bluuebunny/crossref_metadata_2025 huggingface dataset:
The kinetics and the mechanism of the thermal decomposition of bis‐pentafluorosulfurtrioxide (SF5OOOSF5)
Authors: Czarnowski J. , Schumacher H. J.
Published: January 2005

The thermal decomposition of SF5O3SF5 has been investigated between 5 and 25°C. In the presence of sufficient high pressures of O2 the only products formed are SF5O2SF5 and O2:

The reaction is homogeneous. Its rate is strictly first order with respect to the trioxide pressure and independent of the total pressure of the reaction products and of oxygen above a certain limiting pressure:

The experimental results can be explained with the following mechanism:
equation image
In the presence of O2 > 100 Torr the concentration of SF5 is insignificantly small. Therefore reactions (5) and (6) do not have to be considered any more, and steps (2) and (2′) will be of no importance. From reactions (1)–(4) it follows:

The numerical value of the factor [1 + (k′12/2k3k4)1/2] is small. It can be estimated that E3 ≃ 2 ± 1 kcal; therefore, E – E1 ≤ 1 kcal, and D = (26 – 1) ± 1.0 kcal.
Oxidation of fluorenes by ammonium meta vanadate—a kinetic study
Authors: Narasimhan S. , Venkatasubramanian N.
Published: January 2005

The oxidation of fluorene by vanadium(V) in aqueous acetic acid containing sulfuric acid (1.0M) at 50°C produces fluorenone and 2‐hydroxy diphenyl 2′‐carboxaldehyde. The order with respect to each reactant is found to be 1. The order dependence on sulfuric acid concentration is 4, indicating that V(OH)23+ could be the active species. An increase in the acetic acid percentage in the solvent medium increases the rate of the reaction. The effect of solvent variation has been discussed in the light of the acidity function and the polarity of the medium. The effect of substituents on the rate has been studied for seven substituted fluorenes, and a linear relationship exists between log k versus σ values with the slope ρ = ‐3.2. A small isotope effect is observed for the oxidation of the parent compound (kH/kD = 1.2). The effect of temperature on the rate of the reaction has been studied, and the activation parameters are discussed. A mechanism involving the rate‐limiting formation of a cation‐radical intermediate is proposed.
A computational algorithm for the Green's function method of sensitivity analysis in chemical kinetics
Authors: Dougherty Eugene P. , Rabitz Herschel
Published: January 2005

The recent interest in numerical modeling of chemical kinetics has generated the need for proper analysis of the system sensitivities in such models. This paper describes the logic for a program developed by the authors to implement the Green's function method of sensitivity analysis in complex kinetic schemes. The relevant equations and numerical details of the algorithm are outlined, two flow charts are provided, and some special programming considerations are discussed in some detail. Computer storage and computational time considerations are also treated. Finally, applications of sensitivity information to understanding complex kinetic system behavior and analyzing experimental results are suggested.
Aluminium monoacetate complex formation reaction studied by the pressure‐jump method
Authors: Hiraishi M. , Harada S. , Uchida Y. , Kuo H. L. , Yasunaga T.
Published: January 2005

One of two pressure‐jump relaxation processes observed in Al(III) acetate aqueous solution, the slow one, was studied kinetically. The relaxation was ascribed to the Al(III) monoacetate complex formation reaction. The detailed reaction mechanism, including the hydrolysis process, was revealed, and the rate constants were obtained.
Titration of oxygen chemisorbed on platinum: Experiment and simulation
Authors: Tseng Fu‐hsiang , White J. M.
Published: January 2005

The titration of chemisorbed oxygen by carbon monoxide to form carbon dioxide has been studied from 373 to 673 K over polycrystalline platinum. The pressure transients for CO and CO2 have been measured and simulated numerically. A complex Langmuir–Hinshelwood mechanism is found which fits all the data, and it is not necessary to invoke Eley–Rideal kinetics. The results fall into two temperature regimes, above and below 473 K, which are characterized by different Arrhenius parameters. A change in activation energy with oxygen coverage is also found below 473 K.
The rate constant of NO + O3 → NO2 + O2 in the temperature range of 283–443 K
Authors: Lippmann H. H. , Jesser Barbara , Schurath Ulrich
Published: January 2005

The reaction NO + O3 → NO2 + O2 has been studied in a 220‐m3 spherical stainless steel reactor under stopped‐flow conditions below 0.1 mtorr total pressure. Under the conditions used, the mixing time of the reactants was negligible compared with the chemical reaction time. The pseudo‐first‐order decay of the chemiluminescence owing to the reaction of ozone with a large excess of nitric oxide was measured with an infrared sensitive photomultiplier. One hundred twenty‐nine decays at 18 different temperatures in the range of 283–443 K were evaluated. A weighted least‐squares fit to the Arrhenius equation yielded k = (4.3 ± 0.6) × 10−12 exp[‐(1598 ± 50)/T] cm3/molecule sec (two standard deviations in brackets). The Arrhenius plot showed no curvature within experimental accuracy. Comparison with recent results of Birks and co‐workers, however, suggests that a nonlinear fit, as proposed by these authors, is more appropriate over an extended temperature range.
On the gas‐phase free radical displacement reaction CH3 + CD3COCD3 → CD3 + CH3COCD3
Authors: Knoll H. , Richter Gislind , Schliebs R.
Published: January 2005

The gas‐phase free radical displacement reaction
equation image
has been studied in the temperature range of 240–290°C and at 140°C with the thermal decomposition of azomethane (AM) and di‐tert‐butylperoxide (DTBP), respectively, as methyl radical sources. The reaction products of the CD3 radicals were analyzed by mass spectrometry. Assuming negligible isotope effects, Arrhenius parameters for the elementary radical addition reaction
equation image
were derived:

The data are discussed with respect to the back reaction and general features of elementary addition reactions.
On the reaction between ethylene and cyclopentene, a radical mechanism
Authors: Benson Sidney W.
Published: January 2005

The bimolecular reaction
equation image
is shown to proceed via a simple, nonchain, radical mechanism:
equation image
with the net reaction the same as (1). Rate constants are estimated for each step and for each possible competing reaction and shown to yield minor or negligible side reactions in agreement with the observations of Lalonde and Back. Estimated and observed rate constants (1) and (1′) are in excellent agreement with the assumption that k'‐1 is a typical radical disproportionation with zero activation energy.

