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Second-order Kinetics (second-order + kinetics)
Selected AbstractsOxidorhenium(V) Complexes of a Family of Bipyridine-Like Ligands Including Pyridyltriazines and Pyrazinyltriazine: Oxygen-Atom Transfer, Metal Redox and CorrelationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2006Samir Das Abstract The title ligands (general abbreviation L) are bipyridine (bpy), its dimethyl (mbpy) and diphenyl (pbpy) derivatives, phenanthroline (phen), 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (ppyt) and its dimethyl (mpyt) and pyrazinyl (ppzt) analogues. The concerned oxido complexes are [ReOCl3(L)],[ReOBr3(ppyt)] and [ReOBr3(ppzt)]. The chloro and bromo complexes of ppyt and ppzt were prepared by reacting these ligands with [ReOX3(AsPh3)2] (X = Cl, Br). The X-ray structures of [ReOCl3(ppyt)] and [ReOCl3(ppzt)] reveal that the ReCl3 fragment is meridionally disposed and that the L ligand is N,N -coordinated such that the pyridine/pyrazine nitrogen lies trans to the oxido oxygen atom. The Re,O lengths [1.656(10)/1.625(9) Å] correspond to approximate triple bonding. The rate of oxygen-atom transfer from [ReOX3(L)] to triphenylphosphane in solution follows second-order kinetics and is associated with a large and negative entropy of activation (approx. ,30 cal,K,1,mol,1). The initial attack is believed to involve the phosphane lone pair and Re,O ,*-orbitals. Electron withdrawal from the ReVO moiety by varying X or L facilitates oxygen-atom transfer. Thus, the rates follow the orders Br < Cl; mbpy < bpy < phen < pbpy << mpyt < ppyt < ppzt. The reduction potential of the quasireversible ReVIO/ReVO couple displays similar trends and the logarithmic rate constant of oxygen-atom transfer is found to correlate linearly with the reduction potential. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2007Shigang Shen Mephenesin is being used as a central-acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO6)2]5,, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3-(2-methylphenoxy)-2-ketone-1-propanol by mass spectrometry. An overall second-order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH,] and periodate concentration on the observed second-order rate constants k, have been analyzed, and accordingly an empirical expression has been deduced: k, = (ka + kb[OH,])K1/{f([OH,])[IO,4]tot + K1}, where [IO,4]tot denotes the total concentration of periodate, ka = (1.35 ± 0.14) × 10,2M,1s,1 and kb = 1.06 ± 0.01 M,2s,1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with ka and kb have been calculated. A mechanism has been proposed to involve two pre-equilibria, leading to formation of a periodato-Ag(III)-mephenesin complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH, whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre-equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440,446, 2007 [source] Cocatalysis by ruthenium(III) in hydrogen ions catalyzed oxidation of iodide ions: A kinetic studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2004Praveen K. Tandon RuCl3 further catalyzes the oxidation of iodide ion by K3Fe(CN)6, already catalyzed by hydrogen ions. The rate of reaction, when catalyzed only by hydrogen ions, was separated graphically from the rate when both Ru(III) and H+ ions catalyzed the reaction. Reactions studied separately in the presence as well as absence of RuCl3 under similar conditions were found to follow second-order kinetics with respect to [I,], while the rate showed direct proportionality with respect to [Fe(CN)6]3,, [RuCl3], and [H+]. External addition of [Fe(CN)6]4, ions retards the reaction velocity, while changing the ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, the extent of the reaction that takes place without adding Ru(III) was calculated and it was in accordance with the values obtained from the reaction in which only H+ ions catalyzed the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate-determining step. Arrhenius parameters at four different temperatures were also calculated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 545,553, 2004 [source] Micellar catalysis on the redox reaction of glycolic acid with chromium(VI)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2001Kabir-ud-Din Chromium(VI) oxidation of glycolic acid in the absence and presence of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) followed the same mechanism as shown by kinetic study. The reaction followed second-order kinetics, first-order in each reactant. The oxidation is strongly catalyzed by manganese(II) and cationic micelles of CTAB or CPB. The catalytic effect of micelles can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase. Some added inorganic salts (NaCl, NaBr, NaNO3, and Na2SO4) reduce the micellar catalysis by excluding glycolic acid from the reaction site. The reactivity of glycolic acid towards chromium(VI) has been discussed and also compared with those obtained previously for the reaction between chromium(VI) and the reductants oxalic and lactic acids. On the basis of the observed results, probable mechanisms have been proposed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 377,386, 2001 [source] Radical annihilation of ,-ray-irradiated contact lens blanks made of a 2-hydroxyethyl methacrylate copolymer at elevated temperaturesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Young-Shang Lin Abstract The annihilation of the radicals in irradiated 