Showing papers on "Reagent published in 2013"
TL;DR: Analyzing carbon cathodes, cycled in Li-O(2) cells between 2 and 4 V, using acid treatment and Fenton's reagent, and combined with differential electrochemical mass spectrometry and FTIR demonstrates the following: Carbon is relatively stable below 3.5 V, but is unstable on charging above 3.
Abstract: Carbon has been used widely as the basis of porous cathodes for nonaqueous Li–O2 cells. However, the stability of carbon and the effect of carbon on electrolyte decomposition in such cells are complex and depend on the hydrophobicity/hydrophilicity of the carbon surface. Analyzing carbon cathodes, cycled in Li–O2 cells between 2 and 4 V, using acid treatment and Fenton’s reagent, and combined with differential electrochemical mass spectrometry and FTIR, demonstrates the following: Carbon is relatively stable below 3.5 V (vs Li/Li+) on discharge or charge, especially so for hydrophobic carbon, but is unstable on charging above 3.5 V (in the presence of Li2O2), oxidatively decomposing to form Li2CO3. Direct chemical reaction with Li2O2 accounts for only a small proportion of the total carbon decomposition on cycling. Carbon promotes electrolyte decomposition during discharge and charge in a Li–O2 cell, giving rise to Li2CO3 and Li carboxylates (DMSO and tetraglyme electrolytes). The Li2CO3 and Li carboxylat...
1,124 citations
TL;DR: The synergy between the internal and external functionalities of the micromotors results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water.
Abstract: We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxida...
473 citations
TL;DR: A visible-light-mediated hydrotrifluoromethylation of unactivated alkenes that uses the Umemoto reagent as the CF(3) source and MeOH as the reductant is disclosed, characterized by its operational simplicity and functional group tolerance.
Abstract: A visible-light-mediated hydrotrifluoromethylation of unactivated alkenes that uses the Umemoto reagent as the CF3 source and MeOH as the reductant is disclosed. This effective transformation operates at room temperature in the presence of 5 mol % Ru(bpy)3Cl2; the process is characterized by its operational simplicity and functional group tolerance.
358 citations
TL;DR: In this article, a critical review of transition-metal-free nitroxide-catalyzed aerobic oxidation processes is presented, along with the relevant physical properties of nitroxides, their application as oxidation catalysts by using dioxygen as a reagent or terminal oxidant.
259 citations
TL;DR: A copper-catalyzed decarboxylative trifluoromethylation of various α,β-unsaturated carboxylic acids by using a stable and inexpensive solid, sodium trif LUM, Langlois reagent, was developed.
245 citations
TL;DR: In this article, a new method for the oxidative radical azidation of alkenes relies on an azide in combination with a hypervalent iodine reagent, which was shown to be effective in the case of a single alken.
Abstract: This new method for the oxidative radical azidation of alkenes relies on an azide in combination with a hypervalent iodine reagent.
231 citations
TL;DR: Various features of selectivity and reactivity suggest the formation of an organometallic intermediate via rate-determining C-H bond cleavage rather than a free-radical-type reaction pathway.
Abstract: Directed C(sp3)–H bond functionalization has been studied mainly by using precious metal catalysts, such as Pd, Ru, Rh, and Ir under harsh conditions. Generally, these metal-catalyzed C–H functionalization reactions are based on the formation of a C(sp3)-metallacycle. Iron-catalyzed C(sp3)–H functionalization has been studied mainly using radical processes. Functionalization of an unactivated C(sp3)–H bond via formation of a ferracycle intermediate is limited to stoichiometric reactions. We report here an iron/biphosphine-catalyzed directed arylation of a C(sp3)–H bond in an aliphatic carboxamide with an organozinc reagent in high yield under mild oxidative conditions. The choice of the directing group and of the biphosphine ligand was crucial for the success of this reaction. This reaction shows selectivity for a primary C–H over a secondary one and is sensitive to steric factors on both the amide and the Grignard reagent. Various β-arylated aliphatic carboxamides can be readily prepared by using this method.
