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Catalyst Concentration (catalyst + concentration)
Selected AbstractsNanocrystalline non-planar carbons: Growth of carbon nanotubes and curled nanostructuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005S. Orlanducci Abstract We present a variety of non-planar graphitic nanostructures selectively generated in a modified Hot-Filament Chemical Vapour Deposition (HF-CVD) apparatus, using purpose-synthesized amorphous carbon nanoparticles or graphite powders as solid state precursor. The employed methodologies enable to successfully synthesize homogeneous and well organized deposits of single- and multi-walled carbon nanotubes, onion-like nanostructures, and nanotube bundles coated by nano-sized diamond grains. Variations in the morphological aspect of such non-planar graphite-based nanostructures are observed changing the experimental conditions: the solid state reactants, the filament and substrate temperatures, the catalyst concentration, and the atomic hydrogen flux over the substrate play key roles in the phenomenon. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] One-Pot Synthesis of Core-Modified Rubyrin, Octaphyrin, and Dodecaphyrin: Characterization and Nonlinear Optical PropertiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2007Rajeev Kumar Abstract Modified 26, rubyrin, 36, octaphyrin, and 54, dodecaphyrin systems have been synthesized in moderately good yields through acid-catalyzed condensations of terthiophene diols and tripyrranes. The product distributions are decided both by the acid catalyst concentration and by the nature of the meso substituents. For example, a new isomer of [26]hexaphyrin(1.1.1.1.0.0) (rubyrin) was obtained with 0.3 equiv. of p -toluenesulfonic acid, when the meso substituent was mesityl in at least one of the precursors. A change of the mesityl substituent for a p -methoxy substituent in terthiophene diol resulted in the formation of a [3,+,3,+,3,+,3] condensation product , [54]dodecaphyrin(1.1.1.1.0.0.1.1.1.1.0.0) , in addition to the expected rubyrin. Furthermore, an increase in the acid concentration to 0.6 equiv. resulted in the formation of a new [36]octaphyrin(1.1.1.1.1.1.0.0), in addition to the rubyrin and dodecaphyrin. A single-crystal X-ray analysis of octaphyrin represents the first example of a planar conformation of an octaphyrin with six meso links. In rubyrin 19, one thiophene ring, opposite to the terthiophene subunit, is inverted, while in octaphyrin 30 one pyrrole ring and two thiophene rings are inverted. The various conformational possibilities tested for the unsubstituted dodecaphyrin 28, at semiempirical level, suggest that the most stable conformation is a figure-eight. The final geometry optimization of figure-eight dodecaphyrin was done at the B3LYP/6-31G* level of DFT. Octaphyrins and dodecaphyrins bind trifluoroacetate anion effectively in their diprotonated forms, the binding constants (K) being 638 M,1 for dodecaphyrin 28, and 415 M,1 for octaphyrin 30. Electrochemical data reveal HOMO destabilization with increasing , electron conjugation, consistently with the large red shifts of the absorption bands. Preliminary studies on the use of these expanded porphyrins as third-order NLO materials were followed by measurements of their two-photon absorption (TPA) cross-sections [,(2)]. The ,(2) values increase upon going from the 26, rubyrins to the 54, dodecaphyrins, confirming our earlier observation that increases in ,-conjugated electrons increase the TPA values.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Rapid Organocatalytic Aldehyde-Aldehyde Condensation ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2007Anniina Erkkilä Abstract We report the results of the systematic optimization of the ,-methylenation of aldehydes with aqueous formaldehyde. A simple combination of a secondary amine catalyst and a weak acid co-catalyst has been identified, allowing access to ,-substituted acroleins in a matter of minutes. In the absence of formaldehyde, the catalytic system promoted the self-condensation reaction of ,,,-unsaturated aldehydes. Both of these reactions exhibited linear relationships between co-catalyst acidities and reaction rates. A second-order dependence of catalyst concentration was observed, pointing to the involvement of two molecules of the ammonium catalyst in the rate-determining step. