- Indirect inactivation of tyrosinase in its action on 4-tert-butylphenol
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Under anaerobic conditions, the o-diphenol 4-tert-butylcatechol (TBC) irreversibly inactivates met and deoxytyrosinase enzymatic forms of tyrosinase. However, the monophenol 4-tert-butylphenol (TBF) protects the enzyme from this inactivation. Under aerobic conditions, the enzyme suffers suicide inactivation when it acts on TBC. We suggest that TBF does not directly cause the suicide inactivation of the enzyme in the hydroxylase activity, but that the o-diphenol, which is necessary for the system to reach the steady state, is responsible for the process. Therefore, monophenols do not induce the suicide inactivation of tyrosinase in its hydroxylase activity, and there is a great difference between the monophenols that give rise to unstable o-quinones such as L-tyrosine, which rapidly accumulate L-dopa in the medium and those like TBF, after oxidation, give rise to a very stable o-quinone.
- Mu?oz-Mu?oz, Jose Luis,García-Molina, María Del Mar,García-Molina, Francisco,Varon, Ramón,García-Ruiz, Pedro Antonio,Rodríguez-López, Jose Neptuno,García-Cánovas, Francisco
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Read Online
- Metal chlorides or sulfuric acid in ionic liquid solvents convert catechol to p-tert-Butylcatechol
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A series of novel acidic ionic liquids (ILs) mediated in metal chloride or sulfuric acid (IL-RClx or IL-H2SO4, R = Na, K, Al, Ba, Ca) were investigated as catalysts in the alkylation of catechol and methyl tert-butyl ether to p-tert-Butylcatechol. Based on the ILs screening, it was found that N-(4-sulfonic acid butyl) pyridine hydrogen bisulfate (IL2) was the most efficient catalyst (in the reaction). Moreover IL2 modified by sulfuric acid showed the best performance with the yield of p-tert-Butylcatechol approximately 81.7% and the selectivity of 92.5%. For a clear perspective to the influence of H2SO4, IL2 ([C4SO3HPy]HSO4) was systematically studied by the Density Functional Theory at 6-31 + G? level and the results showed that hydrogen bonds inside the ILs were probably the key for acidity enhancement of the modifications.
- Zhang, Wenlin,Yue, Ying,Su, Weiyi,Du, Wei,Wang, Xiaowen,Zhu, Guanyu,Li, Chunli
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Read Online
- Ortho-Hydroxylation of 4-tert-butylphenol by nonheme iron(III) complexes as a functional model reaction for tyrosine hydroxylase
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Hydroxylation of 4-tert-butylphenol to 4-tert-butylcatechol is performed by a catecholatoiron(III) complex-hydroquinone-O2 system which mimicks the roles of Fe2+ and Fe3+ in tyrosine hydroxylase; the ortho-hydroxylation of phenols by iron-oxygen active species is suggested.
- Funabiki, Takuzo,Yokomizo, Tomomasa,Suzuki, Shinko,Yoshida, Satohiro
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Read Online
- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Direct Synthesis of Hydroquinones from Quinones through Sequential and Continuous-Flow Hydrogenation-Derivatization Using Heterogeneous Au–Pt Nanoparticles as Catalysts
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Pt–Au bimetallic nanoparticle catalysts immobilized on dimethyl polysilane (Pt–Au/(DMPSi-Al2O3)) have been developed for selective hydrogenation of quinones to hydroquinones. High reactivity, selectivity, and robustness of the catalysts were confirmed under continuous-flow conditions. Various direct derivatizations of quinones, such as methylation, acetylation, trifluoromethanesulfonylation, methacrylation, and benzoylation were successfully performed under sequential and continuous-flow conditions to afford the desired products in good to excellent yields. Especially, air-sensitive hydroquinones, such as anthrahydroquinones and naphthohydroquinones, could be successfully generated and derivatized under closed sequential and continuous-flow conditions without decomposition.
- Miyamura, Hiroyuki,Tobita, Fumiya,Suzuki, Aya,Kobayashi, Shū
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supporting information
p. 9220 - 9224
(2019/06/13)
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- Catalytic conversion of 4-tert-butylphenol in hydrogen peroxide solutions in the presence of titanium oxide compounds and titanosilicates
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The catalytic conversion of 4-tert-butylphenol (TBP) in hydrogen peroxide solutions in the presence of titanium oxide samples with different phase compositions and crystalline and amorphous titanosilicate samples has been studied. It has been shown that microporous crystalline titanosilicate TS-1 exhibits low activity in the TBP conversion owing to steric restrictions to the diffusion of the substrate molecules to catalytically active sites. The samples of titanium oxide compounds and mesoporous titanosilicates exhibit similar activity, while the selectivity of the latter for 4-tert-butylcatechol (TBC) is higher. The effect of the mesoporous titanosilicate concentration in the reaction mixture and the test temperature and duration on the TBP conversion and the TBC selectivity has been determined.
- Talipova,Kharrasov,Veklov,Badikova,Kutepov
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p. 395 - 402
(2017/07/05)
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- Synthesis of α-oxygenated ketones and substituted catechols via the rearrangement of N-enoxy- and N-aryloxyphthalimides
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A common approach to the synthesis of α-oxygenated carbonyl compounds and catechols is the treatment of a carbonyl compound or a phenol with an electrophilic oxygen source. As an alternative approach to these important structures, formal [3,3]-rearrangements of N-enoxyphthalimides, N-enoxyisoindolinones, and N-aryloxyphthalimides have been explored. When used in combination with an initial Chan-Lam coupling, these transformations facilitate the dioxygenation of alkenylboronic acids for the synthesis of α-oxygenated ketones and the dioxygenation of arylboronic acids for the synthesis of catechols. The rearrangements of N-enoxyisoindolinones have also been shown to be diastereoselective.
