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Dimethylformamide
Terms modified by Dimethylformamide Selected AbstractsElectrochemical Reduction of 4,4,-(2,2,2-Trichloroethane-1,1-diyl)- bis(chlorobenzene) (DDT) and 4,4,-(2,2-Dichloroethane-1,1-diyl)- bis(chlorobenzene) (DDD) at Carbon Cathodes in DimethylformamideELECTROANALYSIS, Issue 4 2006Mohammad Abstract In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4,-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4,-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4,-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU) as principal product (67,94%), together with 4,4,-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 1-chloro-4-styrylbenzene, and traces of both 1,1-diphenylethane and 4,4,-(ethane-1,1-diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon,chlorine bonds of DDT is a two-electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. [source] Cobalt(II) Complexes with Substituted Salen-Type Ligands and Their Dioxygen Affinity in N,N -Dimethylformamide at Various TemperaturesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Andreas Huber Abstract Several unsymmetrically substituted salen-type cobalt(II) Schiff-base complexes CoL [H2L = 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-hexadiene (1); 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (2); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-(2-hydroxyphen-yl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (3); 1-(2-hydroxyphenyl)-6-methyl-2,5-diaza-1,5-nonadien-8-one (4); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-methyl-2,5-di-aza-1,5-nonadien-8-one (5); 1-(2-hydroxyphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (6); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (7)] were prepared and characterized by their UV/Vis absorption spectra, magnetic moments, and oxidation potentials. Except for complex 4 (irreversible oxidation with t½ , 3 h), complexes 1,3 and 5,7 are remarkably resistant against irreversible auto-oxidation in air-saturated N,N -dimethylformamide (DMF) at ambient temperature. To characterize the Lewis acidity of the cobalt center in 1,7, the equilibrium constant Kpy was determined for monoadduct formation with pyridine (CoL + pyCoL·py). An O2 -sensitive optode was used to determine the Henry constant, KH, for the system O2/DMF in the temperature range 298,228 K. The formation of 1:1 adducts of complexes 1,7 with O2 in DMF, as characterized by the equilibrium constant K, was followed spectrophotometrically in the temperature range 298,228 K. The parameters ,Ho, ,So, and K are reported. At 298 K, K ranges from 21.9 M,1 (5) to 155 M,1 (7). The overall spectroscopic information, including EPR spectra obtained with frozen solutions of 3 and 7 in O2 -saturated DMF, confirm that the 1:1 adducts CoL·O2 are cobalt(III) superoxo compounds. The symmetrically substituted salen complex8 [H2L = 1,6-bis(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,4,4-tetramethyl-2,5-diaza-1,5-hexadiene in 8] is shown to catalyze the oxidation of triphenylphosphane and 2,6-di- tert -butylphenol by O2 in DMF at ambient temperature. The correlation of the data obtained for K, Kpy, and the oxidation potential E½ is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] N,N -Dimethylformamide as a Reaction Medium for Metal Nanoparticle SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Isabel Pastoriza-Santos Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N,N -dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF-based metal nanoparticle colloids with tunable size and shape. [source] Effects of Ionic Liquid [Me3NC2H4OH]+[ZnCl3], on , -Radiation Polymerization of Methyl Methacrylate in Ethanol and N,N -DimethylformamideMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2005Guozhong Wu Abstract Summary: Radiation-induced polymerization of methyl methacrylate (MMA) in ethanol (EtOH) and N,N -dimethylformamide (DMF) in the presence of ionic liquid [Me3NC2H4OH]+[ZnCl3], is reported. A substantial increase in monomer conversion and molecular weight is observed at room-temperature ionic liquid (RTIL) >60 vol.