bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyrolysis of Propyne/2‐Methylbut‐1‐ene‐3‐yne mixtures between 350 and 450°C
Authors: Harper Charles , Heicklen Julian
Published: January 2005

2‐Methylbut‐1‐ene‐3‐yne and Propyne mixtures were pyrolyzed at 350–450°C in the absence and presence of O2 and NO. The major product of the reaction is a polymer, but m‐xylene and p‐xylene are also produced and were studied as the species of interest. The C8H10 formation rate is first‐order in C3H4 and C5H6. The rate coefficient is best fitted by

though it is not inconsistent with

where R is the ideal gas constant in kJ/mol‐K. Experiments in the presence of NO show that m‐xylene and p‐xylene formation occur by two processes: a concerted molecular mechanism (≃ 41%) and a singlet diradical mechanism (≃ 59%).
Very low‐pressure pyrolysis (VLPP) of methyl‐ and ethynyl‐cyclopentanes and cyclohexanes
Authors: Brown Trevor C. , King Keith D.
Published: January 2005

Studies of the kinetics of thermal unimolecular decomposition of methylcyclopentane, methylcyclohexane, ethynylcyclopentane, and ethynylcyclohexane have been carried out at temperatures in the range 861–1218 K using the technique of very low‐pressure pyrolysis (VLPP). Multiple reaction pathways and secondary decomposition of primary products results in a complex array of reaction products. VLPP rate data (fall‐off regime) were obtained for the overall decompositions and interpreted via the application of RRKM theory. The data for methylcyclopentane and methylcyclohexane were interpreted in terms of ring‐opening bond fission pathways and bond fission to methyl and cycloalkyl radicals. By selecting Arrhenius parameters consistent with the analogous pathways in open‐chain alkanes, a good fit to the overall decomposition is obtained. The data for ethynylcyclopentane and ethynylcyclohexane were interpreted in terms of ring‐opening bond fission and alkyne to allene isomerization. The A factors for ring opening were based on known values for C‐C fission in open‐chain alkynes and the Arrhenius parameters for isomerization were chosen to be consistent with previously reported alkyne to allene isomerizations. The VLPP data are consistent with the following high‐pressure rate expressions (at < T > = 1100 K) for the dominant primary reaction channel of ring opening adjacent to the substitutent group:

where θ = 2.303RT kJ mol−. Comparison of the activation energies for the ethynyl‐cycloalkanes with those for the methyl‐cycloalkanes shows that the effect of the ethynyl substituent is consistent with the propargyl resonance energy. This evidence supports the assumption of a biradical mechanism for ring opening in these cycloalkanes.
Association reactions of atoms and radicals
Authors: Pilling Michael J.
Published: January 2005

The pressure and temperature dependences of association reactions involving atoms and/or radicals is discussed and illustrated by reference to the reactions CH3 + CH3 → C2H6, CH3 + O2 → CH3O2, CH3 + H → CH4, and H + C2H4 → C2H5. Recent experimental measurements of the rate coefficients, k([M], T) are described, particular attention being paid to experiments designed to measure the rate coefficient over wide ranges of pressure and temperature. Methods of fitting the experimental data, to obtain estimates of the limiting rate coefficients, k0 and k∞, and to permit extrapolation to regions beyond the experimental range, are discussed. These methods include the Troe factorization technique, a combination of master equation and variational RRKM theory, and recent calculations by Wagner and Wardlaw using the technique developed by Wardlaw and Marcus to describe loose transition states.
Kinetics of partly diffusion‐controlled reaction XXI: A simple algorithm for computing the apparent rate of reaction
Authors: Andre J. C. , Baros F. , Sousa A. T. Reis E.
Published: January 2005

Starting from Smoluchowski's hypothesis, a simple algorithm is developed in order to obtain the apparent rate constant at large values of time, t, with some physical and chemical processes, as in the case of diffusion controlled reactions. Some practical examples are illustrated, assuming nonuniform distribution function, space‐dependent diffusion coefficient or short‐range interaction leading to an asymptotic analytical expression of the form α + β/√t, where α and β are constants function of the system of interest.
Stability of N‐chloro‐3‐aminopropanol in aqueous solution. Kinetics of decomposition and disproportion of N‐chloro‐3‐aminopropanol
Authors: Antelo Juan M. , Arce Florencio , Franco Julia , Barro P. Rodriguez , Varela Angel
Published: January 2005

N‐chloro‐3‐aminopropanol was obtained in aqueous solution by mixing the amine with the hypochlorite. The first order decomposition kinetics of the N‐chloramine in strongly alkaline media are explained by a mechanism in which the rate controlling step is the formation of an imine which is subsequently hydrolyzed. Spectrophotometry of the reaction in acid media showed that under these conditions dichloramines are formed: the second order experimental kinetics of this process are explained by a mechanism in which the rate‐controlling step is a reaction between the protonated and free forms of the N‐chloramine.
Micellar hydrolysis of hydroxamic acids. Michaelis‐menten kinetics
Authors: Berndt Donald C. , Angus Jill E. , Wood Michael J. , Atkinson Richard F. , Qureshi Tanveer A. , Shay Brian J. , Provancher Aura I.
Published: January 2005

Rates of reaction for the alkaline hydrolysis of various hydroxamic acids in the presence of cetyltrimethylammonium bromide have been determined. Empirical reaction orders of zero, one‐half, and one were found for the hydroxamic acids depending upon reaction conditions and substrate structure. N‐methylhydroxamic acids exhibited only first‐order kinetics. The results are consistent with the Michaelis‐Menten rate equation.
Importance of steric effect and evaluation of quantitative structure reactivity relationship (QSRR) in the quaternization reaction of benzothiazoles and phenacyl bromide
Authors: Mishra Bijay Kumar , Sharma Arabinda , Behera Gopabandhu
Published: January 2005