- Kroc, Michelle A.,Patil, Aditi,Carlos, Anthony,Ballantine, Josiah,Aguilar, Stephanie,Mo, Dong-Liang,Wang, Heng-Yen,Mueller, Daniel S.,Wink, Donald J.,Anderson, Laura L.
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p. 4125 - 4137
(2017/06/29)
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- A dinuclear iron(II) complex bearing multidentate pyridinyl ligand: Synthesis, characterization and its catalysis on the hydroxylation of aromatic compounds
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A dinuclear iron(II) complex Fe2L2(μ2-Cl)2Cl2 (L = N,N-bis(pyridin-2-ylmethyl)prop-2-yn-1-amine) was prepared and fully characterized by UV–Vis spectroscopy, elemental analysis, electrochemical analysis and X-ray single crystal diffraction analysis. The catalytic activity of the complex was assessed for the hydroxylation of aromatic compounds by using aqueous H2O2 as an oxidant in acetonitrile. The catalytic system was applicable in a wide range of substrates including aromatic compounds with both electron-donating and electron-withdrawing substituents and showed moderate to good catalytic activity and selectivity in the oxidation reactions. Particularly, in the case of benzene the selectivity of phenol achieve to 74% with the reaction conversion of 24.8%.
- Gu, Erxing,Zhong, Wei,Ma, Hongxia,Xu, Beibei,Wang, Hailong,Liu, Xiaoming
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p. 159 - 165
(2018/03/29)
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- A Catalyst-Controlled Aerobic Coupling of ortho-Quinones and Phenols Applied to the Synthesis of Aryl Ethers
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ortho-Quinones are underutilized six-carbon-atom building blocks. We herein describe an approach for controlling their reactivity with copper that gives rise to a catalytic aerobic cross-coupling with phenols. The resulting aryl ethers are generated in high yield across a broad substrate scope under mild conditions. This method represents a unique example where the covalent modification of an ortho-quinone is catalyzed by a transition metal, creating new opportunities for their utilization in synthesis.
- Huang, Zheng,Lumb, Jean-Philip
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supporting information
p. 11543 - 11547
(2016/11/17)
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- Conversion of Simple Cyclohexanones into Catechols
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A novel I2-catalyzed direct conversion of cyclohexanones to substituted catechols under mild and simple conditions has been described. This novel transformation is remarkable with the multiple oxygenation and dehydrogenative aromatization processes enabled just by using DMSO as the solvent, oxidant, and oxygen source. This metal-free and simple system demonstrates a versatile protocol for the synthesis of highly valuable substituted catechols and therefore streamlines the synthesis and modification of biologically important molecules for drug discovery.
- Liang, Yu-Feng,Li, Xinyao,Wang, Xiaoyang,Zou, Miancheng,Tang, Conghui,Liang, Yujie,Song, Song,Jiao, Ning
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supporting information
p. 12271 - 12277
(2016/09/28)
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- Spectroscopic and computational investigations of the thermodynamics of boronate ester and diazaborole self-assembly
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The solution phase self-assembly of boronate esters, diazaboroles, oxathiaboroles, and dithiaboroles from the condensation of arylboronic acids with aromatic diol, diamine, hydroxythiol, and dithiol compounds in chloroform has been investigated by 1H NMR spectroscopy and computational methods. Six arylboronic acids were included in the investigations with each boronic acid varying in the substituent at its 4-position. Both computational and experimental results show that the para-substituent of the arylboronic acid does not significantly influence the favorability of forming a condensation product with a given organic donor. The type of donor, however, greatly influences the favorability of self-assembly. 1H NMR spectroscopy indicates that condensation reactions between arylboronic acids and catechol to give boronate esters are the most favored thermodynamically, followed by diazaborole formation. Computational investigations support this conclusion. Neither oxathiaboroles nor dithiaboroles form spontaneously at equilibrium in chloroform at room temperature. Computational results suggest that the effect of borylation on the frontier orbitals of each donor helps to explain differences in the favorability of their condensation reactions with arylboronic acids. The results can inform the use of boronic acids as they are increasingly utilized in the dynamic self-assembly of organic materials and as components in dynamic combinatorial libraries.
- Goldberg, Alexander R.,Northrop, Brian H.
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p. 969 - 980
(2016/02/18)
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- A Biomimetic Mechanism for the Copper-Catalyzed Aerobic Oxygenation of 4-tert-Butylphenol
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Controlling product selectivity during the catalytic aerobic oxidation of phenols remains a significant challenge that hinders reaction development. This work provides a mechanistic picture of a Cu-catalyzed, aerobic functionalization of phenols that is selective for phenoxy-coupled ortho-quinones. We show that the immediate product of the reaction is a Cu(II)-semiquinone radical complex and reveal that ortho-oxygenation precedes oxidative coupling. This complex is the resting state of the Cu catalyst during turnover at room temperature. A mechanistic study of the formation of this complex at low temperatures demonstrates that the oxygenation pathway mimics the dinuclear Cu enzyme tyrosinase by involving a dinuclear side-on peroxodicopper(II) oxidant. Unlike the enzyme, however, the rate-limiting step of the ortho-oxygenation reaction is the self-assembly of the oxidant from Cu(I) and O2. We provide details for all steps in the cycle and demonstrate that turnover is contingent upon proton-transfer events that are mediated by a slight excess of ligand. Finally, our knowledge of the reaction mechanism can be leveraged to diversify the reaction outcome. Thus, uncoupled ortho-quinones are favored in polar, coordinating media, highlighting unusually high levels of chemoselectivity for a catalytic aerobic oxidation of a phenol. (Chemical Equation Presented).
