bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies in nickel(IV) chemistry. Kinetics of electron transfer from dimethyl sulfoxide to oxohydroxonickel(IV) in aqueous acid medium
Authors: Neogi G. , Acharya S. , Panda R. K. , Ramaswamy D. 
Published: January 2005

AbstractThe kinetics of decomposition of “oxohydroxonickel(IV)” [Ni(IV)] with concomitant intramolecular electron transfer to produce hexaaquanickel(II) and dioxygen in aqueous acid solutions show pseudo‐first‐order dissappearance of the Ni(IV). The pseudo‐first‐order rate constants for the acid decomposition (kad) satisfy

where KMH and kd refer to the equilibrium protonation constant and the decomposition constant of the protonated species of the Ni(IV) respectively. The values of KMH and kd in aqueous medium at 45°C and μ = 2.0M are 25.5 ± 1M−1 and (1.7 ± 0.1) × 10−5 s−1, respectively.The kinetics of the intermolecular electron transfer from dimethyl sulfoxide (DMSO) to the Ni(IV), producing Ni(H2O)62+ and dimethyl sulfone as products, have been investigated by monitoring the formation of Ni(H2O)62+. The pseudo‐first‐order rate constants for the electron transfer kobs are linearly dependent on [DMSO]0 or [H+], attaining limiting values at higher relative [DMSO]0 or [H+], in accordance with

where K1c and K2c represent the formation constants of the precursors involving DMSO and the unprotonated and one‐protonated Ni(IV) species, respectively, and k1x and k2x are the corresponding decomposition rate constants of the precursors. The values of K2c and k2x are (2.3 ± 0.1) × 104M−1 and 19 ± 1 s−1, respectively, at 45°C and μ = 1.0M. Results are interpreted in terms of probable mechanisms involving (1) a rate‐determining decomposition of the protonated Ni(IV) followed by rapid product formation steps, and (2) precursor complex formation between DMSO and the unprotonated or the protonated species of the Ni(IV) followed by rate‐determining decomposition with electron transfer.
A Mass‐spectrometric study of propionaldehyde oxidation in the negative temperature coefficient region
Authors: Kaiser E. W. 
Published: January 2005

AbstractThe oxidation of propionaldehyde has been investigated in a 1‐L Pyrex reactor at total pressures of 50–120 torr and temperatures 553–713 K. Detection of reactants and products was principally by molecular beam mass spectrometry, although certain species could only be measured by gas‐chromatographic analysis. At 553 K the yield of water was ∼83% of the propionaldehyde consumed, leading to the conclusion that OH is the principal chain carrier near the beginning of the negative temperature coefficient region. Many oxygenated organics (CH2O, CH3CHO, C2H5OH, C2H5O2H, CH3O2H) and C2H4 are formed during the oxidation process. These oxidation products are consistent with the important role of O2 addition to C2H5 radicals at 553 K followed by subsequent reactions of the C2H5O2 radical. As the temperature is increased, the product concentrations smoothly change to a much simpler distribution in which C2H4, H2O2, and CO are the dominant products.
Kinetics of the reaction between methane and iodine from 830 to 1150 K in the presence and absence of oxygen
Authors: Pardini Steven P. , Martin Don S. 
Published: January 2005

AbstractThe formation of methyl iodide was determined by radiochemical methods and by massspectroscopic analyses in mixtures of Ar–CH4–I2 and ArCH4I2O2, heated by a reflected shock wave to temperatures of 830–1150 K. The rate of formation of CH3I was consistent with the chain mechanism

where the indicated rate constant for reaction between I and CH4 is given by k2(cm3/mol · s) = 1014.17 exp(−32.9 ± 0.8 kcal/mol/RT). No effect on the reaction rate by the presence of O2 was detected. However, in one experiment at 1097 K with 3.86 mol % O2 the formation of CH2O was indicated by the mass‐spectroscopic analysis, presumably from the reaction of O2 with CH3.
Catalytic isomerization of 1‐hexene on hy zeolite
Authors: Ko A. N. , Wojciechowski B. W. 
Published: January 2005

AbstractThe isomerization of 1‐hexene on 70/80 mesh HY zeolite was studied at 200°C. The observed reaction products are formed via a variety of processes including double bond shift, cis–trans isomerization, skeletal rearrangement, cracking, hydrogen transfer, polymerization, cyclization, and coke formation. By applying the time‐on‐stream theory, the products have been classified as primary, secondary, or both, according to their OPE curves on product selectivity plots. 2‐Ethyl‐1‐butene, which is present as an impurity in the feed, is found to react about 30 times faster than 1‐hexene. Both 2‐hexenes and 3 hexenes are formed primarily from 1‐hexene, while 3 methyl 2 pentenes and 3‐methyl‐1‐pentene formed from 2‐ethyl‐1‐butene. The ratio of the initial rate of deprotonation to that of hydrogen shift in these reactions is ∼15 and ∼100, respectively. All products of skeletal rearrangement are observed to be secondary. Cracking products are produced mainly from precoke, which is also the source of hydrogen in the formation of paraffins. A detailed reaction network along with its associated mechanisms are presented and discussed.
Pyrolysis of 5‐chloropentan‐2‐one and 4‐chloro‐1‐phenylbutan‐1‐one. Participation of the carbonyl group
Authors: Chuchani Gabriel , Domínguez Rosa M. 
Published: January 2005

