Home About us Contact
|
Home About us Contact | ||
|
|
||
Main Products (main + products)
Selected AbstractsCatalytic cleavage of methyl oleate or oleic acidEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 1 2010Angela Köckritz Abstract Different reaction pathways are discussed for the Os-catalyzed oxidation of methyl oleate and oleic acid using O2/aldehyde as oxidation system. Monomethyl azelate and pelargonic acid were the main products obtained in yields of approximately 50,70% starting from methyl oleate. Besides, varying amounts of methyl 9,10-epoxystearate and methyl 9,10-dihydroxystearate were found as by-products. Azelaic acid and pelargonic acid were obtained exclusively from oleic acid used as reactant. Some mechanistic considerations led to the conclusion that the observed products are formed in parallel reaction paths. The effective oxidant for the scission of the C=C double bond seems to be very likely an in situ formed peracid generated by Os-catalysis from O2/aldehyde. Additional investigations concerning the cleavage of oleic acid and methyl oleate with in situ formed performic acid from H2O2/formic acid corroborate this assumption. [source] Oxidation of ,4 - and ,5 -Steroids with Hydrogen Peroxide Catalyzed by Porphyrin Complexes of MnIII and FeIIIEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2004Susana L. H. Rebelo Abstract In this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of ,4 - and ,5 -steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17,-acetoxy-4-androstene (1), 4-cholestene (2) and 3,-acetoxy-5-cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal allows the control of the preferential formation of ,- or ,-epoxides. Porphyrins with bulky, electron-withdrawing groups in the ortho positions of the meso phenyls and with MnIII as the central metal ion, such as [Mn(TDCPP)Cl], gave preferentially the ,-epoxide of ,4 - and ,5 -steroids. [Fe(TPFPP)Cl] catalyzes preferentially the ,-epoxidation of ,4 -steroids and also increases the stereoselectivity for the ,-epoxide in ,5 -steroids, similar to the results obtained with m -CPBA (m -chloroperbenzoic acid) as oxidant. The substrate structure strongly influences the chemoselectivity of the reactions. The X-ray structures of two main products were determined, and two-dimensional NMR techniques allowed the full assignment of 1H and 13C NMR resonances as well as the stereochemistry of these products. A mechanistic proposal involving oxo species for the ,-approach and peroxy species for the ,-approach is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Theoretical study of lipid biosynthesis in wild-type Escherichia coli and in a protoplast-type L-form using elementary flux mode analysisFEBS JOURNAL, Issue 4 2010Dimitar Kenanov In the present study, we investigated lipid biosynthesis in the bacterium Escherichia coli by mathematical modeling. In particular, we studied the interaction between the subsystems producing unsaturated and saturated fatty acids, phospholipids, lipid A, and cardiolipin. The present analysis was carried out both for the wild-type and for several in silico knockout mutants, using the concept of elementary flux modes. Our results confirm that, in the wild type, there are four main products: L1-phosphatidylethanolamine, lipid A, lipid A (cold-adapted), and cardiolipin. We found that each of these compounds is produced on several different routes, indicating a high redundancy of the system under study. By analysis of the elementary flux modes remaining after the knockout of genes of lipid biosynthesis, and comparison with publicly available data on single-gene knockouts in vivo, we were able to determine the metabolites essential for the survival of the cell. Furthermore, we analyzed a set of mutations that occur in a cell wall-free mutant of Escherichia coli W1655F+. We postulate that the mutant is not capable of producing both forms of lipid A, when the combination of mutations is considered to make a nonfunctional pathway. This is in contrast to gene essentiality data showing that lipid A synthesis is indispensable for the survival of the cell. The loss of the outer membrane in the cell wall-free mutant, however, shows that lipid A is dispensable as the main component of the outer surface structure in this particular E. coli strain. [source] Large-Scale Synthesis, Annealing, Purification, and Magnetic Properties of Crystalline Helical Carbon Nanotubes with Symmetrical Structures,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2007J. Tang Abstract Crystalline helical carbon nanotubes (HCNTs) are synthesized as the main products in the pyrolysis of acetylene at 450,°C over Fe nanoparticles generated by means of a combined sol,gel/reduction method. Transmission electron microscopy (TEM) images reveal that there are two HCNTs attached to each Fe3C nanoparticle, and that the two HCNTs are mirror images of each other. Annealing in Ar at 750,°C and purification by immersion in hot (90,°C) HCl solution do not significantly change the structure of the HCNTs, despite the partial removal of Fe nanoparticles by the latter treatment. The magnetic