The kinetics of reaction of substituted 2‐aminobenzothiazoles and phenacyl bromide have been followed conductometrically and in some cases, argentometrically. Both the methods produced almost the same rate constants. Substituents at position 5 of the benzothiazole nucleus behave like para substituents of the benzene ring. A correlation with Hammett σp substituent constants has been obtained with a rho value of −1.04. The rate data of quaternization reaction of 4, 5, and 6 substituted 2‐aminobenzothiazoles with phenacyl bromide have been correlated with Fk, Rk, and Vw values by multiple regression analysis with the equation suggested by Williams and Norrington and modified by us. The values are found to correlate well with the equation, log k = −4.4979 − 0.4815fjFk + 0.5933rjRk − 0.0277Vw.
Mechanistic studies with positive iodine: Kinetics of oxidation of thiocyanate ion by iodine monochloride and aqueous iodine in perchloric acid medium
Authors: Gowda B. Thimme , Bhat J. Ishwara
Published: January 2005

Kinetics of oxidation of thiocyanate ion (NCS−) by iodine monochloride and iodine has been studied in aqueous perchloric acid medium. The rates of oxidations followed the rate laws:

Variations in ionic strength and dielectric constant of the medium had little effects on the rates of reactions with both the oxidants. Mechanisms consistent with the observed rate laws have been suggested. Rate limiting steps have been identified and the constants of some of these steps have been evaluated by varying [NCS−] at each temperature. Activation parameters were computed from the Arrhenius plots. The rate constants predicted from the rate law as [NCS−], and [H+], varied in iodine monochloride oxidation, are in good agreement with the experimental values providing support to the proposed mechanism.
Quenching of I (2P1/2) by halogen cyanides
Authors: Badini Raúl G. , Pasteris Leonor E. , Argüello Gustavo A. , Staricco Eduardo H.
Published: January 2005

Relaxation rate constants for the collisional deactivation of I (2P1/2) by halogen cyanides were measured by time resolved atomic absorption. The values obtained were (1.2 ± 0.1) × 10−15, (5.2 ± 0.7) × 10−15, and (2.6 ± 0.4) × 10−14 cm3 molecule−1 s−1 for ClCN, BrCN, and ICN, respectively. Quenching efficiencies are discussed in view of the stability of linear molecules to form the transient complex as well as the similarities assumed between halogen cyanides and interhalogen diatomic molecules.
Study of the reaction of MoOS2(S2CNR2)2 with PPh3 in 1,2‐dichloroethane: Part II. Detection of reaction intermediate pentavalent molybdenum using ESR method at low temperature
Authors: Xiaoqing Song , Huixing Yang , Degang Han
Published: January 2005

Intermediate product of the reaction of MoOS2(S2CNR2)2 and PPh3 in dichloroethane has been detected by ESR spectroscopy. Two ESR signals have been observed at low temperature in the reaction system which was stopped by quenching it in liquid nitrogen. The g values are 2.020 ± 0.001 and 1.972 ± 0.001 respectively. The signal at g = 2.020 is attributed to a reaction intermediate with pentavalent molybdenum. A reaction mechanism has been proposed which is consistent with the observation of pentavalent molybdenum as the intermediate in the process of reaction.
Cation, solvent, and substituent effects on the decay kinetics of alkali metal salts of diaryl disulfide radical anions in nonaqueous solutions
Authors: Miyashita Tokuji , Matsuda Minoru
Published: January 2005

The transient diaryl disulfide radical anions (RSSR−) were produced in nonaqueous solutions at room temperature by the flash photolysis of a solution of arylthiolate ion pair in the presence of the excess corresponding disulfide. The transient spectra were almost identical with those obtained from γ‐radiolysis of the disulfides in 77 K 2‐methyl‐tetrahydrofuran (MTHF) glassy matrix. The spectra of disulfide radical anions in nonaqueous solutions were changed by cations, solvents, and para‐substituents depending on the ion pair properties. The tighter ion pairs showed a shift of absorption band to the shorter wavelength. The disulfide radical anions decay by a unimolecular dissociation reaction to yield thiolate anion and thiyl radical. The decay kinetics were first‐order in the initial time region. The rate constants obtained were changed by the counter cations in the order Na+ > K+ > Cs+ > Li+, and by solvents. The tighter ion pairs of the disulfide radical anions showed faster dissociation reaction. This is due to stabilization of a transition state with the counter cation.
Vibrational relaxation and collision‐induced dissociation of xenon fluoride by neon
Authors: Wilkins Roger L.
Published: January 2005

Rate coefficients were calculated for vibrational relaxation and collision‐induced dissociation of ground state xenon fluoride in neon at temperatures between 300 and 1000 K for each of nine vibrational levels. These coefficients were calculated using a pairwise additive potential energy surface, which consists of a Morse function for the XeF interaction and Lennard–Jones functions for the NeXe and NeF interactions. Rate coefficients are provided for both temperature and v‐ dependences. The vibrational relaxation and dissociation processes occur by multiquanta transitions. Dissociation can take place from all v‐levels provided that the internal energy of the XeF molecule is close to the rotationless dissociation limit. The order of increase effectiveness of the various forms of energy in promoting dissociation in XeF was found to be translation–rotation‐vibration. At room temperature, neon atoms were found to be more efficient than helium atoms in the dissociation processes; helium atoms were found to be more efficient than neon atoms in the vibrational relaxation of XeF. Strong vibration–rotation coupling in both vibrational relaxation and in the dissociation processes is demonstrated.
Rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals over the temperature range 650–770 K
Authors: Zhang H‐X , Back M. H.
Published: January 2005