2-hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main-chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25,45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second-order kinetics; these were different from the kinetics for the color formation and defect-controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Kinetics of oxidation of acidic amino acids and their monoamides by N -chloroarylsulphonamides in aqueous acidic mediumJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2004B. Thimme Gowda Abstract Twelve sodium salts of N -chloroarylsulphonamides were employed as oxidants for studying the kinetics of oxidation of two acidic amino acids (aspartic and glutamic acid) and their monoamides (aspargine and glutamine) in aqueous acidic medium under various conditions, to see how the oxidative strength of these reagents vary with substitution. The sodium salts of N -chloroarylsulphonamides employed are of the general formulae i -X-C6H4SO2NaNCl·xH2O (where i -X,=,4-C2H5, 4-F, 4-Cl or 4-Br) and i -X- j -Y-C6H3SO2NaNCl·xH2O [where i -X- j -Y,=,2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3 -4-Cl, 2,4-Cl2 and 3,4-Cl2]. The reactions show second-order kinetics in [oxidant], fractional order in [amino acid] and an inverse dependence on [H+]. Addition of the reduced product of the oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. Mechanisms in conformity with the observed kinetics are discussed. The effective oxidizing species of the oxidants is Cl+ in different forms. The oxidizing strengths of N -chloroarylsulphonamides depend on the ease with which Cl+ is released from them. The study reveals that the introduction of electron-withdrawing groups such as halides to the benzene ring eases the release of Cl+ from the reagent and hence increases the oxidizing strengths of the N -chloroarylsulphonamides. The effect of substituents on Ea of the reactions was analysed by optimising Ea with reference to log,A, and log,A with reference to Ea of the parent oxidant. Copyright © 2004 John Wiley & Sons, Ltd. [source] Analysis of the swelling dynamics of crosslinked P(N -iPAAm- co -MAA) copolymers, the corresponding homopolymers and their interpenetrating networks.POLYMER INTERNATIONAL, Issue 6 2003Kinetics of water penetration into the gel above the pKaof MAA comonomeric units Abstract The effect of composition on the swelling kinetics of a series of crosslinked poly(N -isopropylacrylamide)s [P(N -iPAAm)] and poly(methacrylic acid)s [P(MAA)], their statistical copolymers P(N -iPAAm- co -MAA), and some sequential interpenetrating networks (IPNs) has been studied at pHs above the pKa of MAA comonomeric units. The swelling process of the hydrogels upon immersion in buffer solutions was monitored by the weight change as a function of time. First-order kinetics apply better than second-order kinetics which fail, especially for predicting swelling equilibrium values. However, hydrogels presenting hydrogen bonding between MAA and N -iPAAm units do not obey either first-order or second-order kinetics. The high n values found indicate that the swelling process is mostly controlled by polymer relaxation. Copyright © 2003 Society of Chemical Industry [source] Urethanes and polyurethanes based on oxypropylated cork: 1.POLYMER INTERNATIONAL, Issue 10 2001Appraisal, reactivity of products Abstract The reaction of various polyols derived from the oxypropylation of cork with aliphatic and aromatic mono- and diisocyanates was studied in solution at room temperature. In all instances, good second-order kinetics were observed and the corresponding rate constant determined. The reactivity of the aromatic isocyanate was found to be much higher than that of aliphatic counterparts. The ensuing urethanes and polyurethanes were characterised by FTIR and 1H NMR spectroscopy, DSC and sol/gel distribution. © 2001 Society of Chemical Industry [source] Ultrasound-facilitated electro-oxidation for treating cyan ink effluentTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008Chee-Yong Chua Abstract The feasibility of using ultrasonication in combination with the Fenton's reaction was investigated for treating cyan ink effluent. A two-step treatment process was developed,the first step was an ultrasound-assisted electro-oxidation, while the second was chemical oxidation through the addition of hydrogen peroxide. The use of electro-oxidation in the first step significantly reduced the amount of iron needed compared with the conventional Fenton's reaction, resulting in a 98% reduction in the amount of sludge produced. A simple technique based on refractive index measurements was introduced as a rapid way to quantify the amount of sludge produced. It was postulated that ultrasonication in the presence of iron (from electrolysis) in the first step converted the ink components into reaction intermediates which were more amenable to peroxide oxidation in the second step. These intermediates were quantified by ultra-violet absorption at wavelengths of 275,400 nm. The two-step treatment process was able to reduce the COD and copper contents in the ink waste water to within the discharge limit, which conventional Fenton's reaction was unable to meet for copper discharge. The same COD removal was also achieved in about half the time. Kinetics study performed to further understand the reaction mechanisms show second-order kinetics for both steps with activation energies of 18.2 and 20.4 kJ/mol for steps 1 and 2, respectively. On a étudié la possibilité de recourir à l'ultrasonification combinée à la réaction de Fenton pour traiter