-%, and the resulting PMMA has a broad multimodal MWD. A clear difference in the MWD pattern is noted between EtOH/RTIL and DMF/RTIL systems, probably due to the complicated interactions between the solvent and ionic liquid. Gel permeation chromatography traces of poly(methyl methacrylate) obtained by radiation polymerization in EtOH/RTIL and DMF/RTIL mixed solvent. Organic/RTIL (v/v): 1) 100:0; 2) 80:20; 3) 60:40; 4); 40:60; 5) 0:100. [source] Mixed Culture Bioconversion of 16-Dehydropregnenolone Acetate to Androsta-1,4-diene-3,17-dione: Optimization of ParametersBIOTECHNOLOGY PROGRESS, Issue 2 2003Tushar Banerjee Bioconversion of 16-dehydropregnenolone acetate (16-DPA) to androsta-1,4-diene-3,17-dione (ADD), an intermediate for the production of female sex hormones, by mixed culture of Pseudomonasdiminuta MTCC 3361 and Comamonas acidovorans MTCC 3362 is reported. Various physicochemical parameters for the bioconversion of 16-DPA to ADD have been optimized in shake flask cultures. Nutrient broth inoculated with actively growing co-culture proved ideal for bacterial growth and bioconversion. A temperature range of 35,40 °C was most suitable; higher or lower temperatures adversely affected the bioconversion. Dimethylformamide below 2% concentration was the most suitable carrier solvent. Maximum conversion was recorded at 0.5 mg mL,1 16-DPA. A pH of 5.0 yielded a peak conversion of 62 mol % in 120 h incubation period. Addition of 9,-hydroxylase inhibitors failed to prevent further breakdown of ADD to nonsteroidal products. 16-DPA conversion in a 5 L fermenter followed a similar trend. [source] ChemInform Abstract: Convenient N-Formylation of Amines in Dimethylformamide with Methyl Benzoate under Microwave Irradiation.CHEMINFORM, Issue 40 2010Dongsik Yang Abstract Primary and secondary amines are formylated by DMF using methyl benzoate as catalyst. [source] Pd-Catalyzed Reduction of Aryl Halides Using Dimethylformamide as the Hydride Source.CHEMINFORM, Issue 52 2007Anna Maria Zawisza Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Dimethylformamide, Dimethylacetamide and Tetramethylguanidine as Nucleophilic Organocatalysts for the Transfer of Electrophilic Bromine from N-Bromosuccinimide to Alkenes.CHEMINFORM, Issue 19 2007Simon M. Ahmad Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Convenient Dimethylamino Amination in Heterocycles and Aromatics with Dimethylformamide.CHEMINFORM, Issue 3 2005Anu Agarwal No abstract is available for this article. [source] ChemInform Abstract: Lewis Base Promoted Aldol Reaction of Dimethylsilyl Enolates in Aqueous Dimethylformamide: Use of Calcium Chloride as a Lewis Base Catalyst.CHEMINFORM, Issue 27 2002Katsukiyo Miura Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Voltammetric Reduction of a 4-Nitroimidazole Derivative on a Multiwalled Carbon Nanotubes Modified Glassy Carbon ElectrodeELECTROANALYSIS, Issue 13 2008P. Jara-Ulloa Abstract We report the electrochemical behavior of a 4-nitroimidazole derivative, 1-methyl-4-nitro-2-hydroxymethylimidazole (4-NImMeOH), on glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT). As dispersing agents, dimethylformamide (DMF) and water were used. The electrochemical response of the resulting electrodes was evaluated using linear sweep, cyclic and square-wave voltammetry (LSV, CV and SWV). Several parameters such as medium pH, nature and concentration of the CNTs dispersion and accumulation time were tested. The optimal conditions determined for obtain better response were: pH,2, dispersion concentration=4,mg/mL of CNT in water, accumulation time=7,min. The MWCNT-modified GCE exhibited attractive electrochemical properties producing enhanced currents with a significant reduction in the overpotential and good signal-to-noise characteristics, in comparison with the bare GCE. The modified electrode is highly repeatable for consecutive measurements, reaching a variation coefficient of 2.9% for ten consecutive runs. [source] Simultaneous Determination of Quinoline and Pyridine Compounds in Gasoline and Diesel by Differential Pulse VoltammetryELECTROANALYSIS, Issue 6 2007Leonardo Abstract The presence of trace basic organonitrogen compounds such as quinoline and pyridine in derivative petroleum fuels plays an important role in maintaining the engines of vehicles. However, these substances can contaminate the environment and so must be controlled because most of them are potentially carcinogenic and mutagenic. For these reasons, a reliable and sensitive method was developed for the determination of basic nitrogen compounds in fuel samples such as gasoline and diesel. This method utilizes preconcentration on an ion,exchange resin (Amberlyte IR,120,H) followed by differential pulse voltammetry (DPV) on a glassy