Showing papers on "Reagent published in 2008"
TL;DR: An indoline dye (D205), the synthesis method of which is disclosed in this report, gave high-efficiency organic dye-sensitized solar cells (9.52%) using an anti-aggregation reagent (chenodeoxycholic acid).
741 citations
TL;DR: In this paper, a simple and rapid (reaction time ∼1 h) route to Ag nanowires, in which ethylene glycol serves as the solvent and a precursor to the reducing agent.
Abstract: The presence of various ions has been shown to have a strong impact on the shape and size of silver nanostructures produced via the polyol reduction of AgNO3. Here we report a simple and rapid (reaction time ∼1 h) route to Ag nanowires, in which ethylene glycol serves as the solvent and a precursor to the reducing agent. The reaction could be performed in disposable glass vials, with all the reagents being delivered using pipettes. In addition to the use of poly(vinyl pyrrolidone) as a stabilizer, copper (I) or copper (II) chloride had to be added to the reaction to reduce the amount of free Ag+ during the formation of initial seeds and scavenge adsorbed oxygen from the surface of the seeds once formed. In doing so, Ag nanowires were grown preferentially.
537 citations
382 citations
TL;DR: Based on the results of this study, chemical oxidation proved to be an effective remediation technology, amenably applicable for the ex situ remediation of the sediments of concern, and indicated that the optimal oxidant dose must be carefully determined under site-specific conditions.
355 citations
TL;DR: These results demonstrate that reactive nanoiron with good transport properties in water-saturated porous media can be made in a scalable process from inexpensive starting materials by carbothermal reduction.
Abstract: Nanoscale, zero-valent iron is a promising reagent for in situ reduction of a variety of subsurface contaminants, but its utility in full-scale remediation projects is limited by material costs. Iron nanoparticles (20–100 nm diameter) supported on carbon (C−Fe0) were synthesized by reacting iron salts, adsorbed or impregnated from aqueous solutions onto 80 m2/g carbon black, at 600–800 °C under Ar. Similar products were obtained by heating the reactants under air in a covered alumina crucible. X-ray powder diffraction patterns show that Fe3O4 particles are formed at 300–500 °C in the initial stage of the reaction and that these particles are reduced to a mixture of α- and γ-Fe nanoparticles above 600 °C. When C−Fe0 was combined with carboxymethylcellulose in a 5:1 weight ratio in water, the resulting material had similar transport properties to previously optimized nanoiron/polyanion suspensions in water-saturated sand columns. At a 10:3 Fe/Cr mole ratio, C−Fe0 reduced a 10 ppm Cr(VI) solution to ∼1 ppm w...
333 citations
TL;DR: A nickel-catalyzed reductive carboxylation of styrenes using CO2 has been developed and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction.
Abstract: A nickel-catalyzed reductive carboxylation of styrenes using CO2 has been developed. The reaction proceeds under mild conditions using diethylzinc as the reductant. Preliminary data suggests the mechanism involves two discrete nickel-mediated catalytic cycles, the first involving a catalyzed hydrozincation of the alkene followed by a second, slower nickel-catalyzed carboxylation of the in situ formed organozinc reagent. Importantly, the catalyst system is very robust and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction.
331 citations
TL;DR: An iron-catalyzed C-C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 degrees C in a good to quantitative yield.
Abstract: An iron-catalyzed C−C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 °C in a good to quantitative yield. The reaction involves a C−H bond activation directed by a neighboring nitrogen atom. The important additives in this reaction are 1,10-phenanthroline, tetramethylethylenediamine, and 1,2-dichloro-2-methylpropane, in the absence of which a very low product yield was observed.
322 citations
TL;DR: It is described how the apparent activation energy of the whole cycle, so-called energetic span (delta E), is influenced by the energy levels of two species: the TOF determining transition state (TDTS) and the ToF determining intermediate (TDI).
Abstract: A combined kinetic-quantum chemical model is developed with the goal of estimating in a straightforward way the turnover frequency (TOF) of catalytic cycles, based on the state energies obtained by quantum chemical calculations. We describe how the apparent activation energy of the whole cycle, so-called energetic span (δE), is influenced by the energy levels of two species: the TOF determining transition state (TDTS) and the TOF determining intermediate (TDI). Because these key species need not be adjoining states, we conclude that for catalysis there are no rate-determining steps, only rate determining states. In addition, we add here the influence of reactants concentrations. And, finally, the model is applied to the Haber−Bosch process of ammonia synthesis, for which we show how to calculate which catalyst will be the most effective under specific reagents conditions.
270 citations
TL;DR: In this paper, the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent were characterized by Raman spectroscopy.