From the reported data a best value for k′1 is

where θ = 2.303RT kcal/mol.
Peroxy radical reactivities in the cooxidation of ethylbenzene and substituted 3‐phenylindans
Authors: Rafikova V. S. , Maizus Z. K. , Skibida I. P. , Volkov R. N.
Published: January 2005

The rate constants of peroxy radical recombination in the oxidation of 1‐methyl‐3‐phenylindan, 1,3‐dimethyl‐3‐phenylindan, and 1,1‐dimethyl‐3‐phenylindan were measured using the nonstationary‐state technique. A cooxidation method was applied to obtain the reactivities of these compounds with respect to α‐phenylethyl peroxy radicals.
The rate constant for H + i‐C4H8 → t‐C4H9 in the range of 298–563 K
Authors: Canosa Carlos E. , Marshall Roger M. , Sheppard Adrian
Published: January 2005

The overall rate constant for hydrogen‐atom addition to isobutene has been measured in the temperature range of 298–563 K in a flow discharge system coupled to a quadrupole mass spectrometer. Previously published results allow the determination of

where the error limits are 95% confidence limits.
equation image
The pyrolysis kinetics of 4‐chloro‐2‐butanone in the gas phase
Authors: Dominguez Rosa M. , Chuchani Gabriel
Published: January 2005

The rates of pyrolysis of 4‐chloro‐2‐butanone in the gas phase have been determined in a static system seasoned with the products of decomposition of allyl bromide. The reaction is catalyzed by hydrogen chloride. Under maximum catalysis of HCl, the kinetics were found to be of order 1.5 in the substrate suggesting that a complex elimination is involved. The reaction, when maximally inhibited with propene, appears to undergo a unimolecular elimination and follows a first‐order law kinetics. The products are methylvinyl ketone and hydrogen chloride. The kinetics have been measured over the temperature range of 402.0–424.4°C.The rate coefficients are given by the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$ \log k_1 (\sec ^{ - 1}) = (13.67 \pm 0.69) - (225.2 \pm 8.6)\,{\rm kj}/{\rm mol}/2.303RT\angle $\end{document}. Thepyrolysis of 4‐chloro‐2‐butanone is 31 times greater in rate than that of ethyl chloride at 440°C. This large difference in rate may be attributed to the ‐M effect of the acetyl substituent in the pyrolysis of the former halo compound.
Kinetics and mechanism of the thermal decomposition of cyclopentyl cyanide
Authors: King Keith D. , Goddard Richard D.
Published: January 2005

The thermal decomposition of cyclopentyl cyanide has been investigated in the temperature range of 905–1143 K using both conventional stirred‐flow reactor and very low‐pressure pyrolysis (VLPP) techniques. The results from both techniques are consistent. The main primary processes are HCN elimination to form cyclopentene:
equation image
and ring fragmentation to form vinyl cyanide plus propylene and ethylene plus cyanopropenes:
equation image
Under the experimental conditions cyclopentene undergoes further decomposition to cyclopentadiene plus hydrogen. There is evidence for conversion of some of the reactant to a solid residue, presumably polymer. From the stirred‐flow reactor results the following Arrhenius expressions were obtained: log k1(s−1) = (12.8 ± 0.3) − (65.6 ± 1.3)/θ and log k2(s−1) = (16.0 ± 0.3) − (80.0 ± 1.1)/θ, where θ = 2.303RT kcal/mol. Application of RRKM theory shows that the VLPP experimental rate constants are consistent with high‐pressure Arrhenius parameters given by log k1(s−1) = (12.8 ± 0.3) − (67.8 ± 2.5)/θ for HCN elimination, and log k4(s−1) = (16.3 ± 0.3) − (80.1 ± 2.0)/θ for the sum of the ring fragmentation pathways. The rate parameters for HCN elimination are in good agreement with previous VLPP studies of alkyl cyanides and with theoretical predictions. The difference in activation energies for the ring opening of cyclopentane and cyclopentyl cyanide is reasonably close to the established value for the cyano stabilization energy. This supports the assumption of a biradical mechanism.
Kinetics of the formation of primary products of cumeme cracking over a partially exchanged LaY‐Zeolite
Authors: Corma A. , Farag H. , Wojciechowski B. W.
Published: January 2005

The kinetics of formation of primary products from cumene cracking over a partially exchanged LaNaY catalyst have been studied at 400, 450, and 500°C. It has been found that in both the fully and the partially exchanged LaNaY zeolite catalysts the nature of active sites is the same. The higher activity of the fully exchanged catalyst is attributed to a higher concentration of the active sites. It has also been found that an increase in exchange level leads to an increase in the number of both Bronsted and Lewis active sites, but in somewhat different proportions. A comparatively slight increase in the decay rate constant is observed over the same increase in the level of exchange.
High‐energy kinetic study of chemically activated 1,1‐dichlorocyclopropane
Authors: Eichler K. , Heydtmann H.
Published: January 2005