- Askari, Mohammad S.,Esguerra, Kenneth Virgel N.,Lumb, Jean-Philip,Ottenwaelder, Xavier
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supporting information
p. 8665 - 8672
(2015/09/21)
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- Carbon nanotubes as activating tyrosinase supports for the selective synthesis of catechols
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A series of redox catalysts based on the immobilization of tyrosinase on multiwalled carbon nanotubes has been prepared by applying the layer-by-layer principle. The oxidized nanotubes (ox-MWCNTs) were treated with poly(diallyl dimethylammonium chloride) (PDDA) and tyrosinase to yield ox-MWCNTs/PDDA/ tyrosinase I. Catalysts II and III have been prepared by increasing the number of layers of PDDA and enzyme, while IV was obtained by co-immobilization of tyrosinase with bovine serum albumin (ox-MWCNTs/PDDA/BSA-tyrosinase). Attempts to covalently bind tyrosinase provided weakly active systems. The coating of the enzyme based on the simple layer-by-layer principle has afforded catalysts I-III, with a range of activity from 21 units/mg (multilayer, II) to 66 units/mg (monolayer, I), the best system being catalyst IV (80 units/mg). The novel catalysts were fully characterized by scanning electron microscopy and atomic force microscopy, showing increased activity with respect to that of the native enzyme. These catalysts were used in the selective synthesis of catechols by oxidation of meta- and para-substituted phenols in an organic solvent (CH 2Cl2) as the reaction medium. It is worth noting that immobilized tyrosinase was able to catalyze the oxidation of very hindered phenol derivatives that are slightly reactive with the native enzyme. The increased reactivity can be ascribed to a stabilization of the immobilized tyrosinase. The novel catalysts I and IV retained their activity for five subsequent reactions, showing a higher stability in organic solvent than under traditional buffer conditions.
- Subrizi, Fabiana,Crucianelli, Marcello,Grossi, Valentina,Passacantando, Maurizio,Pesci, Lorenzo,Saladino, Raffaele
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p. 810 - 822
(2014/04/03)
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- An efficient strategy for protecting dihydroxyl groups of catechols
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A novel strategy for protecting dihydroxyl groups of catechols has been developed. Base-mediated cyclizations of catechols with 1,3-dibromopropane provided the corresponding benzo[b]1,4-dioxepans, and herefrom the protecting group was easily cleaved by aluminum chloride. The preparation of the antibacterial and antifungal agent 4-(2-aminothiazol-4-yl)benzene-1,2-diol from catechol reliably verified its availability amenable to various harsh reaction conditions. Georg Thieme Verlag Stuttgart - New York.
- Huang, Wei-Bin,Guo, Ying,Jiang, Jian-An,Pan, Xian-Dao,Liao, Dao-Hua,Ji, Ya-Fei
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supporting information
p. 741 - 746
(2013/05/09)
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- Layer-by-Layer coated tyrosinase: An efficient and selective synthesis of catechols
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Agaricus bisporous tyrosinase was immobilized on commercial available epoxy-resin EupergitC250L and then coated by the Layer-by-Layer method (LbL). The two novel heterogeneous biocatalysts were characterized for their morphology, pH and storage stability, kinetic properties (Km, V max, Vmax/Km) and reusability. These biocatalysts were used for the efficient and selective synthesis of bioactive catechols under mild and environmental friendly experimental conditions. Ascorbic acid was added in the reaction medium to inhibit the formation of ortho-quinones, thus avoiding the known enzyme suicide inactivation process. Catechols were obtained mostly in quantitative yields and conversion of substrate. Tyrosinase immobilized on EupergitC250L and coated by the LbL method showed better catalytic activities, higher pH and storage stability, and reusability with respect to immobilized uncoated tyrosinase. Since chemical procedures to synthesize catechols are often expensive and with high environmental impact, the use of immobilized tyrosinase represents an efficient alternative for the preparation of this family of bioactive compounds.
