bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic studies of a catalyzed metalloporphyrin formation
Authors: Adeyemo Adegboye O. , Krishnamurthy M. 
Published: January 2005

AbstractKinetics of the incorporation of mercury(II) ion in tetra (p‐trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO3) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 103 M−1 s−1 and 7 ± 2 × 106 M−1 s−1, respectively. Kinetics of zinc(II) incorporation in tetra(p‐trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady‐state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.
Rate constants for the reaction of OH radicals with a series of alkenes and dialkenes at 295 ± 1 K
Authors: Atkinson Roger , Aschmann Sara M. 
Published: January 2005

AbstractUsing a relative rate technique, rate constants for the gas phase reactions of the OH radical withn‐butane,n‐hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1‐butene, 1.19 ± 0.06; 1‐pentene, 1.19 ± 0.05; 1‐hexene, 1.40 ± 0.04; 1‐heptene, 1.51 ± 0.06; 3‐methyl‐1‐butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09;cis‐2‐butene, 2.13 ± 0.05;trans‐2‐butene, 2.43 ± 0.05; 2‐methyl‐2‐butene, 3.30 ± 0.13; 2,3‐dimethyl‐2‐butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3‐butadiene, 2.53 ± 0.08; 2‐methyl‐1,3‐butadiene, 3.81 ± 0.15;n‐butane, 0.101 ± 0.012; andn‐hexane, 0.198 ± 0.017. From a least‐squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10−11cm3molecule−1s−1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self‐consistent data set for the reactions of OH radicals with a large number of organics at room temperature.
Rate constant for the OH + CO reaction: Pressure dependence and the effect of oxygen
Authors: Demore W. B. 
Published: January 2005

AbstractThe effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200–730 torr. All experiments were at room temperature. The method involved laser‐induced fluorescence to measure steady‐state OH concentrations in the 184.9 nm photolysis of H2O‐CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10%. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.
Rates of OH radical reactions. XII. The reactions of OH with cC3H6, cC5H10, and cC7H14. Correlation of hydroxyl rate constants with bond dissociation energies
Authors: Jolly Gurvinder S. , Paraskevopoulos George , Singleton Donald L. 
Published: January 2005

AbstractAbsolute rate constants for H‐atom abstraction by OH radicals from cyclopropane, cyclopentane, and cycloheptane have been determined in the gas phase at 298 K. Hydroxyl radicals were generated by flash photolysis of H2O vapor in the vacuum UV, and monitored by time‐resolved resonance absorption at 308.2 nm [OH(A2Σ+→X2Π)]. The rate constants in units of cm3 mol−1 s−1 at the 95% confidence limits were as follows: k(cC3H6) = (3.74 ± 0.83) × 1010, k(cC5H10) = (3.12 ± 0.23) × 1012, k(cC7H14) = (7.88 ± 1.38) × 1012. A linear correlation was found to exist between the logarithm of the rate constant per CH bond and the corresponding bond dissociation energy for several classes of organic compounds with equivalent CH bonds. The correlation favors a value of D(cC3H5–H) = (101 ± 2) kcal mol−1.
Reactivities of cis‐ and trans‐buten‐2‐yl free radicals in presence of D2S. I. Relative values of rate constants
Authors: Richard C. , Martin R. 
Published: January 2005

AbstractCis‐ and trans‐buten‐2‐yl free radicals are shown to react with D2S in metathetical steps: magnified image Relative formation rates of monodeuteriated butenes in D2S – 2 – C4H8 mixtures were measured at low extent of reaction in the experimental range: 20–200 torr 2 – C4H8, 0–41‐torr D2S and 717–817 K. In these pressure and temperature ranges, the fractional rate constant values kc/kc′/kt/kt′ remain practically constant and equal to: 0.36/0.17/0.32/0.15. It is concluded from these data that cis‐buten‐2‐yl free radicals are a little more reactive than their trans‐isomers and that the mesomeric form CH3CH:CHCH2 is about twice as reactive as CH3ĊHCH:CH2.
Determination of the energy distribution in unimolecular reactions under soft collision conditions
Authors: Figuera Juan M. , Menéndez Vicente , Rodríguez Juan C. 
Published: January 2005