1,1‐Dichlorocyclopropane has been produced by addition of CH2(1A1) to 1,1‐dichloroethylene. CH2(1A1) was generated by the photolysis of ketene at 277–334 nm. The 1,1‐dichlorocyclopropane was formed in a chemically activated state, had an energy content between 386 and 400 kJ/mol, and reacted in two parallel channels to 2,3‐dichloropropene and 1,1‐dichloropropene. 1,1‐Dichloropropene was also formed directly by insertion of CH2(1A1) into the CH bond of 1,1‐dichloroethylene. As secondary reactions elimination of HCl from chemically activated 2,3‐dichloropropene occurred with 3‐chloropropyne and chloroallene as products. In some of the experiments perfluoropropane was added as an inert gas. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated 1,1‐dichlorocyclopropane and a step‐ladder model for the deactivation verify the proposed reaction scheme.
Kinetics of free‐radical decay reactions in polymeric solids
Authors: Basheer Rafil , Dole Malcolm
Published: January 2005

Kinetic equations for the decay of the free radicals in polymeric solids are given for the following assumptions on which they are based: (1) two simultaneous first‐order but physically separated decay reactions; (2) two simultaneous noninteracting second‐order decay reactions; (3) combined simultaneous but intermingled first‐ and second‐order decay reactions; (4) the same but for independent, i.e., not intermingled, first‐ and second‐order decay reactions; (5) a second‐order decay reaction in the presence of some free radicals that do not decay; and (6) a first‐order decay reaction in the presence of some free radicals that do not decay. In all of the above physical systems the total concentration only can be measured. Hence the above kinetic equations refer to the change of the total concentration with time. It is found that the data for the decay of the free radicals in irradiated isotactic polypropylene and 61% styrene‐39% butadiene block copolymer agree best with the equations for the second‐order decay in the presence of a fraction of nondecaying free radicals.
Flash photolysis of biacetyl in gas phase. Rate constants of reactions between methyl and acetyl radicals
Authors: Timonen Raimo , Kalliorinne Kaarlo , Blomqvist Kurt , Koskikallio Jouko
Published: January 2005

The flash photolysis of biacetyl produces CO, C2H6, and CH3COCH3 as main products, and in small amounts CO2, C2H4, and CH3CHO. The rate constants of reactions (2) and (3)

of thermally equilibrated radicals were calculated from the amounts of products:

.
Disproportionation reactions between CF2H and C2H5radicals in the gas phase
Authors: Nilsson William B. , Pritchard Glyn O.
Published: January 2005

The disproportionation and combination reactions between CF2H and C2H5radicals have been studied in the gas phase from room temperature to 70°C. For the pathway which yields CF2H2+ C2H4, relative to CF2HC2H5, Δ = 0.072 ± 0.019. The competing reaction channel that produces CF2+ C2H6is approximately four times as efficient, with Δ = 0.265 ± 0.038. With CF2D radicals an isotope effect for the CF2+ C2H5D reaction pathway was observed with Δ ≅ 0.2.
Kinetics and mechanism of Rh(III) catalyzed oxidation of styrene, stilbene and phenylacetylene by acid periodate
Authors: Radhakrishnamurti P. S. , Misra S. A.
Published: January 2005

The kinetics of Rh(III) catalyzed oxidative cleavage of styrene, stilbene, and phenylacetylene by periodate have been investigated in the presence of HClO4 in aqueous acetic acid medium. The kinetic orders are completely dependent on the nature of unsaturation. In the cases of styrene and stilbene the reactions are first order in the oxidant and Rh(III), zero order with respect to the substrate, and independent of [H+], whereas in the case of phenyl acetylene the reaction is zero order with respect to the oxidant and first order with respect to the substrate and Rh(III). The reaction is independent of [H+] in the range of 0.01−0.05M studied. A mechanism involving higher Rh(V) species has been postulated in the case of styrene as well as stilbene, and metal ion catalyzed hydration has been postulated in case of phenylacetylene. The influence of the solvent has been investigated, and a comparative analysis of the kinetic orders of styrene and stilbene is made with those of phenylacetylene.
Rate constants for the gas‐phase reaction of OH radicals with a series of ketones at 299 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L. , Pitts James N.
Published: January 2005

Relative rate constants for the reaction of OH radicals with a series of ketones have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of hydroxyl radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3 molecule−1 s−1, the rate constants obtained are (× 1012 cm3 molecule−1 s−1): 2‐pentanone, 4.74 ± 0.14; 3‐pentanone, 1.85 ± 0.34; 2‐hexanone, 9.16 ± 0.61; 3‐hexanone, 6.96 ± 0.29; 2,4‐dimethyl‐3‐pentanone, 5.43 ± 0.41; 4‐methyl‐2‐pentanone, 14.5 ± 0.7; and 2,6‐dimethyl‐4‐heptanone, 27.7 ± 1.5. These rate constants indicate that while the carbonyl group decreases the reactivity of CH bonds in the α position toward reaction with the OH radical, it enhances the reactivity in the β position.
Kinetic and mechanistic studies of oxidation of arginine, histidine, and threonine in alkaline medium by N‐chloro‐N‐sodio‐p‐toluenesulfonamide
Authors: Mahadevappa D. S. , Rangappa K. S. , Gowda N. M. M. , Gowda B. Thimme
Published: January 2005