AbstractThe rates of elimination of 5‐chloropentan‐2‐one and 4‐chloro‐1‐phenylbutan‐1‐one in the gas phase have been determined in a static system, seasoned with allyl bromide, and in the presence of the chain inhibitor propene. The reactions are unimolecular and follow a first‐order rate law. The working temperature and pressure ranges were 339.4–401.1°C and 46–117 torr, respectively. The rate coefficients for the homogeneous reactions are given by the following Arrhenius equations: for 5‐chloropentan‐2‐one, log k1(s−1) = (13.12 ± 0.88) ‐ (207.8 ± 11.0)kJ/mol/2.303RT; and for 4‐chloro‐1‐phenylbutan‐1‐one, log k1(s−1) = (12.28 ± 1.09) ‐ (185.2 ± 12.0)kJ/mol/2.303RT. The carbonyl group at the γ position of the CCl bond of haloketones apparently participates in the rate of pyrolysis. The five‐membered conformation appears to be a favorable structure for anchimeric assistance of the CO group in the gas‐phase elimination of chloroketones.
Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2‐propanol
Authors: Kanakaraj Perumal , Maruthamuthu Pichai 
Published: January 2005

AbstractThe photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2‐propanol at 25°C was found to obey an overall first‐order rate – d[PMS]/dt = kϕ[PMS]. In the absence of 2‐propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] > 2 × 10−M, and is independent of concentration at [PMS] > 2 × 10−2M. The quantum yield in the presence of 2‐propanol was found to be 3.03 at [PMS] = 1 × 10−2M and 4.45 at higher concentrations of PMS. In the pH range of 2–9.0 the quantum yield was found to be independent of pH, and the overall rate constant kϕ was found to be 6.49 × 10−3 s−1 and 1.68 × 10−3 s−1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.
Kinetics and mechanism of the decomposition of N‐brominated alanine in aqueous solution
Authors: Stanbro William D. , Lenkevich Michael J. 
Published: January 2005

AbstractAqueous bromine reacts with alkyl‐sidechain amino acids through a series of steps resulting in the formation of the corresponding alkyl aldelydes and nitriles. The kinetics and the mechanism of the interaction of bromine with alanine are examined. The products and the rates of this reaction are dependent in a complex way on the initial reactant concentration and pH. Acetaldeyde production is favored at low bromine‐to‐alanine ratios, low bromine concentrations, and pH values above 6. The first‐order rate constant for the formation of acetaldelyde from alanine under these conditions is k4 = 1.98 × 1015 e−22,500/RT min−1. At higher concentration the nitrile is formed through a bromoimine intermediate. Under most conditions the nitrile appears to form from a catalyzed decomposition of the bromoimine which is too fast to be followed by the methods used in this study. However, residual amounts of the bromoimine decay by a slower first‐order mechanism. The rate constant for this slower reaction in the case of alanine at pH 6.8–6.9 and alanine concentrations of 1 × 10−4M is k6 = 1.75 × 105 e−10,400/RT min−1.
The gas‐phase decomposition of methylsilane. Part I. Mechanism of decomposition under shock‐tube conditions
Authors: Sawrey B. A. , O'Neal H. E. , Ring M. A. , Coffey D. 
Published: January 2005

AbstractThe gas‐phase decompositions of methylsilane and methylsilane‐d3 have been investigated in a single‐pulse shock tube at 4700 torr total pressure in the temperature range of 1125–1250 K. For CH3SiD3 at 1200 K three primary steps occur in the homogeneous decomposition with efficiencies in parentheses:

,

, and

. For CH3SiH3 at 1200 K the primary CH4 elimination efficiency is 0.09 while the total primary H2 elimination efficiency is 0.91. Minor product formations of C2H4, acetylene, dimethylsilane, and SiH4 are discussed.
Kinetics, mechanism, and endo selectivity of Diels–Alder reactions of alkylmonosubstituted ethenes with cyclohexa‐1,3‐diene in the gas phase
Authors: Huybrechts G. , Poppelsdorf H. , Maesschalck L. , Van Mele B. 
Published: January 2005

