- Active Site Dynamics of Xylene Hydroxylation by Cytochrome P-450 As Revealed by Kinetic Deuterium Isotope Effects
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The cytochrome P-450 catalyzed hydroxylation of o- and p-xylene and five deuterated derivatives of each has been investigated using phenobarbital-induced rat liver microsomes.All possible monohydroxylation products were observed but benzylic hydroxylation predominated strongly (88-96percent).H/D discrimination was strongest when both isotopes were located on the same methyl gorup, less when they were located in different methyl groups on the same xylene molecule, and least when they were located in methyl groups on different molecules.Benzylic hydroxylation is subject to a large intrinsic (intramolecular) deuterium isotope effect (CH3/CD3=7.5-9.5), comprised of a large primary component (5.3-7.8) and a large normal α-secondary component (1.09-1.19).These isotope effects suggest a transition state for benzylic H-abstraction that is linear and symmetrical with substantial rehybridization toward planarity at the benzylic carbon and little residual C-H bond order remaining.In contrast aromatic hydroxylation of o- and p-xylene shows a small inverse α-secondary isotope effect (0.83-0.94).The D(V/K) isotope effect observed for benzylic hydroxylation in intermolecular competitions (ca. 1.9-2.3 for d0/d6 substrate mixtures) is substantially reduced by commitment to catalysis, with Cf=(kH+kr)k-1=3.6 for p-xylene and 5.9 for o-xylene.These results suggest a dynamic picture of catalysis with the following relative rates: methyl group rotation > substrate-orientation within the Michaelis complex (i.e. isotopically sensitive branching to different products) > product formation (i.e. commitment to catalysis) > substrate dissociation prior to hydroxylation.
- Hanzlik, Robert P.,Ling, Kah-Hiing John
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Read Online
- (5,8)Picenophanedienes: Syntheses, Structural Analyses, Molecular Dynamics, and Reversible Intramolecular Structure Conversion
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This study presents an important and efficient synthetic approach to 5,8-dibromo-2,11-di-tert-butylpicene (3), with multigram scale, which was then converted to a new series of picenophanes (6-10). The tub-shaped [2,2](5,8)picenophanediene 8 with two cis-ethylene linkers was explored using X-ray crystallography. The tub-to-tub inversion proceed through the successive bending of the linkers and the barrier for isopropyl-substituted derivative 10 was experimentally estimated to be 18.7 kcal/mol. Picenophanes with a large π-system and semi-rigid structure exhibited anomalous photophysical properties. The ethano-bridged picenophane shows the weak exciton delocalization while the cis-ethylene-bridged picenophane exhibits dual emission rendered by the weakly delocalized exciton and excimer. With the aid of the ultrafast time-resolved emission spectroscopy, the mechanism of the excimer formation is resolved, showing a unique behavior of two-state reversible reaction with fast structural deformation whose lifetime is around 20 ps at 298 K. This work demonstrates that the slight difference in the bridge of tub-shaped picenophanes renders distinct photophysical behavior, revealing the potential of harnessing inter-moiety reaction in the picenophane systems.
- Tang, Min-Chih,Wei, Yu-Chen,Chu, Yen-Chen,Jiang, Cai-Xin,Huang, Zhi-Xuan,Wu, Chi-Chi,Chao, Tzu-Hsuan,Hong, Pei-Hsun,Cheng, Mu-Jeng,Chou, Pi-Tai,Wu, Yao-Ting
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Read Online
- A mild and practical method for deprotection of aryl methyl/benzyl/allyl ethers with HPPh2andtBuOK
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A general method for the demethylation, debenzylation, and deallylation of aryl ethers using HPPh2andtBuOK is reported. The reaction features mild and metal-free reaction conditions, broad substrate scope, good functional group compatibility, and high chemical selectivity towards aryl ethers over aliphatic structures. Notably, this approach is competent to selectively deprotect the allyl or benzyl group, making it a general and practical method in organic synthesis.
- Pan, Wenjing,Li, Chenchen,Zhu, Haoyin,Li, Fangfang,Li, Tao,Zhao, Wanxiang
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p. 7633 - 7640
(2021/09/22)
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- Me3SI-promoted chemoselective deacetylation: a general and mild protocol
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A Me3SI-mediated simple and efficient protocol for the chemoselective deprotection of acetyl groups has been developedviaemploying KMnO4as an additive. This chemoselective deacetylation is amenable to a wide range of substrates, tolerating diverse and sensitive functional groups in carbohydrates, amino acids, natural products, heterocycles, and general scaffolds. The protocol is attractive because it uses an environmentally benign reagent system to perform quantitative and clean transformations under ambient conditions.