The kinetics of oxidation of arginine, histidine, and threonine by chloramine‐T (CAT) have been investigated in alkaline medium at 35°C. The rates are first order in both [CAT] and [amino acid] and inverse fractional order in [OH−] for arginine and histidine. The rate is independent of [OH−] for threonine. Variation of ionic strength and addition of the reaction product, p‐toluenesulfonamide, or Cl− ions had no effect on the rate. A decrease of the dielectric constant of the medium by adding methanol decreased the rate with arginine, while the rates increased with histidine and threonine. The solvent isotope effect was studied using D2O. (kobs)/(kobs) was found to be 0.55 and 0.79 for arginine and histidine, respectively. The reactions were studied at different temperatures, and activation parameters have been computed. The oxidation process in alkaline medium, under conditions employed in the present investigations, has been shown to proceed via two paths, one involving the interaction of RNHCl (formed rapidly from RNCl−), with the amino acid in a slow step to form monochloroamino acid, which subsequently interacts with another molecule of RNHCl in a fast step to give the products, p‐toluenesulfonamide (RNH2), and the corresponding nitrile of the amino acid (R'CN). The other path involves the interaction of RNCl− with the amino acid in a similar way to give RNH2 and R'CN. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted using the derived rate laws, as [OH−] varies, are in excellent agreement with the observed rate constants, thus justifying these rate laws and hence the proposed mechanistic schemes.
Kinetics of oxidative coupling of phenols: Oxidation of naphthols by alkaline hexacyanoferrate (III)
Authors: Bhattacharjee Mitra , Mahanti M. K.
Published: January 2005

The oxidation of naphthols by alkaline hexacyanoferrate(III), at constant ionic strength, gave coupled products. The rate of the reaction was dependent on the first powers of the concentrations of substrate, oxidant, and alkali. The activation energies were 31.8 and 34.5 kJ/mol for α naphthol and β naphthol, respectively. The reaction pathway was via the formation of a radical intermediate, which was detected by electron spin resonance spectroscopy.
The oxidation of HI at low temperatures and the heat of formation of HO2
Authors: Shum Lilian G. S. , Benson Sidney W.
Published: January 2005

The kinetics of the oxidation of hydrogen iodide (HI + O2) at low temperature (414–499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k1 for the first and rate‐determining step
equation image
These data are combined with an estimated A factor A1 = 109.3±0.2 L/mol·s (assuming a tight linear I···H···O— transition state), to calculate the lower limit of the activation energy for the forward reaction E1. This leads to a minimum value for the heat of formation of the HO2 radical, ΔHf298°(HO2) < 3.0 kcal/mol.
Studies in nickel(IV) chemistry. Kinetics of the Cu(II) ion‐mediated acid decomposition of tris(dimethylglyoximato) nickelate(IV) in aqueous acidic medium
Authors: Neogi G. , Acharya S. , Panda R. K. , Ramaswamy D.
Published: January 2005

Kinetics of the Cu(II) ion‐mediated acid decomposition of tris (dimethylglyoximato)nickelate(IV), Ni(dmg)32− (dmg2− = dimethylglyoximate dianion), are reported in aqueous medium in the range of 3.6 ⩽ pH ⩽ 6.6 at 35°C and μ = 0.57 M. The pseudo‐first‐order rate constants of the disappearance of Ni(IV) kobs(M) satisfy the equation

where kad refers to the pseudo‐first‐order rate constants for the proton‐assisted decomposition of the Ni(IV) complex determined independently and is a function of [H+], and kdec(M) to that for the Cu(II) ion‐mediated route and is a function of [H+] and [Cu2+]. Both kobs(M) and kdec(M) are found to increase with increasing [Cu(II)]0, tending to attain limiting values at higher relative [Cu(II)]0. At low [Cu(II)]0 the kdec(M) is found to register a decrease with increasing pH in the pH range of 3.6–4.4, then an increase in the range of 4.4–5.76, and again a decrease in the range of 5.76–6.6. Results on the Cu(II) ion‐mediated acid decomposition are interpreted in terms of a probable mechanism involving pH‐dependent adduct formation equilibria involving the one‐protonated and the two‐protonated species of Ni(IV) and the various species of Cu(II) ion in the media, followed by rate‐determining acid decomposition of the adduct(s) to give Ni(II) aq. and Cu(dmgH)2. While the two‐protonated Ni(IV) complex apparently reacts about five orders of magnitude faster than the one‐protonated species, the aquacopper(II) reacts about two orders of magnitude slower than the hydroxoaquacopper(II).
TI(III) oxidation of alkenes and alkynes and Ru(III) catalysis in the oxidation of alkenes: A kinetic and mechanistic study
Authors: Radhakrishnamurti P. S. , Panda H. P.
Published: January 2005

The oxidation of trans‐stilbene, phenylacetylene, and diphenylacetylene by Tl(OAc)3 in aqueous acetic acid medium in the presence of HClO4 follows the rate law

in [H+] of 0.1–1.0M, the [H+] dependence below 0.1M being marginal. The reactions are strongly dielectric dependent. The order of reactivity among the substrates is styrene > phenylacetylene and trans‐stilbene > diphenylacetylene. A mechanism involving the oxythallation adduct by the Tl+(OAc)2 species has been discussed. The use of Ru(III) as a homogeneous catalyst brings a change in the kinetic orders for trans‐stilbene, the rate law being

The formation constants K for the Ru(III)–alkene π complex at 40, 50, and 60°C are 90.14M−1, 105.2M−1, and 127.7M−1, respectively. Interestingly the oxidation of phenylacetylene and diphenylacetylene does not undergo catalysis by Ru(III). The mechanism involving the metal–arene π complex is discussed.
Kinetics and mechanism of the cerium (IV) oxidation of α‐Hydroxycycloalkanecarboxylic acids and cyclic alcohols in acidic perchlorate media
Authors: Hanna Samir B. , Fenton Jeff Taylor
Published: January 2005

The Ce(IV) oxidation of the five‐, six‐, and seven‐membered ring α‐hydroxycycloalkanecarboxylic (C5, C6, and C7) acids to the corresponding cyclic ketones has been studied in acidic perchlorate media. The data may be interpreted in terms of a mechanism which involves fast preequilibrium complexation steps between Ce(IV) and the hydroxy acids, yielding two complexes which differ only by a proton. Complexation is followed by rate‐determining decarboxylation to an intermediate (free radical?), which reacts quickly with another Ce(IV) to give products. Of the two proposed complexes, the protonated one is virtually unreactive. The C7 ring acid is oxidized more rapidly than the C6 acid, which, in turn, is oxidized faster than the C5 acid.