- Guazzaroni, Melissa,Crestini, Claudia,Saladino, Raffaele
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experimental part
p. 157 - 166
(2012/02/13)
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- Hydroxylation of p-substituted phenols by tyrosinase: Further insight into the mechanism of tyrosinase activity
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A study of the monophenolase activity of tyrosinase by measuring the steady state rate with a group of p-substituted monophenols provides the following kinetic information: kcatm and the Michaelis constant, KMm. Analysis of these data taking into account chemical shifts of the carbon atom supporting the hydroxyl group (δ) and σp+, enables a mechanism to be proposed for the transformation of monophenols into o-diphenols, in which the first step is a nucleophilic attack on the copper atom on the form Eox (attack of the oxygen of the hydroxyl group of C-1 on the copper atom) followed by an electrophilic attack (attack of the hydroperoxide group on the ortho position with respect to the hydroxyl group of the benzene ring, electrophilic aromatic substitution with a reaction constant ρ of -1.75). These steps show the same dependency on the electronic effect of the substituent groups in C-4. Furthermore, a study of a solvent deuterium isotope effect on the oxidation of monophenols by tyrosinase points to an appreciable isotopic effect. In a proton inventory study with a series of p-substituted phenols, the representation of kcatfn/kcatf0 against n (atom fractions of deuterium), where kcatfn is the catalytic constant for a molar fraction of deuterium (n) and kcatf0 is the corresponding kinetic parameter in a water solution, was linear for all substrates. These results indicate that only one of the proton transfer processes from the hydroxyl groups involved the catalytic cycle is responsible for the isotope effects. We suggest that this step is the proton transfer from the hydroxyl group of C-1 to the peroxide of the oxytyrosinase form (Eox). After the nucleophilic attack, the incorporation of the oxygen in the benzene ring occurs by means of an electrophilic aromatic substitution mechanism in which there is no isotopic effect.
- Munoz-Munoz, Jose Luis,Berna, Jose,Garcia-Molina, Maria del Mar,Garcia-Molina, Francisco,Garcia-Ruiz, Pedro Antonio,Varon, Ramon,Rodriguez-Lopez, Jose N.,Garcia-Canovas, Francisco
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scheme or table
p. 228 - 233
(2012/10/18)
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- Synthesis and use of ortho-(branched alkoxy)-tert-butoxybenzenes
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A series of sterically hindered o-(branched alkoxy)-tert-butoxybenzenes was efficiently prepared in good yields owing to a new practical and simple preparation of o-tert-butoxyphenol starting from catechol and isobutene. Use of DMF di-tert-butyl acetal reagent instead of isobutene/H2SO 4 (cat.) for O-tert-butylation was very convenient in case of ortho bulky phenols affording the corresponding tert-butyl ethers in high yield and purity. This general route proved to be useful since no reliable access was available to o-di-t-BuO-substituted arenes. Application to the synthesis of congested phosphorus-based compounds is presented.
- Rast, Slavko,Stephan, Michel,Mohar, Barbara
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supporting information
p. 6815 - 6818
(2013/01/15)
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- Synthesis of catechols from phenols via Pd-catalyzed silanol-directed C-H oxygenation
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A silanol-directed, Pd-catalyzed C-H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product.
- Huang, Chunhui,Ghavtadze, Nugzar,Chattopadhyay, Buddhadeb,Gevorgyan, Vladimir
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p. 17630 - 17633
(2011/12/16)
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- Alkylation of pyrocatechol in tert-butyl alcohol-sulfuric acid-benzene
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Alkylation of pyrocatechol with tert-butyl alcohol in benzene in the presence of sulfuric acid gave 3,5-di-tert-butylbenzene-1,2-diol in a higher yield than in analogous reaction with tert-butyl alcohol. This result was rationalized by reduction of inhibitory effect of liberated water, formation of heterogeneous system, and occurrence of the alkylation process in nonpolar organic phase. Intermediate products were identified and found to undergo intra- and intermolecular tert-butyl group transfer with formation of more stable 3,5-di-tert-butylbenzene-1,2-diol. The formation of p-di-tert-butylbenzene indicated participation of benzene in crossalkylation processes. Pleiades Publishing, Ltd., 2011.
- Vol'eva,Prokof'eva,Belostotskaya,Komissarova,Gorbunov,Kurkovskaya
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experimental part
p. 1310 - 1312
(2011/12/05)
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- Anodic oxidation of catechols in the presence of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring: Selective α-arylation reaction
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The electrochemical oxidation of catechols leads to the formation of o-benzoquinones. This property has been applied to effectively synthesize α-arylated products of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring.
- Zeng, Cheng-Chu,Ping, Da-Wei,Hu, Li-Ming,Song, Xiu-Qing,Zhong, Ru-Gang
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scheme or table
p. 2465 - 2472
(2010/07/06)
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- Chloroindate(iii) ionic liquids as catalysts for alkylation of phenols and catechol with alkenes
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Chloroindate(iii) ionic liquids are shown to be versatile catalysts for the alkylation of phenols with alkenes, giving high conversions to alkylated phenols with high selectivities.
- Gunaratne, H. Q. Nimal,Lotz, Tobias J.,Seddon, Kenneth R.
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scheme or table
p. 1821 - 1824
(2011/01/07)
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- Efficient ortho-oxidation of phenols with diacyl peroxides
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A stable symmetric diacyl peroxide, m-chlorobenzoyl peroxide (mCBPO), and an asymmetric diacyl peroxide, chloroacetyl m-chlorobenzoyl peroxide (CAMCBPO), were synthesized from m-chloroperbenzoic acid. Both peroxides oxidized phenols selectively at the ortho position predoninantly. CAMCBPO gave para-oxidized compounds as minor products from some phenols. The improvement of the yield of ortho-oxidation of phenols with mCBPO was also reported.
- Tada, Masahiro,Ishiguro, Risa,Izumi, Ryohei
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p. 239 - 242
(2008/09/21)
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- Chemistry of 4-alkylaryloxenium ion "precursors": Sound and fury signifying something?