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Factorial design analysis of the catalytic activity of di-imine copper(II) complexes in the decomposition of hydrogen peroxideINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2001W. A. Alves Factorial design analysis was applied to the study of the catalytic activity of di-imine copper(II) complexes, in the decomposition of hydrogen peroxide. The studied complexes show a tridentate imine ligand (apip), derived from 2-acetylpyridine and 2-(2-aminoethyl)pyridine, and a hydroxo or an imidazole group at the fourth coordination site of the copper ion. The factorial design models for both [Cu(apip)imH]2+ and [Cu(apip)OH]+ were similar. Increasing the peroxide concentration from 3.2 × 10,3 to 8.1 × 10,3 mol L,1 resulted in increased oxygen formation. Increasing the pH from 7 to 11 also increased oxygen formation and had an effect about twice as large as the peroxide one. Both complexes also had an important interaction effect between peroxide concentration and pH. However, increasing the catalyst concentration led to a decrease in total oxygen formation. The obtained results were corroborated by further data, achieved by using the usual univariate method, and helped to elucidate equilibrium steps occurring in the studied systems. In very alkaline solutions, the studied [Cu(apip)imH]2+ complex can form the corresponding dinuclear species, [Cu2(apip)2im]3+. While the mononuclear complex proved to be an efficient catalyst in hydrogen peroxide decomposition, the corresponding dinuclear compound seemed to be able to coordinate with the dioxygen molecule, inhibiting its observed release. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 472,479, 2001 [source] Poly(1,3-propylene glycol-hexanedioic acid) grafted hydroxyl multiwall carbon nanotubesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Qing-Jie Meng Abstract Poly(1,3-propylene glycol-hexanedioic acid) grafted hydroxyl multiwall carbon nanotube (PHHCNT) was fabricated in the presence of butyl titanate using 1,3-propylene glycol, hexanedioic acid, and hydroxyl multiwall carbon nanotubes as reactants. The hydroxyl groups at carbon nanotubes reacted with hexanedioic acid and a small amount of carboxyl groups reacted with 1,3-propylene glycol, resulting in the PGHA grafted on the carbon nanotubes. The carbon nanotubes surrounded by the PGHA chains with an average thickness of , 2 nm. The polycondensation reactions can be controlled by the feed contents of HCNTs and the catalyst concentration in the reactants. The content of HCNTs in PHHCNT rises with an increase of the feed contents of HCNTs. In addition, the content of HCNTs in PHHCNT is higher than the feed contents of HCNTs in the reactants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Influence of technological parameters on the epoxidation of 1-butene-3-ol over titanium silicalite TS-2 catalystJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2009Agnieszka Wróblewska Abstract BACKGROUND: The influence of technological parameters on the epoxidation of 1-butene-3-ol (1B3O) over titanium silicalite TS-2 catalyst has been investigated. Epoxidations were carried out using 30%(w/w) hydrogen peroxide at atmospheric pressure. The major product from the epoxidation of B3O was 1,2-epoxybutane-3-ol, with many potential applications. RESULTS: The influence of temperature (20,60 °C), 1B3O/H2O2 molar ratio (1:1,5:1), methanol concentration (5,90%(w/w)), TS-2 catalyst concentration (0.1,6.0%(w/w)) and reaction time (0.5,5.0 h) have been studied. CONCLUSION: The epoxidation process is most effective if conducted at a temperature of 20 °C, 1B3O/H2O2 molar ratio 1:1, methanol concentration (used as the solvent) 80%(w/w), catalyst concentration 5%(w/w) and reaction time 5 h. Copyright © 2009 Society of Chemical Industry [source] Biodiesel production by direct methanolysis of oleaginous microbial biomassJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2007Bo Liu Abstract Biodiesel is a renewable fuel conventionally prepared by transesterification of pre-extracted vegetable oils and animal fats of all resources with methanol, catalyzed by strong acids or bases. This paper reports on a novel biodiesel production method that features acid-promoted direct methanolysis of cellular biomass of oleaginous yeasts and filamentous fungi. The process was optimized for tuning operation parameters, such as methanol dosage, catalyst concentration, reaction temperature and time. Up to 98% yield was reached with reaction conditions of 70 °C, under ambient pressure for 20 h and a dried biomass to methanol ratio 1:20 (w/v) catalyzed by either 0.2 mol L,1 H2SO4 or 0.4 mol L,1 HCl. Cetane numbers for these products were estimated to range from 56 to 59. This integrated method is thus effective and technically attractive, as dried microbial biomass as feedstocks omits otherwise tedious and time-consuming oil extraction processes. Copyright © 2007 Society of Chemical Industry [source] Continuous process for production of hydrogenated nitrile butadiene rubber using a Kenics® KMX static mixer reactorAICHE JOURNAL, Issue 11 2009Chandra Mouli R. Madhuranthakam Abstract A continuous process for hydrogenating nitrile butadiene rubber (NBR) was developed and its performance was experimentally investigated. A Kenics® KMX static mixer (SM) is used in the process as a gas,liquid reactor in which gaseous hydrogen reacts with NBR in an organic solution catalyzed by an organometallic complex such as an osmium complex catalyst. The Kenics® KMX SM was designed with 24 mixing elements with 3.81 cm diameter and arranged such that the angle between two neighboring elements is 90°. The internal structure of each element is open blade with the blades being convexly curved. The