properties of the as-prepared, annealed, and purified HCNTs have been systematically examined. The annealed sample shows relatively high magnetization due to the ferromagnetic ,-Fe nanoparticles encapsulated in the HCNT nodes. In the case of HCl treatment, relatively pure HCNTs are obtained by the removal of ferromagnetic nanoparticles from the double-HCNT nodes. The effects of the amount of catalyst used in the synthesis process on the morphology and yield of the carbon products have also been investigated. [source] New Approaches to 6-Oxoisoaporphine and Tetrahydroisoquinoline DerivativesHELVETICA CHIMICA ACTA, Issue 7 2010Eduardo Sobarzo-Sánchez Abstract 2,3-Dihydro-6-hydroxy-5-methoxy-7H -dibenzo[de,h]quinolin-7-one, 6-hydroxy-5-methoxy-7H -dibenzo[de,h]quinolin-7-one, and 2-(6,7-dimethoxy-3,4-dihydroisoquinolin-1-yl)benzyl benzoate, easily available by a Bischler,Napieralski cyclization, were used as starting materials to afford 6-oxoisoaporphine and 2,3-dimethoxy-5,6,8,12b-tetrahydroisoindolo[1,2- a]isoquinoline as the main products. However, the catalytic hydrogenation of the benzyl benzoate derivative afforded, under mild conditions, 1,2,3,4-tetrahydro-6,7-dimethoxy-1-(2-methylphenyl)isoquinoline. [source] Photocyclodimerization of 5-Methyl-2H -pyran-3(6H)-oneHELVETICA CHIMICA ACTA, Issue 12 2008Ljubov Groesch Abstract The structures of the main products resulting from photocyclodimerization of the title compound 2 and of other 3-methyl-substituted ,oxacyclohex-2-en-1-ones' (=dihydropyranones) were determined by X-ray crystallography. In connection, the 13C-NMR chemical shifts of the cyclobutane C-atoms of these dimers allow a clear differentiation between head-to-head and head-to-tail regioisomers, all structurally related to those of isophorone (1). [source] (E/Z)-Isomerization of 3,-EpiluteinHELVETICA CHIMICA ACTA, Issue 8 2004Péter Molnár 3,-Epilutein (=(all- E,3R,3,S,6,R)-4,,5,-didehydro-5,,6,-dihydro- ,,, -carotene-3,3,-diol; 1), isolated from the flowers of Caltha palustris, was submitted to both thermal isomerization and I2 -catalyzed photoisomerization. The structures of the main products (9Z)- 1, (9,Z)- 1, (13Z)- 1, (13,Z)- 1, (15Z)- 1, and (9Z,9,Z)- 1 were determined based on UV/VIS, CD, 1H-NMR, and MS data. [source] Preparation and (E/Z)-Isomerization of the Diastereoisomers of ViolaxanthinHELVETICA CHIMICA ACTA, Issue 1 2004Péter Molnár Violaxanthin A (=(all- E,3S,5S,6R,3,S,5,S,6,R)-5,6,:,5,,6,-diepoxy-5,6,5,,6,-tetrahydro- ,,, -carotene-3,3,-diol =syn,syn- violaxanthin; 5) and violaxanthin B (=(all- E,3S,5S,6R,3,S,5,R,6,S)-5,6,:,5,,6,-diepoxy-5,6,5,,6,-tetrahydro- ,,, -carotene-3,3,-diol=syn,anti- violaxanthin; 6) were prepared by epoxidation of zeaxanthin diacetate (1) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I2 -catalyzed photoisomerization. The structure of the main products, i.e., (9Z)- 5, (13Z)- 5, (9Z)- 6, (9,Z)- 6, (13Z)- 6, and (13,Z)- 6, was determined by their UV/VIS, CD, 1H-NMR, 13C-NMR, and mass spectra. [source] A Mild, One-Pot Synthesis of Arylamines via Palladium- Catalyzed Addition of Aryl Aldehydes with Amines and Arylboronic Acids in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2009Ajuan Yu Abstract A mild, one-pot synthesis of diarylmethylamines via the palladium-catalyzed addition of aryl aldehydes with amines and arylboronic acids is reported. Best results were obtained in neat water with ammonium chloride as additive, affording diarylmethylamine derivatives as the main products. [source] Theoretical study on the gas-phase reaction mechanism between nickel monoxide and methane for syngas productionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2009Hua-Qing Yang Abstract The comprehensive mechanism survey on the gas-phase reaction between nickel monoxide and methane for the formation of syngas, formaldehyde, methanol, water, and methyl radical has been investigated on the triplet and singlet state potential energy surfaces at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(2d, 2p) levels. The computation reveals that the singlet intermediate HNiOCH3 is crucial for the syngas formation, whereas two kinds of important reaction intermediates, CH3NiOH and HNiOCH3, locate on the deep well, while CH3NiOH is more energetically favorable than HNiOCH3 on both the triplet and singlet states. The main products shall be syngas once HNiOCH3 is created on the singlet state, whereas the main products shall be methyl radical if CH3NiOH is formed on both singlet and triplet states. For the formation of syngas, the minimal energy reaction pathway (MERP) is more energetically preferable to start on the lowest excited singlet state other than on the ground triplet state. Among the MERP for the formation of syngas, the rate-determining step (RDS) is the reaction step for the singlet intermediate HNiOCH3 formation involving an oxidative addition of NiO molecule into the CH bond of methane, with an energy barrier of 120.3 kJ mol,1. The syngas formation would be more effective under higher temperature and photolysis reaction condition. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Synthesis of nitrogen-containing heterocycles 9,.