Rate constants for the reaction OH + CO as functions of temperature and water concentration

Rate constants for the reaction OH + CO have been measured as functions of temperature (340–1220 K) and water concentration in the presence of 1 atm of argon. Results at zero water concentration yield the expression, log k_? (cm³ molecule^?1 S^?1) = ?12.96 + 4.7 × 10^?4 T, for the reaction rate constant as a function of temperature. These results are in very good agreement with previous direct measurements and in reasonable agreement with flame and shock tube measurements. Explanations are offered for the involvement of the water molecule in the present experiments and earlier measurements from this laboratory throughout the entire temperature range. Results are consistent with previous results showing little, if any, pressure effect of Ar on the reaction up to 1 atm of Ar.     

Kinetics and mechanism of formation of manganate(VI) and hypomanganate(V) coordination polymer intermediates during the base‐catalyzed oxidation of carboxymethyl cellulose polymer by permanganate,Part 1

Kinetics and mechanism of the disproportionation of MnO₄^? via [CMC—Mn^VIO₄^2?] intermediate complex formation during the oxidation of carboxymethyl cellulose (CMC) polysaccharide have been investigated spectrophotometrically at pH ≥12 and various temperatures (15–35^°C). The rate law was suggested as Rate = k_obsMnO₄^?]. Kinetic and spectrophotometric measurements revealed the formation of hypomanganate(V) and manganate(VI) transient species, which are base‐catalyzed. A mechanism was postulated that is consistent with the experimental data. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 605–611, 2001     

Thermal decomposition of ethane

The decomposition of C₂H₆ in Ar was studied by laser-absorption and laser-schlieren measurements of the reaction rate behind incident shock waves with 1300 < T < 2500°K and 1.1 < ρ < 4.4 × 10^?6 mol/cm³. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14-reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expression k(cm³/mol˙sec) = 2 × 10¹¹¹ T^?25.26 exp(?80 320/T) was found for the primary dissociation step C₂H₆ + M ? CH₃ + CH₃ + M under the conditions studied; no difference in rate was discernable between M ? Ar and M ? C₂H₆. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low-pressure limiting rate constants and found to be concordant.     

Kinetics of the reverse Diels-Alder reaction of dicyclopentadienecarboxylate groups on cotton cellulose

Cotton cellulose in the form of fabric has been esterified with dicyclopentadienecarboxylic acid to a degree of substitution of 0.44. The kinetics of the reverse Diels-Alder reactions of the dicyclopentadienyl groups of the resulting cellulose ester in the presence of trapping agents and of swelling and nonswelling liquids have been measured with the differential scanning calorimeter. Fiber width measurements indicate that the esterified cotton fibers are swollen in the presence of the trapping agents dibutyl maleate, N-phenylamaleimide, and N-phenylmaleimide in tetraglyme solution, and in the presence of the nonreactive swelling agents tetraglyme and glycerol. The activation parameters for the dissociations in the swollen fibers are: E_a = 28–33 kcal/mole and ΔS^* = ?5 to +5 e.u. These kinetic parameters are similar to those previously found for the dissociation of methyl dicyclopentadienecarboxylate in solution. Fiber width measurements indicate that the esterified cotton fibers are collapsed in the dry state and in the presence of paraffin oil, deposited Carbowax 6000, or deposited glyceryl tristearate. The activation parameters for the dissociations in the collapsed fibers are E_a = 18–24 kcal/mole and ΔS^* = ?20 to ?30 e.u. The kinetics are discussed in terms of the state of the cellulose matrix in the swollen and in the collapsed fibers.     

The Influence of solvent and crown polyethers on the nucleophilic reactivity of potassium tert-Butylperoxide,potassium tert-Butoxide,and some other oxygen bases

The rates of reaction of t-BuOOK, t-BuOK, n-BuOOK, and p-MeC₆H₄OKwith p-nitrophenyl diphenylphosphinate 1 and with p-nitrophenyl benzoate 2 have been measured in toluene both in the absence and in the presence of crown polyether dicyclohexyl-18-crown-6 3a . The rates of nucleophilic displacementon 1 by HOO^?, t-BuOO^?, and some “nonalpha” oxyanions in water have also been determined. Solvent transfer from water to toluene results in increasing the nucleophilic reactivity of the t-butyl hydroperoxide anion. Rate ratios Q_Qa are given which allow one to estimate the enhanced reactivity of t-BuOO^? (an α-nucleophile) compared to oxygen nucleophiles of comparable base strength toward 1 and 2 . These are for substrate 1 , Q_α (water) ? 6.5 and Q_α (toluene) ? 2.7; for substrate 2 , Q_α (water) ? 5.5 and Q_α (toluene) ? 5. The hypothesis is advanced that solvation is not a major factor in determining the α-effect of the t-butylhydroperoxide anion.     