- Gurawa, Aakanksha,Kashyap, Sudhir,Kumar, Manoj
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p. 19310 - 19315
(2021/06/03)
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- REARRANGEMENT OF DIMETHYLPHENYLACYLATES USING ZEOLITES
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The present invention relates to a Fries rearrangement of specific dimethylphenylacylates to form the desired respective hydroxyaryl ketones having two methyl groups bound to the aromatic ring. It has been found that the process is surprisingly very specific in view of the number and position of the methyl group(s) bound to the aromatic ring.
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Page/Page column 9-11
(2021/08/14)
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- Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction
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The regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)-based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.
- Waggoner, Abygail R.,Abdulrahman, Yahya,Iverson, Alexis J.,Gibson, Ethan P.,Buckles, Mark A.,Poole, James S.
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- Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
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Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
- Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
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p. 4348 - 4358
(2020/09/22)
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- Substrate substitution effects in the Fries rearrangement of aryl esters over zeolite catalysts
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The catalytic transformation of aryl esters to hydroxyacetophenones via Fries rearrangement over solid acids is of interest to avoid the use of corrosive and toxic Lewis and Br?nsted acids traditionally applied. Microporous zeolites are known to catalyze the reaction of simple substrates such as phenyl acetate, but their application to substituted derivatives has received limited attention. To refine structure-activity relationships, here we examine the impact of various parameters including the solvent polarity, water content, acidic properties, and framework type on the reaction scheme in the Fries rearrangement of p-tolyl acetate over common solid acids. The results confirm the importance of providing a high concentration of accessible Br?nsted acid sites, with beta zeolites exhibiting the best performance. Extension of the substrate scope by substituting methyl groups in multiple positions identifies a framework-dependent effect on the rearrangement chemistry and highlights the potential for the transformation of dimethylphenyl acetates. Kinetic studies show that the major competitive path of cleavage of the ester C-O bond usually occurs in parallel to the Fries rearrangement. The possibility of sequentially acylating the resulting phenol depends on the substrate and reaction conditions.
- Bonrath, Werner,Létinois, Ulla,Lin, Ronghe,Medlock, Jonathan,Mitchell, Sharon,Netscher, Thomas,Pérez-Ramírez, Javier,Stemmler, René T.
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p. 4282 - 4292
(2020/07/30)
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- A scalable and green one-minute synthesis of substituted phenols
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A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
- Elumalai, Vijayaragavan,Hansen, J?rn H.
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p. 40582 - 40587
(2020/11/18)
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- Method for synthesizing high added value xylenol through isomerization of 2,6-dimethylphenol
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The invention discloses a method for synthesizing high added value xylenol through isomerization of 2,6-dimethylphenol. The method comprises: 1, pouring a catalyst and 2,6-dimethylphenol into a reaction bottle, uniformly stirring, and carrying out a thermal insulation reaction to obtain a reaction product; 2, carrying out a hydrolysis reaction on the reaction product, carrying out standing layering, and separating to obtain a water phase and an organic phase; and 3, combining the extractant obtained by extracting the water phase and the organic phase, and sequentially carrying out washing, drying, decolorization and pressure reducing distillation treatment to obtain xylenol. According to the present invention, 2,6-dimethylphenol is subjected to methyl rearrangement isomerization under theaction of the catalyst to obtain the wide-use and high-added value xylenol including 2,5-dimethylphenol, 3,5-dimethylphenol, 2,3-dimethylphenol and 3,4-dimethylphenol, such that the low value productis converted into the high value product, the raw material and process costs are reduced, the environmental pollution is low, and the method is suitable for industrial production.
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Paragraph 0038-0140
(2019/02/08)
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- Catalytic activation of unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols
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Transition metal catalysis has emerged as an important means for C–C activation that allows mild and selective transformations. However, the current scope of C–C bonds that can be activated is primarily restricted to either highly strained systems or more polarized C–C bonds. In contrast, the catalytic activation of non-polar and unstrained C–C moieties remains an unmet challenge. Here we report a general approach for the catalytic activation of the unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols. The key is to utilize the phenol moiety as a handle to install phosphinites as a recyclable directing group. Using hydrogen gas as the reductant, monophenols are obtained with a low catalyst loading and high functional group tolerance. This approach is also applied to the synthesis of 2,3,4-trisubstituted phenols. A further mechanistic study suggests that the C–C activation step is mediated by a rhodium(i) monohydride species. Finally, a preliminary study on breaking the inert biphenolic moieties in lignin models is illustrated.
- Zhu, Jun,Wang, Jianchun,Dong, Guangbin
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- Regioselectivity of Hydroxyl Radical Reactions with Arenes in Nonaqueous Solutions
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The regioselectivity of hydroxyl radical addition to arenes was studied using a novel analytical method capable of trapping radicals formed after the first elementary step of reaction, without alteration of the product distributions by secondary oxidation processes. Product analyses of these reactions indicate a preference for o- over p-substitution for electron donating groups, with both favored over m-addition. The observed distributions are qualitatively similar to those observed for the addition of other carbon-centered radicals, although the magnitude of the regioselectivity observed is greater for hydroxyl. The data, reproduced by high accuracy CBS-QB3 computational methods, indicate that both polar and radical stabilization effects play a role in the observed regioselectivities. The application and potential limitations of the analytical method used are discussed.