230 citations
TL;DR: A series of α-SCF3 esters that bear a quaternary carbon stereogenic center were obtained with excellent yield and enantioselectivity and can be readily converted into valuable α- SCF3 β-hydroxyesters.
Abstract: Cinchona alkaloid catalysts in combination with air- and moisture-stable N-trifluoromethylthiophthalimide as electrophilic SCF3 source enabled the catalytic enantioselective trifluoromethylsulfenylation. Thus, a series of α-SCF3 esters that bear a quaternary carbon stereogenic center were obtained with excellent yield and enantioselectivity. Moreover, the products can be readily converted into valuable α-SCF3 β-hydroxyesters.
223 citations
TL;DR: In this article, a simple chemical method using hydrazine hydrate as the main reagent was firstly used to modify graphite felt as cathode for efficient electro-Fenton process.
191 citations
TL;DR: The first example of Fe-catalyzed enantioselective azidations of β-keto esters and oxindoles using a readily available N3-transfer reagent is reported.
Abstract: The first example of Fe-catalyzed enantioselective azidations of β-keto esters and oxindoles using a readily available N3-transfer reagent is reported. A number of α-azido-β-keto esters were obtained with up to 93% ee, and this methodology also generates 3-substitued 3-azidooxindoles with high enantioselectivities (up to 94%).
188 citations
TL;DR: A powerful strategy that is based on self-propelled micromotors, for a high-yielding accelerated oxidative decontamination of chemical threats using low peroxide levels and no external agitation is described.
Abstract: Rapid field conversion of chemical weapons into non-toxic products is one of the most challenging tasks in weapons of mass destruction (WMD) science. This is particularly the case for eliminating stockpiles of chemical warfare agents (CWAs) in remote storage field locations, where the use of large quantities of decontaminating reagents, long reaction times, and controlled mechanical agitation is impossible or undesired. New efficient “clean” technologies and (bio)chemical processes are thus sought for detoxifying stored agents, counteracting nerve-agent attacks, and decommissioning chemical weapons. Environmentally friendly solutions of hydrogen peroxide, combined with suitable activators (e.g., bicarbonate), have been shown to be extremely useful for decontaminating a broad spectrum of CWAs to yield nontoxic products. These peroxide-based systems, which rely on the in situ generation of OOH nucleophiles, have recently replaced chlorine-based bleaching processes, which produce undesirable products, and have thus led to effective decontamination of the chemical agents GB (Sarin, isopropyl methylphosphonofluoridate), VX ((S)-[2-(diisopropylamino)ethyl] O-ethyl methylphosphonothioate), GD (Soman, pinacolyl methylphosphonofluoridate), and HD (sulfur mustard). Yet, such an oxidative treatment commonly requires high peroxide concentrations (20–30%; approaching a stoichiometry of 1:50), along with prolonged operation and/or mechanical agitation. Such reaction conditions are not suitable or not desired for eliminating stockpiles of CWAs in remote field settings or hostile storage locations, as large quantities of the reagents may not be transportable on military aircrafts and require special packaging and handling. The efficient elimination of chemical-weapon stockpiles in field locations thus remains a major challenge to the chemistry and defense communities. Herein, we describe a powerful strategy that is based on self-propelled micromotors, for a high-yielding accelerated oxidative decontamination of chemical threats using low peroxide levels and no external agitation. Functionalized synthetic micromotors have recently demonstrated remarkable capabilities in terms of isolation and transport for diverse biomedical and environmental applications, but not in connection to increasing the yield and speed of chemical reactions. The new motor-based method relies on the use of peroxide-driven microtubular engines for the efficient selfmixing of a remediation solution, which dramatically accelerates the decontamination process. Fluid mixing is extremely important for enhancing the yield and speed of a wide range of chemical processes, including