Radiative lifetime and quenching rates of seo2 vapor

A Nd: YAG pumped dye laser system was used 10 excite SeO₂ vapor at 2888 A (¹B₂-X?¹A₁) and the radiative lifetime was measured under collision free conditions by time gated photon counting Rate coefficients for quenching by Ar, N₂ and CO₂ have also been determined. The lifetime measurements covered a 90 μs range and exhibited exponential decay with τ_r = 36.1 = 2.5 μs.     

Kinetics and rate constants for the reaction of tri-n-butylgermanium hydride with methyl iodide and carbon tetrachloride. The combination of methyl and trichloromethyl radicals in solution.

The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH₃? and CCl₃? radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ～1–3 × 10⁹ M^?1 sec^?1. Rate constants for hydrogen atom abstraction by CH₃? and CCl₃? radicals are both ～1?2 × 10⁵ M^?1 sec^?1. Tri-n-butyltin hydride is about 10–20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride. The strength of the germanium–hydrogen bond, D(n-Bu₃Ge–H) is estimated to be approximately 84 kcal/mole.     

The high temperature pyrolysis of 1,3-butadiene II: Pulsed laser flash absorption rate constants,and consideration of possible molecular dissociation pathways

Rate constants for the unimolecular dissociation of 1,3-butadiene have been measured with the pulsed laser flash absorption technique, following butadiene disappearance at 222 nm. The results are in excellent agreement with previous laser-schlieren measurements interpreted with a ΔH°₂₉₈ = 100 kcal/mol heat of dissociation. A new RRKM calculation agreeing with both sets of rate constants gives log k_∞(s^?1) = 17.03 ± 0.3 – 94(kcal/mol)/RT. These data and product measurements using ARAS, single-pulse product analysis, and time-of-flight mass spectrometry, in shock tubes, all provide independent evidence against any major participation by molecular reactions in the dissociation. The only dissociation channel, or combination of channels, consistent with all the measurements is C-C scission to two vinyl radicals. However, the extremely slow rate of H-atom formation seen in ARAS experiments then requires an unacceptably low rate of vinyl dissociation.     

Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl₂^˙? radicals with 2-propen-1-o1 and 2-buten-1-o1 as a function of temperature and with 2, 3-dimethyl-2-butene at room temperature. The rate constants were in the range of 10⁶–10⁹ L mol^?1 s^?1, the activation energies were relatively low (1–10 kJ mol^?1), and the pre-exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, E_T(30), and the hydrogen-bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO₄^˙? with 2-propen-1-o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.     

The free-radical reaction of tri-n-butyltin hydride with peroxides

Rate constants for the tri-n-butyltin radical ( Sn · ) induced decomposition of a number of peroxides have been measured in benzene at 10°C. The values range from ～100 M^?1 sec^?1 for di-t-butyl peroxide to 2.6 × 10⁷ M^?1 sec^?1 for di-t-butyl diperoxyisophthalate. The majority of the peroxides, including diethyl peroxide, diacetyl peroxide, and t-butyl peracetate, have rate constants of ～10⁵ M^?1 sec^?1. It is shown that di-n-alkyl disulfides are ten times as reactive toward Sn · as di-n-alkyl peroxides, although the exothermicities of these reactions are ～15 and ～39 kcal/mole, respectively. The enhanced reactivity of the disulfides is attributed to the easier formation of an intermediate or transition state with 9 electrons around sulfur, compared with an analogous species with 9 electrons around oxygen. The following bond strengths (kcal/mole) have been estimated: D[ Sn ? OR] = 77; D[ Sn ? H] = 82; D[ Sn ? SR] = 83; and D[ Sn ? OC(O)R] = 86, where R = alkyl. Rate constants for reaction of Sn · with some benzyl esters have also been measured. It has been found that t-butoxy radicals can add to benzene and abstract hydrogen from benzene at ambient temperatures.     