- Moores, Lee C.,Kaur, Devinder,Smith, Mathew D.,Poole, James S.
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p. 3260 - 3269
(2019/03/11)
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- Method for preparing hydrocarbyl phenol by catalytic conversion of phenolic compound in presence of molybdenum-based catalyst
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The invention discloses a method for preparing hydrocarbyl phenol by catalytic conversion of a phenolic compound in the presence of a molybdenum-based catalyst. The method comprises mixing a phenoliccompound, a molybdenum-based catalyst and a reaction solvent, adding the mixture into a sealed reactor, feeding gas into the reactor, heating the mixture to 150-350 DEG C, carrying out stirring for areaction for 0.5-2h, then filtering to remove a solid catalyst and carrying out rotary evaporateion to obtain a liquid product. The phenolic compound has a wide source, a cost is low, product alkyl phenol selectivity is high, an added value is high, alcohol or an alcohol-water mixture is used as a reaction solvent, environmental friendliness is realized, pollution is avoided, any inorganic acids and alkalis are avoided in the reaction process, the common environmental pollution problems in the biomass processing technology are solved, the reaction conditions are mild, the process can be carried out at a low temperature, high-efficiency conversion of the reactants can be realized without consuming hydrogen gas and the method is suitable for large-scale industrial trial production.
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Paragraph 0046; 0070
(2018/04/02)
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- Tuning the Reactivity of Peroxo Anhydrides for Aromatic C-H Bond Oxidation
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Phenol moieties are key structural motifs in many areas of chemical research from polymers to pharmaceuticals. Herein, we report on the design and use of a structurally demanding cyclic peroxide (spiro[bicyclo[2.2.1]heptane-2,4′-[1,2]dioxolane]-3′,5′-dione, P4) for the direct hydroxylation of aromatic substrates. The new peroxide benefits from high thermal stability and can be synthesized from readily available starting materials. The aromatic C-H oxidation using P4 exhibits generally good yields (up to 96%) and appreciable regioselectivities.
- Pilevar, Afsaneh,Hosseini, Abolfazl,?ekutor, Marina,Hausmann, Heike,Becker, Jonathan,Turke, Kevin,Schreiner, Peter R.
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p. 10070 - 10079
(2018/09/06)
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- Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: Evidence for a metal-based mechanism
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An iminopyridine Fe(ii) complex, easily prepared in situ by self-assembly of cheap and commercially available starting materials (2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 in a 2 : 2 : 1 ratio), is shown to be an effective catalyst for the direct hydroxylation of aromatic rings with H2O2 under mild conditions. This catalyst shows a marked preference for aromatic ring hydroxylation over lateral chain oxidation, both in intramolecular and intermolecular competitions, as long as the arene is not too electron poor. The selectivity pattern of the reaction closely matches that of electrophilic aromatic substitutions, with phenol yields and positions dictated by the nature of the ring substituent (electron-donating or electron-withdrawing, ortho-para or meta-orienting). The oxidation mechanism has been investigated in detail, and the sum of the accumulated pieces of evidence, ranging from KIE to the use of radical scavengers, from substituent effects on intermolecular and intramolecular selectivity to rearrangement experiments, points to the predominance of a metal-based SEAr pathway, without a significant involvement of free diffusing radical pathways.
- Capocasa, Giorgio,Olivo, Giorgio,Barbieri, Alessia,Lanzalunga, Osvaldo,Di Stefano, Stefano
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p. 5677 - 5686
(2017/12/07)
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- Silica chloride: An efficient promoter for oxidation of arylboronic acids to phenols
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This work reports simple, highly efficient protocol for the oxidation of arylboronic acids. Various arylboronic acids were selectively and completely converted into their corresponding oxidized phenols using H2O2 as an oxidant in presence of catalytic amount of silica chloride. The results show that silica chloride is a suitable and efficient promoter for the oxidation of arylboronic acids. Heterogeneous catalyst, mild reaction conditions, easy availability of the reagent, easy work-up, excellent yield of corresponding phenols, short reaction time and broad substrate scope makes this protocol attractive and a practical alternative to the existing methods.
- Wagh, Ravindra B.,Nagarkar, Jayashree M.
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supporting information
p. 3323 - 3326
(2017/07/27)
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- N-Substituted 3(10H)-Acridones as Visible-Light, Water-Soluble Photocatalysts: Aerobic Oxidative Hydroxylation of Arylboronic Acids
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We disclosed a novel water-soluble photocatalyst that could promote aerobic oxidative hydroxylation of arylboronic acids to furnish phenols in excellent yields. This transformation uses visible-light irradiation under environmentally friendly conditions, that is, water-soluble catalyst, metal-free, green oxidant, room temperature.