decontamination reactions, where quiescent conditions lead to low reaction efficiency and long operations. The observed mixing, which is induced by the peroxide-driven micromotor, is analogous to that reported for the motility of E. coli bacteria, where a large-scale collective motion has been shown to enhance diffusion processes. Enhanced diffusion of passive tracers has also been observed in the presence of catalytic nanowire motors. Although the new micromotor strategy presented herein was applied to the accelerated, high-yielding, and simplified decontamination of organophosphate (OP) nerve agents, the concept could have broad implications for enhancing the efficiency and speed of a wide range of chemical processes in the absence of external agitation. The concept of the micromotor/peroxide-based decontamination of chemical threats is illustrated in Figure 1. This new strategy relies on micromotors without mechanical stirring (Figure 1A). A known number of micromotors were placed in a nerve-agent-contaminated solution, along with hydrogen peroxide (used as the oxidizing agent as well as the micromotor fuel), the peroxide activator (NaHCO3 or NaOH), and the surfactant sodium cholate (NaCh), which was essential for bubble generation. The oxidative conversion of the OP nerve agent into para-nitrophenol (p-NP) was achieved under mild quiescent conditions that involve the in situ generation of OOH nucleophiles with no external stirring (Figure 1B). The decrease in concentration of the OP [*] Dr. J. Orozco, G. Cheng, D. Vilela, Dr. S. Sattayasamitsathit, Prof. R. Vazquez-Duhalt, Dr. G. Vald s-Ram rez, Dr. O. S. Pak, Prof. J. Wang Departments of Nanoengineering and Mechanical Engineering University of California San Diego La Jolla, CA 92093 (USA) E-mail: josephwang@ucsd.edu G. Cheng, Prof. C. Kan Tsinghua University, Beijing, 100084 (China) D. Vilela, Prof. A. Escarpa University of Alcal 28871 Alcal de Henares (Spain)
TL;DR: Yields are good to excellent, and for cyclic systems azidooxygenation occurs with excellent diastereoselectivity, and the C-radical generated after N3-radical addition is efficiently trapped by in situ generated TEMPO.
Patent•
30 Oct 2013
TL;DR: Improved methods and apparatuses for removing residue from the interior surfaces of the deposition reactor are provided in this article, which involve increasing availability of cleaning reagent radicals inside the deposition chamber by generating cleaning reagents in a remote plasma generator and then further delivering in-situ plasma energy while the cleaned reagent mixture is introduced into the deposition room.
Abstract: Improved methods and apparatuses for removing residue from the interior surfaces of the deposition reactor are provided. The methods involve increasing availability of cleaning reagent radicals inside the deposition chamber by generating cleaning reagent radicals in a remote plasma generator and then further delivering in-situ plasma energy while the cleaning reagent mixture is introduced into the deposition chamber. Certain embodiments involve a multi-stage process including a stage in which the cleaning reagent mixture is introduced at a high pressure (e.g., about 0.6 Torr or more) and a stage the cleaning reagent mixture is introduced at a low pressure (e.g., about 0.6 Torr or less).
TL;DR: A novel Pd-catalyzed double C-S bond formation coupling reaction has been developed that provides an efficient method for the synthesis of substituted 1,4-benzothiazine derivates, which are structural elements of numerous bioactivity molecules rendering this protocol attractive to both synthetic and medicinal chemistry.
TL;DR: A multitalented system: N-migratory oxytrifluoromethylation and one-pot three-component reactions of allylamines as well as the aminotrifluorsensation of alkenyl amines all proceeded efficiently in the presence of the Togni reagent and CuI to afford a variety of β-trifloromethylamine derivatives.
Abstract: A multitalented system: N-migratory oxytrifluoromethylation and one-pot three-component reactions of allylamines as well as the aminotrifluoromethylation of alkenyl amines all proceeded efficiently in the presence of the Togni reagent (1) and CuI to afford a variety of β-trifluoromethylamine derivatives (see scheme).
