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Parallel Reactions (parallel + reaction)
Selected AbstractsSynthesis of 1-amino-2-methylindoline by Raschig process: Parallel reactions, modeling, and optimizationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2002M. Elkhatib The reaction between chloramine and 2-methylindoline was studied at pH 12.89, T = 40°C, and for different initial concentrations of reactants. The interaction includes two concurrent bimolecular mechanisms leading to 1-amino-2-methylindoline and 2-methylindole. The rate laws were determined at the first moments of the reaction by using a differential method. By considering the totality of the reactions that occur in the medium, an appropriate mathematical model was developed. It permits to follow the evolution of the system over time and to calculate the final yields of reaction products. An optimization in terms of the initial contents of 2-methylindoline and chloramine was performed. It indicated that the maximum yield of 1-amino-2-methylindoline does not exceed 56%. The results show the limit of the Raschig process for the synthesis of indolic hydrazines in aqueous medium. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 575,584, 2002 [source] Kinetic studies of hydrazine and 2-hydroxyethylhydrazine alkylation by 2-chloroethanol: Influence of a strong base in the mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009V. Goutelle To optimize yields, the study of reaction kinetics related to the synthesis of 2-hydroxyethylhydrazine (HEH) obtained from the alkylation of N2H4 by 2-chloroethanol (CletOH) was carried out with and without sodium hydroxide. In both cases, the main reaction of HEH formation was followed by a consecutive, parallel reaction of HEH alkylation (or dialkylation of N2H4), leading to the formation of two isomers: 1,1-di(hydroxyethyl)hydrazine and 1,2-di(hydroxyethyl)hydrazine. In this study, hydrazine and hydroxyalkylhydrazine alkylations followed SN2 reactions triggered directly by CletOH or indirectly in the presence of a strong base by ethylene oxide, an intermediate compound. The kinetics was studied in diluted mediums by quantifying HEH and CletOH by gas chromatography and gas chromatography coupled with mass spectrometry (GC-MS). The activation parameters of each reaction and the influence of a strong base present in the medium on the reaction mechanisms were established. A global mathematical treatment was applied for each alternative. It allowed modeling the reactions as a function of reagent concentrations and temperature. In the case of direct alkylation by CletOH, simulation was established for semi-batch and batch syntheses and was confirmed in experiments for concentrated mediums (1.0 M , [CletOH]0 , 3.2 M and 15.7 M , [N2H4]0 , 18.8 M). Simulation therefore permits the prediction of the instantaneous concentration of reagents and products, in particular ethylene oxide concentration in the case of indirect alkylation, which must be as weak as possible. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 382,393, 2009 [source] Production of B4C coatings by CVD method in a dual impinging-jet reactor: Chemical yield, morphology, and hardness analysisAICHE JOURNAL, Issue 11 2009Mustafa Karaman Abstract ,-rhombohedral boron carbide (B4C) was deposited on a tungsten substrate from a BCl3H2CH4 gas mixture in a dual impinging-jet chemical vapor deposition reactor. On-line FTIR analysis of the product stream proved the formation of BHCl2 and HCl as by products, in a competing parallel reaction. A maximum of 13% chemical yield of boron carbide was observed, and the yield was found to have increasing trend with an increase in temperature. XRD analysis proved the existence of rhombohedral B4C phase at 1300°C without any other B4C phases or impurities. At this temperature, the formation of 5-fold icosahedral boron carbide crystals up to 30 micron sizes was observed. Such highly symmetric crystalline regions were observed to have a very high hardness value of 4750 kg/mm2 as revealed from the microhardness analysis. The change in product morphology at low substrate temperatures resulted in a decrease in the hardness values. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Oxidation kinetics of pentachlorophenol by manganese dioxideENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2006Ling Zhao Abstract This study examined the abiotic transformation kinetics of pentachlorophenol (PCP) by manganese dioxide (MnO2) at different solution chemistry and initial concentrations of PCP and MnO2. The measured PCP transformation rates were found to be on the order of 1.07 with respect to [PCP] and 0.91 and 0.87 with respect to [MnO2] and [H+], respectively. Dissolved Mn2+ and Ca2+ as background electrolytes considerably decreased the reaction rate because of their adsorption and hence blocking of active sites on MnO2 surfaces. The dechlorination number, 0.59 chloride ions per transformed PCP after a 1-h reaction, suggests that a fraction of the transformed PCP was not dechlorinated and may be coupled directly to dimeric products. Gas chromatography/ mass spectrometry and liquid chromatography/mass spectrometry/mass spectrometry techniques were used to identify two isomeric nonachlorohydroxybiphenylethers as major products and 2,3,5,6-tetrachloro-1,4-hydroquinone and tetrachlorocatechol as minor products. Product identification suggested that the reaction may include two parallel reactions to form either dimers or 2,3,5,6-tetrachloro-1,4-hydroquinone and tetrachlorocatechol via simultaneous dehydrochlorination and hydroxylation. [source] Stabilization of biomass-derived pyrolysis oilsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2010R.H. Venderbosch Abstract BACKGROUND: Biomass is the only renewable feedstock containing carbon, and therefore the only alternative to fossil-derived crude oil derivatives. However, the main problems concerning the application of biomass for biofuels and bio-based chemicals are related to transport and handling, the limited scale of the conversion process and the competition with the food industry. To overcome such problems, an integral processing route for the conversion of (non-feed) biomass (residues) to transportation fuels is proposed. It includes a pretreatment process by fast pyrolysis, followed by upgrading to produce a crude-oil-like product, and finally co-refining in traditional refineries. RESULTS: This paper contributes to the understanding of pyrolysis oil upgrading. The processes include a thermal treatment step and/or direct hydroprocessing. At temperatures up to 250 °C (in the presence of H2 and catalyst) parallel reactions take place including re-polymerization (water production), decarboxylation (limited CO2 production) and hydrotreating. Water is produced in small quantities (approx. 10% extra), likely caused by repolymerization. This repolymerization takes place faster (order of minutes) than the hydrotreating reactions (order of tens of minutes, hours). CONCLUSIONS: In hydroprocessing of bio-oils, a pathway is followed by which pyrolysis oils are further polymerized if H2 and/or catalyst is absent, eventually to char components, or, with H2/catalyst, to stabilized components that can be further upgraded. Results of the experiments suggest that specifically the cellulose-derived fraction of the oil needs to be transformed first, preferably into alcohols in a ,mild hydrogenation' step. This subsequently allows further dehydration and hydrogenation. Copyright © 2010 Society of Chemical Industry [source] The mechanisms of the homogeneous, unimolecular, elimination kinetics of several , -substituted diethyl acetals in the gas-phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2010José R. Mora Abstract The rates of gas-phase elimination of several , -substituted diethyl acetals have been determined in a static system and seasoned with allyl bromide. The reactions, inhibited with toluene, are homogeneous, unimolecular, and follow first-order law kinetics. These elimination processes involve two parallel reactions. The first parallel reaction yields ethanol and the corresponding ethyl vinyl ether. The latter product is an unstable intermediate and further decomposes to ethylene and the corresponding substituted aldehyde. The second parallel reaction gives ethane and the corresponding ethyl ester. The kinetics has been measured over the temperature range of 370,441,°C and pressure range of 23,160,torr. The rate coefficients are given by the following Arrhenius equations: The differences in the rates of ethanol formation may be attributed to electronic transmission of the , -substituent. The comparative kinetic and thermodynamic parameters of the parallel reactions suggest two different concerted polar four-membered cyclic transition state types of mechanisms. Copyright © 2010 John Wiley & Sons, Ltd. [source] Amide and lactam hydrolysis of N -(2-hydroxyacetyl)-2-pyrrolidone: effective catalysis,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2006Lisaedy García Borboa Abstract When N -(2-hydroxyacetyl)-2-pyrrolidone (open form) is dissolved in water at pH,>,8, irreversible cleavage of the exocyclic and endocyclic amide CN bond occurs. The latter rupture corresponds to the lactam opening yielding N -(4-hydroxyacetyl)butanoic acid (NBA). NBA is produced from the ester hydrolysis of the ester-amide macrocycle that is in equilibrium with the cyclol form of the open form. We have previously reported this latter equilibrium for N -(2-aminoacetyl)-2-lactams. 