Abstract: This work presents the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent. The catalysts were prepared by equilibrium adsorption using several molybdenum precursors and aluminas with different acidity values. They were characterized by Raman spectroscopy. The effect of the reaction time, reaction temperature, nature of solvent, concentration of solvent and hydrogen peroxide, content of molybdenum and phosphate in the catalysts were investigated. The results showed that the activity for sulfur elimination depends mainly on the presence of hepta- and octamolybdates species on the catalyst support and the use of a polar aprotic solvent. Likewise, the presence of phosphate markedly increases the sulfur elimination. In this way, it is possible to reduce sulfur level in diesel fuel from about 320 to less than 10 ppmw at 333 K and atmospheric pressure. Additionally, on the basis of the results obtained a mechanistic proposal for this reaction is described, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of hepta- and octamolybdates, but a mechanism involving the singlet oxygen presence can be discarded.
229 citations
TL;DR: The effect of pH in Fenton-based oxidation systems is investigated and kinetic modeling is used to gain insight into the reaction mechanism and speciation of the iron catalyst to reveal the catalytic role iron plays in the oxidation process.
Abstract: This work extends investigations into the development and use of a kinetic model to simulate and improve the iron-catalyzed oxidation of organic compounds using Fenton’s reagent. While a number of ...
209 citations
TL;DR: A novel Pd(OAc)2-catalyzed methylation reaction by dicumyl peroxide via aryl C−H bond activation was discovered and used as both the methylating reagent and the hydrogen acceptor.
Abstract: A novel Pd(OAc)2-catalyzed methylation reaction by dicumyl peroxide via aryl C−H bond activation was discovered. Various 2-phenylpyridine and acetanilides can be used as reactants in these reactions. Peroxide was used as both the methylating reagent and the hydrogen acceptor.
TL;DR: In this article, the synthesis of 1,2,4,5-tetrasubstituted imidazoles using benzil, an aromatic aldehyde and an amine in the presence of ammonium acetate is described.
TL;DR: A detailed experimental analysis was carried out to analyse the effect of the hydrogen peroxide and iron concentrations and the number of reagent additions in the photo-Fenton process, observing that the COD removal ranged from 49% to 78% depending on the H(2)O( 2) dose.
TL;DR: It is reported that CuAAC reactions can be combined with a diazonium-coupling reaction to quantitatively functionalize tyrosine residues with a wide array of starting materials.
Abstract: Cu-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction, renascent of the well-known Huisgen reaction, has recently flourished with applications in organic synthesis, drug discovery, polymer and materials science, and biotechnology. The high reaction yield, simple reaction and purification conditions, wide range of solvent and pH stabilities, and functional group tolerance make the CuAAC reaction a prototypical “click chemistry”, ideal for incorporating functionalities onto desired scaffolds. Over the years it has been widely employed to construct and functionalize polymeric and polyvalent display systems, including polymers, dendrimers, nanoparticles, and surfaces, where an extremely high reaction efficiency for every unit reaction is desirable. In particular, as organic azides and alkynes are almost unreactive with biomolecules and water, CuAAC reactions have been employed in derivatizing biomacromolecules, viruses, and cells with high efficacy under mild reaction conditions. Recently tyrosine residues have been considered as a particularly attractive target for chemoselective modification of proteins because of its subabundant distribution. Francis and coworkers have reported a number of transformations, ranging from the Mannich-type reaction to a transition metal mediated allylation reaction to a diazonium-coupling reaction, which can efficiently target the phenolic group of tyrosine residues at physiological conditions. To overcome the sluggish reactivity with electron-enriched diazonium salts, a sequential reduction/oxidation/Diels–Alder reaction was developed to break the limitation of functionalities being incorporated. In this communication, we report that CuAAC reactions can be combined with a diazonium-coupling reaction to quantitatively functionalize tyrosine residues with a wide array of starting materials. Tobacco Mosaic Virus (TMV) is a classic example of rodlike plant viruses consisting of 2130 identical protein subunits arranged helically around genomic single RNA strand. The length of TMV, that is, 300 nm, is defined by the encapsulated genomic RNA that stabilizes the coat protein assembly. The polar outer and inner surfaces of TMV have been exploited as templates to grow metal or metal oxide nanowires, and conductive polymers have been coated on 1D assembled TMV to produce conductive nanowires. TMV based materials have recently shown great potential with applications in nanoelectronics and energy harvesting devices. In addition, it has been reported that tyrosine residues (Y139) of TMV are viable for chemical ligation using the electrophilic