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(Chemical Equation Presented) Quinol esters 2b, 2c, and 3b and sulfonamide 4c were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester 2b predominantly undergoes ordinary acid- and base-catalyzed ester hydrolysis. The 4-tert-butyl ester 2c decomposes under both acidic and neutral conditions to generate tert-butanol and 1-acetyl-1,4-hydroquinone, 8, apparently by an SN1 mechanism. This is also a minor decomposition pathway for 2b, but the mechanism in that case is not likely to be SN1. Decomposition of 2c in the presence of N 3- leads to formation of the explosive 2,3,5,6-tetraazido-1,4-benzoquinone, 14, produced by N3 -induced hydrolysis of 8, followed by a series of oxidations and nucleophilic additions by N3 . No products suggestive of N3--trapping of an oxenium ion were detected. The 4-isopropyl dichloroacetic acid ester 3b reacts with N3- to generate the two adducts 2-azido-4-isopropylphenol, 5b, and 3-azido-4-isopropylphenol, 11b. Although 5b is the expected product of N3- trapping of the oxenium ion, kinetic analysis shows that it is produced by a kinetically bimolecular reaction of N3- with 3b. No oxenium ion is involved. The sulfonamide 4c predominantly undergoes a rearrangement reaction under acidic and neutral conditions, but a minor component of the reaction yields 4-tert-butylcresol, 17, and 2-azido-4-tert-butylphenol, 5c, in the presence of N3-. These products may indicate that 4c generates the oxenium ion 1c, but they are generated in very low yields (ca. 10%) so it is not possible to definitively conclude that 1c has been produced. If 1c has been generated, the N3--trapping data indicate that it is a very short-lived and reactive species in H2O. Comparisons with similarly reactive nitrenium ions indicate that the lifetime of 1c is ca. 20-200 ps if it is generated, so it must react by a preassociation process. Density functional theory calculations at the B3LYP/6-31G*//HF/6-31G* level coupled with kinetic correlations also indicate that the aqueous solution lifetimes of 1a-c are in the picosecond range.
- Novak, Michael,Brinster, Aaron M.,Dickhoff, Jill N.,Jones, Matthew P.,Leopold, Samuel H.,Vollman, Andrew T.,Wang, Yue-Ting,Glover, Stephen A.
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p. 9954 - 9962
(2008/09/18)
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- ALKYLATION OF HYDROXYARENES WITH OLEFINS, ALCOHOLS AND ETHERS IN IONIC LIQUIDS
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Hydroxyarenes are alkylated using an ionic liquid catalyst system with olefins, alcohols, or ethers as alkylating agents. The ionic liquid catalyst system comprises chloroindate (III) anions. The reactions may be conducted at moderate temperatures and pressures to yield commercially relevant alkylated hydroxyarene compounds.
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Page/Page column 26
(2008/06/13)
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- Decomposition of phenolic endocrine disrupting chemicals by potassium permanganate and γ-ray irradiation
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The decomposition of phenolic endocrine disrupting chemicals (P-EDCs), such as phenol, 4-t-butylphenol (BuP), and bisphenol A (BPA), in aqueous solutions by potassium permanganate (KMnO4) was studied, and its efficiency was compared with that of hydroxyl radicals (OH?) generated by 60Co γ-ray irradiation. Various organic acids and inorganic carbon were formed in the decomposition of P-EDCs due to either KMnO4 or OH?. They were formed via direct aromatic ring cleavage in the case of KMnO4 and via OH? addition-substitution reactions, followed by aromatic ring cleavage, in the case of OH?. Comparing the decrease in the P-EDCs based on the number of electrons, the amount of KMnO4 spent to completely eliminate BuP and BPA was comparable to that of OH?. Although three-times more KMnO4 was needed for phenol decomposition than OH?, the complete conversion of phenol into organic acids and inorganic carbon was achieved with 720 μM of electrons in both cases.
- Abe, Yasuhiro,Takigami, Machiko,Sugino, Kouji,Taguchi, Mitsumasa,Kojima, Takuji,Umemura, Tomonari,Tsunoda, Kin-Ichi
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p. 1681 - 1685
(2007/10/03)
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- Polymeric enzyme mimics: catalytic activity of ribose-containing polymers for a phosphate substrate.
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The polymers containing ribose rings: poly(5'-acrylamido-5'-deoxy-1',2'-O-isopropylidene-alpha-D-ribose) (11), poly(5'-acrylamido-5'-deoxy-alpha-D-ribose) (12) and poly(5'-acrylamido-5'-deoxy-1'-O-methyl-D-ribose) (13) were prepared as enzyme mimics. Polymers 12 and 13 with free vic-cis-diol groups catalyzed the hydrolysis of phosphodiester (ethyl p-nitrophenyl phosphate and N-methylpyridinium 4-tert-butylcatechol cyclic phosphate) and phosphomonoester substrates with a rate acceleration of 10 approximately equal to 10(3) compared with the uncatalyzed reaction. They also catalyzed the reverse reactions, i.e., the esterification of phosphomonoester to phosphodiester and the phosphorylation of alcohols with phosphate ions. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. The catalytic activity was negligible for polymer 11 where vic-cis-diol groups were blocked with isopropylidene groups. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles.