For comparison, the oxidation of the five‐, six‐, and seven‐membered ring cyclic alcohols to the corresponding cyclic ketones by Ce(IV) in acidic perchlorate was also studied. The order of reactivity is cyclopentanol > cycloheptanol > cyclohexanol. The differences in observed reactivities between the hydroxy acids and the cyclic alcohols are explained in terms of differences in transition state structure.

The stepwise hydrolysis constants of Ce(IV) leading to Ce(OH)3Plus; and Ce(OH)22+ were determined. In the case of the hydroxy acids, evidence is in favor of Ce(OH)3+ as the reactive ceric species in aqueous acidic perchlorate media.
Sensitivity analysis in chemical kinetics by the method of polynomial approximations
Authors: Hwang Jenn‐Tai
Published: January 2005

A new approach, the method of polynomial approximations (PAM), to the sensitivity analysis in chemical kinetics is presented. The method is based on first dividing the time domain of interest into subintervals, and then, within each subinterval, using low‐degree interpolation polynomials to mimic the system temporal behavior. This procedure forces all parametric dependences of the system to reside in the expansion coefficients and transforms the differential sensitivity equations into a set of algebraic ones. The major computational effort of PAM is proportional to the number of components in the system, not to the number of parameters. In addition, higher order sensitivity coefficients in PAM can be generated quite readily once first‐order ones are known. The information required to divide the time domain comes from a preliminary simulation study of the system temporal behavior, which is always available in any kind of modeling studies. Typically, for an interpolation polynomial of degree 3–4, only 10–20 subintervals are needed to attain satisfactory accuracy. The application of PAM is well suited to large‐scale kinetic models, especially when an inexpensive scanning of the system sensitivity behavior is desired. The extremely high computational speed of PAM in securing sensitivity informations was demonstrated by two illustrative kinetic examples. Furthermore the problem of utilizing sensitivity information to unravel the functional dependence of a species concentration upon rate coefficients, to simplify a complex reaction model, and to elucidate mechanistic details of a reaction process was examined in detail.
Kinetics and mechanism of the reactions of the superoxide ion in solutions. III. Kinetics and mechanism of the reaction of the superoxide ion with ethyl acetate in dimethylformamide, acetonitrile, and their mixtures
Authors: Afanas′ev I. B. , Kuprianova N. S.
Published: January 2005

The kinetics of the reaction of the superoxide ion with ethyl acetate have been studied in DMF, AN, and their mixtures. It was shown that the rate constants depend on the ethyl acetate concentration, which indicates the formation of an intermediate in this process. Equilibrium constants for the process of the intermediate formation and the rate constants for its decay have been determined. It is concluded that aprotic solvents affect mainly the stage of the intermediate decay in this reaction.
Kinetic study of the reactions of CL and BR with H2O2
Authors: Heneghan Shawn P. , Benson Sidney W.
Published: January 2005

The reactions of Cl and Br atoms with H2O2 have been studied in the range of 300–350 K using the very‐low‐pressure‐reactor technique. It was found that metathesis to produce HX and HO2 is the only significant process (≤99%). For the reaction of Br

k2 (300 K) = 1.3 ± 0.45 × 10−14 and k2 (350 K) = 3.75 ± 1.1 × 10−14 cm3/molecules·s, with an activation energy of 4.6 ± 0.7 kcal/mol. Using an estimated A factor for A2, we find

suggesting that a best choice is E2 = 3.9 ± 0.4 kcal/mol. The relation of these values to ΔH (HO2) is discussed.
Rate constants for quenching of O2(1Δg) with sulfur compounds
Authors: Raja Nalini , Chatha J. P. S. , Arora P. K. , Vohra K. G.
Published: January 2005

The rate constants for the quenching of O2(1Δg) with carbon disulfide, dimethyl sulfide, dimethyl disulfide, diallyl disulfide, ethyl mercaptan, and thiophene have been determined in a discharge flow system in the absence of oxygen atoms. The rate constants are found to be (6.5 ± 0.6) × 104, (1.8 ± 0.2) × 104, and (3.5 ± 0.6) × 103 L/mol · s for dimethyl sulfide, ethyl mercaptan, and thiophene, respectively. The other compounds have rate constants <9.9 × 102 L/mol · s. In the case of dimethyl sulfide, even when NO2 concentration is more than what is required to remove oxygen atoms completely, the rate constants are found to vary with different amounts of NO2. No correlation is found to exist between the logarithm of the rate constants and the ionization potentials of the compounds.
Kinetics of partly diffusion‐controlled reactions. XIV. Effects of reversible energy transfer
Authors: Guillard R. , Andre J. C. , Bouchy M.
Published: January 2005

The general effect of back energy transfer is to reduce the apparent quenching constant which is an important parameter in the interpretation of energy transfer data. However, this interpretation may be erroneous when possible diffusion effects and the existence of nonuniform configurational distributions are not taken into account.
Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K
Authors: Atkinson Roger , Carter William P. L. , Aschmann Sara M. , Winer Arthur M. , Pitts James N.
Published: January 2005

Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n‐butane of 2.58 × 10−12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2‐methylbutane, 3.97 ± 0.11; 2,2‐dimethylbutane, 2.66 ± 0.08; 2‐methylpentane, 5.68 ± 0.24; 3‐methylpentane, 5.78 ± 0.11; 2,2,3‐trimethylbutane, 4.21 ± 0.08; 2,4‐dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3‐tetramethylbutane, 1.06 ± 0.08; and 2,2,4‐trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2‐dimethylbutane, 2,4‐dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.
Reaction of methyl radicals with haloalkanes
Authors: Sidebottom Howard , Treacy Jack
Published: January 2005

The kinetics of reactions involving halogen atom abstraction from haloalkanes by methyl radicals have been studied in the gas phase. Arrhenius parameters for halogen atom transfer were determined relative to those for methyl radical combination:
equation image

RX
log10A2(L/mol · s)
E2(kcal/mol)

CFCl3
8.3 ± 0.2
10.7 ± 0.4

CF3CCl3
7.9 ± 0.3
9.7 ± 0.6

CF2Cl2
9.1 ± 0.4
11.3 ± 0.7

CF3Cl
8.8 ± 0.5
11.8 ± 1.0

CF3CF2Cl
8.3 ± 0.3
10.9 ± 0.7

CF3Br
8.6 ± 0.2
9.3 ± 0.5

CF3I
8.1 ± 0.1
4.3 ± 0.2

CH3CH2I
8.9 ± 0.3
7.4 ± 0.6

The rate data obtained are used to provide information on the importance of polar effects for halogen abstraction processes.
Deactivation of I(52P1/2) by CF3I, CH3I, C2H5I, and CH4
Authors: Gu Z‐N. , Young A. T. , Houston P. L.
Published: January 2005

The technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time‐resolved detection of the 1.3‐μm emission from I*(2P1/2) has been used to measure the rate constants for deactivation of I* by CH3I, C2H5I, CF3I, and CH4. The recommended values are (2.76± 0.22) × 10−13, (2.85 ± 0.40) × 10−13, (3.5 ± 0.5) × 10−17, and (7.52 ± 0.12) × 10−14, respectively, in units of cm3 molecule−1 S−1.
The heat of formation of the ethyl radical
Authors: Cao J‐R. , Back M. H.
Published: January 2005

An examination of the results of measurements of the forward and reverse rate constants for the reaction

shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol−1. This system therefore provides further support for the recent measurement of this quantity.
Gas/wall collision efficiencies in very low pressure pyrolysis experiments
Authors: Dick Paul G. , Gilbert Robert G. , King Keith D.
Published: January 2005

A readily applicable empirical formula is obtained for the collisional efficiency for energy transfer between a highly vibrationally excited reactant and a seasoned (usually quartz) wall, in terms of the molecular weight, potential well depth and dipole moment of the reactant. This expression is used to examine corrections due to nonunit wall collision efficiency in the high‐pressure rate parameters obtained from very low‐pressure pyrolysis experiments. It is found that these corrections are up to ca. ±5 kJ/mol in the high‐pressure activation energy and a factor of ca. 2 in the high‐pressure frequency factor, for molecules with molecular weight less than ca. 100 and where experiments are carried out at temperatures exceeding 1000 K.
The kinetics and mechanism of aqueous cleavage of imide bond in 5, 5‐diethyl barbituric acid (5, 5‐diethyl‐2,4,6‐(1H, 3H) pyrimidinetrione) in a highly alkaline medium
Authors: Khan M. Niyaz , Khan A. Aziz
Published: January 2005

The kinetic study of alkaline hydrolysis of 5, 5‐diethyl barbituric acid has been carried out at various [OH] and different temperatures ranging from 85–95°C. The reaction follows an irreversible first‐order consecutive reaction path of the type \documentclass{article}\pagestyle{empty}\begin{document}${\rm A}\buildrel{{k1{\rm obs}}}\over\longrightarrow{\rm B}\buildrel{{k2{\rm obs}}}\over\longrightarrow$\end{document} X under pseudo‐first‐order kinetic conditions. A, B, and X represent for 5, 5‐diethyl barbituric acid, diethyl malonuric acid, and ammonia, respectively. The pH‐rate profiles obtained at three different temperatures reveal distinct phases which are attributed to a change in rate‐determining step with change in [OH]. On the basis of the observed data, a possible mechanism has been discussed.
Gas phase reactions of CF3, C2F5, and n‐C3F7 with carbon tetrachloride
Authors: de Vöhringer C. M. , Staricco E. H.
Published: January 2005

The reactions of some perfluoroalkyl radicals with carbon tetrachloride have been studied using the photolysis of the corresponding perfluoroalkyl iodide as the free radical source. The Arrhenius parameters, based on the value of 2.3 × 1013 cm3 mol−1 s−1 for the self‐combination rate constant of all radicals are:

Reaction
log(A/cm3 mol−1 s−1)
E/kcal mol−1

CF3 + CCl4
12.8
11.3

C2F5 + CCl4
12.8
11.6

n‐C3F7 + CCl4
12.9
12.0
Termolecular reactions of alkali metal atoms with O2 and OH
Authors: Patrick Roger , Golden David M.
Published: January 2005

Calculations of low‐pressure limit, third‐order rate constants are presented for the association reactions A + O2 + N2 and A + OH + N2 (A = Li, Na, K) over the temperature range 200–2000 K and a comparison is made with the available experimental data.
Mechanism of the chain process forming H2 in the photooxidation of formaldehyde
Authors: Veyret Bernard , Roussel Pascal , Lesclaux Robert
Published: January 2005