carbon electrode. The electrochemical behavior of quinoline and pyridine as studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion-controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF4 0.1,mol L,1) for quinoline (,1.95,V) and pyridine (,2.52,V) vs. Ag|AgCl|KClsat reference electrode. The proposed DPV method displayed a good linear response from 0.10 to 300,mg L,1 and a limit of detection (LOD) of 5.05 and 0.25,,g L,1 for quinoline and pyridine, respectively. Using the method of standard additions, the simultaneous determination of quinoline and pyridine in gasoline samples yielded 25.0±0.3 and 33.0±0.7,mg L,1 and in diesel samples yielded 80.3±0.2 and 131±0.4,mg L,1, respectively. Spike recoveries were 94.4±0.3% and 101±0.5% for quinoline and pyridine, respectively, in the fuel determinations. This proposed method was also compared with UV-vis spectrophotometric measurements. Results obtained for the two methods agreed well based on F and t student's tests. [source] The Electrochemical Oxidation of N,N -Diethyl- p -Phenylenediamine in DMF and Analytical Applications.ELECTROANALYSIS, Issue 11 2003Part I: Mechanistic Study Abstract The electrochemical oxidation of N,N -diethyl- p -phenylenediamine in dimethylformamide has been studied at platinum and gold microdisk electrodes of various radii between 6.7 and 66,,m. The voltammetric responses revealed two electrochemically reversible waves the second of which becomes larger at higher concentrations and bigger electrode radii. The voltammetric signals have been modelled and the electrochemical oxidation reaction is not inconsistent with an ECrevECE reaction. Kinetic parameters are reported. [source] Magneto,Structural Correlations in Discrete MnII -WV Cyano-Bridged Assemblies with Polyimine LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2010Robert Podgajny Abstract We present the magneto,structural correlations for two novel discrete cyano-bridged assemblies based on cationic complexes of manganese(II) with diimine ligands and octacyanotungstate(V) ions. The crystal structure of [MnII(terpy)(dmf)(H2O)2][MnII(terpy)(H2O)(dmf)(,-NC)WV(CN)7]2·6H2O (1) (terpy = 2,2,;6,,2,-terpyridine, dmf = dimethylformamide) contains dinuclear {MnIIWV}, cyano-bridged anions, while the crystal structure of [MnII(phen)3]2[MnII(phen)2(,-NC)2WV(CN)6]2(ClO4)2·9H2O (2) (phen = 1,10-phenanthroline) is built of tetranuclear {MnII2WV2}2, square anions. Intramolecular Mn,W magnetic interactions through the cyano bridges are represented by magnetic coupling constants J = ,39 cm,1 for the {MnIIWV}, unit in 1 and J1 = ,25.7 and J2 = ,16.7 cm,1 for the {MnII2WV2}2, unit in 2. J and J1 represent relatively strong W,CN,Mn interactions and are ascribed to the bridges in b positions of TPRS-8 (trigonal prism square-face bicapped) of [W(CN)8]3, polyhedra, favoring the strongest electronic interactions between the d,d orbital of W and the ,* orbitals of CN,, whereas J2 is related to the m vertex of [W(CN)8]3,. The magnetic properties of 1 and 2 are compared with reference compounds and discussed in the context of the type of coordination polyhedra of [W(CN)8]3, as well as the metric parameters of cyano-bridged W,CN,Mn linkages. We found the type of coordination polyhedra and bridging mode of [W(CN)8]3, to be the most important factors influencing the magnitude of the Mn,W magnetic interaction. [source] Synthesis, Structure, Characterization, and Redox Properties of the Porous MIL-68(Fe) SolidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2010Alexandra Fateeva Abstract A new porous FeIII -based MOF, formulated Fe(OH)(BDC)·(dmf)x with x , 1.1 and presenting the MIL-68 topology, was prepared by reaction of an iron(III) salt and terephthalic acid (H2BDC) in N,N, -dimethylformamide (dmf) under acidic conditions. The structure and properties of this solid were studied by means of X-ray diffraction, thermogravimetric analysis, nitrogen sorption, 57Fe Mössbauer spectrometry, and electrochemical lithium insertion. [source] Studies on the Formation of CdS Nanoparticles from Solutions of (NMe4)4[Cd10S4(SPh)16]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2010Maria Bendova Abstract The stepwise cluster growth, and formation of CdS nanoparticles from solutions of (NMe4)4[Cd10S4(SPh)16] in dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and acetonitrile was investigated. Cluster growth is fast in DMSO and DMF at room temperature, and slow in acetonitrile at