substitution reaction at the ortho position of the phenol ring with diazonium salts. This reaction is very efficient, yet has two distinct disadvantages for broader applications. First, it is difficult to synthesize desired starting materials; and second, the reaction is not compatible with acid-labile functional groups and suitable for electron-deficient anilines only. To embrace the structural diversity of various starting materials, TMV offers an ideal polyvalent display system which allows us to test the efficiency of CuAAC reaction in combining with the tyrosine ligation reaction. As shown in Scheme 1, TMV was first treated with the diazonium salt generated from 3-ethynylaniline 1 in situ adapted from the protocol reported by Francis and co-workers. MALDI-TOF MS analysis indicated that >95% of the capsid monomers were converted into alkyne derivatives 2 (Figure 1) despite the absence of a strong electron withdrawing group in the diazonium reagent. Encouraged by this result, the CuAAC reactions between 2 and azides were explored. For bioconjugation reactions using CuAAC, the Cu catalysts are either generated directly by addition of Cu salts, or in situ from soluble Cu sources and a reducing agent, such as a copper wire, phosphines, thiols, or ascorbate. Multidentate heterocyclic ligands are often required for enhancing the reaction efficiency. Upon screening a series of reaction conditions, we found that the combination of CuSO4/sodium ascorbate (NaAsc) gave the best results. Whereas it is destructive to most other protein complex systems, ascorbate is evidently benign to TMV and has no impact on its structural integrity. 3-Azido-7-hydroxy-coumarin a was first employed as the ACHTUNGTRENNUNGazido counterpart in the reaction, which could be easily monitored by UV-visible absorption at 340 nm (Figure 1B). As a general protocol, 2 (2 mgmL ) and a (3 mm) were added to a solution of CuSO4 (1 mm) and NaAsc (2 mm) in Tris buffer (10 mm, pH 7.8) with 20% DMSO (used to increase the solubility of the azide component). After incubation for 18 h at room temperature, the viral particles were separated from the small molecules by sucrose gradient sedimentation. The integrity of TMV was confirmed by TEM and size-exclusion chromatography (SEC) analysis (data not shown). A strong absorption at 340 nm indicated the successful attachment of coumarin motifs (Figure 1B). MALDI-TOF MS analysis indicated a near quantitative transformation of surface alkynes to triazoles as shown in Figure 1A. [a] M. A. Bruckman, G. Kaur, L. A. Lee, F. Xie, J. Sepulveda, Dr. Q. Wang Department of Chemistry and Biochemistry and Nanocenter University of South Carolina 631 Sumter Street, Columbia, South Carolina 29208 (USA) Fax: (+1)803-777-9521 E-mail : wang@mail.chem.sc.edu [b] R. Breitenkamp, X. Zhang, M. Joralemon, Dr. T. P. Russell, Dr. T. Emrick Polymer Science and Engineering Department, University of Massachusetts Conte Center for Polymer Research, Massachusetts 01003 (USA)
TL;DR: The Co/Peroxymonosulfate system was shown to be an effective disinfection reagent, since 99.99% (4-log) kill of E. coli was achieved in 60 min of treatment and it is still not efficacious enough to qualify as an EPA-registered sanitizer for swimming pools.
TL;DR: In this article, aldol condensation was investigated as a catalytic route for the conversion of liquid alkanes in a biphasic system between various furfurals (furaldehyde (FUR), methyl furfural, and 5-hydroxylmethylfurfural (HMF)) and ketones (acetone, acetol, dihydroxyacetone and 2-hexanone) derived from biomass.
Abstract: Production of liquid alkanes in the range of C8–C15 from renewable sources, such as xylose and fructose (C5 and C6), requires the formation of CC bonds between the carbon chains. We have investigated aldol condensation as a catalytic route for this conversion in a biphasic system between various furfurals (furaldehyde (FUR), methyl furfural, and 5-hydroxylmethyl furfural (HMF)) and ketones (acetone, acetol, dihydroxyacetone, 2-hexanone, and 3-hexanone) derived from biomass. This system employs a reactive aqueous phase containing a basic NaOH catalyst, an organic extracting phase to remove the aldol-adducts from the homogeneous catalyst, with the addition of salt (NaCl) to the aqueous phase employed to expand the miscibility gap between the aqueous and organic phases. The effect of reagent ratios and reaction conditions on the final product distribution, such as ketone to furfural and base to furfural ratio, was investigated and a simple first order model was used to gain insight into the reaction network. High yields to single and double condensation products can be achieved for acetone condensation with furfural compounds by proper choice of reagent ratios. Degradation of HMF appears to be catalyzed by base, leading to the formation of organic acids that subsequently neutralize the base catalyst. This degradation process limits the recycling of the aqueous phase and also decreases the condensation yield of species such as hexanones that do not readily dissolve in the aqueous phase. FUR, which does not readily degrade, is more completely condensed to form products; however, because FUR is less soluble in the reactive aqueous phase compared to HMF, high concentrations of base must be used to increase the rate of reaction.