AbstractThe effective energy distribution of activated molecules at the time of reaction under soft collision conditions ƒ′(E, ω) is pressure dependent and therefore difficult to recover from unimolecular decomposition data obtained at different pressures. We show in this work that the part of this function restricted to the condition that the collision frequency ω has to be equal to the microscopic rate constant k(E) at the energy given ƒ″[E,ω = k(E)] is a reasonable approximation to the input energy distribution ƒ(E) for quite soft collisions. This function is not pressure dependent and then recoverable at least in principle and as a matter of fact is not conceptually far from the function that the already reported deconvolution methods based in physical approximations attempt to recover. The deconvolution methods have been checked under soft collision conditions. We have found that the input energy distribution is recovered with reasonable accuracy for energies transferred by collision 〈ΔE〉 above 5 kcal mol−1, conditions common in polyatomic systems.
Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films
Authors: Amorebieta V. T. , Colussi A. J. 
Published: January 2005

AbstractThe decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low‐pressure flow reactor between 850–1280 K. Whereas CH3Cl is thoroughly stable, molecular chlorine readily dissociates by a first‐order process with an activation energy about a half of its bond energy. The decompositions of CH2Cl2 and CCl4 over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.
N2O5 photolysis products investigated by fluorescence and optoacoustic techniques
Authors: Barker J. R. , Brouwer L. , Patrick R. , Rossi M. J. , Trevor P. L. , Golden D. M. 
Published: January 2005

AbstractPulsed laser photolysis of N2O5 near 290 nm coupled with fluorescence detection (calibrated by NO2 photolysis) showed that the O(3P) quantum yield is ≤0.1. A pulsed laser optoacoustic technique in a flow tube (ca. 6 torr of N2) was tested by photolysis of NO2 and then applied to N2O5. Nitric oxide was added to react with NO3 free radical and the resulting increase in the optoacoustic signal confirmed the presence of NO3 free radicals. Based on the relative optoacoustic signals observed for NO2 and N2O5, the quantum yield for NO3 production is 0.8 ± 0.2.
Mechanism of the silane decomposition. I. Silane loss kinetics and rate inhibition by hydrogen. II. Modeling of the silane decomposition (all stages of reaction)
Authors: White R. T. , Espino‐Rios R. L. , Rogers D. S. , Ring M. A. , O'Neal H. E. 
Published: January 2005

AbstractPart I: Kinetic data for the static system silane pyrolysis (from 640–703 K, 60–400 torr) are presented. For conversion from 3–30%, first‐order kinetics are obtained, with silane loss rates equal to half the hydrogen formation rates. At conversions greater than 40%, rate inhibition attributable to the back reaction of hydrogen with silylene occurs. Overall reaction rates are not surface sensitive, but disilane and trisilane yield maxima under some conditions are. A nonchain mechanism capable of describing quantitatively all stages of the silane pyrolysis is proposed. Post 1.0% initiation is both homogeneous (gas phase) and heterogeneous (on the walls), and reaction intermediates are silylenes and disilenes. Free radicals are not involved at any stage of the reaction. Rate data at high conversions and with added hydrogen provide kinetics for the addition of silylene to hydrogen [reaction (−1)1] relative to its addition to silane [reaction (2)]: k−1,/k2 = 10−0.65 × e−3200 cal/RT. With E2 = 1300 cal, this gives a high pressure activation energy for silylene insertion into hydrogen of E−1 = 8200 cal.Part II: An analysis is made of each rate constant of the silane mechanism and the modeling results are compared with experimental results. Agreement is excellent. It is concluded that the dominant sink reaction for silylene intermediates is 1,2—H2 elimination from disilane (followed by Si2H4 polymerization and wall deposition). The model is in accord with slow isomerization between disilene and silylsilylene and near exclusive 1,2—H2 elimination from Si2H6. It is also concluded that disilene is about 10 kcal/mol more stable than silylsilylene and that the activation energy for isomerization of silylsilylene to disilene is greater than 26 kcal/mol.
Rate constants for the reactions of conjugated olefins with NO2 in the gas phase
Authors: Ohta Tomohiro , Nagura Hiroaki , Suzuki Shin 
Published: January 2005