l'effluent d'encre de cyan. Un procédé de traitement en deux étapes a été mis au point: la première étape consiste en une électro-oxydation assistée par ultrasons, tandis que la seconde consiste en une oxydation chimique par ajout de peroxyde d'hydrogène. Le recours à l'électro-oxydation dans la première étape réduit significativement la quantité de fer requis comparé à la réaction de Fenton classique, entraînant une réduction de 98% de la quantité de suspension produite. Une technique simple basée sur des mesures d'indice de réfraction a été introduite comme une façon rapide d'établir la quantité de suspension produite. On a posé comme postulat que l'ultrasonification en présence de fer (de l'électrolyse) dans la première étape convertit les composantes de l'encre en des intermédiaires de réaction qui étaient plus propices à l'oxydation du peroxyde dans la seconde étape. Ces intermédiaires ont été quantifiés par l'absorption des ultraviolets à des longueurs d'ondes de 275 nm à 400 nm. Ce procédé de traitement en deux étapes a permis de réduire la DCO et les teneurs en cuivre dans l'eau usée de l'encre pour les amener à la limite des normes de rejet, ce que la réaction de Fenton classique n'a pu permettre de réaliser pour le cuivre. Le même retrait de DCO a été également réalisé dans un temps inférieur de 50%. L'étude de cinétique effectuée pour mieux comprendre les mécanismes de réaction montre une cinétique de second ordre pour les deux étapes avec des énergies de désactivation de 18,2 et 20,4 kJ/mol pour les étapes 1 et 2, respectivement. [source] Studies on the disproportionation of trichloromethyltinAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2003Christopher A. Bertelo Abstract The rate of disproportionation of trichloromethyltin in various solvents was studied by two methods, derivatization with sodium tetraethylborate and 13C NMR measurements, which gave similar results. The reaction followed second-order kinetics and was more rapid in coordinating solvents than in uncoordinating ones. Moreover, it was catalyzed by nucleophiles, such as amines or alcohols, which is in favor of a nucleophile-assisted electrophilic reaction. Copyright © 2003 John Wiley & Sons, Ltd. [source] Energetic aspects of locked nucleic acids quadruplex association and dissociationBIOPOLYMERS, Issue 6 2006Luigi Petraccone Abstract The design of modified nucleic acid aptamers is improved by considering thermodynamics and kinetics of their association/dissociation processes. Locked Nucleic Acids (LNA) is a promising class of nucleic acid analogs. In this work the thermodynamic and kinetic properties of a LNA quadruplex formed by the TGGGT sequence, containing only conformationally restricted LNA residues, are reported and compared to those of 2,-OMe-RNA (O-RNA) and DNA quadruplexes. The thermodynamic analysis indicates that the sugar-modified quadruplexes (LNA and O-RNA) are stabilized by entropic effects. The kinetic analysis shows that LNA and O-RNA quadruplexes are characterized by a slower dissociation and a faster association with respect to DNA quadruplex. Interestingly, the LNA quadruplex formation process shows a second-order kinetics with respect to single strand concentration and has a negative activation energy. To explain these data, a mechanism for tetramer formation with two intermediate states was proposed. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 584,594, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Mechanistic Investigation of the Dipolar [2+2] Cycloaddition,Cycloreversion Reaction between 4-(N,N -Dimethylamino)phenylacetylene and Arylated 1,1-Dicyanovinyl Derivatives To Form Intramolecular Charge-Transfer ChromophoresCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2010Yi-Lin Wu Abstract The kinetics and mechanism of the formal [2+2] cycloaddition,cycloreversion reaction between 4-(N,N -dimethylamino)phenylacetylene (1) and para -substituted benzylidenemalononitriles 2,b,2,l to form 2-donor-substituted 1,1-dicyanobuta-1,3-dienes 3,b,3,l via the postulated dicyanocyclobutene intermediates 4,b,4,l have been studied experimentally by the method of initial rates and computationally at the unrestricted B3LYP/6-31G(d) level. The transformations were found to follow bimolecular, second-order kinetics, with =13,18,kcal,mol,1, ,,30,cal,K,1,mol,1, and =22,27,kcal,mol,1. These experimental activation parameters for the rate-determining cycloaddition step are close to the computational values. The rate constants show a good linear free energy relationship (,=2.0) with the electronic character of the para -substituents on the benzylidene moiety in dimethylformamide (DMF), which is indicative of a dipolar mechanism. Analysis of the computed structures and their corresponding solvation energies in acetonitrile suggests that the rate-determining attack of the nucleophilic, terminal alkyne carbon onto the dicyanovinyl electrophile generates a transient zwitterion intermediate with the negative charge developing as a stabilized malononitrile carbanion. The computational analysis predicted that the cycloreversion of the postulated dicyanocyclobutene intermediate would become rate-determining for 1,1-dicyanoethene (2,m) as the electrophile. The dicyanocyclobutene 4,m could indeed be isolated as the key intermediate from the reaction between alkyne 1 and 2,m and characterized by X-ray analysis. Facile first-order cycloreversion occurred upon further heating, yielding as the sole product the 1,1-dicyanobuta-1,3-diene 3,m. [source] | |||||||||||||