- Xie, Hong-Yan,Han, Li-Shuai,Huang, Shan,Lei, Xiantao,Cheng, Yong,Zhao, Wenfeng,Sun, Hongbin,Wen, Xiaoan,Xu, Qing-Long
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p. 5236 - 5241
(2017/05/24)
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- Construction of Acid–Base Synergetic Sites on Mg-bearing BEA Zeolites Triggers the Unexpected Low-Temperature Alkylation of Phenol
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Novel Mg-bearing BEA zeolites are synthesized to simultaneously endow significantly enhanced basicity without compromising acidity over the zeolite framework. Serving as efficient solid acid–base bifunctional catalysts, they achieve the liquid-phase selective methylation of phenol with methanol to produce o- and p-cresol (o/p=2) under mild conditions. The method is readily extendable to the alkylation of phenols with various alcohols. Stereo- and regioselectivity (>95 % for p-product) was attained on the alkylation of phenol with bulky tert-butyl alcohol, rendering the first acid–base cooperative shape-selective catalysis relying on the basicity of zeolites. A preliminary mechanistic analysis reveals that the remarkable activity and shape-selectivity come from the superior special acidic–basic synergetic catalytic sites on the uniform microporous channels of the BEA zeolite.
- Xie, Jingyan,Zhuang, Wenxia,Zhang, Wei,Yan, Ning,Zhou, Yu,Wang, Jun
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p. 1076 - 1083
(2017/03/27)
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- Highly Selective and Efficient Ring Hydroxylation of Alkylbenzenes with Hydrogen Peroxide and an Osmium(VI) Nitrido Catalyst
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The OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
- Kwong, Hoi-Ki,Lo, Po-Kam,Yiu, Shek-Man,Hirao, Hajime,Lau, Kai-Chung,Lau, Tai-Chu
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p. 12260 - 12263
(2017/09/06)
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- Graphite encapsulated molybdenum carbide core/shell nanocomposite for highly selective conversion of guaiacol to phenolic compounds in methanol
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Graphite encapsulated molybdenum carbides (Mo2C@C) were synthesized via the hydrothermal carbonization of a solution of glucose and ammonium molybdate followed by temperature programmed reduction. Characterization and structural analyses revealed that the synthesized Mo2C@C nanoparticles had a molybdenum core/carbon shell structure with a particle size ranging from 50 nm to 100 nm and a core size range of 5–45 nm. The catalytic performance of the graphite encapsulated molybdenum carbides was evaluated on conversion of guaiacol to phenolic compounds in methanol. At 340 °C under 2.8 MPa hydrogen pressure, a 76.3% guaiacol conversion was obtained with selectivities of 68.6% for phenol and 93.5% for phenolic compounds. Thus, Mo2C@C showed high selectivity for phenolic compounds in methanol.
- Li, Rui,Shahbazi, Abolghasem,Wang, Lijun,Zhang, Bo,Hung, Albert M.,Dayton, David C.
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p. 123 - 130
(2016/10/25)
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- Improved oxidation of aromatic and aliphatic hydrocarbons using rate enhancing variants of P450Bm3 in combination with decoy molecules
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Enzyme performance can be improved using decoy molecules or engineered variants to accelerate the activity without affecting selectivity. Here we combine a rate accelerator variant of cytochrome P450Bm3 with decoy molecules to enhance the oxidation activity of a range of small organic molecules. This combined approach offers superior biocatalytic efficiency without modifying the product distribution.
- Munday, Samuel D.,Shoji, Osami,Watanabe, Yoshihito,Wong, Luet-Lok,Bell, Stephen G.
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supporting information
p. 1036 - 1039
(2016/01/16)
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- Catalytic ortho -acetoxylation of masked benzyl alcohols via an exo -directing mode
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A Pd-catalyzed ortho-acetoxylation of masked benzyl alcohols to synthesize various 2-hydroxyalkylphenol derivatives is reported. The 2,6-dimethoxyl benzaldoxime proved to be an efficient exo-type directing group for arene (sp2) C-H functionalization. Two strategies were demonstrated to remove the directing group through N-O and C-O bond cleavages. A high catalyst turnover (>1000) was obtained to illustrate the practicality of this method.