- Han, Man Jung,Yoo, Kyung Soo,Kim, Young Heui,Chang, Ji Young
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p. 2276 - 2282
(2007/10/03)
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- A quantitative approach to the recycling of α-tocopherol by coantioxidants
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A systematic investigation is reported on the regeneration of α-tocopherol (α-TOH) in homogeneous solution by coantioxidants in order to better understand the mechanism and the factors responsible for the effectiveness of this process. The current availability of thermochemical data concerning the reactants involved in the regeneration reactions, as well as a large number of the kinetic constants for the various reactions involved, allowed us to rationalize the experimental observations collected so far. Three limiting cases have been considered. The first case is that of a coantioxidant irreversibly regenerating α-TOH, where the effectiveness of the recycling process depends on the magnitude of the rate constant kr. The second case is that of a coantioxidant reversibly recycling α-TOH, where regeneration can only be observed if the bond dissociation enthalpy value of the coantioxidant is lower or at least close to that of the O-H bond of α-tocopherol. The third case is that of a catechol derivative (chosen as a model compound for polyphenolic antioxidants), where recycling of α-TOH is feasible even though the BDE value is significantly higher than that of vitamin E. In this case, the driving force for the recycling process is the removal of the semiquinone radical from the catechol derivative by the α-tocopheroxyl radical, which makes the regeneration of α-TOH practically irreversible.
- Amorati, Riccardo,Ferroni, Fiammetta,Lucarini, Marco,Pedulli, Gian Franco,Valgimigli, Luca
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p. 9295 - 9303
(2007/10/03)
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- 5-(β-Cyclodextrinylamino)-5-deoxy-α-D-riboses as models for nuclease, ligase, phosphatase, and phosphorylase
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β-Cyclodextrin derivatives crowned with ribose rings (such as 1) catalyzed the hydrolysis, esterification, and phosphorylation of catechol- derived phosphate esters. The vicinal cis-diols on the ribose groups appear to play a major role in the catalytic activity of these enzyme models by the formation of hydrogen bonds which activate the phosphorus atom to nucleophilic attack.
- Han, Man Jung,Yoo, Kyung Soo,Chang, Ji Young,Ha, Tae-Kyu
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p. 347 - 349
(2007/10/03)
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- Substituent effects on the benzene ring. Determination of the intramolecular interactions of substituents in tert-alkyl-substituted catechols from thermochemical measurements
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Chemical equilibria of reactions of transalkylation among tert-butylphenols and tert-butylcatechols in the liquid phase were investigated in the temperature range 373-483 K. The molar enthalpies of fusion ΔcrlH°m of the catechol, 4-tert-butylcatechol, and 3,5-di-tert-butylcatechol were measured by DSC. The standard (p° = 0.1 MPa) molar enthalpies of formation ΔfH°m (cr) at the temperature T = 298.15 K were measured by means of combustion calorimetry for 4-tert-butylcatechol and 3,5-di-tert-butylcatechol. The standard molar enthalpies of sublimation of these compounds, and also the enthalpy of vaporization of 3-tert-butylcatechol, were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The measured reaction enthalpies were utilized for reconciliation of calorimetrically derived standard molar enthalpies of formation of tert-butyl-substituted phenols and catechols, as a stringent test of thermodynamic consistency of results derived from the diverse techniques employed in this work. Resulting values of ΔfH°m(g) of tert-butylcatechols were obtained at the temperature T = 298.15 K and used to derive their strain enthalpies. The intramolecular interactions of the substituents were discussed in terms of deviations of ΔfH°m(g) from the group additivity rules. No peculiarities in the interaction energy among alkyl groups and the hydroxyl groups in the ortho-, para-, and meta-positions of alkylcatechols in comparison with those of alkyl-substituted phenols were detected. Thus, no new parameters are needed for the prediction of the ΔfH°m(g) values of alkylcatechols by using the group-additive procedure.
- Verevkin, Sergey P.,Schick, Christoph
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p. 946 - 952
(2007/10/03)
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- Sodium Bis(trimethylsily)amide and Lithium Diisopropylamide in Deprotection of Alkyl Aryl Ethers: α-Effect of Silicon
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Removal of methyl, benzyl, and methylene groups from alkyl aryl ethers is among the most popular deprotecting methods in organic synthesis. Alkali organoamides NaN(SiMe3)2 and LiN(i-Pr)2, often used as organic bases, have been developed as efficient deprotecting agents. Treatment of aryl methyl ethers with 1.5 equiv of NaN(SiMe3)2 or LiN(i-Pr)2 in THF and 1,3-dimethyl-2-imidazolidinone in a sealed tube at 185 °C produced the corresponding phenol derivatives in good to excellent yields (80-97percent). Removal of the methylene unit from benzodioxole derivatives was also accomplished by use of 2.5 equiv of these alkali organoamides. The corresponding catechols were obtained in 93-99percent yields. The activity of NaN(SiMe3)2 was proven lower than that of LiN(i-Pr)2; it is due to the steric congestion and the α-stabilizing effect of the silyl groups. Thus selective mono-O-demethylation of o-dimethoxybenzenes can be achieved by the use of NaN(SiMe3)2 but not LiN(i-Pr)2. O-Debenzylation of aryl benzyl ethers, however, can be accomplished by the use of LiN(i-Pr)2.