elevated temperatures. Larger sulfide clusters (initially Cd32, then Cd54) are initially formed, which upon further growth eventually give rise to CdS nanoparticles. Strong evidence was found that the byproduct formed during the reaction in DMSO is mononuclear [Cd(SPh)x(DMSO)y](2,x) (x , 3). [source] A Polymer-Bound Oxidovanadium(IV) Complex Prepared from an L -Cysteine-Derived Ligand for the Oxidative Amination of StyreneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2008Mannar R. Maurya Abstract The ligand H2sal-cys (I) derived from salicylaldehyde and L -cysteine has been covalently bonded to chloromethylated polystyrene cross-linked with 5,% divinylbenzene. Upon treatment with [VO(acac)2] in dimethylformamide (DMF) the polystyrene-bound ligand PS-H2sal-cys (II) gave the oxidovanadium(IV) complex, PS-[VO(sal-cys)·DMF] (1). The corresponding neat complex, [VO(sal-eta)]2 (2), has also been prepared similarly in methanol. These complexes have been characterised by IR, electronic, EPR spectroscopic studies, magnetic susceptibility measurements and thermal as well as scanning electron micrographs studies. Complex [VO(sal-eta)]2 exhibits a medium intensity band at 980 cm,1 in the IR spectrum due to ,(V=O) stretch. Broad features of the EPR spectrum for the neat complex along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interaction between two vanadium centers in close proximity. Both complexes catalyze the oxidative amination of styrene, in mild basic conditions, with secondary amines (diethylamine, imidazole, and benzimidazole) and gave a mixture of two aminated products in good yields. Amongst the two aminated products, the anti-Markovnikov product is favored over the Markovnikov one due to the steric hindrance posed by the secondary amines. The polymer-anchored heterogeneous catalyst is free from leaching during catalytic action and recyclable.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Unprecedented Rearrangement of Molybdenum(VI) Oxide to (,2 -Oxido)bis[dioxidomolybdenum(VI)] HexamolybdateEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2007María R. Pedrosa Abstract MoO2(acac)2 reacts with water, amides, sulfoxides, and phosphane oxides in aqueous methanol, under mild conditions, to afford a new family of molybdates of composition [Mo2O5L6][Mo6O19] (L = H2O, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dibutyl sulfoxide, tributylphosphane oxide, triphenylphosphane oxide, hexamethylphosphoramide). The crystal and molecular structures of the two first structurally characterized (,2 -oxido)bis[dioxidomolybdenum(VI)] hexamolybdates were established by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Structural and Theoretical Insights into Metal,Scorpionate Ligand ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2007Matthias Schwalbe Abstract The syntheses of the complexes [M(TmMe)(CO)2(NO)] (M = Mo, W) by reaction of NOBF4 with [M(TmMe)(CO)3], are reported and their spectroscopic characterisation and crystal structures are described. The analogous Cr complex could not be prepared by this methodology. The complexes adopt the expected pseudo-octahedral geometry. Complexes [M(L)(CO)2(NO)] (M = Cr, Mo, W; L = Cp, Tp and TmMe) together with the hypothetical [Mo(CO)2(NO)]+ cation were subjected to DFT calculations. Geometry-optimised structures closely parallel the crystallographic determinations and indicate that the complex [Cr(TmMe)(CO)2(NO)] is not inherently unstable. The DFT calculations allow the assignment of the C,O and N,O stretches in the IR spectrum and give insight into both the M,NO bonding and the metal to tripodal ligand bonding. The electron-donor strengths are confirmed to lie in the order TmMe > Tp > Cp. A side reaction of the B,H moiety of the TmMe anion with NO+ results in the isolation of the dimethylformamide adduct of (trismethimazolyl)borane, providing further evidence that the reaction pathways of the TmR ligands are more varied and less passive than in the chemistry of the nitrogen-based scorpionates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Coordination Chemistry of N,N,N,,N, -Tetraethylpyridine-2,6-dithiocarboxamide (S -dept) , X-ray Crystal Structures and Magnetic Properties of [Co(S -dept)X2] (X = Br, I, and NCS)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Ramesh Kapoor Abstract Mononuclear cobalt(II) complexes [Co(S -dept)X2] [X = Br (1), I (2) and NCS (3)] were synthesized using N,N,N,,N, -tetraethylpyridine-2,6-dithiocarboxamide (S -dept), and characterised by conductivity, spectral and single-crystal X-ray diffraction studies. These studies reveal that the compounds consist of discrete monomeric molecules in which the cobalt atoms are five-coordinate in an environment that is best described as being distorted square-pyramidal. In dimethylformamide the iodo complex shows significant ionic dissociation (1:1 electrolyte) and its crystal field absorption spectrum is interpretable in terms of an octahedral structure [Co(S -dept)(DMF)2I]+. The temperature dependence of the magnetic susceptibility data is indicative of a high-spin compound with an important zero-field splitting. The best fitwas obtained with |D| = 20.5 cm,1 and g = 2.53 for 1, |D| = 14.2 cm,1 and g = 2.38 for 2 and |D| = 17.7 cm,1 and g = 2.35 for 3. The X-band EPR spectra at low temperature is also characteristic of an S = 3/2 state with important zero-field splitting. The most important band appears at low fields (ca. 1200 G). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Cobalt(II) Complexes with Substituted Salen-Type Ligands and Their Dioxygen Affinity in N,N -Dimethylformamide at Various TemperaturesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Andreas Huber Abstract Several unsymmetrically substituted salen-type cobalt(II) Schiff-base complexes CoL [H2L = 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-hexadiene (1); 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (2); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-(2-hydroxyphen-yl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (3); 1-(2-hydroxyphenyl)-6-methyl-2,5-diaza-1,5-nonadien-8-one (4); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-methyl-2,5-di-aza-1,5-nonadien-8-one (5); 1-(2-hydroxyphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (6); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (7)] were prepared and characterized by their UV/Vis absorption spectra, magnetic moments, and oxidation potentials. Except for complex 4 (irreversible oxidation with t½ , 3 h), complexes 1,3 and 5,7 are remarkably resistant against irreversible auto-oxidation in air-saturated N,N -dimethylformamide (DMF) at ambient temperature. To characterize the Lewis acidity of the cobalt center in 1,7, the equilibrium constant Kpy was determined for monoadduct formation with pyridine (CoL + pyCoL·py). An O2 -sensitive optode was used to determine the Henry constant, KH, for the system O2/DMF in the temperature range 298,228 K. The formation of 1:1 adducts of complexes 1,7 with O2 in DMF, as characterized by the equilibrium constant K, was followed spectrophotometrically in the temperature range 298,228 K. The parameters ,Ho, ,So, and K are reported. At 298 K, K ranges from 21.9 M,1 (5) to 155 M,1 (7). The overall spectroscopic information, including EPR spectra obtained with frozen solutions of 3 and 7 in O2 -saturated DMF, confirm that the 1:1 adducts CoL·O2 are cobalt(III) superoxo compounds. The symmetrically substituted salen complex8 [H2L = 1,6-bis(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,4,4-tetramethyl-2,5-diaza-1,5-hexadiene in 8] is shown to catalyze the oxidation of triphenylphosphane and 2,6-di- tert -butylphenol by O2 in DMF at ambient temperature. The correlation of the data obtained for K, Kpy, and the oxidation potential E½ is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Structural Proliferation of 2,6-Difluoropyridine through Organometallic IntermediatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2004Manfred Schlosser Abstract Contrary to a literature claim, 2,6-difluoropyridine-3-carboxaldehyde can be readily prepared by consecutive treatment of 2,6-difluoropyridine with lithium diisopropylamide and N,N -dimethylformamide. Regioselective displacements of fluorine from the aldehyde by nucleophiles were carried out. To demonstrate the versatility of the organometallic approach, some two dozens of further 2,6-difluoropyridine derivatives were prepared applying a combination of modern organometallic methods such as site selective hydrogen/metal and halogen/metal permutations and deprotonation-triggered heavy halogen migrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] High-Nanofiller-Content Graphene Oxide,Polymer Nanocomposites via Vacuum-Assisted Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Karl W. Putz Abstract Highly ordered, homogeneous polymer nanocomposites of layered graphene oxide are