Showing papers on "Reagent published in 2010"
TL;DR: In this paper, the deoxygenation efficiency of graphene oxide suspensions by different reductants (sodium borohydride, pyrogallol, and vitamin C, in addition to hydrazine), as well as by heating the suspensions under alkaline conditions, was compared.
Abstract: The preparation of solution-processable graphene from graphite oxide typically involves a hydrazine reduction step, but the use of such a reagent in the large-scale implementation of this approach is not desirable due to its high toxicity. Here, we compare the deoxygenation efficiency of graphene oxide suspensions by different reductants (sodium borohydride, pyrogallol, and vitamin C, in addition to hydrazine), as well as by heating the suspensions under alkaline conditions. In almost all cases, the degree of reduction attainable and the subsequent restoration of relevant properties (e.g., electrical conductivity) lag significantly behind those achieved with hydrazine. Only vitamin C is found to yield highly reduced suspensions in a way comparable to those provided by hydrazine. Stable suspensions of vitamin C-reduced graphene oxide can be prepared not only in water but also in common organic solvents, such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP). These results open the perspective ...
1,269 citations
TL;DR: It is shown that the F-C reagent is significantly reactive toward other compounds besides phenols, which should be seen as a measure of total antioxidant capacity rather than phenolic content.
Abstract: A thorough study was done to test the reactivity of the Folin−Ciocalteu (F-C) reagent toward various compound classes. Over 80 compounds were tested. Compound classes included phenols, thiols, vitamins, amino acids, proteins, nucleotide bases, unsaturated fatty acids, carbohydrates, organic acids, inorganic ions, metal complexes, aldehydes, and ketones. All phenols, proteins, and thiols tested were reactive toward the reagent. Many vitamin derivatives were also reactive, as were the inorganic ions Fe+2, Mn2+, I−, and SO32−. Other compounds showing reactivity included the nucleotide base guanine and the trioses glyceraldehyde and dihydroxyacetone. Copper complexation enhanced the reactivity of salicylate derivatives toward the reagent, whereas zinc complexation did not. Several amino acids and sugars that were reported to be reactive toward the F-C reagent in earlier studies were found not to be reactive in this study, at least in the concentrations used. Reaction kinetics of each compound with the F-C rea...
635 citations
TL;DR: In this article, mesoporous silica supported Cu/TiO 2 nanocomposites were synthesized through a one-pot sol-gel method, and the photoreduction experiments were carried out in a continuous-flow reactor using CO 2 and water vapor as the reactants under the irradiation of a Xe lamp.
Abstract: Photoreduction of CO 2 to hydrocarbons is a sustainable energy technology which not only mitigates emissions but also provides alternative fuels. However, one of the largest challenges is to increase the overall CO 2 photo-conversion efficiency when water is used as the reducing reagent. In this work, mesoporous silica supported Cu/TiO 2 nanocomposites were synthesized through a one-pot sol–gel method, and the photoreduction experiments were carried out in a continuous-flow reactor using CO 2 and water vapor as the reactants under the irradiation of a Xe lamp. The high surface area mesoporous silica substrate (>300 m 2 /g) greatly enhanced CO 2 photoreduction, possibly due to improved TiO 2 dispersion and increased adsorption of CO 2 and H 2 O on the catalyst. CO was found to be the primary product of CO 2 reduction for TiO 2 –SiO 2 catalysts without Cu. The addition of Cu species, which was identified to be Cu 2 O by the XPS, markedly increased the overall CO 2 conversion efficiency as well as the selectivity to CH 4 , by suppressing the electron–hole recombination and enhancing multi-electron reactions. A synergistic effect was observed by combining the porous SiO 2 support and the deposition of Cu on TiO 2 . The peak production rates of CO and CH 4 reached 60 and 10 μmol g-cat −1 h −1 , respectively, for the 0.5%Cu/TiO 2 –SiO 2 composite that has the optimum Cu concentration; the peak quantum yield was calculated to be 1.41%. Deactivation and regeneration of the catalyst was observed and the mechanism was discussed. Desorption of the reaction intermediates from the active sites may be the rate limiting step.