AbstractGas‐phase rate constants for the reaction of NO2 with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono‐olefins by factors of 103–104. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies: k1,3‐cyclohexadiene = 5.8 × 10−14 exp[−(6.1 ± 1.6)/RT] cm3 molecule−1 s−1; kcis‐2‐butene = 4.68 × 10−14 exp(−11.2/RT) cm3 molecule−1 s−1 [2]. A linear free energy relationship between the reactions of OH and NO2 with conjugated diolefins was observed.
The use of transition‐state theory to extrapolate rate coefficients for reactions of O atoms with alkanes
Authors: Cohen N. , Westberg K. R. 
Published: January 2005

AbstractConventional transition‐state theory is used for extrapolating rate coefficients for reactions of O atoms with alkanes to temperatures above the range of experimental data. Expressions are developed for estimating structural properties of the activated complex necessary for calculating enthalpies and entropies of activation. Particular attention is given to the problem of the effect of the O atom adduct on the internal rotations in the activated complex. Differences between primary, secondary, and tertiary attack are discussed, and the validity of representing the activated complexes of all O + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Experimental data for reactions of O atoms with 15 different alkanes (CH4, C2H6, C3H8, C4H10, C5H12, C6H14, C7H16, C8H18, i–C4H10, (CH3)4C, (CH3)2CHCH(CH3)2, (CH3)3CC(CH3)3, c–C5H10, c–C6H12, c–C7H14) are reviewed.The following approximate expressions for ΔS‡(298) and E(298), the entropy and energy of activation, respectively, are consistent with the experimental data and with the calculations:
magnified image
where nC = number of carbon atoms in the alkane and nH = the number of “equivalent” H atoms. Using the conventional transition state theory expression, k(298) = 1015.06 exp(ΔS‡/R) exp(–E(298)/298R) L mol−1s−1, one then obtains:

These expressions agree with experimental values within a factor approximately 2 for alkanes larger than C3H8.
The thermodynamic state of the hot gas behind reflected shock waves: Implication to chemical kinetics
Authors: Michael J. V. , Sutherland J. W. 
Published: January 2005

AbstractProcedures are discussed to correct for nonideality in a shock tube used in the reflected mode in conjunction with flash photolysis and atomic resonance absorption to measure chemical kinetics of atoms at high temperatures. Experimentally, pressure time profiles for the incident and reflectedshock regions are made close to the location of the observation windows through which absorbance is measured. The corresponding temperatures are calculated from the adiabatic equation of state. Justification for this procedure is provided by extending Mirels' boundary layer theory to take intoaccount interaction of the reflected wave with the flowing gas in the free stream and in the boundary layer. These theoretical methods are described for calculating the thermodynamic and hydrodynamic states behind the reflected wave from initial values of pressure and temperature and the measured velocity of the incident wave. The implication of these results to kinetic measurements at high temperature is discussed.
An Ab initio determination of the rate constant for H2 + CN → H + HCN
Authors: Wagner Albert F. , Bair Raymond A. 
Published: January 2005

AbstractThe reactants, products, and saddle point for the reaction H2 + CN → H + HCN have been studied by ab initio calculations. The computed structures, frequencies, and energetics are compared directly to available measurements and, indirectly, to experimental rateconstants. The theoretical rate constants used in the comparison are calculated with conventional transition state theory. By reduction of the computed reaction barrier to 4.1 kcal mol,−1 good agreement with experimental rate constants is obtained over a 3250‐K temperature range. This computed rate constant is well represented by the form 4.9 × 10−18 T2.45 e−1, 126/T over the temperature range of 250 K–3500 K. Substantial reaction rate curvature is found due to low‐frequency bending modes at the saddle point. The results for this reaction are compared to other abstraction reactions involving H atom transfer to identify correlations between reaction exothermicity and both abstraction barriers and reaction rate curvature.
The high temperature pyrolysis of ethylbenzene
Authors: Pamidimukkala K. M. , Kern R. D. 
Published: January 2005

AbstractThe thermal decomposition of ethylbenzene has been investigated behind reflected shock waves over the temperature and pressure ranges of 1350–2080 K and 0.25–0.5 atm using a 1.6% C8H10  Ne mixture. Major products of the pyrolysis are C7H8, C7H7, C6H6, C4H2, C2H4, C2H2, and CH4; C8H8 appears throughout the temperature range as a minor product. Comparison of the product profiles obtained by time‐of‐flight mass spectrometry and the results of model calculations strongly supports the initiation step of β CC bond homolysis for C8H10 dissociation. A 51 kinetic step reaction mechanism with 24 species was formulated to model the temperature and time dependence of the major products observed in our experiments.
Characterization of solid solutions composed of oxides of Cu, Zn, and Cr for methanol synthesis
Authors: Gadalla A. M. , Haddad A. 
Published: January 2005