Structure-Reactivity correlations in the addition of water to aromatic substrates

The addition of water to 1-(4-Z-2,6-dinitrophenyl)-3-methylimidazolium chloride (Z = CN, NO₂, and CF₃) is catalyzed by carboxylate bases. There is a decrease in ρ with increasing basicity of the catalyst with ?ρ/?pK_BH = ?0.090. The results indicate that the mechanism of the reaction involves the addition of water to the aromatic substrates catalyzed by general bases. The changes in the structure-reactivity parameters with changing pK of the catalysts or Z in the substrate are rationalized in terms of changing bond lengths in the transition state. The activation parameters and the kinetic solvent isotopic effect were determined for the water, acetate, and OH^? catalyzed reactions and are consistent with the proposed mechanism.     

Kinetics and mechanism of the reaction between dibenzyl triselenocarbonate and oxygen-bases

The base-induced solvolysis of dibenzyl triselenocarbonate in DMSO/water (4:1) has been studied by UV spectrophotometric measurements under pseudo-first order conditions, using KOH, Me₄NOH, Bu₄ⁿNOH and Bu₄ⁿNHCO₃ as bases. The reaction is first order with respect to the substrate as well as to the base. Rate constants and activation parameters for the four bases indicate that the rate determining step is the nucleophilic attack by the base, as an ionic couple, on the substrate. Fast reactions, due to strong nucleophilic selenolate species, may follow this slow step; a tentative mechanism is proposed on the basis of experimental evidence.     

The anomeric effect: Ab-initio studies on molecules of the type X?CH2?O?CH3

The anomeric effect of the functional groups X = C?N, C?CH, COOH, COO^?, O? CH₃, NH₂, and NH⁺₃ has been studied with ab initio techniques. Geometry effects upon rotation around the central C? O bond in X? CH₂? O? CH₃ have been compared in the various compounds. The energy differences between the conformers with a gauche and trans (X? C? O? C) arrangement were calculated at the 6-31G* level in the fully optimized 4-21G geometries. Energy differences calculated at the 4-21G level appeared not to be reliable, especially for the groups X that contain non-sp³ hybridized atoms. The 6-31G* energy differences indicate a normal anomeric effect for X = COO^?, O? CH₃, and NH₂(g⁺) (ca. 13 kJ/mol) and a small anomeric effect for X = COOH, C?N, and C?CH (ca. 6 kJ/mol). For X = NH₂(t) and NH⁺₃ a reverse anomeric effect occurs. These observations are in line with experimental results and evidence is given for a competition among various stereoelectronic interactions that occur at the same anomeric center. Geometry variations can be understood in terms of simple rules associated with anomeric orbital interactions. Trends followed when the group X is varied cannot be related in a straightforward way to the energy differences between the trans and the gauche forms in these compounds. Only the variation in the gauche torsion angle X? C? O? C follows roughly the same trend.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Influence de la concentration en bromure et rôle du solvant sur la réactivité des anisoles au cours de la réaction de bromation

Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO₂, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br₂ and Br^?₃ present as the A⁺Br^?₃ form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br₂] [A⁺Br^?]_T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of k^o,p_g {1 + K′[A⁺Br^?]_T}VS[A⁺Br^?]_T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO₂ helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO₂ than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p⁺_p = ?7.83; p⁺_o= ?10.47).     

Adsorption of toluene-soluble polymers at the toluene–water interface

The adsorption of several toluene-soluble polymers at the toluene–water interface has been investigated by using the duNouy ring method of measuring interfacial tension γT /W . Polystyrene and poly(ethylene-co-vinyl acetate) (11.1 mole-% vinyl acetate) have little affinity for this interface at 29°C, but poly(methyl methacrylate) (PMMA) (M?_n = 420,000) and ethyl cellulose (EC) (M?_n = 50,100; 49.1% ethoxyl) adsorb significantly at concentrations as low as 1.0 × 10^?4 g/100ml. A plot of interfacial tension lowering versus initial logarithm of initial bulk phase polymer concentration is linear from 1.0 × 10^?4 to 1.0 × 10^?1 g/100 ml for EC and 1.0 × 10^?4 to 1.0 × 10^?2 g/100 ml for PMMA. When the PMMA concentration increases to 1.15 × 10^?1 g/100 ml, its adsorption behavior changes markedly. Prolonged time effects occur and adsorption becomes dependent upon dissolved water content of the toluene prior to formation of the toluene/water interface. Such effects are not observed with the other solutions studied. Increasing temperatures have variable effects on values of γT /W for the polymer solutions studied. Experiments with various polymer mixtures indicate that the polymer lowering T /W the most is preferentially adsorbed at the toluene–water interface and rapidly displaces less strongly adsorbed polymers.     