470 citations
TL;DR: In this paper, the first-order kinetic model was used to investigate the effect of pH, pH, dosages of persulfate and Fe2+, temperature, and presence of inorganic ions (Cl−, NO3−, HCO3− and H2PO4−) on OG degradation.
404 citations
TL;DR: Evaluating the usefulness of formic acid for conversions of 5-(Hydroxymethyl)furfural (HMF) found that the diformate ester of BHMF (BFMF) is quantitatively converted into DMF in refluxing THF upon the addition of Pd/C, given the lability of BFMF.
Abstract: Biofuels that are obtainable from renewable sources have attracted recent interest. The ultimate goal of current research is the conversion of our most abundant renewable hydrocarbons, lignocellulose, into liquid fuels for motor vehicles. Such carbon-neutral resources, in addition to being more geographically disperse than petroleum reserves, promise to minimize the emission of greenhouse gases. The majority of lignocellulose is cellulose, a polymer derived from glucose. The main approaches to the utilization of cellulose involves acid-catalyzed hydrolysis followed by either chemical or biological conversions of glucose. Glucose readily isomerizes into fructose, from which one can envision a number of promising liquid fuels such as 2,5-dimethylfuran (DMF), g-valerolactone (VL), and ethyl levulinate (EL) (Scheme 1). DMF is particularly attractive because of its nearly ideal boiling point (92–94 8C), its high energy density (30 kJ cm ), and its high research octane number (RON = 119). Furthermore it is immiscible with water and is easier to blend with gasoline than ethanol. 5-(Hydroxymethyl)furfural (HMF) is a compound of interest since it is an intermediate in biofuel conversions as well as a valued fine chemical. HMF can either undergo hydrogenation/hydrogenolysis to form DMF or acid-catalyzed conversion into levulinic acid (LA), a precursor to VL. In considering alternative conversions 11] of fructose that ultimately lead to DMF, we conceived of a process whereby several steps could be conducted in one pot. Key to our strategy is the use of formic acid (FA), which has the potential to serve as an acid catalyst, a source of hydrogen (H2), and a deoxygenation agent. FA has attracted much recent interest in the area of green chemistry because of its potential as a hydrogen carrier and as a means of utilizing carbon dioxide. FA is currently produced industrially by the hydration of carbon monoxide as well as the hydrogenation of carbon dioxide. FA is also generated as a by-product from biomass degradation processes. Initial experiments were aimed at evaluating the usefulness of formic acid for conversions of HMF. As expected, HMF can be readily hydrogenated into bis(hydroxymethyl)furan (BHMF) using formic acid (4 equiv) in the presence of Pd/C. The conversion is essentially quantitative in refluxing tetrahydrofuran (THF). No additional reactions occurred even after prolonged reaction times. Featuring two benzyliclike alcohol groups, BHMF is well suited for hydrogenolysis to deliver DMF. Indeed, the gas-phase conversion of BHMF into DMF has been conducted at 220 8C with 6.8 bar H2 over a copper/ruthenium catalyst. Formic acid provides a milder pathway for this conversion. Specifically, we found that the diformate ester of BHMF (BFMF) is quantitatively converted into DMF in refluxing THF upon the addition of Pd/C [Eq. (1)]. Given the lability of BFMF, we turned our attention to conditions for the formation of BFMF from BHMF. We found that a THF solution of BHMF and formic acid (10 equiv) converted into BFMF at 120 8C upon the addition of small amounts (0.13 equiv) of H2SO4. The intermediate monoester was observed spectroscopically. Scheme 1. Conversions of glucose into liquid fuels.
397 citations
TL;DR: In this paper, an environmentally friendly leaching process for the recovery of cobalt and lithium from the cathode active materials of spent lithium-ion batteries was investigated, where the easily degradable organic acid DL-malic acid (C4H5O6) was used as a leaching reagent.
373 citations
TL;DR: This reaction provides a general, straightforward, and practically useful method to prepare trifluoromethylated acetylenes.