Measurements rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals relative to the corresponding rate constants for abstraction from hydrogen, over the temperature range 650–770 K, are reported. The methodis based on the effect of the addition of small quantities of hydrogen on the rates of formation of methane and ethane in the thermalchain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions:
equation image
measurements of the relative rates of formation of methane and ethane in the presence and absence of hydrogen gave the following ratios of rate constants: (R = 8.314 Joule mol−1 K−1)

With values from the literature for 𝓀1 and 𝓀3 the following values were obtained for 𝓀2 and 𝓀4:
Identification of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time‐of‐flight velocity‐spectra measurements
Authors: Behrens Richard
Published: January 2005

The pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H2O, HCN, CO, CH2O, NO, N2O, methylformamide, C2H6N2O, octahydro‐1‐nitroso‐3,5,7‐trinitro‐1,3,5,7‐tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time‐of‐flight (TOF) velocity spectra to assist mass‐spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.
The photolysis of trans‐3,4‐dimethylcyclopentanone. II. Short Wavelengths
Authors: Becerra Rosa , Frey H. Monty
Published: January 2005

The photolysis of trans‐3,4‐dimethylcyclopentanone has been investigated in the gas phase at 100°C using light of 206 and 193 nm. The photolytic products are propene, 1,2‐dimethylcyclobutane, and the butene isomers. Small quantities of 3,4‐dimethylpent‐4‐enal were also detected. Relative yields of these products were determined as a function of the ketone pressure and also of that of added nitrogen. A mechanism for the photochemical decomposition based on that suggested for the photolysis of cyclopentanone using short wavelength radiation, is consistent with the experimental results and is simpler than that required to account for the long wavelength photolysis reported earlier.
Effect of solvent on the reactions of coordination complexes. Part 10. kinetics of solvolysis of cis(chloro)(1‐amino‐propan‐2‐ol)bis‐(ethylenediamine)cobalt(III) in methanol + water, propan‐2‐ol + water, and t‐butanol + water media
Authors: Dash Anadi C. , Das Prafulla K.
Published: January 2005

The solvolysis of cis(chloro)(1‐amino‐propan‐2‐ol)bis(ethylenediamine)cobalt(III) in aqueous alcoholic media using methanol, propan‐2‐ol, t‐butanol as cosolvents, resulted in the formation of the (N,O) chelated productcis[Co(en)2(NH2CH2CHOHCH3)]3+. The pseudo first order rate constant decreased with increasing molfraction (Xorg) of alcohols, the decrease being less marked as the bulkiness of hydrophobic moiety of alcohol increased. The plots of log 𝓀obs vs. reciprocal of the bulk dielectric constant of the solvents, log 𝓀obs vs. Grunwald‐Winstein solvent parameter and log 𝓀obs, vs. Xobs under isodielectric condition (Ds = 50, at 50°C) for CH3OH/H2O, C2H5OH/H2O, (CH3)2CHOH/H2O, (CH3)3COH/H2O, (CH2)2(OH)2/H2O, and (CH3)2 C  O/H2O in water rich media indicated that both solvent structural effects and presumably the hydrophobic interaction appreciably mediate the reaction. The calculated values of the relative transfer free energy at 25°C[ΔGt(C3−)‐ΔGt(i.s)(s←w)] where C3+ and i.s. denote the dissociative transition state {cis[Co(en)2(NH2CH2CHOHCH3)]3+}* and the initial state, respectively, indicated that the tripositive transition state is more effectively solvated by the mixed solvent media, than the dipositive initial state, the effect appeared to be more significant with increasing Xorg. The plots of activation enthalpy and entropy against Xorg exhibited maxima and minima indicating that enthalpy and entropy changes associated with the solvent shell reorganization of the reactant contribute to the overall activation parameters.
Kinetics and mechanism of the reaction of Ozone with Aliphatic alcohols
Authors: Rakovski S. , Cherneva D.
Published: January 2005

Kinetic parameters of the reaction of ozone with aliphatic alcohols of different structures are obtained. The ratio between the relative reactivities of the primary: secondary: tertiary alcohols was found to be 1:15:138. The bond energy changes in the same sense as the activation energy. The rate‐controlling step of ozone reaction with alcohols is the abstraction of a hydrogen atom being in α‐position with respect to the OH group. The pre‐exponential factors (A) are calculated by the collision and activated complex methods and compared with the experimentally obtained values. The results from the calculations represent convincing evidence that the mechanism of the rate‐controlling step of the reaction is associated with the formation of an activiated complex which has a linear shape ensuring free rotation of its fragments.
Kinetics of chlorination of some Ortho‐, Meta‐, and Para‐substituted phenols by N‐chloro‐3‐methyl‐2,6‐diphenylpiperidin‐4‐one: A LFER study
Authors: Ganapathy K. , Palaniappan An.
Published: January 2005

The kinetics of chlorination of a number of ortho‐, meta‐, and para‐substituted phenols by N‐chloro‐3‐methyl‐2,6‐diphenylpiperidin‐4‐one (NCP) in acid medium have been investigated. The reaction is of first order with respect to oxidant and the order with respect to the substrate varies depending on the nature of the substituent present in the ring. With cresols and m‐chlorophenol the order is unity, with p‐methoxyphenol, zero and with the other phenols, a fraction. Isokinetic and Exner plots give straight lines with fine correlation coefficients. But the Hammett plot gives a curve that was concave downwards, instead of a straight line. The observed Hammett plot deviation has been accounted for suitably. Regression analyses of the rate data of ortho‐substituted phenols by using Taft and Charton equations to separate steric effects from electronic effects have been carried out. In this reaction, the localized electronic effect plays a major role while steric and resonance effects play a minor role.
Kinetics and mechanism of base‐catalyzed hydrolysis of Cu(II)‐salicylamide complex
Authors: Niaz M. Arif , Khan A. Aziz
Published: January 2005

