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Dehydration Reaction (dehydration + reaction)
Selected AbstractsUnusual Mobility of Cesium via a Reversible Topotactic Dehydration Reaction in a New Hydroxygallophosphate with an Intersecting Tunnel Structure.CHEMINFORM, Issue 34 2006J. Lesage 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] Innovative Katalysatoren zur oxidativen Dehydrierung in der Gasphase , Metallische KurzfasernCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 6 2004R. Brüning Abstract Metallische Kurzfasern in ausgesuchter Legierungszusammensetzung und Gefügestruktur wurden auf ihre katalytische Aktivität bei der oxidativen Dehydrierung (ODH) von Propan zu Propen und von Isopropanol zu Aceton untersucht. Die über das Schmelzextraktions-Verfahren hergestellten Kurzfasern wurden einer intensiven Charakterisierung ihrer werkstoffseitigen Eigenschaften unterworfen. Dabei kamen lichtmikroskopische, DSC-, XRD-, REM- und EDX-Untersuchungen zum Einsatz, um Zusammenhänge zwischen der Werkstoffzusammensetzung, dem Gefüge und den katalytischen Eigenschaften zu ermitteln. Es werden ausgewählte Ergebnisse zur Temperaturabhängigkeit des Propan-Umsatzes bzw. der Propen-Selektivität präsentiert. So wurde Propen bei einem Propan-Umsatz von mehr als 50,% mit einer Ausbeute von 35,% gebildet. Auch die Selektivoxidation von Isopropanol zu Aceton erfolgte mit attraktiven Ausbeuten von über 80,%. Die Ergebnisse insgesamt belegen das hohe Innovationspotenzial der Metallfaserwerkstoffe. Innovative Catalysts for Oxidative Dehydration Reactions in the Gas Phase , Metallic Short Fibres The catalytic activity of metallic short fibres with chosen alloy composition and texture was investigated in the oxidative dehydration (ODH) of propane to yield propene, and of isopropanol to yield acetone. The short fibres were synthesised using a melt extraction process and the properties of the fibres were intensely characterised. A correlation between the structure and the catalytic activity of the material was established. Thus, light-optical microscopic-, DSC-, XRD-, REM- and EDX-methods were used to characterise the fibres. Selective results of the dependency of the temperature on the propane conversion are presented in this work. A yield of more than 35,% propene is obtained at a propane conversion of 50,%. The ODH of isopropanol to acetone occurred with attractive yields of over 80,%. The results demonstrate the high innovative potential of the metal fibre materials. [source] Dehydration Reactions in Water.CHEMINFORM, Issue 10 2003Broensted Acid, Dithioacetal Formation in Water., Ether, Surfactant-Combined Catalyst for Ester, Thioether Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Dehydration Reactions in Water.CHEMINFORM, Issue 5 2002Surfactant-Type Broensted Acid Catalyzed Direct Esterification of Carboxylic Acids with Alcohols in an Emulsion System. 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] Matrix-assisted laser desorption/ionisation mass spectrometry for the direct analysis of enzymatically digested kappa - iota - and hybrid iota/nu -carrageenans,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2005Aristotelis Antonopoulos Enzymatically digested oligosaccharides of kappa -, iota - and hybrid iota/nu -carrageenans were analysed using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry in the negative-ion mode. nor -Harmane was used as matrix. Depending on the stock concentration and the laser intensity applied, the oligosaccharides exhibited losses of sulphate units (neutralised by the Na+ ion, and thus non-stable), leaving the primary backbone structure in most cases with only the deprotonated sulphate groups (carrying the negative charge, stable). This meant that kappa - and iota -oligosaccharides could not be easily distinguished from one another since they share the same primary backbone structure. However, for the hybrid iota/nu -oligosaccharides the primary backbone structure could be identified since the nu -carrageenan repeating unit differs from that of the kappa/iota -carrageenan unit. For all types of oligosaccharides, the results indicated cleavage of an anhydrogalactose unit from the non-reducing end. Specifically, for the hybrid oligosaccharides of iota/nu -carrageenans, this type of fragmentation means that the nu -carrageenan unit is not positioned on the non-reducing end of the hybrid oligosaccharides. Dehydration reactions, and exchange reactions of Na+ with K+ and Ca2+, were also observed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Photochemistry of Salicylaldoxime in Solid Argon: An Experimental and Theoretical StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Joanna Grzegorzek Abstract The photochemistry of salicylaldoxime in solid argon