- Ren, Zhi,Schulz, Jonathan E.,Dong, Guangbin
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supporting information
p. 2696 - 2699
(2015/06/16)
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- Study of gas phase m-cresol alkylation with methanol on solid acid catalysts
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The gas-phase alkylation of m-cresol with methanol was studied at 523 K on Al-MCM-41 and zeolites ZnY, HBEA, HZSM5 and HMCM22. The acidity was determined by ammonia TPD and FTIR of adsorbed pyridine. On acid sites of moderate strength (Al-MCM-41), initially the O-alkylation rate was higher than the C-alkylation rate. In contrast, formation of dimethylphenols by C-alkylation was highly favored on ZnY and HMCM22 which have both strong acidity although different nature; Lewis (ZnY) and Bronsted and Lewis (HMCM22). High selectivity of 2,5-DMP was observed on HZSM5, probably due to diffusional constraint. All catalysts, except Al-MCM-41, showed deactivation by coke formation.
- Acevedo,Bedogni,Okulik,Padr
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p. 1946 - 1954
(2015/02/19)
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- CYCLIC PEROXIDE OXIDATION OF AROMATIC COMPOUND PRODUCTION AND USE THEREOF
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The present invention provides a method for converting an aromatic hydrocarbon to a phenol by providing an aromatic hydrocarbon comprising one or more aromatic C-H bonds and one or more activated C-H bonds in a solvent; adding a phthaloyl peroxide to the solvent; converting the phthaloyl peroxide to a di-radical; contacting the di-radical with the one or more aromatic C-H bonds; oxidizing selectively one of the one or more aromatic C-H bonds in preference to the one or more activated C-H bonds; adding a hydroxyl group to the one of the one or more aromatic C-H bonds to form one or more phenols; and purifying the one or more phenols.
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Page/Page column 9; 10
(2014/10/15)
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- NEW PROCESSES FOR PREPARING 4-SUBSTITUTED IMIDAZOLES
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There is provided a novel process for the preparation of a compound of formula (I), (Formula (I)). There is also provided novel processes to intermediates of the compound of formula (I), as well as novel intermediates themselves.
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Page/Page column 40; 41
(2013/03/26)
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- Metal-free oxidation of aromatic carbon-hydrogen bonds through a reverse-rebound mechanism
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Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Bronsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity.
- Yuan, Changxia,Liang, Yong,Hernandez, Taylor,Berriochoa, Adrian,Houk, Kendall N.,Siegel, Dionicio
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p. 192 - 196
(2013/08/23)
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- Chemo- and regioselective direct hydroxylation of arenes with hydrogen peroxide catalyzed by a divanadium-substituted phosphotungstate
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Peroxide in, phenol out: The catalyst [-PW10O38V 2(μ-OH)2]3- showed high activity in the hydroxylation of various aromatic compounds with aqueous H2O 2. The system was regioselective, producing para-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain Ca spa 3-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Copyright
- Kamata, Keigo,Yamaura, Taiyo,Mizuno, Noritaka
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supporting information; experimental part
p. 7275 - 7278
(2012/08/28)
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- One-pot synthesis of phenols by hydroxylation of aromatics with hydroxylamine
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In this study, a new approach for one-pot synthesis of phenols is presented, i.e., benzene, ethylbenzene, and xylene were hydroxylated with hydroxylamine to give the corresponding phenols in good yield using molybdenum as a key catalyst.
- Zhang, Dongsheng,Gao, Liya,Xue, Wei,Zhao, Xinqiang,Wang, Shufang,Wang, Yanji
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scheme or table
p. 369 - 371
(2012/06/01)
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- Synthesis, structural properties, and catalytic behavior of Cu-BTC and mixed-linker Cu-BTC-PyDC in the oxidation of benzene derivatives
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Mixed-linker metal-organic frameworks based on the Cu-BTC structure have been synthesized in which the benzene-1,3,5-tricarboxylate (BTC) linkers have been partially replaced by pyridine-3,5-dicarboxylate (PyDC). X-ray-based techniques (powder XRD and XAS), thermal analysis, and infrared spectroscopy proved that a desired amount of PyDC (up to 50%) can be incorporated without changing significantly the crystal structure. The pyridine unit can be seen as a defect site in the local coordination environment of the dimeric copper units, which is significantly altering their electronic structure and the catalytic properties. Both Cu-BTC and the mixed Cu-BTC-PyDCs catalyze the demanding direct hydroxylation of toluene both in acetonitrile and in neat substrate. Different selectivity toward the desired ortho- and para-cresol and other oxidation products (benzaldehyde, benzyl alcohol, methylbenzoquinone) was observed for Cu-BTC and the Cu-BTC-PyDCs, respectively. Leaching tests and comparison with homogeneously dissolved Cu catalysts indicate mainly a heterogeneous reaction pathway.