Abstract: An efficient copper-mediated trifluoromethylation of terminal alkynes with nucleophilic trifluoromethylating reagent (Me3SiCF3) was developed. Both aromatic alkynes and aliphatic alkynes were effective, and a variety of functionalities such as amino, -OMe, -CO2Et, -Br, and -NO2 were tolerated under the reaction conditions. This reaction provides a general, straightforward, and practically useful method to prepare trifluoromethylated acetylenes.
244 citations
TL;DR: A novel palladium-catalyzed intermolecular aminofluorination of styrenes, with N-fluorobenzenesulfonimide (NFSI) functioning not only as a fluorinating re agent but also as an aminating reagent, has been developed, which afforded vicinal fluoroamine products with very high regioselectivity.
Abstract: A novel palladium-catalyzed intermolecular aminofluorination of styrenes, with N-fluorobenzenesulfonimide (NFSI) functioning not only as a fluorinating reagent but also as an aminating reagent, has been developed. The reaction afforded vicinal fluoroamine products with very high regioselectivity. This transformation may involve fluoropalladation of styrene as a key step for C-F bond formation. The bidental nitrogen ligand is crucial to achieving the transformation successfully.
232 citations
TL;DR: The principle of such high-resolution reaction-time control, which can be achieved only by flow microreactors, and its applications to synthetic reactions including Swern-Moffatt-type oxidation, as well as the generation and reactions of aryllithium compounds bearing electrophilic substituents, such as alkoxycarbonyl groups are presented.
Abstract: This article addresses a fascinating aspect of flash chemistry, high-resolution reaction-time control by virtue of a flow microreactor system, and its applications. The length of time that the solution remains inside the reactor is called the residence time. The residence time between the addition of a reagent and that of a quenching agent or the next reagent in a flow microreactor is the reaction time, and the reaction time can be greatly reduced by adjusting the length of a reaction channel in a flow microreactor. This feature is quite effective for conducting reactions involving short-lived reactive intermediates. A reactive species can be generated and transferred to another location to be used in the next reaction before it decomposes by adjusting the residence time in the millisecond to second timescale. The principle of such high-resolution reaction-time control, which can be achieved only by flow microreactors, and its applications to synthetic reactions including Swern-Moffatt-type oxidation, as well as the generation and reactions of aryllithium compounds bearing electrophilic substituents, such as alkoxycarbonyl groups, are presented. Integration of such reactions using integrated flow microreactor systems is also demonstrated.
223 citations
TL;DR: Alcohols, carboxylic acids, and water can be employed as oxygen nucleophiles, thus providing an efficient entry into beta-aryl ethers, esters, and alcohols from alkenes.
Abstract: The three-component coupling of terminal alkenes with arylboronic acids and oxygen nucleophiles is described. The reaction employs a binuclear gold(I) bromide as a catalyst and Selectfluor reagent as the stoichiometric oxidant. Alcohols, carboxylic acids, and water can be employed as oxygen nucleophiles, thus providing an efficient entry into β-aryl ethers, esters, and alcohols from alkenes.
215 citations
TL;DR: Ratiometric fluorescence response was achieved for receptor A on binding to CN(-, and this reagent was used for imaging bacterial cells pre-exposed to 1.42 microM CN(-) solution.
TL;DR: In this paper, the degradation of Rhodamine B, a waste dye effluent, has been studied using a hydrodynamic cavitational reactor with intensification studies in the presence of hydrogen peroxide, carbon tetrachloride and Fenton's reagent as possibly intensifying additives.
TL;DR: It is reported that gold nanoparticles grafted on nanoparticulate diamond catalyze the formation of hydroxyl radicals from hydrogen peroxide with at least 79 % efficiency and reach a turnover number of 321 000, many orders of magnitude higher than any currently available catalysts.