has been investigated by FTIR spectroscopy and DFT calculations. The salicylaldoxime molecule trapped in the matrix from the vapor above the solid sample has the most stable syn1 conformation with an intramolecular hydrogen bond. Irradiation (, > 320 nm) leads to conversion of the syn1 conformer into the syn3 one, in which the C(H)NOH and (C)OH groups are rotated around the C,C and C,O bonds, respectively, and the intramolecular hydrogen bond is broken. The photochemistry of syn3 involves three possible routes: (i) conversion of syn3 into anti2 conformer, this process requires rearrangement of the NOH group with respect to the C=N bond; (ii) photodissociation of salicylaldoxime into 2-cyanophenol and water, which form a hydrogen-bonded complex; and (iii) regeneration of the syn1 conformer. The third route is a very small contribution to the overall process. The study performed with [D2]salicylaldoxime indicates that the dehydration reaction of salicylaldoxime involves cleavage of the N,O bond and formation of OH and Ph(OH)C(H)N radicals in the first step. Then, the OH radical abstracts a hydrogen atom from the CH group to form 2-cyanophenol and water molecules. When the sample is exposed to the full output of the mercury lamp the 2-cyanophenol complex with water becomes the dominating product. [source] Thermal properties of gypsum plasterboard at high temperaturesFIRE AND MATERIALS, Issue 1 2002Geoff Thomas Light timber frame wall and floor assemblies typically use gypsum-based boards as a lining to provide fire resistance. In order to model the thermal behaviour of such assemblies, the thermo-physical properties of gypsum plasterboard must be determined. The relevant literature and the chemistry of the two consecutive endothermic dehydration reactions that gypsum undergoes when heated are reviewed. The values determined for the thermo-physical properties are modified to create smooth enthalpy and thermal conductivity curves suitable for input into a finite element heat transfer model. These values are calibrated within a reasonable range and then validated using furnace and fire test data. The type of plasterboard used in these tests is an engineered product similar to the North American type C board. The temperature at which the second dehydration reaction occurs is altered to be consistent with later research with little apparent affect on the comparison with test results. Values for specific heat, mass loss rates and thermal conductivity for gypsum plasterboard that are suitable for use in finite element heat transfer modelling of light timber frame wall and floor assemblies are recommended. Copyright © 2002 John Wiley & Sons, Ltd. [source] Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Homayoon Bahrami The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an ,-amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual ,-amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4-dimethylpiperazine-2,5-dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some ,-amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the "critical ratio." The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the "delayed autocatalytic behavior" of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first-order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first-order dependence on Mn2+ ions in catalytic pathways. The correspondence of pseudo-order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified "critical ratio" as well as "delayed autocatalytic behavior" concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689,703, 2009 [source] An efficient and regiospecific preparation of trifluoromethyl substituted 4-( 1H -pyrazol-1 -yl)-7-chloroquinolinesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2005Helio G. Bonacorso A new series of 4-[3-alkyl(aryl)(heteroaryl)-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H -pyrazol-1-yl]-7-chloroquinolines, where [alkyl = CH3; aryl = C6H5, 4-CH3C6H4, 4-FC6H4, 4-ClC6H4, 4-BrC6H4, 4-CH3OCgH4, 4-NO2CgH4, 4-biphenyl, 1-naphthyl; heteroaryl = 2-furyl and 2-thienyl] has been regiospecifi-caly obtained from the reaction of 7-chloro-4-hydrazinoquinoline with 4-substituted-l,1,1-trifluoro-4-methoxybut-3-en-2-ones in 61 - 96 % yield. Subsequently, dehydration reaction of 4,5-dihydropyra-zolylquinolines under acid conditions furnished a new series of 4-(3-substituted-5-trifluoromethyl-1H -pyra-zol-1-yl)-7-chloroquinolines in 73 - 96 % yield. [source] Kinetic study of the decomposition of 2-butanol on carbon-based acid catalystAICHE JOURNAL, Issue 6 2010J. Bedia Abstract The catalytic conversion of 2-butanol on a carbon-based acid catalyst prepared by chemical activation of olive stone with phosphoric acid was investigated. The carbon catalyst showed a considerable