A mechanism for the formation in a chain of H2, CO, and HCOOH in the photooxidation of formaldehyde is proposed. This mechanism is initiated by the addition of HO2 to formaldehyde. Hydrogen atoms are produced by the thermal dissociation of the HOCH2O radical: HOCH2O → H + HCOOH; ΔH = + 3.2 kcal/mol [5]. Photolysis of CH2OO2NO mixtures and product analysis were carried out in conjunction with kinetic simulation yielding an estimate for the activation energy of the dissociation reaction : E5 = 14.9 ± 1.0 kcal/mol. Previous observations of this chain process are considered in view of this mechanism.
The kinetics and the mechanism of the thermal reaction between sulfurtetrafluoride (SF4) and trifluoromethylhypofluorite (CF3OF)
Authors: Gonzalez Alicia C. , Schumacher H. J.
Published: January 2005

The kinetics of the thermal reaction between SF4, and CF3OF has been studied between 142°C and 185°C. The reaction was found to be homogeneous and the only products formed are equimolecular amounts of SF6 and CF3O2CF3 and smaller amounts of CF3OSF5. The reaction mechanism was not affected by the total pressure, the oxygen pressure, or by the buildup of products. The experimental data can be explained by the following mechanism:
equation image
The rate constants can be expressed as
The kinetic study of thermal dehydration stages of SrCl2 · 2H2O and its deuterium analog
Authors: Tanaka Haruhiko , Shimada Satoshi , Negita Hisao
Published: January 2005

The kinetic deuterium isotope effect in the thermal dehydration stages of powdered SrCl2 · 2H2O was examined by means of both isothermal and dynamic gravimetries. These dehydration processes proved to be controlled by a random nucleation and its subsequent growth mechanism. No significant kinetic isotope effect was seen in these dehydration stages. It seems that there exists a kinetic compensation effect between the hydrate and its deuterium analog, if any isotopic differences in activation energy and frequency factor could exist.
Hydrogen abstraction from substituted aromatic compounds
Authors: Lissi E. A. , Collados J. , Olea A.
Published: January 2005

The reactivity of tert‐butoxy radicals with methyl substituted aromatic compounds is almost exclusively determined by the aromatic moiety and almost independent of the methyl group position. The hydrogen abstraction from the carbon α to the aromatic ring is hardly sensitive to the produced radical stabilization. This lack of dependence can be explained in terms of the large exothermicity of the process.
The electronic effects of substituents at the acyl carbon in the gas‐phase elimination kinetics of tert‐butyl α‐substituted acetates
Authors: Reikonnen Nadejda , Martin Ignacio , Chuchani Gabriel , Lubinkowski Jacek
Published: January 2005

The gas‐phase eliminations of several tert‐butyl esters, in a static system and in vessels seasoned with allyl bromide, have been studied in the temperature range of 171.5–280.1°C and the pressure range of 23–98 torr. The rate coefficients for the homogeneous unimolecular elimination of these esters are given by the following Arrhenius equations: for tert‐butyl pivalate, log k1(s−1) = (13.44 ± 0.30) − (169.1 ± 3.1) kJ · mol−1 (2.303RT)−1; for tert‐butyl trichloroacetate, log k1(s−1) = (12.41 ± 0.08) − (141.1 ± 0.7) kJ · mol−1 (2.303RT)−1; and for tert‐butyl cyanoacetate log k1(s−1) = (11.31 ± 0.44) − (137.8 ± 4.1) kJ · mol−1 (2.303RT)−1. The data of this work together with those reported in the literature yield a good linear relationship when plotting log k/k0 vs. σ* values (ρ* = 0.635, correlation coefficient r = 0.972, and intercept = 0.048 at 250°C). The positive ρ* value suggests that the movement of negative charge to the acyl carbon in the transition state is rate determining. The present results along with previous investigations ratify the generalization that electron‐withdrawing substituents at the acyl side of ethyl, isopropyl, and tert‐butyl esters enhance the elimination rates, while electron‐releasing groups tend to reduce them. The negative nature of the acyl carbon and the polarity in the transition state increases slightly from primary to tertiary esters.
Thermal decomposition of ethane in shock waves
Authors: Hidaka Yoshiakai , Shiba Shoichi , Takuma Hirokazu , Suga Masao
Published: January 2005

The thermal decomposition of ethane was studied behind reflected shock waves over the temperature range 1200–1700 K and over the pressure range 1.7−2.5 atm, by both tracing the time variation of absorption at 3.39 μm and analyzing the concentration of the reacted gas mixtures. The mechanism to interpret well not only the earlier stage of C2H6 decomposition, but also the later stage was determined. The rate constant of reactions, C2H6 → CH3 + CH3, C2H6 + C2H3 → C2H5 + C2H4, C2H5 → C2H4 + H were calculated. The rate constants of the other reactions were also discussed.
Effects of ring strain on gas‐phase rate constants. 3. NO3 radical reactions with cycloalkenes
Authors: Atkinson Roger , Aschmann Sara M. , Long William D. , Winer Arthur M.
Published: January 2005

