- Solvolysis of 4-halogeno-4-alkyl-2,6-di-tert-butylcyclohexa-2,5-dienones induced by positive halogen donors as electrophiles
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Positive halogen donors such as N-iodosuccinimide (NIS) induce solvolysis of dienones 1, as model 4-halogenocyclohexa-2,5-dienones, in different hydroxylic solvents (ROH), yielding the 4-RO-cyclohexa-2,5-dienones (2). The rate of the solvolysis with NIS is highly dependent on the structure of ROH. The problem of such dependency is overcome by running the reaction in ROH diluted with MeCN, a polar aprotic solvent, in place of pure ROH; the rate of the reaction in the ROH-MeCN solvent mixture is almost independent of the structure (or the polarity) of ROH, and the reaction is completed faster or markedly faster than in neat ROH. The results suggest that the solvolysis rate is controlled by the polarity of the solvent system, although the hydrogen-bond acceptability of MeCN for dilution also accelerates the reaction. A mechanism for the solvolysis is proposed, involving electrophilic attack of a positive halogen donor at the halogen atom of 1, generating the 4-oxocyclohexa-2,5-dienyl cation intermediates (8) via the rate-limiting polar transition states. CSIRO 2013.
- Omura, Kanji
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p. 1386 - 1392
(2013/12/04)
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- P-quinols and p-quinol Ethers from 2,4,6-trialkylphenols
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The oxidation of 2,4,6-trialkylphenols with lead(IV) oxide and 70% perchloric acid in water-acetone or in alcohols gives p-quinols or p-quinol ethers, respectively. Some nonmetallic oxidants serve the same purpose. Georg Thieme Verlag Stuttgart.
- Omura, Kanji
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experimental part
p. 208 - 210
(2010/03/03)
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- Electron transfer between protonated and unprotonated phenoxyl radicals
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(Chemical Equation Presented) The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO2 to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H2O containing an added acid provides eventually p-benzoquinone 39 and 4,4′-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.
- Omura, Kanji
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p. 858 - 867
(2008/09/19)
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- Bromide-assisted oxidation of substituted phenols with hydrogen peroxide to the corresponding p-quinol and p-quinol ethers over WO4 2--exchanged layered double hydroxides
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A simple and efficient one-pot synthesis of p-quinols and their ethers occurs over tungstate-exchanged layered double hydroxides (WO4 2--LDHs), which catalyze the bromide-assisted oxidation of substituted phenols to the corresponding 4-alkoxy- and 4-hydroxycyclohexa-2,5- dienones in high yields (see scheme).
- Sels,De Vos,Jacobs
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p. 310 - 313
(2007/10/03)
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- Oxidation Using Quaternary Ammonium Polyhalides. IX. Oxidation of Hindered Phenols with Benzyltrimethylammonium Tribromide
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Reactions of hindered phenols, such as 2,6-di-t-butyl-4-methylphenol, 3,5-di-t-butyl-4-hydroxybenzyl alcohol, and 2,6-di-t-butylphenol, with benzyltrimethylammonium tribromide were carried out in dichloromethane in the presence of water, t-butyl alcohol, or aqueous sodium hydroxide at room temperature.Sequential reaction processes were provided by the obtained products.
- Kajigaeshi, Shoji,Morikawa, Yukihiro,Fujisaki, Shizuo,Kakinami, Takaaki,Nishihira, Keigo
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p. 1060 - 1062
(2007/10/02)
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- Catalytic Oxidation of 2,6-Di-t-butyl-4-methylphenol by a Supported Iron Complex
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The catalytic oxidation of 2,6-di-t-butyl-4-methylphenol using a catalyst of K4 supported on acid-modified τ-Al2O3 is reported.
- Homs, Narcis,Piscina, Pilar Ramirez de la,Borrull, Francesc
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p. 1075 - 1076
(2007/10/02)
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- Anodic Pyridination of 2,6-Di-tert-butyl-4-methylphenol
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Anodic pyridination of 2,6-di-tert-butyl-4-methylphenol (1) in acetonitrile gave the corresponding 4-pyridinated cyclohexadienone and side-chain pyridinated phenol.The yield of the former dienone decreased and that of the latter product increased with increase in the amount of added bases, pyridine and/or 2,6-lutidine.On the other hand, the product distribution in the methoxylation of 1 in methanol or in acetonitrile containing methanol was little affected by the addition of 2,6-lutidine, and 4-methoxylated dienone was the main product.Keywords: 2,6-di-tert-butyl-4-methylphenol; controlled potential electrolysis; anodic pyridination; anodic methoxylation; cyclohexadienones
- Ohmori, Hidenobu,Ueda, Chihiro,Tokuno, Yoshimi,Masui, Masaichiro
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p. 3786 - 3790
(2007/10/02)
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- Anodic Pyridination of 2-Hydroxy-3-methoxy-5-methylbenzaldehyde and its Schiff's Base Derivatives
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Anodic oxidation of substituted phenols, 2-hydroxy-3-methoxy-5-methylbenzaldehyde (1) and its Schiff's base derivatives (2) in acetonitrile containing an excess of pyridine gave pyridinated phenols.Pyridination occured at the methyl group of the hydroxybenzaldehyde (1) and the Schiff's base (2g) derived from p-nitroaniline, while for the other Schiff's base derivatives of (1) studied the pyridinium group was on the ring meta to the hydroxy and ortho to the imino group.The pyridination process was investigated by cyclic voltammetry and controlled potential and constant current electrolysis of (1), (2), and related phenols including 2-hydroxy-3-methoxybenzaldehyde Schiff's bases (4).Two different routes are suggested for pyridination, a process involving a phenoxonium ion and one involving a quinone methide.Under the conditions of controlled potential electrolysis, ring pyridination proceeds through the phenoxonium ion route and side-chain pyridination through the quinone methide route.The role of the imino group in the anodic oxidation of the phenolic Schiff's bases (2) and (4) is discussed.The principal mode is suggested to be catalysis of the dimerisation of the corresponding cation radicals by accepting the proton of the hydroxy-group intramolecularly to remove the positive charge from the reaction centre.
- Ohmori, Hidenobu,Matsumoto, Akiteru,Masui, Masaichiro
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p. 347 - 357
(2007/10/02)
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