amount of surface phosphorus, presumably in form of phosphate groups, as revealed by XPS, despite a washing step carried out after the activation process. Conversion of 2-butanol yields mainly dehydration products, mostly cis-2-butene and trans-2-butene with lower amounts of 1-butene, and a very small amount of mek as dehydrogenation product. Kinetic interpretation of the experimental data was performed using two elimination mechanisms for the dehydration reaction; an E1-mechanism (two-step mechanism) and an E2-mechanism (one-step mechanism). The rate expressions derived from both models fit properly the experimental results, suggesting that probably the two mechanisms occur simultaneously. This is supported by the similar rate constant obtained for the formation of the carbocation and the olefins in the E1 and E2 mechanisms, respectively. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] H2O2 -mediated oxidation of tetrahydrobiopterin: Fourier transform Raman investigations provide mechanistic implications for the enzymatic utilization and recycling of this essential cofactorJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2002Jeremy Moore The oxidation of (6R)- L - erythro -5,6,7,8-tetrahydrobiopterin (6BH4) by H2O2 was examined by Fourier transform Raman spectroscopy. Initial investigations indicated that oxidation proceeds by incorporation of the H2O2 into the 6BH4 molecule without the formation of any additional water. In addition, the pyrimidine ring is affected with the shift of the double bond from the N1,C2 to the C2,N3 position. Such rearrangements of this double bond are observed after the production of either a carbinolamine or quinonoid species. Using deuterium exchange experiments, it was possible to substantiate that the oxidation of 6BH4 initially proceeds by the formation of a 4a-OH-carbinolamine intermediate prior to its spontaneous dehydration yielding the quinonoid dihydro species (qBH2). Furthermore, the hydrogen on the hydroxyl group of the carbinolamine interacts with the oxygen of the carbonyl group at the C4 position of the pyrimidine ring. It is proposed that this interaction facilitates the dehydration of the carbinolamine, thus explaining its instability. Furthermore, a mechanism for the dehydration reaction is suggested, wherein the 4a-hydroxyl group forms an H-bond to the carbonyl group, thus making the oxygen of the hydroxyl group more susceptible to attack by the proton at position N5 of the pyrazine ring, resulting in qBH2 production concomitant with the loss of a water molecule. Upon increasing the concentration of H2O2 the qBH2 converts to 7,8-BH2, which is further oxidized to L -biopterin. Taken together, our results do not support an earlier proposed mechanism implicating a hydroperoxide intermediate in this oxidation reaction. Copyright © 2002 John Wiley & Sons, Ltd. [source] Systematic Regulation of the Enzymatic Activity of Phenylacetaldoxime Dehydratase by Exogenous LigandsCHEMBIOCHEM, Issue 12 2006Katsuaki Kobayashi Dr. Abstract Phenylacetaldoxime dehydratase from Bacillus sp. OxB-1 (OxdB) contains a heme that acts as the active site for the dehydration reaction of aldoxime. Ferrous heme is the active form, in which the heme is five coordinate with His282 as a proximal ligand. In this work, we evaluated the functional role of the proximal ligand for the catalytic properties of the enzyme by "the cavity mutant technique". The H282G mutant of OxdB lost enzymatic activity, although the heme, which was five coordinate with a water molecule (or OH,) as an axial ligand, existed in the protein matrix. The enzymatic activity was rescued by imidazole or pyridine derivatives that acted as the exogenous proximal ligand. By changing the electron-donation ability of the exogenous ligand with different substituents, the enzymatic activity could be regulated systematically. The stronger the electron-donation ability of the exogenous ligand, the higher was the restored enzymatic activity. Interestingly, H282G OxdB with 2-methyl imidazole showed a higher activity than the wild-type enzyme. Kinetic analyses revealed that the proximal His regulated not only the affinity of substrate binding to the heme but also the elimination of the OH group from the substrate. [source] Thermal properties of gypsum plasterboard at high temperaturesFIRE AND MATERIALS, Issue 1 2002Geoff Thomas Light timber frame wall and floor assemblies typically use gypsum-based boards as a lining to provide fire resistance. In order to model the thermal behaviour of such assemblies, the thermo-physical properties of gypsum plasterboard must be determined. The relevant literature and the chemistry of the two consecutive endothermic dehydration reactions that gypsum undergoes when heated are