dimensions of the SM reactor are: 3.81 cm ID 80 S and 123 cm length and was operated cocurrently with vertical upflow. The NBR solutions of different concentrations (0.418 and 0.837 mol/L with respect to [CC]) were hydrogenated by using different concentrations of the osmium catalyst solution at various residence times. The reactions were conducted at a constant temperature of 138°C and at a constant pressure of 3.5 MPa. From the experimental results, it is observed that a conversion and/or degree of hydrogenation above 95% was achieved in a single pass from the designed continuous process. This is the first continuous process for HNBR production that gives conversions above 95% till date. Optimum catalyst concentration for a given mean residence time to achieve conversions above 95% were obtained. Finally, a mechanistic model for the SM reactor performance with respect to hydrogenation of NBR was proposed and validated with the obtained experimental results. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.AICHE JOURNAL, Issue 3 2009Abstract We conducted terephthalic acid (TPA) synthesis from p-xylene in high-temperature liquid water (HTW) at 300°C. The p-xylene concentration at the reaction condition was 0.2 mol L,1, which is the highest to date in research that achieved at least 80 mol % yields of TPA in HTW. Pure oxygen gas was the oxidant. Increasing the MnBr2 catalyst concentration increased the rate of TPA formation only slightly. In contrast, whether oxygen was fed in small, quick, discrete bursts, or fed continuously significantly affected the p-xylene conversion and the TPA selectivity. Adding oxygen in quick bursts and small increments led to high selectivities (>90 mol %) of TPA. Continuous addition of oxygen failed to do so. In addition to identifying the sensitivity of this synthesis to the oxygen feed method, these results also demonstrate the feasibility of HTW for TPA synthesis at higher concentrations, and hence high TPA production per unit reactor volume. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Characterization of downflowing high velocity fluidized bedsAICHE JOURNAL, Issue 3 2000Chunshe Cao A downer-riser circulating high velocity fluidization apparatus was developed to study the fundamentals of downflowing gas-solid particle mixtures. The acceleration and deceleration of solids due to the influences of the entrance and exit sections result in a relatively uniform axial solids distribution. Radial solid density profiles detected with an X-ray imaging system in the downer show the existence of a core-annulus flow with a dilute core surrounded by a denser wall region. Local solids flux profiles were obtained with an aspirating probe device and the solid velocity profile obtained from the two measured quantities. These confirm that the majority of solids segregates in a wall region that flows faster than the dilute core region. Thus, the shorter residence time in the high-speed downer wall region is coupled with faster reaction rates due to the accompanying high concentration of catalyst, while the dilute core has slower reaction rates with longer residence time due to the lower catalyst concentration and flow velocity. This results in much more uniform reaction extent over the cross-sectional area of the downer and, therefore, should improve the product selectivity. [source] Syntheses of cyclic polycarbonates by the direct phosgenation of bisphenol M,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005Hans R. Kricheldorf Abstract Bisphenol M was subjected to interfacial polycondensations in an NaOH/CH2Cl2 system with triethylamine as a catalyst. Regardless of the catalyst concentration, similar molecular weights were obtained, and matrix-assisted laser desorption/ionization time-of-flight mass spectra exclusively displayed mass peaks of cycles (detectable up to 15,000 Da). With triethyl benzyl ammonium chloride as a catalyst, linear chains became the main products, but the contents of the cycles and the molecular weights strongly increased with higher catalyst/bisphenol ratios. When the pseudo-high-dilution method was applied, both diphosgene and triphosgene yielded cyclic polycarbonates of low or moderate molecular weights. Size exclusion chromatography measurements, evaluated with the triple-detection method, yielded bimodal mass distribution curves with polydispersities of 5,12. Furthermore, a Mark,Houwink equation was elaborated, and it indicated that the hydrodynamic volume of poly(bisphenol M carbonate) was quite similar to that of poly(bisphenol A carbonate)s with similar concentrations of cyclic species. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1248,1254, 2005 [source] Novel cyclohexyl-substituted salicylaldiminato,nickel(II) complex as a catalyst for ethylene homopolymerization and copolymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Junquan Sun Abstract The cyclohexyl-substituted salicylaldiminato,Ni(II) complex [O(3-C6H11)(5-CH3)C6H2CHN-2,6-C6H3iPr2]Ni(PPh3)(Ph) (4) has been synthesized and characterized with 1H NMR and X-ray structure analysis. In the presence of phosphine scavengers such as bis(1,5-cyclooctadiene)nickel(0) [Ni(COD)2], triisobutylaluminum (TIBA), and triethylaluminum (TEA), 4 is an active catalyst for ethylene polymerization and copolymerization with the polar monomers tert -butyl-10-undecenoate, methyl-10-undecenoate, and 4-penten-1-ol under mild conditions. The polymerization parameters affecting the catalytic activity and viscosity-average molecular weight of polyethylene, such as the temperature, time, ethylene pressure, and catalyst concentration, are discussed. A polymerization activity of 3.62 × 105 g of PE (mol of Ni h),1 and a weight-average molecular weight of polyethylene of 5.73 × 104 g.mol,1 have been found for 10 ,mol of 4 and a Ni(COD)2/4 ratio of 3 in a 30-mL toluene solution at 45 °C and 12 × 105 Pa of ethylene for 20 min. The polydispersity index of the resulting polyethylene is about 2.04. After the addition of tetrahydrofuran and Et2O to the reaction system, 4 exhibits still high activity for ethylene polymerization. Methyl-10-undecenoate (0.65 mol %), 0.74 mol % tert -butyl-10-undecenoate, and 0.98 mol % 4-penten-1-ol have been incorporated into the polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6071,6080, 2004 [source] Solid-phase incorporation of gaseous carbon dioxide into oxirane-containing copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2004Bungo Ochiai Abstract Carbon dioxide was incorporated into poly(glycidyl methacrylate- co -methyl methacrylate) by a solid-phase reaction, which transformed the pendent oxirane moieties into cyclic carbonate moieties, with quaternary ammonium halide catalysts. The incorporation of carbon dioxide into the copolymer led to soluble carbonate-containing polymers, whereas the incorporation of carbon dioxide into the glycidyl methacrylate homopolymer produced an insoluble product. The copolymer composition, reaction temperature, and catalyst amount affected the incorporation efficiency and the side reaction that caused crosslinking. Effective incorporation was achieved under the following reaction conditions: the glycidyl methacrylate content was less than approximately 50%, the temperature was greater than the glass-transition temperature, and the catalyst concentration was 1.5,6 mol %. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3812,3817, 2004 [source] A new tetradentate ligand for atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004Shijie Ding Abstract The properties of a ligand, including molecular structure and substituents, strongly affect the catalyst activity and control of the polymerization in atom transfer radical polymerization (ATRP). A new tetradentate ligand, N,N,-bis(pyridin-2-ylmethyl-3-hexoxo-3-oxopropyl)ethane-1,2-diamine (BPED) was synthesized and examined as the ligand of copper halide for ATRP of styrene (St), methyl acrylate (MA), and methyl methacrylate (MMA), and compared with other analogous linear tetrdendate ligands. The BPED ligand was found to significantly promote the activation reaction: the CuBr/BPED complex reacted with the initiators so fast that a large amount of Cu(II)Br2/BPED was produced and thus the polymerizations were slow for all the monomers. The reaction of CuCl/BPED with the initiator was also fast, but by reducing the catalyst concentration or adding CuCl2, the activation reaction could be slowed to establish the equilibrium of ATRP for a well-controlled living polymerization of MA. CuCl/BPED was found very active for the polymerization of MA. For example, 10 mol% of the catalyst relatively to the initiator was sufficient to mediate a living polymerization of MA. The CuCl/BPED, however, could not catalyze a living polymerization of MMA because the resulting CuCl2/BPED could not deactivate the growing radicals. The effects of the ligand structures on the catalysis of ATRP are also discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3553,3562, 2004 [source] Novel, biodegradable, functional poly(ester-carbonate)s by copolymerization of trans -4-hydroxy- L -proline with cyclic carbonate bearing a pendent carboxylic groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Ren-Shen Lee Abstract Water-soluble poly(ester-carbonate) having pendent amino and carboxylic groups on the main-chain carbon is reported for the first time. This article describes the melt ring-opening/condensation reaction of trans -4-hydroxy- N -benzyloxycarbonyl- L -proline (N -CBz-Hpr) with 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the copolymers was investigated. The polymerizations were carried out in bulk at 110 °C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester-carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, 1H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (Mn = 6000,14,700 g mol,1) with reasonable molecular weight distributions (Mw/Mn = 1.11,2.23). The values of the glass-transition temperature (Tg) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the Tg increased from 16 to 48 °C. The relationship between the poly(N -CBz-Hpr- co -MBC) Tg and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N -CBz-Hpr- co -MBC)s was evaluated from weight-loss measurements and the change of Mn and Mw/Mn. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester-carbonate), 4, with pendent amino and carboxylic groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2303,2312, 2004 [source] A Rapid Eco-Friendly Synthesis of Poly(butylene succinate) by a Direct Polyesterification under Microwave IrradiationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2005Sivan Velmathi Abstract Summary: A rapid and eco-friendly synthesis of poly(butylene succinate) (PBS) using microwaves was developed in the presence of 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane as catalyst. To determine the optimum conditions, the effect of catalyst concentration, bulk vs. solution polymerization, reaction time, temperature, and stoichiometry of the monomers were studied. Based on the optimum conditions, PBS with a weight-average molecular weight of 2.35,×,104 was obtained in a short time of 20 min. Synthesis of poly(butylene succinate) under microwave irradiation. [source] Novel Biodegradable Aliphatic Polycarbonate Based on Ketal Protected DihydroxyacetoneMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2004Lian-Sheng Wang Abstract Summary: A novel aliphatic polycarbonate based on ketal protected dihydroxyacetone was synthesized by ring-opening polymerization of cyclic carbonate monomer, 2,2-ethylenedioxypropane-1,3-diol carbonate (EOPDC), in bulk. Effects of polymerization conditions such as catalysts, catalyst concentration, reaction temperature and reaction time on the polymerization were investigated. The polycarbonate obtained was characterized by GPC, FTIR, 1H NMR, 13C NMR and DSC. The study on in vitro degradation of PEOPDC shows that the degradation mainly results from surface erosion. Synthesis of an aliphatic polycarbonate with a high molecular weight by ring-opening polymerization of cyclic carbonate monomer EOPDC. [source] Mathematical Modeling of Atom-Transfer Radical Polymerization Using Bifunctional InitiatorsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Mamdouh Al-Harthi Abstract Summary: Bifunctional initiators can produce polymers with higher molecular weight at higher initiator concentrations than monofunctional initiators. In this study, we developed a mathematical model for ATRP with bifunctional initiators. The most important reactions in ATRP were included in the model. The method of moments was used to predict monomer conversion, average molecular weights and polydispersity index as a function of polymerization time in batch reactors. The model was used to understand the mechanism of ATRP and to quantify how polymerization conditions affect monomer conversion and polymer properties by examining the effect of several rate constants (activation, deactivation, propagation and chain termination) and of catalyst and initiator concentration on polymerization kinetics and polymer properties. When compared to monofunctional initiators, bifunctional initiators not only produce polymers with higher molecular weight averages at higher polymerization rates, but also control their molecular weight distributions more effectively. Effect of initial catalyst concentration on polydispersity index as a function of time. [source] Ring-opening polymerization of D,L -lactide by rare earth 2,6-dimethylaryloxidePOLYMER INTERNATIONAL, Issue 8 2004Lifang Zhang Abstract Ring-opening polymerization of D,L -lactide (LA) has been successfully carried out by using rare earth 2,6-dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L -lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol,1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol,1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ,coordination,insertion' mechanism with selective cleavage of the acyl,oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry [source] Highly Efficient Biomimetic Oxidation of Sulfide to Sulfone by Hydrogen Peroxide in the Presence of Manganese meso -TetraphenylporphyrinCHINESE JOURNAL OF CHEMISTRY, Issue 6 2008Xian-Tai ZHOU Abstract Low amount of manganese meso -tetraphenyl porphyrin [Mn(TPP)] was used for highly efficient selective oxidation of sulfide to sulfone by hydrogen peroxide at room temperature. Sulfones were produced directly with yields generally around 90% while the catalyst concentration was only 4×10,5 mol·L,1. In a large-scale experiment of thioanisole oxidation, the isolated yield of sulfone (87%) was obtained and the turnover number (TON) reached up to 8×106, which is the highest TON for the oxidation systems of sulfide to sulfone catalyzed by metalloporphyrins. [source] New Iron(II) Complexes for Atom-Transfer Radical Polymerization: The Ligand Design for Triazacyclononane Results in High Reactivity and Catalyst PerformanceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Mitsunobu Kawamura Abstract Mononuclear cordinatively unsaturated iron(II) complexes having a triazacyclononane ligand were developed as highly efficient and environmentally friendly catalysts for the atom-transfer radical polymerization (ATRP). These iron catalysts showed high performance in the well-controlled ATRP of styrene, methacrylates, and acrylates. The high reactivity of these catalysts led to well-controlled polymerization and block copolymerization even with lower catalyst concentrations. [source] The Aerobic Oxidative Cleavage of Lignin to Produce Hydroxyaromatic Benzaldehydes and Carboxylic Acids via Metal/Bromide Catalysts in Acetic Acid/Water MixturesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Walt Partenheimer Abstract Roughly 30% of all woody plants is composed of lignin. Five different lignin samples, from wood and bagasse, were oxidized in air with a cobalt/manganese/zirconium/bromide (Co/Mn/Zr/Br) catalyst in acetic acid as a function of time, temperature, pressure, and lignin and catalyst concentrations. 18 products were identified via gas chromatography-mass spectrometry (GC/MS). The most valuable products from lignin were 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy-3-methoxybenzoic acid (vanillic acid), 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde) and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid). 10.9,wt% of the lignin was converted to the aromatic products. By the use of model compounds we demonstrate that 1) the presence of the phenolic functionality on an aromatic ring does inhibit the rate of reaction but that the alkyl group on the ring still does oxidize to the carboxylic acid, 2) that the masking of phenol by acetylation occurs at a reasonable rate in acetic acid, 3) that the alkyl group of the masked phenol does very readily oxidize, 4) that an acetic anhydride/acetic acid mixture is a good oxidation solvent and 5) that a two-step acetylation/oxidation to the carboxylic acid is feasible. [source] Effect of grafting methacrylate monomers onto jute constituents with a potassium persulfate initiator catalyzed by Fe(II)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Md. Ibrahim H. Mondal Abstract The graft copolymerization of methyl methacrylate and ethyl methacrylate monomers onto jute fiber was carried out in an aqueous medium with potassium persulfate as an initiator under the catalytic influence of ferrous sulfate in the presence of air. The effects of parameter variables, such as the monomer, initiator, and catalyst concentrations, the reaction time, and the temperature, on grafting and the effect of grafting the monomers onto jute constituents were studied. The degree of grafting depended on the kinds of monomers and the parameter variables. The maximum graft yield percentages with methyl methacrylate and ethyl methacrylate under optimized conditions were 18.9 and 38.8%, respectively, and the grafting onto jute fiber was largely affected by one of its main constituents, such as hemicellulose. The graft copolymers were characterized, and their improved properties were also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2369,2375, 2007 [source] Kinetic study of the manganese-based catalytic hydrogen peroxide oxidation of a persistent azo-dyeJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Chedly Tizaoui Abstract BACKGROUND: The discharge of synthetic dyes by the textile industry into the environment poses concerns due to their persistence and toxicity. New efficient treatment processes are required to effectively degrade these dyes. The aim of this work was to study the degradation of a persistent dye (Drimarene Brilliant Reactive Red K-4BL, C.I.147) using H2O2 oxidation catalysed by an Mn(III)-saltren catalyst and to develop a kinetic model for this system. RESULTS: Dye oxidation with H2O2 was significantly improved by the addition of the catalyst. As the pH was increased from 3 to 10, the oxidation rates increased significantly. The kinetic model developed in this study was found to adequately explain the experimental results. In particular, dye oxidation can be described at high pH by pseudo-first-order kinetics. A Michaelis,Menton type equation was developed from the model and was found to adequately describe the effect of H2O2 and catalyst concentrations on the apparent pseudo-first-order rate constant. Optimum catalyst and H2O2 concentrations of 500 mg L,1 and 6.3 g L,1, respectively, were found to give maximum reaction rates. CONCLUSION: Catalytic H2O2 oxidation was found to be effective for the removal of persistent dye and the results obtained in this work are of significance for design and scale-up of a treatment process. Copyright © 2009 Society of Chemical Industry [source] Fluoropolyethers end-capped by polar functional groups.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Abstract The kinetics of the dibutyltin dilaurate (DBTDL)-catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z-DOL H-1000 of various molecular weights (100,1084 g mol,1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30,60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl-containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero-order, first-order, second-order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771,3795, 2002 [source] | |||||||||||||