- Hwu, Jih Ru,Wong, Fung Fuh,Huang, Jiann-Jyh,Tsay, Shwu-Chen
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p. 4097 - 4104
(2007/10/03)
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- Monooxovanadium(V) mixed ligand complexes of schiff bases and catecholates: Synthesis, spectral and electrochemical characterization
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Mixed ligand, monooxovanadium(V) complexes of Schiff bases with catechol, p-tertbutylcatechol or pyrogallol have been synthesized and characterized by various spectral techniques, such as FTIR, UV-vis, 51V NMR and electrochemistry. All of these complexes exhibited a six coordinated VO3+ center. The stability and the conversion of these complexes to pentacoordinated VO+2 species with the loss of a bidentate catecholate ligand in DMSO were demonstrated using absorption, 51V NMR and electrochemical studies. 51V NMR studies further suggested the formation of two possible isomers in the case of p-tertbutylcatechol and pyrogallol complexes of VO3+. Electrochemistry of these complexes showed one reversible V(V)/V(IV) couple and another irreversible V(IV)/V(III) response. The mixed ligand, VO3+ complexes are more resistant to reduction as compared to the corresponding tris catecholate complexes. Copyright
- Asgedom, Gebray,Sreedhara, Alavattam,Rao, Chebrolu P.,Kolehmainen, Erkki
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p. 3731 - 3739
(2008/10/09)
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- Enzymatically amplified voltammetric sensor for microliter sample volumes of salicylate
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A new voltammetric sensing strategy for salicylate employing two enzymes and applicable to microliter sample volumes is demonstrated. The method involves the use of the enzyme salicylate hydroxylase to convert salicylate to catechol, which is oxidized at a carbon electrode. The product of this oxidation reaction, o-quinone, is then reduced by a second enzyme, glucose oxidase, to regenerate catechol. Reoxidation of catechol results in a signal that is amplified due to repeated cycling of catechol molecules between the oxidized and reduced states. This chemistry is implemented in two configurations. (i) A paper disk into which both enzymes have been absorbed is mounted on a coplanar three-electrode assembly for aqueous experiments. Determination of salicylate in a nonprescription dermatological product is demonstrated. (ii) A small solution volume confined directly on the coplanar electrodes is used for determination of salicylate in whole blood. The advantages of the use of two enzymes and of monitoring steady-state catalytic currents are discussed.
- Moore, Thea J.,Joseph, Melissa J.,Allen, Barry W.,Coury Jr., Louis A.
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p. 1896 - 1902
(2007/10/02)
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- SELECTIVE ORTHO-HYDROXYLATION OF PHENOLS IN COPPER (I) COMPLEXES
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Several catechols are obtained by reacting excess of the corresponding phenols with the tetrahydroborato copper(I) complex (4) and subsequent dioxygen oxidation of the intermediate copper(I) phenoxo complex (1).
- Chioccara, Francesco,Gennaro, Patricia Di,Monica, Girolamo La,Sebastiano, Roberto,Rindone, Bruno
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p. 4429 - 4434
(2007/10/02)
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- Effect of Crown Ether Lipophilicity on the Facilitated Transport of Guanidinium Thiocyanate through an Immobilized Liquid Membrane
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The flux of guanidinium thiocyanate through a supported liquid membrane has been measured for substituted benzo crown ethers and dibenzo crown ethers.This flux depends on the water solubility of the carrier.The more lipophilic crown ethers (7-14 and 16) show a higher flux and form more stable supported liquid membranes.The effect of the lipophilic substituents on the partition coefficient of the benzo crown ethers has been calculated and verified by partition experiments.The observed fluxes have been interpreted by a developed general model for the transport of salts through supported liquid membranes containing crown ethers.This thermodynamic model takes into account the interface equilibria, viz. the partition of crown ether and salt, as well as complexation equilibria in the membrane and aqueous phase.The model has been applied for the calculation of the complexation constants in the membrane phase.The lipophilic benzo crown ethers with 27 ring atoms show lower complexation constants than the corresponding benzo crown ether with 30 ring atoms.The complexation constants of the dibenzo crown ethers and guanidinium thiocyanate are smaller than those of the corresponding complexes of the substituted benzo crown ethers.During the diffusion process of the complex through the membrane phase complexation and decomplexation take place continuously as was concluded from the small value of the inverse Damkoehler number.
- Stolwijk, Theodorus B.,Sudhoelter, Ernst J. R.,Reinhoudt, David N.
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p. 6321 - 6329
(2007/10/02)
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- Evaluation of the cytotoxic potential of catechols and quinones structurally related to butylated hydroxyanisole
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The cytotoxicity of 2- and 3-butylated hydroxyanisole (BHA) and 18 related aromatic compounds has been determined employing cultured P388 and KB cells. The phenolic compounds, 3-BHA and 2-BHA, had moderately low cytotoxic activity. Their corresponding catechols had ED50 values that were much lower than those of the parent compounds. This substantial increase in the cytotoxic activity is attributed to the presence of the catechol group, which is known to undergo one-electron oxidation readily to give the corresponding semiquinone radical. Other related catechols had similar cytotoxic activity. In general, derivatization of the catechol functionality resulted in a decrease of the cytotoxic potential of the compounds. Monoacetylation or monomethylation of the catechols gave products that were less potent cytotoxic agents than the parent compounds. Further loss of activity was observed when both hydroxy groups of the catechol function were blocked. Substitution of a methoxy group in place of a hydrogen atom in these compounds resulted in a significant increase of cytotoxicity, whereas the replacement of a methoxy group with a methyl group reduced the cytotoxicity. The catechols and quinones derived from 2-BHA were more active when compared with those derived from 3-BHA. The t-butyl group adjacent to the catechol or quinone moiety in the 3-BHA derivatives appeared to exert a significant steric effect toward the cytotoxic potential of these compounds. These results suggest the potential use of o-quinones and catechols as cytotoxic and antitumor agents.