AbstractThe reactions magnified image where Y = CH3 (M), C2H5 (E), iC3H7 (I), and tC4H9 (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by

The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.
Pyrolysis of methyl chloride, a pathway in the chlorine‐catalyzed polymerization of methane
Authors: Weissman Maia , Benson Sydney W. 
Published: January 2005

AbstractThe reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine‐catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 ‐ initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol):
The role of electronically excited states in recombination reactions
Authors: Smith Ian W. M. 
Published: January 2005

AbstractMethods are described for including the participation of bound electronically excited states in calculations on radical recombination reactions. These methods are illustrated by applying them to the reactions

For O2, accurate ab initio potentials are used in calculations which show that the electronic degeneracy and long‐range part of the potential are likely to be crucial in determining the contribution of a given electronic state to the overall reaction, as long as the state is not so weakly bound that it dissociates thermally before being electronically quenched. Weak collision effects are allowed for using a Monte Carlo technique and an assumed exponential form for the distribution of energies transferred in collisions with a third body. For larger systems it is evident that the role of bound excited states in the low‐pressure regime falls rapidly as the size of the system increases. As the high‐pressure limit is approached, however, the contribution of excited states is likely to come close to that expected simply on the basis of electronic degeneracy.
Sensitivity analysis in chemical kinetics: Recent developments and computational comparisons
Authors: Kramer Mark A. , Rabitz Herschel , Calo Joseph M. , Kee Robert J. 
Published: January 2005

AbstractThe advantages and disadvantages of various methods of parametric sensitivity analysis in chemical kinetic modeling are discussed. Particular attention is given to estimates of computational labor for realistic problems, and quantitative comparisons are made utilizing a 52‐reaction, 11‐species CO oxidation mechanism. The authors′ CHEMSEN/AIM program compares favorably to other techniques in many circumstances, and provides the additional convenience of accepting input information in familiar chemical notation. This paper also reviews recent developments in theory of sensitivity analysis, relevant to chemical kinetic modeling.
Kinetics of thermal decomposition of CuSO4 · 5H2O to CuO
Authors: Gadalla Ahmed M. 
Published: January 2005

AbstractThe effect of particle size, type of crucible, and heating rate on the thermal curves obtained simultaneously for CuSO4 · 5H2O were discussed. The dissociation steps were confirmed. Thermogravimetric techniques for determining the rate‐controlling processes and kinetic parameters were applied for the dehydration steps and the calcination of CuSO4 and CuSO4 · CuO. For the dehydration of the monohydrate one mechanism operates but the activation energy and preexponential factor vary over wide ranges. Differentiating between various mechanisms using the same technique was sometimes difficult giving completely different values for the kinetic parameters. In view of such difficulties the various methods were assessed, the best techniques to treat similar results were recommended and the operating mechanisms and kinetic parameters for the various steps were thus established.
The very‐high‐temperature pyrolysis of ethane: Evidence against high rates for dissociative recombination reactions of methyl radicals
Authors: Kiefer J. H. , Budach K. A. 
Published: January 2005

AbstractThe pyrolysis of 1 and 2% ethane in krypton has been studied in shock waves by the laser‐schlieren technique over 1700–4800 K. For 2400–2800 K an effective zero density gradient is seen following the rapid dissociation of the ethane. Through simulation with various mechanisms it is evident that the high rates for the dissociative recombination reactions of methyl radicals

obtained in recent shock‐tube studies, are incompatible with this observation; these rates must be reduced at least an order of magnitude. On the basis of theory and previous low‐temperature (T) measurements, k = 7.8 × 1011 (‐6562/T) (cm3/mol s) is recommended for the second of these reactions.
Kinetics and mechanism of the shock induced thermal decomposition of n‐propylsilane
Authors: Sawrey B. A. , O'Neal H. E. , Ring M. A. , Coffey D. 
Published: January 2005

AbstractThe kinetics and mechanism of the thermal decomposition of n‐propylsilane have been studied by the single pulse shock tube‐comparative rate technique at pressures around 4700 torr between 1095–1240 K. The primary dissociation processes are 1,1 and 1,2 H2 elimination with ø1,1 ⋍ 0.75 and ø1,2 ⋍ 0.25, respectively. Subsequent decompositions of the primary process product, n‐propylsilylene, to propylene and ethylene is complete even in the presence of excess butadiene. Possible mechanistic paths for these decompositions are discussed and an activation energy range of 30 ± 4 kcal is established for both processes. Induced decomposition via silylene chains accounts for 36–46% of the overall reaction in the uninhibited decomposition of n‐propylsilane. The silylene chains are quenched in excess butadiene, and studies under maximum inhibition give overall decomposition kinetics of, log k(nPrSiD3, s−1) = 15.26–65,300 ± 1950 cal/2.303. Computer modeling results of the overall reaction both in the absence and presence of butadiene are also presented and shown to be in acceptable agreement with the experimental observations.
Kinetics of hydrogen oxidation near the lower explosion limit
Authors: Aleksandrov E. N. , Arutyunov V. S. , Dubrovina I. V. , Kozlov S. N. 
Published: January 2005