- Marx, Stefan,Kleist, Wolfgang,Baiker, Alfons
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experimental part
p. 76 - 87
(2011/08/04)
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- The balance of acid, basic and redox sites in Mg/Me-mixed oxides: The effect on catalytic performance in the gas-phase alkylation of m-cresol with methanol
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The reactivity of Mg/Me-mixed oxides (Me = Fe, Cr, Al) in m-cresol gas-phase methylation with methanol was studied, with the aim of finding relationships between catalytic performance and surface/bulk features. All systems exhibit similar surface properties (basically due to the presence of basic and Lewis-type acid sites), but the presence of extra cations in the MgO framework affects greatly the products obtained in the mentioned catalytic reaction, depending on the possible co-presence of redox capacity. In particular, (i) the Mg/Al/O system, characterized by no redox capacity, shows catalytic behaviour quite similar to that of conventional Bronsted-type acid catalysts, though with the advantage of exhibiting almost no deactivation during use (a rather common problem for acid catalysts activating methanol for phenol attack); (ii) the Mg/Cr/O catalyst shows a reactivity typical of a basic catalyst, with high chemo- and regio-selectivity and the favoured formation of 2,5-dimethylphenol; (iii) the Mg/Fe/O system presents a catalytic behaviour closer to that of Mg/Cr/O, if referred to the distribution of phenolic products, but it also exhibits a better activity in methanol dehydrogenation to formaldehyde (that is the true electrophilic reactant for m-cresol ring methylation), and in the decomposition of formaldehyde into light compounds. This behaviour causes a poor selectivity to dimethylphenols with respect to converted methanol, whereas the selectivity with respect to converted m-cresol is not different from that shown by Mg/Cr/O system.
- Crocella,Cerrato,Magnacca,Morterra,Cavani,Cocchi,Passeri,Scagliarini,Flego,Perego
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body text
p. 125 - 135
(2010/06/12)
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- Synthesis of phenol, aromatic ether, and benzofuran derivatives by copper-catalyzed hydroxylation of aryl halides
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A smooth operator: The copper-catalyzed synthesis of phenols from aryl halides was carried out under relatively mild reaction conditions. Alkyl aryl ethers and benzofurans could also be prepared smoothly by one-pot domino protocols based on hydroxylation of aryl iodides (see scheme).
- Zhao, Dongbing,Wu, Ningjie,Zhang, Shuai,Xi, Peihua,Su, Xiaoyu,Lan, Jingbo,You, Jingsong
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supporting information; experimental part
p. 8729 - 8732
(2010/01/16)
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- Reaction of atomic carbon with isomeric cresols
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Reaction of atomic carbon with isomeric cresols generates methyltropones and xylenols. Methyltropone to xylenol ratio was found to be highest for m-cresol and lowest for p-cresol. Stability of singlet carbenes produced after insertion of atomic carbon int
- Soekmen, Ilkay,Ece, Abdulilah,Duez, Buelent,Sevin, Fatma
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experimental part
p. 650 - 653
(2010/06/16)
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- Continuous chemoselective methylation of m-cresol and phenol with supercritical methanol over solid acid and base metal oxide catalysts
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The chemoselective methylation of m-cresol and phenol with supercritical methanol (scCH3OH) promoted by metal oxide catalysts (MgO, ZrO 2, Cs-P-Si and Fe-V/SiO2) was investigated in a continuous flow fixed bed reactor. The use of scCH3OH as a carrier medium led to a significant change in the product selectivity compared to that attained in the gas phase reaction, and caused a marked suppression of the degradation of CH3OH during the reaction, resulting in an improvement in the catalyst lifetime. The chemoselective outcome of the reaction was highly influenced by the acid-base character on the solid catalysts examined under supercritical conditions.
- Oku, Tomoharu,Arita, Yoshitaka,Ikariya, Takao
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p. 1553 - 1557
(2007/10/03)
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- Ortho-alkylation of phenol with methanol using Pb-Cr promoted magnesium oxide catalysts
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In this study, Pb-Cr promoted magnesium oxide catalysts were used to catalyze the ortho-alkylation of phenol in the presence of excess methanol. The Cr/MgO catalyst exhibited a high conversion of phenol and a relatively high selectivity for the ortho-alkylation of phenol. The catalytic activity and the stability of Cr/MgO were improved by the addition of a fairly small amount of Pb. The Pb-Cr/MgO catalyst showed specificity for the ortho-alkylation of phenol, which was proved by a series of phenol derivative reactions with methanol.
- Ke, Jyh-Harng,Zena, Jyh-Myng,Wang, Fey-Long
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p. 1407 - 1410
(2007/10/03)
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- Process for functionalising a phenolic compound carrying an electron-donating group
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The invention concerns a method for functionalizing a phenolic compound bearing an electron-donor group, in said group para position, inter alia a method for the amidoalkylation of a phenolic compound bearing an electron-donor group, and more particularly, a phenolic compound bearing an electron-donor group preferably, in the hydroxyl group ortho position. The method for functionalizing in para position with respect to an electron-donor group carried by a phenolic compound is characterised in that the phenolic compound bearing an electron-donor group is subjected to the following steps: a first step which consists of protecting the hydroxyl group in the form of a sulphonic ester function; a second step which consists in reacting the protected phenolic compound with an electrophilic reagent; optionally, a third step deprotecting the hydroxyl group.
