3602-55-9Relevant articles and documents
Size effect of gold nanoparticles supported on carbon nanotube as catalysts in selected organic reactions
Jawale, Dhanaji V.,Gravel, Edmond,Geertsen, Valérie,Li, Haiyan,Shah, Nimesh,Kumar, Rahul,John, Jubi,Namboothiri, Irishi N.N.,Doris, Eric
, p. 6140 - 6145 (2014)
Carbon nanotube-supported gold nanoparticles of different sizes (diameter of 3 or 20 nm) were evaluated as catalysts in four selected organic transformations. The nanohybrids were shown to efficiently catalyze the investigated reactions, regardless of the size of the supported gold nanoparticles. However, some differences were observed as regards turnover frequency values although size effect turned out to be less significant when only gold surface atoms were considered.
Tert -butylhydroquinone as a spectroscopic probe for the superoxide radical scavenging activity assay of biological samples
Bekdeser, Burcu,Oezyuerek, Mustafa,Gueclue, Kubilay,Apak, Resat
, p. 5652 - 5660 (2011)
As a more convenient and less costly alternative to electron spin resonance (ESR) and nonspecific nitroblue tetrazolium (NBT) and cytochrome c assays of superoxide radical (SR, O2?-) detection, a novel probe, tert-butylhydroquinone (TBHQ), is introduced for SR nonenzymatically generated in the phenazine methosulfate-β-nicotinamide adenine dinucleotide (PMS-NADH) system. SR attacks both TBHQ and SR scavengers incubated in solution for 30 min where scavengers compete with TBHQ for the O2 ?- produced. TBHQ, but not its O2?- oxidation product, tert-butyl-1,4-benzoquinone (TBBQ), is responsive to the CUPRAC (cupric reducing antioxidant capacity) spectrophotometric assay. The CUPRAC absorbance of the ethyl acetate extract of the incubation solution arising from the reduction of Cu(II)-neocuproine reagent by the remaining TBHQ was higher in the presence of O2?- scavengers (due to less conversion to TBBQ), the difference being correlated to the SR scavenging activity (SRSA) of the analytes. With the use of this reaction, a kinetic approach was adopted to assess the SRSA of amino acids, vitamins, and plasma and thiol antioxidants. This assay, applicable to small-molecule antioxidants and tissue homogenates, proved to be efficient for cysteine, uric acid, and bilirubin, for which the widely used NBT test is nonresponsive. Thus, conventional problems of NBT assay arising from formazan insolubility and direct reduction of NBT by tested scavengers were overcome.
Simple homopolymer-incarcerated gold nanoclusters prepared by self-assembled encapsulation with aluminum reagents as crosslinkers: Catalysts for aerobic oxidation reactions
Yasukawa, Tomohiro,Miyamura, Hiroyuki,Kobayashi, Shu
, p. 50 - 52 (2015)
Simple homopolymer-incarcerated gold nanocluster catalysts were developed using a self-assembled encapsulation strategy. In this method, Red-Al acting as a reductant also played the role of an inter-crosslinker via the formation of tetraalkoxyaluminate with the hydroxy groups in a homopolymer. Gold nanoclusters could be immobilized at high loadings without aggregation, and high catalytic activities were observed in several aerobic oxidation reactions.
Some kinetic properties of deoxytyrosinase
Munoz-Munoz,Garcia-Molina,Garcia-Ruiz,Varon,Tudela,Garcia-Canovas,Rodriguez-Lopez
, p. 173 - 182 (2010)
Passing a nitrogen stream over a preparation of oxy-tyrosinase (Eox) gives rise to the relaxed deoxy-tyrosinase form (EdR), which, under anaerobic conditions, slowly transforms into tense deoxy-tyrosinase (EdT). In the presence of oxygen, regeneration of the form Eox from EdR is rapid but from EdT it is a slow process. However, when two substrates (oxygen/o-diphenol or oxygen/monophenol) are simultaneously added, both the EdR and EdT forms rapidly revert to the active Eox form, pointing to a synergistic effect of both substrates. However, the activity obtained in the case of EdT is less than that of the native enzyme and of the enzyme that can be generated rapidly by pre-incubation with oxygen of the EdR recently formed by passage of the nitrogen stream, or that generated slowly by pre-incubating the EdT form with oxygen. Although the Vmax of the forms EdR and EdT are very similar, the Michaelis constant of the latter is higher. The kinetic properties of EdR are similar to those of the native enzyme. The behaviour of the monophenols is similar to that of the o-diphenols, although, while the latter inactivate the enzyme under anaerobic conditions, the former protect it from inactivation. The pH affects the transition from EdR to EdT, which is more rapid at pH 6.5, at which value the kinetic properties of the native enzyme and of EdT are similar and the oxygenation step in which EdT regenerates Eox is more rapid. At pH values other than 6.5, the transition of EdR to EdT takes place slowly. From a study of the effect of pH on the transition of EdR to EdT and of the re-oxygenation of EdT to Eox, the possible existence of two apparent pKas, with approximate values of 6.0 and 6.8, may be surmised. At high pH, the enzyme contains two acid/base groups carrying negative charges, which repel (pH > 6.8) or two positive charges (at pH 6.0), which also repel, while at ～pH 6.5 one positive and one negative group exists, which prevents the separation of the two copper atoms.