AbstractKinetics of hydrogen oxidation near the lower explosion limit in the kinetic region of chain termination has been studied. Major effects, causing deviations of the reaction kinetics from calculations by the linear theory of branched chain processes, are shown to be (1) the inhibition of the reacting mixture by the products of interaction of active centers with vacuum grease or with impurities contained in it and (2) the heterogeneous negative interaction of reaction active centers. The kinetics of hydrogen oxidation in this region has been calculated with consideration of the heterogeneous negative chain interaction. A set of parameters has been obtained that make it possible to determine by the shape of the kinetic curves the sign and the value of nonlinear interaction of chains near the lower explosion limit. It has been shown that the experimental data are in good agreement with the calculations, provided the heterogeneous negative chain interaction is taken into consideration and the inhibiting effect of impurities is eliminated. The rate of heterogeneous generation of chains on a quartz surface treated with hydrofluoric or boric acid has been determined.
Kinetic study for addition of the phenylthio radicals to vinylpyridines
Authors: Ito Osamu , Matsuda Minoru 
Published: January 2005

AbstractThe absolute rate constants for reversible addition of the substituted phenylthio radicals to vinylpyridines in solution at 23°C have been determined by flash photolysis method. For each phenylthio radical, the reactivities of vinylpyridines is 3–5 times lower than that of styrene. The relative equilibrium constants estimated with flash photolysis indicate that the stabilities of the adduct carbon‐centered radicals generated from vinylpyridines are similar to that from styrene. The Hammett plots suggest that the difference in the reactivities originates in the polar transition state; the nitrogen atom in 4‐vinylpyridine withdraws the electrons of vinylic double bond.
An investigation of the dark formation of nitrous acid in environmental chambers
Authors: Pitts James N. , Sanhueza Eugenio , Atkinson Roger , Carter William P. L. , Winer Arthur M. , Harris Geoffrey W. , Plum Christopher N. 
Published: January 2005

AbstractThe formation of nitrous acid (HONO) in the dark from initial concentrations of NO2 of 0.1–20 ppm in air, and the concurrent disappearance of NO2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300‐ and 5800‐L volume (both with surface/volume ratios of 3.4 m−1). In these environmental chambers the initial HONO formation rate was first order in the NO2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo‐first‐order consumption rate of NO2 was (2.8 ± 1.2) × 10−4 min−1 in the 5800‐L Teflon‐coated evacuable chamber and (1.6 ± 0.5) × 10−4 min−1 in a 4300‐L all‐Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO2 reacted in the evacuable chamber and ca.10–30% in the all‐Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NOx− organic‐air mixtures, and of HONO formation in polluted atmospheres, are discussed.
The rate of the reaction of OH with HCl
Authors: Molina M. J. , Molina L. T. , Smith C. A. 
Published: January 2005

AbstractThe absolute rate constant for the OH + HCl reaction has been measured from 240 to 295 K utilizing the techniques of laser/flash photolysis‐resonance fluorescence. The HCl concentrations were monitored continuously by ultraviloet and infrared spectrophotometry. The results can be fit to the following Arrhenius expression:

The rate constant values obtained in this study are 20–30% larger than those recommended previously for modeling of stratospheric chemistry.
VLPR study of the reaction Br + CH3CHO
Authors: Islam Tajmeri S. A. , Marshall Roger M. , Benson Sidney W. 
Published: January 2005

AbstractThe reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k1 = 2.1 × 1012 cm3/mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k‐1 = 1 × 1010 cm3/mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction:

in which step 2 is shown to be rate limiting under VLPR conditions and k2 is estimated at 1012.6 cm3/mol s from recent theoretical models for radical recombination. It is also shown that 0 ⩽ E1 ⩽ 1.4 kcal/mol using theoretical models for calculation of A1 and is probably closer to the lower limit. Reaction −1 is negligible under conditions used.
Kinetics of the redox reactions between ceric sulfate and lactic and atrolactic acids in the medium HClO4‐Na2SO4‐NaClO4
Authors: Calvaruso Giuseppe , Cavasino F. Paolo , Sbriziolo Carmelo 
Published: January 2005

AbstractThe kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4‐Na2SO4‐NaClO4 at 25.0°C and ionic strength 2.0 mol dm−3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression

where kobs indicates the observed pseudo‐first‐order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO] concentrations. Moreover, three equilibria involving cerium(IV) and HSO (or SO) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.