The kinetics of hydrolysis of Cu(II)‐salicylamide complex have been studied in sodium hydroxide solution (0.5 to 2.5M). The observed pseudo‐first‐order rate constants vary according to the empirical equation 1/𝓀obs = B1 + B2/[ŌH] up to 2.0 M sodium hydroxide concentration. The mechanism of base‐catalyzed hydrolysis has been proposed and it is concluded that the reaction proceeds by the interaction of complex with the nucleophile, forming tetrahedral intermediate which then breaks down to products. The rate equation has been derived. Thermodynamic parameters have also been reported.
A product study of the gas‐phase reaction of Methacrolein with the OH radical in the presence of NOx
Authors: Tuazon Ernesto C. , Atkinson Roger
Published: January 2005

The gas‐phase reaction of methacrolein with the OH radical, in the presence of NOx, was investigated at 298 ± 2 K and atmospheric pressure of air. Hydroxyacetone, methylglyoxal, a peroxyacyl nitrate identified as CH2  C(CH3)C(O)OONO2 (peroxymethacryloyl nitrate), formaldehyde, CO, and CO2 were observed to be the major products. The product yield data for these compounds show that OH radical addition to the >C  C< bond accounts for ca. 50% of the overall reaction, with the remaining ca. 50% proceeding via H—atom abstraction from the CHO group. The data suggest that the alkoxy radical
equation image
formed following the addition of OH to the terminal carbon atom, decomposes primarily to give the formyl radical plus hydroxyacetone. A lower limit ratio of 5: 1 has been estimated for OH radical addition to the terminal carbon atom of the double bond relative to addition on the inner carbon atom.
Thermal decomposition kinetics of polysilanes: Disilane, trisilane, and tetrasilane
Authors: Martin J. G. , O'Neal H. E. , Ring M. A.
Published: January 2005

The decomposition kinetics of disilane with added butadiene, trisilane both neat and with added butadiene, trimethylsilane or H2, and normal and iso‐tetrasilane both neat and in the presence of added butadiene are reported. Arrhenius parameters of the primary dissociation reactions are determined: A‐factors suggest that polysilane decompositions (1) have similar intrinsic activation entropies (ΔS‡ ≈︁ 6.2 ± 5 e.u.) and (2) have activation energies which increase with increasing reaction endothermicities. Relative trapping efficiencies of SiH4, Si2H6, Si3H8, C4H6, Me3SiH, and H2 toward SiH2 and SiH3SiH are also determined. Other results include the heat of formation of silylsilylene, ΔH (SiH3SiH) = 75.3 Kcal/mol, and the activation energy for 1,1‐H2 elimination from disilane (EH2 = 57.8 kcal/mol).
Kinetics of the solvolysis of [Co(3Rpy)4Cl2]+ ions (R = Me or Et) in water and in water + methanol mixtures
Authors: El‐Subruiti Gehan M. , Wells Cecil F. , Sidahmed Ibrahim M.
Published: January 2005

Rates of solvolysis of ions [Co(3Rpy)4Cl2]+ with R = Me and Et have been measured over a range of temperatures for a series of water‐rich water + methanol mixtures to investigate the effect of changes in solvent structure on the solvolysis of complexes presenting a largely hydrophobic surface to the solvent. The variation of the enthalpies and entropies of activation with solvent composition has been determined. A free energy cycle relating the free energy of activation in water to that in water + methanol is applied using free energies of transfer of individual ionic species from water into water + methanol. Data for the free energy of transfer of chloride ions ΔG(Cl−) from both the spectrophotometric solvent sorting method and the TATB method for separating ΔG(salt) into ΔG(i) for individual ions are used: irrespective of the source of ΔG(Cl−), in general, −ΔG(Co(Rpy)4Cl2+) > −ΔG(Co(Rpy)4Cl2+), where Rpy = py, 4Mepy, 4Etpy, 3Etpy, and 3Mepy, showing that changes in solvent structure in water‐rich water + methanol mixtures generally stabilize the cation in the transition state more than the cation in the initial state for this type of complex ion. A similar result is found when the free energy cycle is applied to the solvolysis of the dichloro (2,2′,2″‐triaminotriethylamine)cobalt(III) ion. The introduction of a Me or Et group on the pyridine ring in [Co(Rpy)4Cl2]+ has little influence on the difference {ΔG(Co(Rpy)4Cl2+)−ΔG(Co(Rpy)4Cl2+)} in water + methanol with the mol fraction of methanol < 0.20.
On finding the rate constants of linear and nonlinear systems
Authors: Liddell G. F. , Evans A. B. , Buckingham D. A.
Published: January 2005

In lowest approximation, a certain chemical reaction is described by a system of first‐order linear differential equations with unknown constant coefficients. One can therefore write down an expression for the state of the system at time t, and from this find the endpoint of the reaction in terms of the initial state and the rate constants. The relative values of some rate constants can then be estimated from experimental data.

A better approximation in which the differential equations are nonlinear is also considered, and it turns out that because of symmetry in the reaction, the relationship between the final state and the ratios of the rate constants is unchanged. Although the differential equations now appear much less tractable, the problem of relating the rate constants to the endpoint of the reaction can be formulated and solved in terms of probabilities.