Abstract: The Fenton reaction consists of the generation of highly aggressive hydroxyl radicals from hydrogen peroxide and is widely used to degrade organic pollutants. Due to its general applicability, the Fenton reaction is employed in water and soil disinfection/remediation and for removal of non-biodegradable chemicals. The main limitation of the Fenton reaction is the consumption of stoichiometric amounts of transition metals, mostly iron. There is considerable incentive in developing a catalytic Fenton process using exclusively hydrogen peroxide and a catalyst. Herein we report that gold nanoparticles grafted on nanoparticulate diamond catalyze the formation of hydroxyl radicals from hydrogen peroxide with at least 79 % efficiency and reach a turnover number of 321 000, many orders of magnitude higher than any currently available catalysts. This extraordinary activity is derived directly from the nanometric diameters of gold and diamond (“nanojewels”) and from the remarkable inertness of the diamond surface. The Fenton reaction, in which highly aggressive hydroxyl radicals (HOC) are generated from H2O2 by reduction with Fe II ,C u II , or other transition metal salts, is a general process that can be used for the degradation/mineralization of recalcitrant organic pollutants as well as for disinfection. [1–4] In spite of the wide applicability of the Fenton reaction for decomposing almost any organic compound, its widespread use for pollution abatement and disinfection is limited by the need for stoichiometric amounts of Fe II or other transition metals. Most of the efforts to transform the Fenton reaction from a stoichiometric to a catalytic process have met with failure or at best can produce HOC with remarkably low efficiency. [5] For instance, the photo-Fenton process requires transparency of the solution (a prerequisite not frequently fulfilled in polluted waters or soils) and consumes “expensive” photons as stoichiometric reagents. A large number of iron-containing solids such as iron-exchanged zeolites and montmorillonites have also been reported as heterogeneous
TL;DR: United the authors stand!
Abstract: United we stand! Cooperative activation of the hypervalent-iodine reagent TIPS-EBX with a gold catalyst and a Bronsted acid allowed the first direct ethynylation of thiophenes at room temperature (see scheme; TFA=trifluoroacetic acid). The obtained ethynylthiophenes are important building blocks for organic dyes and electronic materials.
TL;DR: In this paper, manganese oxides with a cryptomelane-type octahedral molecular sieve (OMS-2) structure were used to replace platinum as a cathode catalyst in microbial fuel cells.
TL;DR: In this article, a green procedure for preparation of silica powders from rice husk ash (RHA) via a carbonation route was developed, where Na2CO3 was used as the extraction reagent and waste gas was the precipitator.
TL;DR: Difluoromethyl 2-pyridyl sulfone, a previously unknown compound, was found to act as a novel and efficient gem-difluOroolefination reagent for both aldehydes and ketones.
TL;DR: The mild reaction conditions allowed the first ethynylation reactions of linear keto, cyano and nitro esters in high yields to give all-carbon quaternary centers or non-natural amino acids after selective reduction of the nitro group.
Abstract: Hot alkyne! The in situ generation of Ethynyl-1,2-BenziodoXol-3(1H)-one (EBX) from the corresponding silyl protected reagent using TBAF is reported. EBX displayed exceptional acetylene transfer ability to stabilized enolates, even at –78 °C. The mild reaction conditions allowed the first ethynylation reactions of linear keto, cyano and nitro esters in high yields to give all-carbon quaternary centers or non-natural amino acids after selective reduction of the nitro group.
TL;DR: P4S10 vs Lawesson’s Reagent (LR) 3473 3.2.
Abstract: 2.3. Amides and Lactams 3435 2.4. Imides 3448 2.5. Thiophenes 3451 2.6. Thiazolines, Thiazoles, and Thiazines 3454 2.7. Dithiazoles 3456 2.8. Thiadiazoles 3456 2.9. Imidazolines and Pyrimidines 3456 2.10. Alcohols 3458 2.11. PdO to PdS 3461 2.12. Reduction 3462 2.13. Nucleotides, Purines, and Pyrimidines 3463 2.14. Miscellaneous 3467 2.15. P4S10 vs Lawesson’s Reagent (LR) 3473 3. Conclusion 3473 4. Acknowledgments 3473 5. References 3473
TL;DR: The first example of intramolecular oxyalkynylation of nonactivated alkenes using oxidative Pd chemistry is reported and the discovery of the superiority of benziodoxolone-derived hypervalent iodine reagent 3d as an alkyne transfer reagent further expands the rapidly increasing utility of hypervalents iodine reagents in catalysis.
