibited hydroxyl radical scavenging capacities in aqueous solution.
- Inami, Keiko,Iizuka, Yuko,Furukawa, Miyuki,Nakanishi, Ikuo,Ohkubo, Kei,Fukuhara, Kiyoshi,Fukuzumi, Shunichi,Mochizuki, Masataka
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body text
p. 4049 - 4055
(2012/09/08)
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- S-Glutathionyl-(chloro)hydroquinone reductases: A novel class of glutathione transferases
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Sphingobium chlorophenolicum completely mineralizes PCP (pentachlorophenol). Two GSTs (glutathione transferases), PcpC and PcpF, are involved in the degradation. PcpC uses GSH to reduce TeCH (tetrachloro-p- hydroquinone) to TriCH (trichlorop-hydroquinone)
- Xun, Luying,Belchik, Sara M.,Xun, Randy,Huang, Yan,Zhou, Huina,Sanchez, Emiliano,Kang, ChulHee,Board, Philip G.
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experimental part
p. 419 - 427
(2011/02/25)
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- ELECTROCHEMICAL BEHAVIOUR OF SUBSTITUTED HYDROQUINONES
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The oxidation potentials of thirteen hydroquinones substituted by chlorine, pyrazol-1-yl and 3,5-dimethylpyrazol-1-yl groups were experimentally determined by cyclic voltammetry.The estimated half-wave potentials E1/2 have been discussed taking into account the inductive and conjugative substituent effects.Key words: Cyclic voltammetry, Hydroquinones, Redox, Pyrazoles
- Claramunt, R. M.,Escolastico, C.,Maria, M. D. Santa,Lopez, V.
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p. 368 - 371
(2007/10/02)
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- Properties of chlorinated dihydroxybenzenes - components of pulp bleaching effluents
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Gas chromatography and mass spectrometry data are given for the chlorodihydroxybenzenes which are components of wood pulp bleaching effluents and biologically-treated effluents, and are proposed intermediates in the chlorination of humic acids. The chlorohydroxybenzenes include the nine chlorocatechols, the six chlorohydroquinones and the seven known chlororesorcinols. The 22 chlorinated compounds were generally well separated on a phenyl methyl silicone column with the exception of three dichloro compounds. The chloro compounds with the same level of chlorine substitution were not able to be distinguished on the basis of their electron impact mass spectra.
- Smith, Terrence J.,Wearne, Ross H.,Wallis, Adrian F. A.
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p. 1555 - 1560
(2007/10/03)
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- ON THE 1,6-ADDITION OF ALKYLALUMINIUM COMPOUNDS TO para-QUINONES
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Ethyl, n-butyl and i-butylaluminium dichlorides undergo 1,6-addition to a conjugated bond system O=C-C=C-C=O of para-quinones.Methylaluminium dichloride is inactive in this addition, and triethylaluminium gives low yields.The reactivities of the quinones vary with their electron affinities, and the highest yields of 1,6-addition are obtained in the reactions of chlorine derivatives of 1,4-benzoquinone.The results are discussed in terms of a radical mechanism involving a homolytic cleavage of the Al-C bond in the donor-acceptor complex formed between the reactants followed by combination of alkyl radicals and aluminium derivatives of semiquinone within a cage.The stable donor-acceptor complexes and aluminium derivative of semiquinone were isolated and characterized from the reactions of aluminium trichloride with 2,3,5,6-tetramethyl-1,4-benzoquinone and 2,3,5,6-tetrachloro-1,4-benzoquinone, respectively.
- Florjanczyk, Zbigniew,Szymanska-Zachara, Ewa
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p. 127 - 138
(2007/10/02)
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