The results illustrate an important property of reaction schemes in which some of the steps are reversible. More generally, this is a property of differential equations: provided that they continue to satisfy certain linear constraints, the parameters of a linear system of ordinary differential equations can vary without affecting the asymptotic solution.
Kinetics and mechanism of oxidation of phenylhydrazine and P‐bromophenylhydrazine by hexacyanoferrate(III) in acidic medium
Authors: Al‐Subu M. M. , E‐Halawa R. Abu , Abed H. M.
Published: January 2005

Kietics of oxidation of phenylhydrazine and p‐bromophenylhydrazine by hexacyanoferrate(III) in acidic medium have been studied. The reactions follow similar kinetics, being first order with respect to both hydrazine and exacyanoferrate(III) and inverse first order with respect to the hydrogen ion. Addition of hexacyanoferrate(II) has no retarding effect on the rate of oxidation. The effects of varying ionic strength, dielectric constant, and temperature on the reaction rates have been investigated. A plausible mechanism has been proposed to account for the experimental results. Benzene and bromobenzene have been identified as the oxidation products.
Kinetics of the oxidation of aliphatic aldehydes by Os(VIII) in alkaline solution
Authors: Sharma Vinita , Chowdhury Kakuli , Banerji Kalyan K.
Published: January 2005

Kinetics of oxidation of six aliphatic aldehydes by Os(VIII) in alkaline solutions have been studied. The reaction is of first order with respect to each of the aldehyde and Os(VIII). The pseudo‐first order rate constants decreased with an increase in the concentration of hydroxyl ions. The oxidation of deuterioacetaldehyde (MeCDO) exhibited a substantial primary kinetic isotope effect. Separate rate constants for the oxidation of hydrate and free aldehyde forms have been evaluated. The aldehyde hydrate is postulated as the active reductant. Ionic strength has no noticable effect on the rate. The rate‐determining step is, therefore, postulated to be a bimolecular reaction between the aldehyde hydrate and [OsO4(OH)2]−2. The value of the limiting rate constant exhibited an excellent correlation with Taft σ* values; reaction constant being negative. A mechanism involving transfer of a hydride ion from the aldehyde hydrate to Os(VIII) has been proposed.
A simple method for extending the range of pseudo‐order kinetic measurements
Authors: Jensen James L. , Kanner Richard C. , Shaw Gregory R.
Published: January 2005

Data are presented demonstrating the validity of a new method of measuring pseudo‐order rate constants, based on an iterative computational procedure long in use for kinetic conditions where the “infinity” value is not experimentally accessible. This new method requires that the kinetic order be known for the limiting reagent, but is otherwise general. It allows measurement of the pseudo‐order rate constant even at a ratio of reactants of 1:1 by maximizing the fit of three half‐lives of data to the appropriate pseudo‐order kinetic equation, treating the “infinity” value as a variable.
The elimination kinetics of secondary Alkyl Bromides in the gas phase
Authors: Chuchani Gabriel , Martín Ignacio , Rotinov Alexandra , Domínguez Rosa M.
Published: January 2005

Elimination kinetics of 2‐bromohexane and 2‐bromo‐4‐methylpentane in the gas phase were examined over the temperature range of 310–360°C and pressure range of 46–213 torr. The reactionsin seasoned, static reaction vessels, and in the presence of the free radical inhibitor cyclohexene, are homogeneous, unimolecular, and follow first order rate laws. The overall rate coefficients are described by the following Arrhenius equations: For 2‐bromohexane, log𝓀1(s−1) = (13.08 ± 0.70) − (185.7 ± 8.2) kJ mol−1 (2.303RT)−1; for 2‐bromo‐4‐methylpentane, log𝓀1(s−1) = (13.08 ± 0.33) − (183.4 ± 3.8) kJ mol−1 (2.303RT)−1. The electron releasing effect of alkyl groups influences the overall elimination rates. The olefin products isomerize in the presence of HBr gas until an equilibrium mixture is reached.
Kinetic studies of the deactivation of O2(1Σg+) and O(1D)
Authors: Shi Jichun , Barker John R.
Published: January 2005

The kinetics of the deactivation of O2(1Σg+) is studied in real time. O2(1Σg+) is generated in this system by the O(1D) + O2 reaction following O3laser flash photolysis in the presence of excess O2, and it is monitored by its characteristic emission band at 762 nm. Quenching rate constants were obtained for O2, O3, N2, CO2, H2O, CF4and the rare gases. Since O(1D) is the precursor for the formation of O2(1Σg+), the addition of an O(1D) quencher effectively lowers the initial concentration of O2(1Σg+). By measuring the initial intensity of the 762 nm fluorescence signal, the relative quenching efficiencies were determined for O(1D) quenching by N2, CO2, Xe, and Kr with respect to O2; the results are in good agreement with literature values.
Kinetics of the esterification of palmitic acid with isobutyl alcohol
Authors: Goto Shigeo , Tagawa Tomohiko , Yusoff Asma
Published: January 2005

Kinetics of the sulfuric acid catalyzed esterification of palmitic acid with isobutyl alcohol has been studied and reviewed critically. A theoretical rate equation is derived by the following reaction mechanism: (1) The reaction of sulfuric acid and isobutyl alcohol produces isobutyl sulfuric acid which acts as a catalyst; (2) Palmitic acid is protonated by the catalyst to form the reaction intermediate; and (3) The esterification proceeds reversibly. The experimental results are consistent with this rate equation.
Hydrolysis of 3,4‐diphenyl‐1,2,5‐thiadiazole‐1,1‐dioxide. Acid and base catalysis
Authors: Mirifico M. V. , Vasini E. J. , Sicre J. E.
Published: January 2005

We have performed a product and kinetic study of the hydrolysis of 3,4‐diphenyl‐1,2,5‐thiadiazole‐1,1‐dioxide in aqueous solution. Benzil and sulfamide are the only products of hydrolysis and are formed in equimolar yields.

The kinetic results indicate that a first order law is followed up to 90% conversion. The observed rate constant is independent of substrate concentration.