TL;DR: In this article, the electrochemical Fenton treatment of aromatic pollutants in aqueous medium always leads to the formation of short-chain carboxylic acids, which account for the slower degradation rate at the final stages of the process.
TL;DR: An efficient method for catalytic asymmetric allylic alkylation (AAA) of allylic phosphates with vinylaluminum reagents is reported, and the hydroalumination/catalytic AAA sequence can be performed in a single vessel, on gram scale.
Abstract: An efficient method for catalytic asymmetric allylic alkylation (AAA) of allylic phosphates with vinylaluminum reagents is reported. The vinylmetal reagents are prepared by reaction of commercially available DIBAL-H and a terminal alkyne. The resulting vinylaluminum reagent can be used directly, without isolation or purification. AAA reactions are promoted in the presence of 0.5−2.5 mol % of a readily available chiral N-heterocyclic carbene (NHC) complex and 1−5 mol % commercially available and air stable Cu salt (CuCl2·2H2O). The desired products are typically obtained within 2−12 h in 74% to 95% isolated yield, 77% to >98% ee, and in >98% E selectivity; >98% SN2‘ selectivity is obtained in all but one instance (90%). The hydroalumination/catalytic AAA sequence can be performed in a single vessel, on gram scale.
TL;DR: In this article, the coupling of primary and secondary unactivated alkyl bromides with Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (Cocl 2.2LiI, 4TMEDA).
Abstract: The coupling of primary and secondary unactivated alkyl bromides with alkyl-Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (Cocl 2 .2LiI, 4TMEDA). The reaction is very chemoselective since ketone, ester and nitrile functions are tolerated.
TL;DR: In this article, a Johnson-type methyl transfer reagent was designed for electrophilic trifluoromethylation of carbon nucleophiles, which was used for the first time for dicyanoalkylidenes.
TL;DR: Metal nitrenes for use in C-H insertion reactions were obtained from N-tosyloxycarbamates in the presence of an inorganic base and a rhodium(II) dimer complex catalyst and the reaction proceeds smoothly, and the potassium tosylate that forms as a byproduct is easily removed by filtration or an aqueous workup.
Abstract: Metal nitrenes for use in C-H insertion reactions were obtained from N-tosyloxycarbamates in the presence of an inorganic base and a rhodium(II) dimer complex catalyst. The C-H amination reaction proceeds smoothly, and the potassium tosylate that forms as a byproduct is easily removed by filtration or an aqueous workup. This new methodology allows the amination of ethereal, benzylic, tertiary, secondary, and even primary C-H bonds. The intramolecular reaction provides an interesting route to various substituted oxazolidinones, whereas the intermolecular reaction gives trichloroethoxycarbonyl-protected amines that can be isolated with moderate to excellent yields and that cleave easily to produce the corresponding free amine. The development, scope, and limitations of the reactions are discussed herein. Isotopic effects and the electronic nature of the transition state are used to discuss the mechanism of the reaction.
TL;DR: It was shown that HCTU can be used as an affordable, efficient coupling reagent for fast Fmoc solid‐phase peptide synthesis without reducing the crude peptide purities.
Abstract: 1H-Benzotriazolium 1-[bis(dimethyl-amino)methylene]-5-chloro-hexafluorophosphate (1-),3-oxide (HCTU) is a nontoxic, nonirritating and noncorrosive coupling reagent. Seven biologically active peptides (GHRP-6, 65–74ACP, oxytocin, G-LHRH, C-peptide, hAmylin1–37, and β-amyloid1–42) were synthesized with reaction times reduced to deprotection times of 3 min or less and coupling times of 5 min or less using HCTU as the coupling reagent. Expensive coupling reagents or special techniques were not used. Total peptide synthesis times were dramatically reduced by as much as 42.5 h (1.8 days) without reducing the crude peptide purities. It was shown that HCTU can be used as an affordable, efficient coupling reagent for fast Fmoc solid-phase peptide synthesis. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
TL;DR: The reaction of the 10-I-3 hypervalent iodine electrophilic trifluoromethylation reagent with 2,4,6-trimethylphenol, after deprotonation with NaH and in the presence of 18-crown-6 in a polar, nonprotic solvent, affords 1,3,5-trimenol (4) only as a byproduct.