2-pyrrolidone (lactam) and glycolic acid are produced from direct hydrolysis of the open form by means of the amide exocyclic cleavage. The [NBA]/[lactam] ratio increases at higher pH since the NBA production is second order with respect to [OH,] while the corresponding lactam formation is only first order. The obtained kobs is hence the sum of the rate constants that yield lactam and NBA, respectively. This kobs is uncatalyzed and specific base catalyzed with unusually high rate constants of 2.1,×,10,6,s,1 and 0.025,M,1,s,1, respectively. The stability of the corresponding tetrahedral intermediate formed and the intramolecular alkoxy nucleophilic attack on the lactam carbonyl group combined with an effective protonation of the lactam nitrogen that promotes the CN cleavage, contribute to increase the reaction rates and lactam opening. Rate constants for the two parallel reactions are obtained from kobs and [NBA]/[lactam] versus pH plots. Copyright © 2006 John Wiley & Sons, Ltd. [source] Supramolecular catalysis induced by polysaccharides.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Homogeneous hydrolysis of p -nitrobenzyl amylose xanthate Abstract p -Nitrobenzyl amylose xanthate (AmXNB) was synthesized and characterized by 13C NMR spectroscopy in solution and the solid state. The degree of substitution (DS), calculated from the sulfur content, was 7.0, and this value was similar to that obtained from solid-state 13C NMR using the signal of C-1 as internal standard. The hydrolysis of AmXNB was studied in 10% (v/v) DMSO with,µ,=,0.5 (KCl) at 25,°C. The basic hydrolysis was pseudo-first order, but the water-catalyzed hydrolysis in the pH range 7,9 showed a biphasic plot of ln (,Absorbance) vs time, as has been observed for cellulose xanthate esters, occurring through two parallel reactions with rate constants k,H2O (fast),=,5.3,×,10,5 s,1 and k,H2O (slow),=,3.3,×,10,6 s,1. The fast hydrolysis was more than three orders of magnitude faster than that of the O -ethyl analog. The activation parameters were ,H,,=,20.5,kcal,mol,1 and ,S,,=,+10 cal K,1,mol,1. They showed that the acceleration of the fast hydrolysis of AmXNB and cellulose analogs is due to an entropy of activation effect. There is a linear increase of logk,H2O (fast) with increase in the concentration of the small Li+ ion that produces an increase of the 3-D hydrogen-bond network of water while the large singly charged iodide ion has a considerable inverse effect. These results are strongly consistent with the theory that the supramolecular catalysis induced by modified polysaccharide esters is due to the 3-D hydrogen-bond network of the water in the solvation shell. Copyright © 2003 John Wiley & Sons, Ltd. [source] Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low TemperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Faezeh Bagheri-Tar Abstract Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane-to-oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions. On décrit le couplage oxydant du méthane (OCM) en présence d'une couronne CC dans un réacteur tubulaire étroit en verre à la pression atmosphérique et à des températures en dessous de 200°C. La couronne est créée en appliquant 2200 V entre une pointe et une électrode plate distantes de 1,5 mm. La sélectivité du C2 ainsi que la conversion du méthane sont des fonctions du rapport méthane-oxygène, du temps de séjour du gaz et du courant électrique. À un rapport de CH4/O2 de 5 et un temps de séjour d'environ 30 ms, un rendement de C2 de 23,1 % est obtenu. Les principaux produits de ce procédé sont l'éthane, l'éthylène, l'acétylène, ainsi que le CO et le CO2 avec des rapports de CO/CO2 aussi élevés que 25. On propose l'idée que le méthane est activé par des espèces d'oxygène électrophiles pour former des radicaux de méthyle et que les produits du C2 sont produits par un mécanisme consécutif, tandis que les COx se forment lors de réactions parallèles. [source] | ||||||||||