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2000- a][, Preparation, ]-triazolo[, ]triazine] derivatives, carbon-carbon bond cleavage of spiro[cycloalkane[, related compounds Diaminomethylenehydrazones of cyclic ketones 1,5 reacted with ethyl N -cyanoimidate (I) at room temperature or with bis(methylthio)methylenecyanamide (II) under brief heating to give directly the corresponding spiro[cycloalkane[1,,2,,4,]triazolo[1,,5,,- a][1,,3,-5,]triazine] derivatives 7,12 in moderate to high yields. Ring-opening reaction of the spiro[cycloalkanetriazolotriazine] derivatives occurred at the cycloalkane moiety upon heating in solution to give 2-alkyl-5-amino[1,2,4]triazolotriazines 13,16. Diaminomethylenehydrazones 17,19, of hindered acyclic ketones, gave 2-methyl-7-methylthio[1,2,4]-triazolo[1,5- a][1,3,5]triazines 21,23 by the reaction with II as the main products with apparent loss of 2-methylpropane from the potential precursor, 2- tert -butyl-2-methyl-7-methylthio[1,2,4]triazolo[1,5- a]-[1,3,5]triazines 20, in good yields. In general, bis(methylthio)methylenecyanamide II was found to be a favorable reagent to the one-step synthesis of the spiro[cycloalkanetriazolotriazine] derivatives from the diaminomethylenehydrazones. The spectral data and structural assignments of the fused triazine products are discussed. [source] Air drying of milk droplet under constant and time-dependent conditionsAICHE JOURNAL, Issue 6 2005Xiao Dong Chen Abstract Spray drying is the prime process for many years for manufacturing food powders. Dairy powders are one of the main products consumed worldwide. There has been a stream of studies published previously on both modeling the drying characteristics of a single milk droplet and the dryer wide simulations incorporating computational fluid dynamics (CFD). In CFD simulations, large numbers of particles of different sizes need be tracked to represent the size distribution; it is desirable to have an accurate yet simple model for drying of a single droplet, which does not require partial differential equation. Here for the first time, two such models are validated. One model is of the characteristic drying rate curve approach and the other (new) model is of the reaction engineering approach. The model predictions are compared against a very wide range of experimental results including isothermal and time-varying temperature conditions. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [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] Catalytic Effects of Metals on the Conversion of Methane in Gliding DischargesPLASMA PROCESSES AND POLYMERS, Issue 7-8 2007Krzysztof Schmidt-Sza, owski Abstract Plasma-catalytic methane conversion was studied under gliding-discharge conditions using a mobile (spouted) catalytic bed of fine particles. A new model of the GD reactor was tested for the non-oxidative methane coupling using alumina-supported catalysts containing Cu, Ni, Ag or Pt resistant against the plasma action. C2 hydrocarbons, besides hydrogen, were the main products, with some amounts of non-volatile substances (mainly soot). With Cu/Al2O3, Ni/Al2O3, Ag/Al2O3, and alumina beds, acetylene was mainly produced from the CH4,+,H2 mixture with none or a minor share of other C2 hydrocarbons. Using Pt/Al2O3, an increased ethylene and ethane content was found with lower acetylene content. [source] Synthesis and Characterization of Hydroxy-Functionalized Models for the Active Site in Fe-Only-HydrogenasesCHEMISTRY & BIODIVERSITY, Issue 9 2007Ulf-Peter Apfel Abstract The reactions of dl -1,4-disulfanylbutane-2,3-diol and 1,3-disulfanylpropan-2-ol with dodecacarbonyltriiron have been investigated. As main products, the iron complexes 1 and 2 were isolated and characterized by spectroscopic methods, as well as single crystal X-ray analysis. Additionally, the unusually large bond angles in the dithiolato bridge was investigated via density-functional theory (DFT) calculations. Moreover, the electrochemical features have been studied by cyclic voltammetry. [source] Nickel(II) Complexes Bearing NH2CH2CH2CH2NH2 and o -C6H4(NH2)2 Ligands: Synthesis, Structures and Their Ethylene Polymerization BehaviorCHINESE JOURNAL OF CHEMISTRY, Issue 2 2009Xiaoming LU Abstract Two nickel complexes [Ni(NH2CH2CH2CH2NH2)3]Cl2 (1) and [Ni(C6H4N2H4)2Cl2] (2) have been obtained and characterized by IR and single crystal X-ray diffraction analysis. In complex 1, the nickel atom was in a chiral pseudo-octahedral [NiN6] geometry environment, which was coordinated by three 1,3-propylenediamine to form three six-membered rings. However in complex 2, besides connected with two o -phenylenediamine through four Ni,N bonds to form two five-membered rings, the nickel center was coordinated by two Cl to form trans -Ni-Cl2, which was different from general reported diimine nickel complexes. Activated with MAO, MMAO or Et2AlCl, these nickel complexes exhibited considerable good catalytic activity [up to 3.59×106 g·mol,1·h,1 for complex 2] for ethylene polymerization with main products as dimers or trimers of ethylene. [source] | |||||||||||||||||||||||||