- Lam,Garg,Swanson,Pezzuto
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p. 393 - 395
(2007/10/02)
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- Photolysis of the Ozonide Derived from 1,4-Benzodioxins. Synthesis of Labile o-Benzoquinones
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By the photolysis of the ozonide derived from 1,4-benzodioxins, o-benzoquinones were obtained in moderate yields independent of the stability of o-benzoquinones and of the substituent groups, except the nitro group.Through the mechanistic studies, it was indicated that o-benzoquinones were formed through a radical decomposition pathway, while catechols were formed through an ionic decomposition pathway induced by acidic impurities.
- Kashima, Choji,Tomotake, Atsushi,Omote, Yoshimori
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p. 5616 - 5621
(2007/10/02)
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- SYNTHESIS OF 1,2-BENZOQUINONES FROM 1,4-BENZODIOXINS USING THE REACTION WITH OZONE FOLLOWED BY PHOTOLYSIS
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Ozonolysis followed by photolysis of 1,4-benzodioxins (1) was carried out, and 1,2-benzoquinones (3) and catechols (4) were obtained as products.It was noteworthy that labile 4-chloro-1,2-benzoquinone (3b) was obtained in a moderate yield as much as that of stable 4-tert-1,2-benzoquinone (3c).Mechanistic study was also discussed.
- Kashima, Choji,Tomotake, Atsushi,Omote, Yoshimori
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p. 363 - 366
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- 4'-tert-AlkylbenzoCrown-5-Ether. Syntheses and Complexes with Potassium Thiocyanate
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The title compounds 4 are synthesized either by alkylation of pyrocatechole 1 in 4-position and followed by ring closure with 1,11-dichloro-3,6,9-trioxaundecane or by alkylation of benzo-crown-5 3.In most cases the way first mentioned gives better results.Analytical samples of the alkylated benzocrown-5 ethers 4 are obtained through complexing with KSCN.Physical data and 1H-n.m.r.-spectra of 5 new pyrocatecholes 2 and 6 new benzocrown-5 ethers 4 are given.
- Beger, J.,Meerbote, M.
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- Silica Gel as an Effective Catalyst for the Alkylation of Phenols and Some Heterocyclic Compounds
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In the presence of silica gel, the reaction of phenol with t-BuBr was examined under a variety of conditions and it was found that silica gel is an effective catalyst for the alkylation.As a result of this work 2-tert-butyl-, 2,6-di-tert-butyl-, and 2,4,6-tri-tert-butylphenols, all of which are hard to obtain directly by the Friedel-Crafts process, could be prepared easily by this one-step reaction.Several other alkyl halides were also used in this reaction.The alkylations of some heterocyclic aromatic compounds which cannot be alkylated by the conventional Friedel-Crafts method were also succesfully performed by this reaction.
- Kamitori, Yasuhiro,Hojo, Masaru,Masuda, Ryoichi,Izumi, Tatsuo,Tsukamoto, Shuichi
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p. 4161 - 4165
(2007/10/02)
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- STABLE ISOBENZOFURAN ENDOPEROXIDE AND ITS USE FOR OXIDATION OF OLEFINS AND AROMATIC COMPOUNDS
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1,3-Di-tert-butylisobenzofuran reacts with singlet oxygen with rate constant of 2.8E9 M-1 sec-1 to give stable endoperoxide 4.Thermolysis of the endoperoxide (4) in the presence of norbornene and naphthalene gave the corresponding epoxide and naphthols, respectively.Addition of Pd(OAc)2 improved the yield of naphthols considerably.
- Saito, Isao,Nakata, Akira,Matsuura, Teruo
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p. 1697 - 1700
(2007/10/02)
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- Hair dyeing composition containing an aryldiamine and a substituted catechol
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A composition for use in the dyeing of keratinous fibre such as hair includes an aqueous anaerobic solution of an aryldiamine and a substituted catechol. Optionally, an aromatic coupling agent can also be incorporated in the composition to modify the shade of color produced. Anaerobic storage conditions can, for example, be maintained by packing the composition in an aerosol container with a halocarbon propellant.
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- The Reactions of Lignin with Alkaline Hydrogen Peroxide. Part IV. Products from the Oxidation of Quinone Model Compounds
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Simple para- and orhto-quinoid structures related to lignin have been oxidized with hydrogen peroxide under mild alkaline conditions.Most of the reaction products, i.e. carboxylic acids formed by oxidative cleavage of the quinoid ring together with acids formed by more extensive degradation of the starting materials, were identified after conversion into esters.In addition, small amounts of hydroxylated quinones were found.Mechanisms for the formation of these products are suggested and the significance of the results for the bleaching of mechanical pulps with hydrogen peroxide is briefly discussed.
- Gellerstedt, Goeran,Hardell, Hanne-Lise,Lindfors, Eva-Lisa
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p. 669 - 674
(2007/10/02)
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- Method for manufacture of dihydric phenols
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Dihydric phenols are produced preferentially in high yields by having monohydric phenols or phenyl ethers oxidized by an organic peracid using, as a catalyst, at least one member selected from the group consisting of peracid stabilizers, polycarboxylic acids containing N or OH and possessed of a structure from which heavy metal ion-chelating property can theoretically be assumed, magnesium salts, sodium salts and potassium salts thereof, sodium salt, potassium salt and lower alkyl esters of phosphoric acid, and sodium salt and lower alkyl esters of pyrophosphoric acid.
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