AbstractSolid solutions of Cu2O alone and Cu2O with ZnO or Cr2O3 in ZnO · Cr2O3 as well as solid solutions of ZnO in Cu2O · Cr2O3 have activities and selectivities for methanol synthesis comparable to solid solutions of Cu2O in ZnO. Addition of a secondary phase to these solid solutions limits the grain growth and produces higher surface areas.
The kinetics and mechanism of alkaline hydrolysis of N‐substituted phthalimides
Authors: Khan M. Niyaz 
Published: January 2005

AbstractThe aqueous cleavage of N‐(2‐bromoethyl)phthalimide (NBEPH), N‐(3‐bromopropyl)phthalimide (NBPPH), and N‐carbethoxyphthalimide (NCPH) have been studied within the [ŌH] range of 5 × 10−4 M to 2 × 10−3 M, pH range of 8.82 to 10.62 and 8.06 to 8.66, respectively. The observed pseudo‐first‐order rate constants, kobs, reveal a linear relationship with [ŌH] with essentially zero intercept. The alkaline hydrolysis of N‐(hydroxymethyl)phthalimide (NHMPH) has been studied within the [ŌH] range of 5.64 × 10−6 M to 2.0 M. The [OH]‐rate profile reveals that both ionized and nonionized NHMPH are reactive toward ŌH. The second‐order rate constant, kOH, for the reaction of ŌH with non‐ionized NHMPH is ca. 104 times larger than that with ionized NHMPH. The values of kOH obtained for NBEPH, NBPPH, NCPH, and nonionized NHMPH show a reasonable linear relationship with Taft substituent constants, and the slope (ρ*) of the plot is 1.01 ± 0.10. The low value of ρ* of 1.01 is attributed to nucleophilic attack as the rate‐limiting. The kOH value for ionized NHMPH reveals nearly 103‐fold negative deviation from the linear Taft plot.
Kinetics of cerium(IV) oxidation of macrocyclic complexes of chromium(III) and fate of chromium(IV) intermediates
Authors: Nair Balachandran Unni , Ramasami T. , Ramaswamy D. 
Published: January 2005

AbstractKinetics and mechanism of the cerium(IV) oxidation of Cr(III) complexes of a series of macrocyclic (or pseudomacrocyclic) ligands with [14]‐membered intraligand ring‐sizes have now been investigated at I = 1.0 M (LiClO4) Temp. 30°C. The complexes of the formulation Cr(macrocycle)(X)(H2O) where X = CHCl2 and H2O, n = 0 or 1 undergo oxidation to Cr(VI) with the formation of chromium(IV) intermediates. The observed kinetic parameters for the Ce(IV) oxidation of Cr(III) macrocyclic complexes have been discussed in terms of changes brought about by the macrocyclic ligands on the Cr(III)—Cr(IV) redox potentials and in specific rates for Cr(IV)—Cr(V) conversion. On the basis of this study, it has been suggested that the trapping of Cr(IV) is easier when a macrocyclic ligand having a symmetrical intra‐ligand ring size and unsaturation in the cyclic structure is coordinated equatorially. Cyclic voltammetric studies indicate the formation of Cr(IV) transient in the case of electrochemical oxidation of trans‐Cr(Me4[14]tetraene)(H2O).
Micellar catalysis by perfluorooctanoic acid
Authors: Berndt D. C. , Ayoub M. E. , Akhavan‐Tafti M. H. 
Published: January 2005

AbstractRates of acidic hydrolysis of hexano‐, octano‐, and decanohydroxamic acids and of 4‐bromophenylaceto‐ and phenylacetohydroxamic acids have been determined in aqueous perfluorooctanoic acid—a reactive counterion surfactant system. Typical micellar catalysis was observed for the hydrolyses of the n‐alkyl hydroxamic acids but not for the arylacetohydroxamic acids. The Arrhenius activation energy for hydrolysis of octano‐hydroxamic acid is smaller above the cmc of the surfactant than it is below the cmc.
Kinetics of methylchlorosilane formation on Zn‐promoted Cu3Si
Authors: Agarwala J. P. , Falconer John L. 
Published: January 2005