TL;DR: An amine-N-oxide-ligated palladium complex, in conjunction with a silver cocatalyst, catalyzes imidation of arenes by the reagent N-fluorobenzenesulfonimide, requiring no coordinating directing group on the substrate, and giving synthetically useful yields with only 1 equiv of arene.
Abstract: An amine-N-oxide-ligated palladium complex, in conjunction with a silver cocatalyst, catalyzes imidation of arenes by the reagent N-fluorobenzenesulfonimide. The reaction enables imidation of a variety of arenes at or below room temperature, requires no coordinating directing group on the substrate, and gives synthetically useful yields with only 1 equiv of arene. Mechanistic data implicate an unusual mechanism devoid of commonly invoked organometallic intermediates: oxidation of the Pd catalyst occurs as the turnover-limiting step, while C–H bond functionalization occurs subsequently at a high oxidation state of the catalyst.
TL;DR: Substantial progress has recently been made in the development of trifluoromethylation reactions that allow the selective introduction of CF3 groups into functionalized, late-stage synthetic intermediates.
Abstract: The development of methods for the introduction of trifluoromethyl groups into functionalized molecules is of great importance due to their presence in many top-selling pharmaceuticals, agrochemicals, and functional materials Trifluoromethyl groups are known to impart desirable properties, such as higher metabolic stability, increased lipophilicity, and stronger dipole moments to druglike molecules Celecoxib, dutasteride, fluoxetine, and sitagliptin are some examples of top-selling pharmaceuticals featuring trifluoromethyl groups, and beflubutamid, diflufenican, and norfluazon examples of agrochemicals However, traditional methods to access benzotrifluorides, for example, the Swarts reaction, typically require harsh conditions and have a low substrate scope, so that they are confined to the beginning of a synthetic sequence (Scheme 1a) Building on pioneering work on Cu– and Pd–perfluoroalkyl complexes by McLoughlin, Yagupolskii, Burton, Chambers, Grushin, and others, substantial progress has recently been made in the development of trifluoromethylation reactions that allow the selective introduction of CF3 groups into functionalized, late-stage synthetic intermediates A wealth of new reactions has been disclosed, which can be roughly divided into five categories (Scheme 1b–f) The first are couplings of aryl halides with nucleophilic CF3 reagents (reaction type b), usually copper–CF3 complexes in stoichiometric amounts These complexes may also be generated in situ from copper salts and Ruppert s reagent (CF3SiMe3), [7] fluoroform, potassium (trifluoromethyl)trimethoxyborate, trifluoroacetate salts, methyl trifluoroacetate, or fluorosulfonyldifluoroacetic acid Grushin, Sanford, and Buchwald also disclosed trifluoromethylations of aryl halides based on palladium complexes Palladium complexes also promote C H functionalizations of arenes with trifluoromethylating reagents (reaction type c) Examples are the ortho-trifluoromethylation of donor-substituted arenes with Umemoto s reagent described by Yu et al and the Pd-catalyzed coupling of arenes with perfluoroalkyl iodides reported by Sanford et al C H trifluoromethylations of heteroarenes have recently been reported also with nucleophilic trifluoromethylation reagents under oxidative conditions Examples of couplings of aryl nucleophiles with electrophilic CF3 sources (reaction type d) include the coupling of arylboronic acids with Togni s and Umemoto s reagent disclosed by Shen and Liu, respectively Sanford et al employed a copper/ruthenium photocatalyst system to promote a radical trifluoromethylation of boronic acids The copper-catalyzed syntheses of benzotrifluorides from boronic acids and CF3SiMe3 or K [CF3B(OMe)3] developed by Qing et al and ourselves exemplify oxidative couplings of aryl nucleophiles with nucleophilic CF3 reagents (reaction type e) The radical trifluoromethylation of arenes (reaction type f) was pioneered by Langlois Baran and MacMillan recently reported modern variants of this reaction concept based on peroxide or ruthenium initiators From a practical standpoint, nucleophilic reagents are appealing for the introduction of trifluoromethyl groups for the following reasons CF3SiMe3 and K [CF3B(OMe)3] are available in large quantities for a reasonable price, and are easy to store and handle They are accessible not only from halofluorocarbons, but also from fluoroform, a by-product in the production of Teflon One of the most widely used methods for the introduction of halides and related nucleophiles is the Sandmeyer reaction Aromatic amines, which are available in great structural diversity, are diazotized using, for example, NaNO2 or organic nitrites Upon treatment with the appropriate copper(I) halides, nitrogen gas is released, and a halide group is installed regiospecifically in the position Scheme 1 Strategies for the introduction of trifluoromethyl groups
TL;DR: In this paper, a novel reducing reagent, Lawesson's reagent (LR), is used to directly reduce graphene oxide (GO) films and single GO sheets and obtain highly conductive GOLR films.