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- Synthesis and spectroscopic characterization of 1-13C- and 4-13C-plastoquinone-9
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This paper presents the synthesis of 1-13C- and 4-13C-plastoquinone-9 and their characterization with NMR spectroscopy and mass spectrometry. The synthetic scheme has been further adapted to introduce 13C-labeled plastoquinones on all individual and on each combination of positions in the quinone ring. Also a two-step scheme is disclosed to prepare unlabeled plastoquinone-9. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Boers, Rutger B.,Randulfe, Yolanda Pazos,Van Der Haas, Hendrikus N. S.,Van Rossum-Baan, Marleen,Lugtenburg, Johan
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p. 2094 - 2108
(2007/10/03)
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- Comparison of cresol transformation on USHY and HZSM-5
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In the commercial synthesis of cresols, the most common processes include the alkylation of phenol with methanol. The cresol (methylphenol) transformation on zeolite USHY was studied and compared with HZSM-5 with different pore size, structure, and different acidity in a flow reactor at 380°C and 0.1 bar. The cresol turnover numbers for USHY were pretty similar, whereas on HZSM-5, the cresols reactivities followed the sequence p- ≥ m- > o-cresol. The cresols reacted over the zeolites mainly through two parallel reactions, isomerization and disproportionation, whose relative importance depends on the catalysts characteristics (pore structure and acidity), on the reacting cresol itself, and on the reaction conditions (temperature, total pressure, reactant partial pressure, etc). The USHY selectivity toward the monomolecular isomerization reaction was by far lower than that of HZSM-5, due to its size/shape selectivity. On USHY and HZSM-5 catalysts, the o-cresol showed higher disproportionation selectivity than the other two cresol isomers, this proportionation occurring via diphenylmethane intermediates. The cresol isomerization selectivity was limited by product desorption even on a large pore zeolite like USHY. The cresol isomer composition at high conversions on USHY was 44, 42, and 14% for o-, m-, and p-cresol, respectively. Xylenols underwent a rapid isomerization once formed.
- Imbert,Guisnet,Gnep
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p. 279 - 286
(2007/10/03)
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- Ytterbium triflate mediated selective deprotection of acetates
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Ytterbium triflate mediated selective deprotection of acetates in isopropyl alcohol at reflux temperature is reported. Unlike hafnium triflate, under the present reaction conditions aryl acetates also undergo deacetylation instead of Fries migration.
- Sharma,Ilangovan
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p. 1963 - 1965
(2007/10/03)
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- Para-hydroxyalkylation of hydroxylated aromatic compounds
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Hydroxylated aromatic compounds devoid of substituents in the para-position to the hydroxyl group thereof are para-hydroxyalkylated, e.g., into optionally substituted p-hydroxymandelic acid compounds, more particularly p-hydroxymandelic acid and 3-methoxy-p-hydroxymandelic acid, by condensing same with an organic carbonyl compound in the presence of a quaternary ammonium hydroxide.
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- Process for the preparation of 2,3-dimethylphenol and of 3,4-dimethylphenol
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In a process for the preparation of mixtures of 2,3-dimethylphenol and 3,4-dimethylphenol a mixture of 2,3-dimethyl-bromobenzene and 3,4-dimethyl-bromobenzene is hydrolized in an aqueous alkaline solution in the presence of a copper compound catalyst of the formula: R represents --O or --OH or a residue of an inorganic or of an organic acid; n is 1 or 2; and m is 0, 1 or 2; the reaction being carried out at a temperature in the range between 200° and 300° C.
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- ORTHO-METHYLATION OF PHENOLS WITH ETHYL(IODOMETHYL)ZINC
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The regioselective ortho-methylation of phenols by in situ generated ethyl(iodomethyl)zinc via an internal alkylation process is described.
- Lehnert, Erich K.,Sawyer, J. Scott,Macdonald, Timothy L.
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p. 5215 - 5218
(2007/10/02)
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- Preparation of and addition of carbanions to 6-methyl-6-nitrocyclohexa-2,4-dienones
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Nitration of 2-methylphenols with nitric acid and trifluoroacetic anhydride in ether at -78 deg C gives 6-methyl-6-nitrocyclohexa-2,4-dienones that can be isolated.Carbanions add to 5,6-dimethyl-6-nitrocyclohexa-2,4-dienone to give the 5-substituted 2,3-dimethyl-2-nitrocyclohex-3-enone anion, which, with additional carbanion, gives the 5-substituted 2,3-dimethylphenoxide anion by elimination of nitrous acid.Key words: nitration, dienone, addition, carbanion, nucleophilic.