Ionic strength and buffer concentration do not affect the rate constant, but the reaction is acid‐base catalyzed. The rate‐pH profile has been determined and a mechanism that fits the experimental data satisfactorily is proposed. Corresponding rate constants and equilibrium constants for the protonation of the substrate are reported.
Electron transfer. 102. Some oxidations by bromite (BrO2−)
Authors: Jhanji Amrit K. , Gould E. S.
Published: January 2005

Bromite, BrO2−, in aqueous carbonate or borate buffers (pH 9–11), reacts rapidly with H3AsO3, with the tartrate complex of Sb(III), and with the EDTA complexes of Sn(II) and U(IV). Each reaction yields Br−, even when BrO2− is taken in excess. Reaction rates with Sb(III) and Sn(II) are independent of pH, but the acidity pattern observed with As(III) points to competing bimolecular reductions by H2AsO3− and H3AsO3 having specific rates 3.4 and 1.2 M−1 s−1 (25°C, μ = 0.5M). Reduction by U(IV) is strongly inhibited by carbonate; data for carbonate buffers are in accord with the operation of two contributing reaction paths (specific rates 0.45 and 6.3 M−1 s−1) with the activated complex for the slower featuring one more carbonate than that for the rapid. Reactions of BrO2− with single electron reductants, or with reagents that can undergo both 1e and 2e changes, are generally complicated by variable induction periods, inhibition by O2, catalyzed decomposition of BrO2−, or combinations of these. The much smoother reductions by 2e− reagents must pass through OBr−, which reacts much more rapidly than BrO2− in each case. An inner‐sphere path, operating through an oxygen‐bridged transition state and culminating in oxygen atom transfer, is proposed for the 2e reductants. Hypophosphite, despite its highly negative formal potential, is not oxidized by BrO2− under our conditions. Here it is likely that the substitution‐inert character of the coordinatively saturated P(I) center rules out formation of the precursor required for redox.
Oxidation of amino acids by peroxomonophosphoric acid—a kinetic study
Authors: Panigrahi Ganesh P. , Paichha Ramesh C.
Published: January 2005

Aliphatic amino acids are smoothly oxidized by peroxomonophosphoric acid (PMPA) in the pH region 6–10. Kinetic studies reveal second order dependence in the amino acid not observed hitherto in any of the PMPA oxidations. Dependence in PMPA is unity. Rate‐pH profile yields a maximum around pH 8. The reaction path includes oxidation steps due to H2PO5− and HPO52−. Second order dependence in the amino acid has been attributed to participation of two Zwitter‐ionic molecules of the amino acid to form a nucleophile.
The gas phase reaction of CF3 radicals with C6F5H in the temperature range 373–658 K
Authors: Lane S. I. , Oexler E. V. , Staricco E. H.
Published: January 2005

CF3 radicals were generated by the photolysis of perfluoroacetic anhydride. In the presence of pentafluorobenzene, the CF3 radicals react according to the following mechanism:
equation image

It was found that the addition reaction (3) becomes reversible above ca. 453 K. The addition rate parameters have been revised and they satisfactorily agree with those reported previously.

At temperatures higher than 593 K, only true H‐abstraction occurs. The rate constant kH for reaction (5) is given by:

where θ = 2.303 RT kJmol−1 and kc is the rate constant for combination of CF3 radicals. The reactions of CF3 with benzene and pentafluorobenzene are compared.
The decomposition kinetics of hydrogen peroxide catalyzed by diethylenetriaminepentaacetatoiron(III) complex
Authors: Anis Samy S. , Mansour Mohamed A.
Published: January 2005

The rate of reaction of (Fe(DTPA)) with H2O2 was investigated at various temperatures. The observed rate law is given by the expression.

The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate. The results are compared with previously data for Fe EDTA complex.
Disproportionation reactions between alkyl and fluoroalkyl radicals. VI. Difluoromethyl and n‐propyl radicals
Authors: Pritchard G. O. , Abbas S. H. , Piasecki M. L. , Meleason M. A.
Published: January 2005

Cross‐disproportionation to combination ratios for CF2H and n‐C3H7 radicals have been determined (the hydrogen acceptor radical is given first) to be Δ(n‐C3H7, CF2H) = 0.30 ± 0.01 and Δ(CF2H, n‐C3H7) = 0.057 ± 0.006.
The flash photolysis of di‐μ‐oxo‐bis(oxo‐molybdate(V)) acid aqueous solutions in the presence of excess thiocyanate
Authors: Martire D. O. , González M. C. , Feliz M. R. , Cafferata L. , Capparelli A. L.
Published: January 2005

The flash photolysis of the mono and di‐thiocyanate complexes of μ‐oxo bis(oxo‐molybdenum(V)) (Mo2O4(NCS)x(H2O)6−x(2−x)+ where x = 1, 2) has been studied in the system composed of perchloric acid solutions of Mo2O4(H2O)62+ in the presence of excess thiocyanate.

Irradiation with light in the wavelength range 250–340 nm induced the formation of three reaction intermediates identified as μ‐oxo‐bis (oxo‐molybdenum(V)) species: Mo2O3(H2O)84+ (A), Mo2O3(NCS) (H2O)73+ (B), and Mo2O3(NCS)2(H2O)62+ (C). A rapid equilibria between the transient species is established before they decay following a first order kinetics. Intermediate A is the only species effective in promoting the observed decay leading to the end products Mo(VI) and H2.