AbstractThe kinetics of the direct synthesis reaction (Si + 2CH3Cl → (CH3)2SiCl2) were measured on a Cu3Si alloy containing 1.2 atom % Zn. Reaction was carried out in a differential reactor (520–595 K, 1 atm) attached to an ultrahigh vacuum (UHV) system. Auger spectroscopy was used to characterize the surface before and after reaction. Zinc does not significantly change the overall rate of reaction, but it changes selectivity to dimethyldichlorosilane (the desired product), surface composition, activation energies, and induction times. The rate of silicon diffusion to the surface is not limiting in the presence of zinc. Zinc is found to be a promoter for improved selectivity only in low concentrations, and only a fraction of the surface appears to be active for reaction. The kinetics appear relatively insensitive to the surface composition or the form of surface carbon. A Cu3Si surface with Zn is shown to be a good model catalyst for the direct synthesis reaction.
Photoenhancement of the nitrous acid formation in the surface reaction of nitrogen dioxide and water vapor: Extra radical source in smog chamber experiments
Authors: Akimoto Hajime , Takagi Hiroo , Sakamaki Fumio 
Published: January 2005

AbstractThe surface reaction of NO2 and H2O vapor to emit HONO into the gas phase was studied in the evacuable and bakeable photochemical chamber under the irradiation of UV‐visible light (≳ 290 nm). Kinetic analysis of the NO, NO2, and HONO with the aid of computer modeling strongly suggested that the formation of HONO by the surface reaction is photoenhanced. When a linear regression was assumed, the photoenhancement factor defined by {(k′21/k21) − 1} was expressed as (6.8 ± 2.5)k1 under our experimental conditions, where k1 is the primary photolysis rate of NO2, and k21, k′21 are the second‐order‐equivalent rate constants of the HONO formation reaction in dark and under irradiation, respectively. The discussion was made that this photocatalitic enhancement of HONO formation would explain the nature of the extra OH radical flux in the smog chamber experiments, which has been discussed as “unknown radical source” and has still been unexplained by the surface dark reaction of NO2 and H2O to emit HONO.
The kinetics of oxiranes addition to bis/2‐hydroxyalkyl/disulfides and bis/2‐hydroxyalkyl/sulfides in the presence of N,N‐dimethylcyclohexylamine
Authors: Wilk Kazimiera A. , Sokołowski Adam , Burczyk Bogdan , Chlebicki Jan 
Published: January 2005

AbstractRate constants for the reaction of oxiranes with bis/2‐hydroxyalkyl/disulfides, bis/2‐Hydroxyalkyl/sulfides, and 1,6‐Hexanediol in the presence of N,N‐dimethylcyclohexylamine were studied at the temperature range of 50–90°C. A mechanism of these reactions has been proposed and its kinetic equation has been presented.
The kinetics and mechanisms of the gas phase elimination of 4‐(methylthio)‐1‐butyl acetate and 1‐chloro‐4‐(methylthio)‐butane
Authors: Chuchani Gabriel , Martin Ignacio , Dominguez Rosa M. 
Published: January 2005

AbstractThe gas phase elimination of 4‐(methylthio)‐1‐butyl acetate and 1‐chloro‐4‐(methylthio)‐butane has been investigated in a seasoned, static reaction vessel over the temperature range of 310–410°C and the pressure range of 46–193 Torr. The presence of the inhibitors propene, cyclohexene, and/or toluene had no effect on the rates. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for 4‐(methylthio)‐1‐butyl acetate, log k1(s−1) = (12.32 ± 0.29) − (192.1 ± 3.6) kJ/mol/2.303RT; for 1‐chloro‐4‐(methylthio)‐butane, log k1(s−1) = (12.23 ± 0.59) − (175.7 ± 6.8) kJ/mol/2.303RT. The CH3S substituent in 1‐chloro‐4‐(methylthio)‐butane has been found to participate in the elimination reaction, where tetrahydrothiophene and methyl chloride formation may result from an intimate ion‐pair type of mechanism. The yield of a cyclic product in gas phase reactions provides additional evidence of an intimate ion pair mechanism through neighboring group participation in gas phase elimination of special types of organic halides.