- Fischer, Alfred,Henderson, George N.,Sankararaman, S.
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p. 1244 - 1246
(2007/10/02)
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- A quantitative examination of the photoisomerization of some protonated phenols
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The photoisomerization of a series of protonated, methyl substituted phenols to protonated bicyclohexenones has been examined.These reactions, which were carried out in CF3SO3H as a strong acid solvent at ambient temperatures, provide a convenient route to a variety of bicyclohexenones.The quantum yields for these photoisomerizations vary from 0.018 for protonated 3,5-dimethylphenol to 0.65 for protonated 2,6-dimethylphenol.This variation in efficiency can be understood in terms of a competition between ring opening, to regenerate the starting phenol, or cyclopropyl migration, to give product, of aninitially formed intermediate.
- Childs, Ronald F.,George, Baha E.
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p. 1343 - 1349
(2007/10/02)
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- Thermal isomerizations of protonated bicyclohexenones
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The thermal isomerizations of a wide range of protonated methyl substituted bicyclohex-3-en-2-ones to protonated phenols has been examined using triflic acid as a strong acid solvent.The rate constants and activation energies of these isomerization has been determined.The barriers to the isomerizations were shown to be dependent on the number and position of the methyl substituents.The results show that three different mechanisms are needed to account for these isomerizations, two of which involve a preliminary circumambulatory rearrangement prior to ring opening and the other process involving a direct ring opening of the initial protonated bicyclohexenone to give an intermediate meta-protonated phenol.
- Childs, Ronald F.,George, Baha E.
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p. 1350 - 1354
(2007/10/02)
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- Process for treating 2-ethylhexyl p-methoxycinnamate in the presence of a phenol
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A process for treating 2-ethylhexyl p-methoxycinnamic acid ester is described. The process comprises heating, preferably distilling, the ester in the presence of a phenol to insure that the ester is considered Ames negative.
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- Rate and Equilibrium Studies of the Reaction of Oxyanions with 2-Phenyloxazol-5(4H)-one
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Equilibrium constants for the reaction of phenoxide ions with 2-phenyloxazol-5(4H)-one at 25 deg C and 1M ionic strength obey a Broensted relationship (log kOH/kArO = log K' = -173pKArOH - 15.81) and are not subject to steric effects from ortho-substituents.Both forward and reverse rate parameters exhibit steric effects, and the Broensted equations for meta- and para-substituted species are log kOH = -0.81 pKArOH + 9.75, and log kArO = 0.95pKArOH - 6.40.There is no break in the Broensted line in the region of pKArOH 5-11, consistent with a single transition-state.An upward deviation exists for oxyanions with low basicity (pKXOH 5); one of these oxyanions, betaine, has a solvent deuterium oxide isotope effect for its reaction with the oxazolone greater than 2, consistent with a general base mechanism for attack for these species.The results for nucleophilic attack of phenolate anions are in agreement with a concerted displacement at the carbonyl group.
- Chrystiuk, Edwin,Jusoh, Adelina,Santafianos, Dino,Williams, Andrew
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p. 163 - 168
(2007/10/02)
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- The Gas-Flow Thermolysis of 1-Isobutenyl Alkynyl and 2-Methylphenyl Alkynyl Ketones. Synthesis of Methylenomycin B
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The gas-flow thermolysis of 1-isobutenyl alkynyl or 2-methyphenyl alkynyl ketones were found to lead to phenols and cyclopentenones or to naphthols and indanones, respectively.These conversions involve two cyclization processes so far unknown with α-alkynones; they are interpreted as intramolecular additions of an allylic or a benzylic C,H bond to a triple bond which may occur in two directions.In addition, the cyclopentenones formed by the α-alkynone cyclization, a known carbene process yielding 5-rings, were also found.The available evidence ruled out a carbene process yielding 6-rings.The addition process yielding 5-rings was applied to a short (but low yield) synthesis of methylenomycin B.
- Koller, Manuel,Karpf, Martin,Dreiding, Andre S.
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p. 560 - 579
(2007/10/02)
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- THE FLOW THERMOLYSES OF 1-ISOBUTENYL ALKYNYL- AND 2-METHYLPHENYL ALKYNYL KETONES. SYNTHESIS OF METHYLENOMYCIN B
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The gas flow thermolyses of 1-isobutenyl alkynyl and 2-methylphenyl alkynyl ketones were found to lead to phenols and to cyclopentenones.The results are explained by a 5-ring carbene process (the known α-alkynone cyclization) and a 6-ring as well as a 5-ring addition process.The latter two (novel) processes are thought to be intramolecular "C-H to CC additions" in two directions.The 5-ring addition process was used in a short (but low yield) synthesis of methylenomycin B.
- Koller, Manuel,Karpf, Martin,Dreiding, Andre S.
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