reviewed. The values determined for the thermo-physical properties are modified to create smooth enthalpy and thermal conductivity curves suitable for input into a finite element heat transfer model. These values are calibrated within a reasonable range and then validated using furnace and fire test data. The type of plasterboard used in these tests is an engineered product similar to the North American type C board. The temperature at which the second dehydration reaction occurs is altered to be consistent with later research with little apparent affect on the comparison with test results. Values for specific heat, mass loss rates and thermal conductivity for gypsum plasterboard that are suitable for use in finite element heat transfer modelling of light timber frame wall and floor assemblies are recommended. Copyright © 2002 John Wiley & Sons, Ltd. [source] Geochemical and stable isotope resetting in shear zones from Täschalp: constraints on fluid flow during exhumation in the Western AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2003I. Cartwright Abstract Fluid flow at greenschist facies conditions during exhumation of the western Alps occurred in several penecontemporaneous systems, including shear zones at lithological contacts, deformed contacts between serpentinite bodies and metabasalts, albite veins within metabasalts, and calcite + quartz veins within calcareous schists. Fluid flow in shear zones that juxtapose metasediments and ophiolitic rocks within the Piemonte Unit reset O and H isotope ratios. ,18O values are buffered by the wall rocks; however, calculated fluid ,2H values are similar within all the shear zones suggesting that they formed an interconnected network. The similarity of ,2H values of the sheared rocks and those of unsheared calcareous schists suggests that the fluids were derived from, or had equilibrated with, the schists that envelop the ophiolite rocks. Time-integrated fluid fluxes at the sheared contacts estimated from changes in Si in metabasalts were up to 105 m3 m,2, with the fluid flowing up temperature driven either by topography or seismic pumping. Individual shear zones were active for c. 2,3 Myr, implying average fluid fluxes of up to 10,9 m3 m,2 s,1. Rocks in shear zones within the ophiolite away from contacts with the metasediments show much less marked isotopic and geochemical changes, implying that fluid volumes decreased into the ophiolite unit, consistent with the source of fluids being the metasediments. Fluids were generated by dehydration reactions that were intersected during exhumation and, while many rocks show the affects of fluid,rock interaction, large-scale fluid flow between major units was not common. [source] Occurrence of calcite in Sanbagawa pelitic schists: implications for the formation of garnet, rutile, oligoclase, biotite and hornblendeJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2002A. Goto Abstract The frequency of occurrence of minerals in 1876 samples of Sanbagawa pelitic schist in central Shikoku is summarized on the basis of microscopic observation accompanied, in part, by use of an electron microprobe. All samples contain quartz, plagioclase, phengite, chlorite and graphite. More than 90% of samples contain clinozoisite, titanite and apatite. Garnet is present in 95% of samples from the garnet zone, and biotite is present in 64% of samples from the albite-biotite zone. Calcite is found in about 40% of samples of the pelitic schist collected from outcrop, but occurs in 95% of the pelitic schist from drill cores. Calcite was apparently ubiquitous in the pelitic schist during the Sanbagawa metamorphism, but must have been dissolved recently by the action of surface or ground water. The mineral assemblages of the Sanbagawa pelitic schist have to be analyzed in the system with excess calcite, quartz, albite (or oligoclase), clinozoisite, graphite and fluid that is composed mainly of H2O, CO2 and CH4. In the presence of calcite, reactions that produce garnet, rutile, oligoclase, biotite and hornblende, some of which define isograds of the metamorphic belt, should be written as mixed volatile equilibria that tend to take place at lower temperature than the dehydration reactions that have been proposed. The presence of calcite in pelitic schist suggests that fluid composition is a variable as important in determining mineral assemblages as pressure and temperature. Thus Ca-bearing phases must be taken into account to analyze the phase relations of calcite-bearing pelitic schist, even if CaO content of Sanbagawa pelitic schist is low. As calcite is a common phase, the mineral assemblages of the biotite zone pelitic schist may contravene the mineralogical phase rule and warrant further study. [source] | ||||||||||||||||||||||