Rate constants for the gas‐phase reactions of NO3 radicals with a series of cycloalkenes have been determined at 298 ± 2 K, using a relative rate technique. Using an equilibrium constant for the NO2 + NO3 ⇄ N2O5 reactions of 3.4 × 10−11 cm3 molecule−1, the following rate constants (in units of 10−13 cm3 molecule−1 s−1) were obtained: cyclopentene, 4.52 ± 0.52; cycloheptene, 4.71 ± 0.56; bicyclo[2.2.1]‐2‐heptene, 2.41 ± 0.28; bicyclo[2.2.2]‐2‐octene, 1.41 ± 0.17; bicyclo[2.2.1]‐2,5‐heptadiene, 9.92 ± 1.13; and 1,3,5‐cycloheptatriene, 12.6 ± 2.9. When combined with previous literature rate constants for cyclohexene and 1,4‐cyclohexadiene, these data show that the rate constants for the nonconjugated cycloalkenes studied depend to a first approximation on the number of double bonds and the degree and configuration of substitution per double bond. No obvious effects of ring strain energy on these NO3 radical addition rate constants were observed. Our previous a priori predictive techniques for the alkenes and cycloalkenes can now be extended to strained cycloalkenes.
Studies on the rate of isotopic oxygen exchange between [Re(py)4O2]+ and solvent water
Authors: Kashani Fred F. , Murmann R. Kent
Published: January 2005

The rate of oxygen exchange between trans‐[Re(py)4O2]+ and solvent water in pypyH+ buffer solution follows simple first‐order kinetics and both oxygens are equivalent. The half‐life for isotopic oxygen exchange is about 12 h at a pH of 5.0, 25°C, and [py] = 0.10 M. The observed rate constant for exchange increases with acidity, in the pH range 4 to 6, decreases with [py], and is nearly independent of ionic strength. A small but significant increase of kobs occurs with increasing complex concentration. The rate of exchange follows the rate equation kobs/2 = k0 + k1/[py] with k0 = 1.4 × 10−5(2) s−1 and k1 = 4.7 × 10−7(1) M, s−1 at 25°C. The activation parameters for the reaction at pH = 7.15 (predominately the k0 term) are: ΔH* = +137.(1) kJ/M and ΔS* = +126.(1) J/MK. The pH effect and complex concentration effect are discussed in mechanistic terms. These results are compared to those found for [Re(en)2O2]+ and [Re(CN)4O2]3−.
“Complex” versus “free radical” mechanism for the catalytic decomposition of H2O2 by ferric ions
Authors: Kremer Mordechai L.
Published: January 2005

Kinetic and spectrophotometric measurements made during the Fe3+ ion catalyzed decomposition of H2O2 have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k3/KM = 4.94 M−1 min−1, k4 = 193 M−1 min−1, εI/KM = 52.3 M−2 cm−1, εII = 25.7 M−1 cm−1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O2 evolved in the reaction using [H2O2] ∼ 10−2 M has been calculated and found to be nearly stoichiometric. O2 evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O2 and the “free radical mechanism” predicting exactly stoichiometricamounts of O2. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H2O2 both with Fe2+ and Fe3+ ions, as well as other reactions assumed to proceed via free radicals.
Rate constants of reactions of chlorine atoms with aliphatic hydrocarbons and halogen derivatives in the liquid phase
Authors: Sergeev G. B. , Smirnov V. V. , Porodenko E. V. , Pukhovsky A. V.
Published: January 2005

The kinetics of liquid phase chlorination of methane in a difluorodichloromethane medium has been studied in a temperature interval of 293–150 K. The value of activation energy found for the hydrogen abstraction stage by a chlorine atom (E1) equals 14.2 ± 2.5 kJ/mol, with the processes of chlorine atoms recombination and the cage effect being taken into account. The method of competitive reactions has been employed to assess the constants of reaction of chlorine atoms (k1) with ethane, propane, hexane, ethylene, allyl bromide, allyl chloride, ethyl chloride, and cyclohexane in nonpolar solvents, viz. difluorodichloromethane and 1,2‐dibromotetrafluoroethane. The values (k1) obtained in the liquid phaseare two to four orders lower than those in the gas phase, while the activation energy is 2–6 kJ/mol higher.
The influence of the effective potential on the strong collision limiting low–pressure rate coefficients
Authors: Cobos Carlos J.
Published: January 2005

The influence of the effective potential energy curves on the calculation of the strong collision limiting low‐pressure rate coefficients of thermal dissociation‐recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero‐point barriers, as originallyproposed by Troe, was performed. A comparison between calculations realizedwith an exactly fitted looseness parameter, α, and with a standard value of α = 1.0 Å−1, indicates that the use of this last value is satisfactorily justified in the evaluation of thestrong collision limiting low‐pressure rate coefficients. A study interms of restrictive relationships between the looseness and Morse parameters and ab initio, radial potentials (for CH4, CH3O2, and HO2) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long‐range potentials are also briefly discussed.
Drug‐binding to biological macromolecules. A kinetic study of the system chlorodiazepoxide (librium) and bovine serum albumin
Authors: Nissani Edna , Perlmutter‐Hayman Berta
Published: January 2005

The Kinetics of the binding of librium to bovine serum albumin were investigated at an ionic strength of 0.15 M, in the pH‐range between 5.5 and 10.5, using the temperature‐jump method. Two relaxation times were observed. The first, rapid one is assigned to the equilibrium between reactants and complex, whereas the second, slower relaxation time measures a conformational change of this complex. Both relaxation times are independent of pH up to about 8.0 when they increase sharply to a new plateau at a pH of about 9.3. A possible parallelism between this behavior and the N ⇌ B transition of albumin is discussed. The overall equilibrium constant K, as well as the equilibrium constant between the two conformers, K2, were estimated from our kinetic results. Whereas the change of K with changing pH was within the experimental error, the equilibrium between the two conformers of the complex is somewhat shifted by an increase of the pH. At all values of pH, however, they are present in comparable concentrations. The value of K was also measured spectrophotometrically. The results of the two methods showed reasonable agreement. The relaxation times were affected very little by a change in temperature between 12 and 25°C from which it is concluded that the isomerization has a high negative value of ΔS‡.