The relative absorption spectrum of species A, B, and C are reported, as well as the measured stability constants for the formation of B and C in the temperature range 20–45°C. An overall mechanism is proposed.
Kinetics and mechanism of silver(I) catalyzed oxidation of tris(1,10‐phenanthroline)iron(II) with peroxodiphosphate in acetate buffers
Authors: Parasher P. , Hussain J. , Sharma P. D.
Published: January 2005

A kinetic study of the silver(I)‐catalyzed oxidation of tris(1,10‐phenanthroline)iron(II) with peroxodiphosphate was carried out by estimating tris‐complex at 510 nm. The reaction is found to conform to the rate law (i).
equation image
with K2 and K3 being the acid dissociation constants of H3P2O8− and H2P2O82−, respectively. The silver(I) catalysis in the reaction has been explained on the basis of complex formation between pdp and silver(I).
Rate constants for the reaction of atomic and molecular bromine with gallium arsenide
Authors: Salusbury I. M. , Ogryzlo E. A.
Published: January 2005

The reaction of the (100) face of a gallium arsenide single crystal with atomic and molecular bromine has been studied in a discharge flow system at temperatures between 100 and 225°C and pressures between 0.1 and 40 torr. The reaction with Br2 was found to be first order in Br2 only at pressures below 1 torr. Temperature dependence studies in the linear range gave the activation energy and preexponential factor for the rate controlling reaction in the low pressure regime. The results are summarized in the following Arrhenius equation:

Deviations from linearity at high pressures are discussed in terms of two alternative mechanisms.

The reaction of GaAs with atomic bromine was also studied as a function of temperature, and found to have a temperature dependence described by the following Arrhenius equation:
Reactions of primary and secondary butoxy radicals in oxygen at atmospheric pressure
Authors: Heiss A. , De Maleissye J. Tardieu , Viossat V. , Sahetchian K. A. , Pitt I. G.
Published: January 2005

The reaction pathways of n‐butoxy and s‐butoxy radicals have been investigated by TLC and HPLC analysis of end products, particularly peroxides and carbonyl compounds. The butoxy radicals were produced by the pyrolysis of very low concentrations of the corresponding dibutylperoxide in an atmosphere of oxygen and nitrogen, at atmospheric pressure. The decomposition reaction (3) s‐BuO → C2H5 + CH3CHO and the reaction (2) s‐BuO + O2 → HO2 + CH3COC2H5 have been studied, and the ratio k3/k2 has been determined in the temperature range 363–503 K by kinetic modeling of the formation of the observed acetaldehyde and methylethylketone. The rate constant k3 obtained was:

A good agreement was observed between experimental data and RRKM theory. The implications of the results for atmospheric chemistry and combustion are discussed. At room temperature, the reaction with O2, yielding HO2 radicals and methylethylketone is, by far, the main channel for s‐BuO radicals. In the field of low temperature combustion, the decomposition of s‐BuO radicals producing C2H5 and CH3CHO is the main pathway; the route s‐BuO + O2 decreases tremendously in importance as the temperature is raised above 393 K.
Kinetics of the oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N‐bromoacetamide
Authors: Moondra Anu , Mathur Abha , Banerji Kalyan K.
Published: January 2005

The oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N‐bromoacetamide (NBA) in acid solution, results in the formation of corresponding higher oxyacids of phosphorus. The reaction is first order with respect to NBA, second order in the oxyacid and inverse first in hydrogen ions. The oxidation of deuteriated phosphorus oxyacids showed the presence of a substantial primary kinetic isotope effect. The reaction failed to induce polymerization of acrylonitrile. Added acetamide has no effect on the reaction rate. It has been shown that the ‘inactive’ tautomer of the phosphorus oxyacids, RHP(O)OH, participates in the oxidation process. A rate‐determining step involving transfer of a hydride ion from the PH bond to the oxidant has been proposed.
Reactivity of tert‐butoxyl radicals towards substituted indole derivatives
Authors: Encinas M. V. , Lissi E. A. , Majmud C. , Olea A. F.
Published: January 2005

Tert‐butoxyl radicals react with indole and methyl substituted derivatives by hydrogen abstraction. For those compounds which are unsubstituted at the N‐atom, hydrogen abstraction takes place almost exclusively at the NH bond. The reactivity of these compounds correlates with their donor electron capacity, pointing to significant contribution of charge transfer to the transition state stability. Substitution at the N atom considerably decreases the reactivity.
Kinetics and mechanism of base‐catalyzed hydrolysis of Cu(II)‐malonamide complex
Authors: Niaz M. Arif , Khan A. Aziz
Published: January 2005

A kinetic study of base‐catalyzed hydrolysis of Cu(II)‐malonamide complex has been performed in sodium hydroxide solution (0.2–1.25M). The reaction follows an irreversible first‐order consecutive path:

The variation of k1obs and k2obs with alkali concentration was found to be in good agreement with the equations:

where B1, B2, C1, and C2 are empirical constants. The mechanism of hydrolysis of Cu(II)‐malonamide complex has been discussed and rate equations have been derived. Retardation of rate of hydrolysis due to coordination of Cu(II) with malonamide, in alkaline medium, has been explained in terms of comparatively slow breakdown of the CN bond of the tetrahedral intermediate (TI). Thermodynamic parameters have also been evaluated.
Studies of unusual oxidation states of transition metals III‐kinetics and mechanism of oxidation of triethanolamine by diperiodatoargenate(III) ion in aqueous alkaline medium
Authors: Shi Tie‐Sheng , He Jin‐Tian , Ding Tian‐Hui , Wang An‐Zhou
Published: January 2005