TL;DR: In this paper, the methods for dimethyl carbonate and its use as a methylating and carbonate production were discussed and a special atten- methoxycarbonylating agent was considered.
Abstract: The published data on dimethyl carbonate as a The published data on dimethyl carbonate as a non-toxic reagent and solvent in organic synthesis are non-toxic reagent and solvent in organic synthesis are generalized and discussed. The methods for dimethyl generalized and discussed. The methods for dimethyl carbonate production and its use as a methylating and carbonate production and its use as a methylating and methoxycarbonylating agent are considered. Special atten- methoxycarbonylating agent are considered. Special atten- tion is paid to the eco-friendly processes that meet the tion is paid to the eco-friendly processes that meet the 'Green chemistry' requirements. The bibliography includes 'Green chemistry' requirements. The bibliography includes 104 references 104 references..
TL;DR: A new kinetic model was established according to the generally accepted mechanism of high active OH oxidation in order to well describe the Fenton oxidation reaction in HA aqueous solution and indicated that this analytical model could better describe the kinetics of Fenton reaction mathematically and chemically.
TL;DR: The efficient asymmetric total synthesis of (-)-oseltamivir, an antiviral reagent, has been accomplished by using two "one-pot" reaction sequences, with excellent overall yield and only one required purification by column chromatography.
Abstract: The efficient asymmetric total synthesis of (―)-oseltamivir, an antiviral reagent, has been accomplished by using two "one-pot" reaction sequences, with excellent overall yield (60 % ) and only one required purification by column chromatography. The first one-pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/ Horner―Wadsworth―Emmons reaction combined with retro-aldol/Horner― Wadsworth―Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base-catalyzed isomerization. Six reactions can be successfully conducted in the second one-pot reaction sequence; these are deprotection of a tert-butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column-free synthesis of (—)—oseltamivir has also been established.
TL;DR: Investigations detailed herein demonstrate that the formation of either alkoxy- or hydroxy-Ti(III) complexes considerably decreases the energy of activation for C-O bond homolysis, and two new synthetic applications of Nugent's reagent in organic chemistry are described.
Abstract: Investigations detailed herein, including density functional theory (DFT) calculations, demonstrate that the formation of either alkoxy− or hydroxy−Ti(III) complexes considerably decreases the energy of activation for C−O bond homolysis. As a consequence of this observation, we described two new synthetic applications of Nugent’s reagent in organic chemistry. The first of these applications is an one-step methodology for deoxygenation−reduction of alcohols, including benzylic and allylic alcohols and 1,2-dihydroxy compounds. Additionally, we have also proved that Ti(III) is capable of mediating carbonyl coupling−olefination. In this sense, and despite the fact that for over 35 years it has been widely accepted that either Ti(II) or Ti(0) was the active species in the reductive process of the McMurry reaction, the mechanistic evidence presented proves the involvement of Ti(III) pinacolates in the deoxygenation step of the herein described Nugent’s reagent-mediated McMurry olefination. This observation shed...
TL;DR: The optimized electro-Fenton's oxidation system was successfully applied for complete decolorization and approximately 85-90% mineralization of both azo-dyes in real industrial wastewater samples collected from textile dyeing house at El-Mahalla El-Kobra, Egypt.
TL;DR: In this article, the authors describe effective reagent combinations for removal of silicates by reverse cationic flotation from magnetic concentrate in magnetite ores processing, based on a hypothesis that a further development in reverse-cationic reagent flotation of iron ores implies a more detailed consideration of the nature of the Fe-bearing gangue minerals.
TL;DR: Aryltrimethylammonium triflates and tetrafluoroborates were found to be highly reactive electrophiles in the Pd-catalyzed cross coupling with aryl Grignard reagents.
TL;DR: Protein unfolding induced by chemical and/or thermal denaturation in the electrospray droplet appears to be the primary origin of the enhanced charging observed for noncovalent protein complexes formed from aqueous solutions that contain these supercharging reagents, although other factors almost certainly influence the extent of charging.