prepared using a vacuum-assisted self-assembly (VASA) technique. In VASA, all components (nanofiller and polymer) are pre-mixed prior to assembly under a flow, making it compatible with either hydrophilic poly(vinyl alcohol) (PVA) or hydrophobic poly(methyl methacrylate) (PMMA) for the preparation of composites with over 50 wt% filler. This process is complimentary to layer-by-layer assembly, where the assembling components are required to interact strongly (e.g., via Coulombic attraction). The nanosheets within the VASA-assembled composites exhibit a high degree of order with tunable intersheet spacing, depending on the polymer content. Graphene oxide,PVA nanocomposites, prepared from water, exhibit greatly improved modulus values in comparison to films of either pure PVA or pure graphene oxide. Modulus values for graphene oxide,PMMA nanocomposites, prepared from dimethylformamide, are intermediate to those of the pure components. The differences in structure, modulus, and strength can be attributed to the gallery composition, specifically the hydrogen bonding ability of the intercalating species [source] Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1-Functionalized Poly (N -vinylcarbazole) Film via Solution-Phase Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Xiao-Dong Zhuang Abstract A nanoaggregated dispersed red 1-grafted poly(N -vinylcarbazole) (abbreviated PVDR) is self-assembled via ,,, stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N -dimethylformamide to dichloromethane. Upon self-assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non-aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write-once read-many-times (WORM) memory device is shown whereby a pre-assembled solution of PVDR is spin-coated as the active layer and is sandwiched between an aluminum electrode and an indium-tin-oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 105 and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non-nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON- and OFF-states after more than one hundred million (108) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high-performance polymer memory devices. [source] Conductivity and Methanol Permeability of Nafion,Zirconium Phosphate Composite Membranes Containing High Aspect Ratio Filler Particles,FUEL CELLS, Issue 4 2009M. Casciola Abstract Gels of exfoliated ,-zirconium phosphate (ZrPexf) in dimethylformamide (DMF) were used to prepare Nafion/ZrPexf composite membranes with filler loadings up to 7,wt.-% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2,wt.-% ZrP gels in DMF. TEM pictures showed that the ZrPexf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability (P) and through-plane (,thp) and in-plane (,inp) conductivity measurements at 40,°C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrPisg) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned out to be strongly dependent on the filler morphology. As a general trend, both permeability and swelling decreased according to the sequence: Nafion/ZrPisg > Nafion > Nafion/ZrPexf. The maximum selectivity (,thp/P,=,1.4,×,105,S,cm,3,s) was found for the membrane filled with 1,wt.-% ZrPexf: this value is seven times higher than that of Nafion. For the Nafion/ZrPexf membranes, the ratio ,inp/,thp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface. [source] N,N -Dimethylformamide as a Reaction Medium for Metal Nanoparticle SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Isabel Pastoriza-Santos Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N,N -dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF-based metal nanoparticle colloids with tunable size and shape. [source] Microporous Metal,Organic Frameworks with High Gas Sorption and Separation Capacity,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007Y. Lee Abstract The design, synthesis, and structural characterization of two microporous metal,organic framework structures, [M(bdc)(ted)0.5]·2,DMF·0.2,H2O (M,=,Zn (1), Cu (2); H2bdc,=,1,4-benzenedicarboxylic acid; ted,=,triethylenediamine; DMF: N,N -dimethylformamide) is reported. The pore characteristics and gas sorption properties of these compounds are investigated at cryogenic temperatures, room temperature, and higher temperatures by experimentally measuring argon, hydrogen, and selected hydrocarbon adsorption/desorption isotherms. These studies show that both compounds are highly porous with a pore volume of 0.65 (1) and 0.52,cm3,g,,1 (2). The amount of the hydrogen uptake, 2.1,wt,% (1) and 1.8,wt,% (2) at 77,K (1,atm; 1,atm,=,101,325,Pa), places them among the group of metal,organic frameworks (MOFs) having the highest H2 sorption capacity. [Zn(bdc)(ted)0.5]·2,DMF·0.2,H2O adsorbs a very large amount of hydrocarbons, including methanol, ethanol, dimethylether (DME), n -hexane, cyclohexane, and benzene, giving the highest sorption values among all metal,organic based porous materials reported to date. In addition, these materials hold great promise for gas separation. [source] CdS-Nanoparticle/Polymer Composite Shells Grown on Silica Nanospheres by Atom-Transfer Radical Polymerization,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2005T. Cui Abstract In this paper we describe the combined use of surface-initiated atom transfer radical polymerization (ATRP) and a gas/solid reaction in the direct preparation of CdS-nanoparticle/block-copolymer composite shells on silica nanospheres. The block copolymer, consisting of poly(cadmium dimethacrylate) (PCDMA) and poly(methyl methacrylate) (PMMA), is obtained by repeatedly performing the surface-initiated ATRP procedures in N,N -dimethylformamide (DMF) solution at room temperature, using cadmium dimethacrylate (CDMA) and methyl methacrylate (MMA) as the monomers. CdS nanoparticles with an average size of about 3,nm are generated in situ by exposing the silica nanospheres coated with block-copolymer shells to H2S gas. These synthetic core,shell nanospheres were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). These composite nanospheres exhibit strong red photoluminescence in the solid state at room temperature. [source] Removal of gutta-percha from root canals using an Nd:YAG laserINTERNATIONAL ENDODONTIC JOURNAL, Issue 10 2003D. Vidu Abstract Aim, To examine the use of an Nd:YAG laser in removing gutta-percha fillings from root canals when used in conjunction with eucalyptol, dimethylformamide (DMF) or no solvent. Methodology, Root-canal fillings (sealer and gutta-percha) were removed with laser irradiation of 20 Hz/1.5 W from 30 roots randomly divided in three groups. In group 1, the solvent was eucalyptol; in group 2, the solvent was DMF; and in group 3, no solvent was used. Laser irradiation was performed until the temperature measured on the root surface increased by 4 °C over room temperature. The treatment was deemed complete when the apical foramen was reached with the optical fibre and a reamer. The samples were split longitudinally, and the area of remaining gutta-percha on the root-canal walls was determined with the aid of a computer program. The total number of laser pulses to achieve length and the highest temperature recorded was determined for each tooth. The results were statistically analysed using Student's t -test (P < 0.05) for independent samples. Results, The average temperature increase in group 1 was 9.17 ± 0.56 °C; in group 2, 9.56 ± 0.28 °C; and in group 3, 8.29 ± 0.41 °C. The shortest time to achieve length was in group 3 (6.4 ± 0.49 min), then in group 1 (6.7 ± 0.85 min) and group 2 (7.05 ± 0.79 min). The area of remaining gutta-percha was the largest in group 2 (6.13 ± 5.76%), whilst the smallest was for group 3 (4.69 ± 4.03%), but the difference was not statistically significant. The number of pulses was not statistically significant between the groups. Conclusions, Use of an Nd:YAG laser alone is capable of softening gutta-percha. The addition of solvents did not improve the retreatment, either in terms of the time required for the procedure or in terms of the area of remaining gutta-percha on root-canal walls. [source] A Dramatic Substituent Effect in Silver(I)-Catalyzed Regioselective Cyclization of ortho -Alkynylaryl Aldehyde Oxime DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Hongyin Gao Abstract A dramatic substituent effect was found in the silver(I)-catalyzed cyclization reaction of ortho -alkynylaryl aldehyde oxime derivatives. When R is an alkyl group, the Ag(I)-catalyzed reaction in dimethylacetamide at 110,°C (conditions A) affords isoquinolines in good to excellent yields, in contrast, isoquinolin-1(2,H)-ones were produced in moderate to high yields under conditions B (dimethylformamide, room temperature) when R is an acetyl group. A plausible mechanism was proposed for this product selectivity control reaction (PSCR) by subtle structure modification. [source] | ||||||||||||||||||||||||||||||||||