Abstract: The reaction of the 10-I-3 hypervalent iodine electrophilic trifluoromethylation reagent 1-trifluoromethyl-1,2-benziodoxol-3-(1H)-one (2) with 2,4,6-trimethylphenol, after deprotonation with NaH and in the presence of 18-crown-6 in a polar, nonprotic solvent, affords 1,3,5-trimethyl-2-(trifluoromethoxy)benzene (4) only as a byproduct. Trifluoromethylation occurs preferentially at the ortho- and para-positions of the aromatic core, giving the corresponding trifluoromethylcyclohexadienones 5 and 6. In case the ortho- and/or para-positions are not substituted, the corresponding products of an aromatic, electrophilic substitution are obtained in moderate yield, for example, 2-trifluoromethyl-4-tert-butylphenol (10a) from 4-tert-butylphenol (10).
TL;DR: In this article, a simple approach for the aqueous room temperature synthesis of marigold shape single crystalline fluorescent gold nanoflowers without using seeds or structure-regulating reagent and their SERS and electrocatalytic activity is described.
Abstract: A simple approach for the aqueous room temperature synthesis of marigold shape single crystalline fluorescent gold nanoflowers without using seeds or structure-regulating reagent and their SERS and electrocatalytic activity is described.
TL;DR: In this article, the state of the art of chemical modification of cellulose applying ionic liquids (ILs) as reaction media considering own research results is discussed. But, the main scope of the review is to discuss the present state-of-the-art of chemical modifications applying ILs to cellulose.
Abstract: Some general comments about ionic liquids (ILs) and carbohydrates are given. The main scope of the review is to discuss the present state of the art of chemical modification of cellulose applying IL as reaction media considering own research results. ILs, namely i-butyl-3-methylimidazolium chloride (BMIMCl), 1-ethyl-3-methylimidazolium chloride (EMIMCI), 1-butyl-2,3-dimethylimidazolium chloride (BDMIMCI), 1-allyl-2,3-dimethylimidazolium bromide (ADMIMBr) and 1-ethyl-3-methylimidazolium acetate (EMIMAc) are solvents for cellulose (even for high molecular bacterial synthesized cellulose) and can easily be applied as reaction media for cellulose modification. We investigated the homogeneous acylation, carbanilation and silylation of the biopolymer cellulose. Under mild conditions and within short reaction time at low temperature (65 C to 80 °C) and low excess of reagent, various cellulose esters and carbanilates, dendronized cellulose and trimethylsilyl cellulose were obtained. The DS of the cellulose derivatives can be controlled by varying the reaction time, reaction temperature and the IL used as reaction medium.
TL;DR: In this article, the formation mechanism of monoclinic α-Ag2S nanospheres was determined and the optical absorption spectra showed very broad absorption peaks centered at about 515 nm in wavelength.
Abstract: Ag2S nanospheres were synthesized by a hydrothermal reaction using l-cysteine as the sulfur source and chelating reagent. The X-ray diffraction patterns and X-ray photoelectron spectra confirmed that the products were monoclinic α-Ag2S. The optical absorption spectra of the Ag2S nanospheres showed very broad absorption peaks centered at about 515 nm in wavelength. Photoluminescence spectra exhibited emission peaks centered at ∼637 nm in wavelength accompanied by weaker shoulder peaks at ∼590 nm in wavelength when the sample was excited with a wavelength of 490 nm. In addition, the formation mechanism of the Ag2S nanospheres was also determined. The l-cysteine-assisted hydrothermal route using l-cysteine as the sulfur source and chelating reagent provides an alternative approach to generate sulfide nanocrystals.
TL;DR: A highly efficient protocol for the benzyl or allylic C-H functionalization of simple hydrocarbons has been developed using stoichiometric amounts of N-hydroxyphthalimide and PhI(OAc)2 in the presence of CuCl catalyst.
Abstract: A highly efficient protocol for the benzyl or allylic C−H functionalization of simple hydrocarbons has been developed using stoichiometric amounts of N-hydroxyphthalimide and PhI(OAc)2 in the presence of CuCl catalyst. The reaction was revealed to proceed via a radical pathway, in which phthalimide N-oxyl (PINO) radical plays a dual role, serving as a catalytic hydrogen abstractor from hydrocarbons as well as a stoichiometric reagent to couple with the resultant alkyl radicals.
TL;DR: Fenton's reagent (Fe2+ +H2O2) has been electrogenerated in situ in an undivided electrolytic cell from the effective reduction of Fe3+ and O2 at carbon-felt cathode for the treatment of aqueous solutions of four triphenylmethane dyes (TPMs).
TL;DR: In this article, a hybrid advanced oxidation technique called sonoelectro-Fenton (sono-EF) was applied for the degradation of organic pollutants in aqueous medium.