The kinetics of oxidation of triethanolamine (TEA) by diperiodatoargenate(III) anion, [Ag(HIO6)2]5−, has been studied in aqueous alkaline medium by conventional spectrophotometry. The reaction is pseudo‐first‐order in [Ag(III)] disappearance with kobs = (k1 + k2[OH−]) K1K2[TEA]/{[H2IO63−]e + K1 + K1K2[TEA]}, where k1 = 8.05 × 10−3 S−1, k2 = 0.46 M−1 S−1, K1 = 6.15 × 10−4 M, and K2 = 537 M−1 at 25°C, and μ = 0.30 M. Based on the inference that an inner‐sphere complex is formed by indirect replacement of a ligand of [Ag(HIO6)2]5− by a TEA molecule, a reaction mechanism has been proposed. The complex undergoes redox by two modes, both internal and one hydroxide ion assisted.
Kinetics and mechanism of intramolecular general base‐catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles
Authors: Khan M. Niyaz
Published: January 2005

The alkanolysis of ionized phenyl salicylate, PS−, has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH2CH2OH and CH3OH) contents of 15–74 or 92%, v/v. The alkanolysis of PS− involves intramolecular general base catalysis. At a constant concentration of SDS, [SDS]T, the observed pseudo first‐order rate constants, kobs, for the reactions of ROH with PS− obtained at different concentration of ROH, [ROH]T, obey the relationship: kobs = k[ROH]T/(1 + KA[ROH]T) where k is the apparent second‐order rate constant and KA is the association constant for dimerization of ROH molecules. Both k and KA decrease with increase in [SDS]T. At a constant [ROH]T, the rate constants, kobs, show a decrease of nearly 2‐fold with increase in [SDS]T from 0.0–0.3M. These results are explained in terms of pseudo‐phase model of micelle. The rate constants for alkanolysis of PS− in micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous‐alkanol pseudophase. This is attributed largely to considerably low value of [ROH] in the specific micellar environment where micellar bound PS− molecules exist. The increase in [ROH]T decrease the value of the binding constant of PS− with SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PS− are explained in terms of the porous cluster micellar structure.
Kinetics of ring‐opening radical polymerization of vinyloxiranes
Authors: Ito Osamu , Ishizuka Tatsushi , Iino Masashi , Matsuda Minoru , Endo Takeshi , Yokozawa Tsutomu
Published: January 2005

Ring‐opening radical polymerization has been followed by the flash photolysis method. As an initiator radical, the arylthiyl radical (ArS˙) was used; the addition reaction rate constants of ArS˙ to vinyl monomer containing epoxy‐ring such as vinyloxiranes have been determined at first. The rate constant of ring opening reaction of the adduct radical changing to ArSCH2CH  CROCH2˙ were determined in the form of the relative values, which were converted to the absolute values. The ring‐opening reaction rate constants were ca. 106 s−1, which indicates that the ring‐opening rates are faster than usual radical propagation rates. The rate constants for vinyl monomer with 5‐member ring (1,4‐epoxy‐1,4‐dihydronaphthalene) were similarly evaluated.
Gas‐phase oxidation of 1,4‐dioxane
Authors: Battin F. , Scacchi G. , Baronnet F.
Published: January 2005

An experimental investigation in a conventional static apparatus of the oxidation of equimolecular mixtures 1,4‐dioxane‐O2 has shown that 1,4‐dioxane reacts with oxygen more readily than most hydrocarbons. Cool flames and ignitions were observed above 200°C in a pressure range up to 300 torr.

The products of the slow reaction and cool flame were analyzed by gas chromatography and GC‐MS; the slow reaction gives only CO, CO2, H2CO, H2, C2H4, and H2O.

A radical chain mechanism is suggested and discussed by using an evaluation of the rate constants of the possible elementary steps by the methods of thermochemical kinetics.
Oscillatory kinetics and mechanism of the chromate catalyzed decomposition of hydrogen peroxide
Authors: Beck Mihály T. , Nagy István P. , Székely Gabriella
Published: January 2005

Oscillatory change of pH occurs during the chromate‐catalyzed decomposition of hydrogen peroxide in a weakly acidic medium at elevated temperature and at high initial concentration of hydrogen peroxide. In a closed system, there are only two or three periods, but sustained oscillation occurs in a CSTR. In a CSTR bistability is also found. In closed systems the temperature exhibits a great maximum (up to 15°C increase), in a CSTR sustained oscillation occurs at a constant stationary temperature.
Rate constants for reactions of perfluorobutylperoxyl radical with alkenes
Authors: Nahor G. S. , Neta P.
Published: January 2005

Perfluorobutylperoxyl radicals were produced by radiolytic reduction of perfluorobutyl iodide in aerated methanol solutions. Rate constants for the reactions of this peroxyl radical with various organic compounds were determined by kinetic spectrophotometric pulse radiolysis. The rate constants for alkanes and alkenes were determined by competition kinetics using chlorpromazine as a reference. The results indicate that hydrogen abstraction from aliphatic compounds takes place with a rate constant that is too slow to measure in our system (<105 M−1 s−1), and that abstraction of allylic and doubly allylic hydrogens is slow compared with addition. Addition to alkenes takes place with rate constants of the order of k = 106 − 108 M−1 s−1. Good correlation was obtained between log k and the Taft substituent constants σ* for the various substituents on the double bond. Perfluorobutylperoxyl radical is found to be more reactive than trichloromethylperoxyl and other peroxyl radicals.
Micellar catalysis in the oxidation of acetophenones by Ce(IV)
Authors: Panigrahi Ganesh P. , Sahu Bimal P.
Published: January 2005

Rate of oxidation of acetophenones by Ce(IV) in aqueous acetic acid 80:20 (v/v) either slows down or remains constant over a range of cetyltrimethyl ammonium bromide (CTAB) concentration exceeding the cmc value. The rate is then found to increase sharply as the surfactant concentration increases with no sign of reaching a maximum or constant value. From Fluorescence quenching, binding constant for p‐nitro acetophenone has been evaluated. The rate data have been rationalized on the basis of a reaction between the acetophenones situated on the micelle surface and active Ce(IV) species in the bulk aqueous phase.