Aerobic Oxidation of Dihydroxyarenes Substrates Catalyzed by Polymer-Supported RuII-Pheox/Silica-Gel: A Beneficial Route for Purification of Industrial Water
Abu-Elfotoh, Abdel-Moneim
supporting information, p. 236 - 243 (2022/04/09)
A broad class of dihydroxyarenes were easily oxidized by aerobic oxygen to quinone products in excellent yields under the catalytic effect of polymer-supported RuII-Pheox/silica-gel catalyst. By using this combined catalyst, hydroquinone and catechol derivatives with electron-donating groups were easily oxidized by molecular oxygen to quinone products in 90% to >99% yield, while in the case of electron-withdrawing group, only 70% was obtained. The biologically useful 1,4-Naphthoqinone products were obtained in 83% to 90%. The catalyst was easily obtained and reused many times without a significant decrease in reactivity. Interestingly, a sample of industrial water contaminated with phenolic compounds was subjected to aerobic oxidation by using this catalyst, and the resultant quinones were detected within one day and the catalyst was removed and reused several times with different contami-nating samples with the same efficiency. Other catalytic oxidations by using this promising catalyst were investigated.
Benzoquinone Cocatalyst Contributions to DAF/Pd(OAc)2-Catalyzed Aerobic Allylic Acetoxylation in the Absence and Presence of a Co(salophen) Cocatalyst
Kozack, Caitlin V.,Tereniak, Stephen J.,Jaworski, Jonathan N.,Li, Bao,Bruns, David L.,Knapp, Spring M. M.,Landis, Clark R.,Stahl, Shannon S.
, p. 6363 - 6370 (2021/05/29)
Palladium(II)-catalyzed allylic acetoxylation has been the focus of extensive development and investigation. Methods that use molecular oxygen (O2) as the terminal oxidant typically benefit from the use of benzoquinone (BQ) and a transition-metal (TM) cocatalyst, such as Co(salophen), to support oxidation of Pd0 during catalytic turnover. We previously showed that Pd(OAc)2 and 4,5-diazafluoren-9-one (DAF) as an ancillary ligand catalyze allylic oxidation with O2 in the absence of cocatalysts. Herein, we show that BQ enhances DAF/Pd(OAc)2 catalytic activity, nearly matching the performance of reactions that include both BQ and Co(salophen). These observations are complemented by mechanistic studies of DAF/Pd(OAc)2 catalyst systems under three different oxidation conditions: (1) O2 alone, (2) O2 with cocatalytic BQ, and (3) O2 with cocatalytic BQ and Co(salophen). The beneficial effect of BQ in the absence of Co(salophen) is traced to the synergistic roles of O2 and BQ, both of which are capable of oxidizing Pd0 to PdII. The reaction of O2 generates H2O2 as a byproduct, which can oxidize hydroquinone to quinone in the presence of PdII. NMR spectroscopic studies, however, show that hydroquinone is the predominant redox state of the quinone cocatalyst in the absence of Co(salophen), while inclusion of Co(salophen) maintains oxidized quinone throughout the reaction, resulting in better reaction performance.
Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
, p. 8591 - 8603 (2021/11/17)
Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
Oxidative radical coupling of hydroquinones and thiols using chromic acid: One-pot synthesis of quinonyl alkyl/aryl thioethers
Adarsh Krishna, T. P.,Chinnasamy, Suresh,Ilangovan, Andivelu,Pandaram, Sakthivel
, p. 19454 - 19462 (2020/06/04)
An efficient, simple and practical protocol for one-pot sequential oxidative radical C-H/S-H cross-coupling of thiols with hydroquinones (HQs) and oxidation leading to the formation of quinonyl alkyl/aryl thioethers using H2CrO4was developed. This cross-coupling of thiyl and aryl radicals offers mono thioethers in good to moderate yield and works well with a wide variety of thiols. Similarly, this method works well for coupling of 2-amino thiophenol and HQs to form phenothiazine-3-ones5a-c. C-S bond formationviathioether synthesis was observed using a chromium reagent for the first time. Theoretical studies on the pharmacokinetic properties of compounds5a-crevealed that due to drug-like properties, compound5bstrongly binds with Alzheimer's disease (AD) associated AChE target sites.
Tert-butylhydroquinone preparation method
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Paragraph 0025-0031, (2020/04/02)
The invention relates to the technical field of organic synthesis, and relates to a tert-butylhydroquinone preparation method, which comprises: 1) sequentially adding 2-tert-butylphenol, a transitionmetal copper (I) cooperation compound and a solvent to a high pressure reaction kettle, introducing oxygen to achieve a specified pressure, heating and stirring to a specified temperature, and carrying out a reaction for 0.5-3 h; 2) after the reaction is finished, evaporating out the solvent, washing the residual solid with a solvent, and carrying out steam stripping to obtain 2-tert-butyl p-benzoquinone; 3) sequentially adding the 2-tert-butyl p-benzoquinone obtained in the step 1), a catalyst and a solvent into a high-pressure reaction kettle, introducing hydrogen to a specified pressure after gas exchange is completed, heating and stirring to a specified temperature, and carrying out a reaction for 0.5-3 hours; and 4) after the reaction is finished, evaporating out the solvent, and rectifying to obtain the tert-butylhydroquinone product. According to the invention, the method has the advantages of high product yield, convenient operation, cheap raw materials, economy and reliability, and is suitable for large-scale production.
Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria
Bruns, David L.,Musaev, Djamaladdin G.,Stahl, Shannon S.
supporting information, p. 19678 - 19688 (2020/12/18)
Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.