Rate constants for the gas‐phase reaction of hexamethylbenzene with OH radicals and H atoms and of 1,3,5‐trimethylbenzene with H atoms

Rate constants for the gas‐phase reaction of hexamethylbenzene (HMB) with OH radicals and H atoms and of 1,3,5‐trimethylbenzene (TMB) with H atoms have been obtained in a flow system at 295 ± 2 K and a pressure of 25 mbar He using MS measurements. Obtained rate constants from a relative rate technique are k_(OH+HMB) = (1.13 ± 0.11) 10⁻¹⁰, k_(H+HMB) = (5.9 ± 3.4) 10⁻¹³ and k_(H+TMB) = (4.6 ± 2.7) 10⁻¹³ cm³ molecule⁻¹ s⁻¹, respectively. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 124–129, 2001     

Kinetics of substitution atcis-tetracarbonylbis(4-methylpyridine)-tungsten(0)

Summary Rate constants have been obtained for reactions ofcis-tetracarbonylbis(4-methylpyridine)tungsten(0),cis-[W(CO)₄(4Mepy)₂], with 1, 10-phenanthroline, 2,2-bipyridyl, and related diimine ligands in toluene solution at 298.2K. Effects of varying the nature and concentration of the entering ligand, and of addition of 4-methylpyridine, indicate the operation of a limiting dissociative (D) mechanism. This is confirmed by the establishment of an activation volume of + 8 cm³ mol^–1, in toluene at 298.2K.     

Kinetics of OH radical reaction with phenanthrene: New absolute rate measurements and comparison with other PAHs

Using an in situ pulsed laser photolysis/pulsed laser‐induced fluorescence/technique, the OH reaction kinetics of a three‐ring polycyclic aromatic hydrocarbon (PAH), phenanthrene (and its deuterated form), was investigated over the temperature range of 373–1000 K. This study represents the first examination of the OH kinetics for phenanthrene at elevated temperatures using the absolute rate technique. The phenanthrene results indicate a temperature dependence similar to its isomer anthracene, reported previously in R. Ananthula, T. Yamada, and P. H. Taylor, J Phys Chem A 2006, 100, 3559–3566, over a similar temperature range. The phenanthrene rate constants are similar to anthracene at high temperature (ca. 1000 K) and a factor of ca. 2 lower at low temperatures (373–700 K). The rate measurements were best fitted by the following two‐parameter expression of the form ATⁿ: k₁(373–1000 K) = 4.98 ± 2.96 × 10^?6 * T^?1.97±0.10 (in units of cm³ molecule^?1 s^?1, error limits ±1σ). Rate measurements with deuterated phenanthrene below 725 K were indistinguishable from the phenanthrene rate measurements, within random error limits, providing strong evidence for an OH‐addition mechanism. The effects of PAH size on their reactivity with OH radicals based on selected data over the temperature range of 243–1200 K are discussed. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 629–637, 2007     

High Pressure 17O-FT-NMR. Evidence for the Associative Nature of Substitution Reactions on Mn2+ in Water

The water exchange on [Mn(H₂O)₆](ClO₄)₂ in aqueous solution has been studied as a function of pressure (up to 250 MPa), measuring ¹⁷O-FT-NMR. linewidths of the free water resonance at 8.13 MHz. A pressure independent volume of activation, ΔV≠ = ?6.2 ± 0.2 cm³ mol^?1 is obtained, producing a clear evidence that, contrary to general belief, the mechanism for solvent exchange on Mn²⁺ is an associative interchange (I_a).     

Homoatomare Cluster E93– mit E = Ge,Sn und Pb: EPR‐Spektren,Magnetismus und Elektrochemie

Homoatomic Clusters E₉^3– with E = Ge, Sn, and Pb: EPR Spectra, Magnetism and Electrochemistry The properties of the compounds [K‐([2.2.2]‐crypt)]₃E₉ (E = Ge ( 1 ), Sn ( 2 ), Pb ( 3 )), which contain isolated E₉ units, have been examined by EPR measurements at room temperature and at 77 K, magnetic susceptibility measurements in the range from 2 K to 300 K and cyclovoltammetric experiments. The EPR signals of powder samples and of single crystals are analyzed using three g tensor components, indicating low symmetric E₉^3– clusters. Magnetic susceptibility data of 2 and 3 follow the expression (χ_mol = C/(T – θ_p) + χ₀, with θ_p ≈ 0 and C corresponding to the presence of about 50% paramagnetic E₉^3– species (S = ¹/₂). In solution, 2 and 3 show irreversible oxidation processes. Current intensities and peak forms indicate that adsorption processes play an important role irrespective of the material of the working electrode (silver, platinum, glassy carbon).