Abstract: A novel reducing reagent, Lawesson's reagent (LR), is used to directly reduce graphene oxide (GO) films and single GO sheets. The as-prepared reduced graphene oxide (GOLR) is fully characterized by XPS, Raman, FTIR, 13C NMR and XRD. Most of the oxygen-containing groups are efficiently removed by LR and the conjugated graphene networks are restored. Highly conductive GOLR films and sheets are obtained. As a proof of concept, thin film field-effect transistors based on pentacene using patterned GOLR films as electrodes are fabricated and show high performances. Common cotton threads coated with GOLR can be used as flexible connecting wires to illuminate commercial light-emitting diodes. After low temperature annealing, such as 300 °C, higher conductivity and mobility of GOLR are obtained due to the removal of additional oxygen groups and better ordering of graphene sheets.
TL;DR: An efficient method for the synthesis of enantioenriched 1,1-diarylalkanes from readily available racemic benzylic alcohols is developed and has been applied to a gram-scale synthesis of a precursor to Zoloft.
Abstract: A tertiary stereogenic center that bears two different aryl substituents is found in a variety of bioactive compounds, including medicines such as Zoloft and Detrol. We have developed an efficient method for the synthesis of enantioenriched 1,1-diarylalkanes from readily available racemic benzylic alcohols. Formation of a benzylic mesylate (which is not isolated), followed by treatment with an arylzinc reagent, LiI, and a chiral nickel/bis(oxazoline) catalyst, furnishes the Negishi cross-coupling product in high ee and good yield. A wide array of functional groups (e.g., an aryl iodide, a thiophene, and an N-Boc-indole) are compatible with the mild reaction conditions. This method has been applied to a gram-scale synthesis of a precursor to Zoloft.
TL;DR: In this article, an environmental, economic and highly effective method for carbon fiber hydroxylated-functionalization based on Fenton's reagent treatment is used to improve the electrochemical activity of graphite felt (GF) as the positive electrode in all vanadium redox flow battery (VRFB).
TL;DR: The synthesis and characterization of the air-stable nickel(II) complex trans-(PCy(2)Ph)(2)Ni(o-tolyl)Cl is described in conjunction with an investigation of its use for the Mizoroki-Heck-type, room temperature, internally selective coupling of substituted benzyl chlorides with terminal alkenes.
Abstract: The synthesis and characterization of the air-stable nickel(II) complex trans-(PCy2Ph)2Ni(o-tolyl)Cl is described in conjunction with an investigation of its use for the Mizoroki–Heck-type, room temperature, internally selective coupling of substituted benzyl chlorides with terminal alkenes. This reaction, which employs a terminal alkene as an alkenylmetal equivalent, provides rapid, convergent access to substituted allylbenzene derivatives in high yield and with regioselectivity greater than 95:5 in nearly all cases. The reaction is operationally simple, can be carried out on the benchtop with no purification or degassing of solvents or reagents, and requires no exclusion of air or water during setup. Synthesis of the precatalyst is accomplished through a straightforward procedure that employs inexpensive, commercially available reagents, requires no purification steps, and proceeds in high yield.
TL;DR: Simplified syntheses suited for large scale preparations of the two hypervalent iodine reagents 1 and 2 for electrophilic trifluoromethylation are reported, where the stoichiometric oxidants sodium metaperiodate and tert-butyl hypochlorite have been replaced by trichloroisocyanuric acid.
Abstract: Simplified syntheses suited for large scale preparations of the two hypervalent iodine reagents 1 and 2 for electrophilic trifluoromethylation are reported. In both cases, the stoichiometric oxidants sodium metaperiodate and tert-butyl hypochlorite have been replaced by trichloroisocyanuric acid. Reagent 1 is accessible in a one-pot procedure from 2-iodobenzoic acid in 72% yield. Reagent 2 was prepared via fluoroiodane 11 in a considerably shorter reaction time and with no need of an accurate temperature control.
TL;DR: In this article, a mechanochemical approach for the cleavage of β-O-4-linkages in lignin is reported, which is transition metal and solvent free, requires only inexpensive reagents, and tolerates the presence of water and standard reagent impurities.
TL;DR: In this article, a copper/N-heterocyclic carbene catalyzed hydroboration of carbon dioxide has been developed to give a formic acid derivative selectively under mild conditions.
TL;DR: In this article, the contribution of methanol (CH3OH) sacrificing reagent to the photocatalytic evolution of H2 from aqueous solutions has been studied by tracing the reaction of D2O over a Cu/S-TiO2 catalyst under...
Abstract: The contribution of methanol (CH3OH) sacrificing reagent to the photocatalytic evolution of H2 from aqueous solutions has been studied by tracing the reaction of D2O over a Cu/S-TiO2 catalyst under...
TL;DR: The development and characterization of a portable nanoparticle based-assay, similar to a small sensor patch, for rapid and sensitive detection of food antioxidants, based on the use of immobilized ceria nanoparticles, which change color after interaction with antioxidants by means of redox and surface chemistry reactions.
Abstract: Methods and assay for the portable colorimetric detection of an antioxidant in a food sample. According to one aspect the method comprises the steps of providing a colorimetric reagent comprising a plurality of ceria nanoparticles immobilized to a support, contacting the colorimetric reagent with the food sample, and detecting an optical property of the colorimetric reagent, wherein a change in the optical property of the colorimetric reagent is associated with the presence of antioxidant in the food sample, and further wherein the change in the optical property of the colorimetric reagent is dependent upon the concentration of the antioxidant in said food sample.
TL;DR: The efficient azidation of β-keto esters and silyl enol ethers using a benziodoxole-derived azide transfer reagent is reported, achieving in up to quantitative yields in the absence of any catalyst.
TL;DR: The cysteine equivalent thiol content (CETC) values of various biothiols using the DTNB-Au-NP assay were comparable to those of the conventional DTNB assay, showing that the immobilized DTNB reagent retained its reactivity toward thiols.
TL;DR: In this article, a simple, environmentally friendly and cost-effective synthetic method has been developed to prepare highly stable aqueous colloidal solutions of small (2-14 nm) silver nanoparticles using aminocellulose (AMC) as a combined reducing and capping reagent.
TL;DR: A reaction mechanism involving epoxide activation by electrophilic bromine and CO2 activation by an amide is proposed, which results in cyclic carbonate products obtained in good to excellent yield.
Abstract: A continuous method for the formation of cyclic carbonates from epoxides and carbon dioxide (CO2) is described. The catalysts used are inexpensive and effective in converting the reagents to the products in a residence time (t(R)) of 30 min. The cyclic carbonate products are obtained in good to excellent yield (51-92%). On the basis of a series of kinetics experiments, we propose a reaction mechanism involving epoxide activation by electrophilic bromine and CO2 activation by an amide.