Kinetics of the DS-radical reactions with CINO and NO2

The rate constants for the reactions of the DS radical with NO₂ (reaction 1) and ClNO (reaction 2) have been measured using the discharge-flow technique at 2 torr total pressure of helium. The DS radical was monitored by laser-induced fluorescence. The reactions were found to have the following bimolecular rate constants (95% confidence level, in units of cm³ molecule^?1 s^?1): This expression for k₁ is found to be in excellent agreement with one of several previous studies. The magnitude of k₂ is examined within the framework of a well-established reactivity trend. © 1994 John Wiley & Sons, Inc.     

Rate constants for the addition of the 2-hydroxy-2-propyl radical to alkenes in solution

Absolute rate constants for the addition of the 2-hydroxy-2-propyl radical to 18 substituted alkenes (CH₂ = CXY) were determined at (296 ± 1) K in 2-propanol by time-resolved electronspin-resonance spectroscopy. With alkene substitution the rate constants vary by more than 6 orders of magnitude. For 3,3-dimethyl-but-1-ene the temperature dependence is given by log k/M^?1 · s^?1 = 6.4 minus;; 19.1/Θ where Θ = 2.303 RT in kJ/mol^?1. As shown by a good correlation with the alkene electron affinities, log k₂₉₆/M^?1 · s^?1 = 6.46 + 1.71 · EA/eV (r = 0.930), 2-hydroxy-2-propyl is a very nucleophilic radical, and its addition rates are highly governed by polar effects. © 1993 John Wiley & Sons, Inc.     

Reaction of the NO3 radical with some thiophenes: Kinetic study and a correlation between rate constant and EHOMO

The rate constants and activation energies for the reactions of some thiophenes with the NO₃ radical were measured using the absolute fast‐flow discharge technique at 263–335 K and low pressure. The proposed Arrhenius expressions for 2‐ethylthiophene, 2‐propylthiophene, 2,5‐dimethylthiophene, and 2‐chlorothiophene are k = (4.2 ± 0.28) ×10^?16 exp[(2280 ± 70)]/T, k = (7.0 ± 2) × 10^?18 exp[(3530 ± 70)]/T, k = (1 ± 1) × 10^?14 exp[(1648 ± 240)]/T, and k = (8 ± 2) × 10^?17 exp[(2000 ± 200)]/T (k = cm³ molecule^?1 s^?1), respectively. The reactions of this radical with 2‐chlorothiophene and 3‐chlorothiophene were also studied by a relative method in a Teflon static reactor at room temperature and atmospheric pressure. The effect of substitution on thiophene reactivity is discussed, and a relationship between the rate constants and the ionization potential (IP = ?E_HOMO) has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 570–576, 2006     

Determinations of the rate constants of the reactions Cl + N3Cl and N3 + NO at 295 K

The kinetics of reactions involving the ground-state azide radical, N₃ (X²Π_g, have been investigated in a discharge-flow system using mass spectrometric detection with molecular-beam sampling. The following rate constants have been determined at 295 K: Cl + N₃Cl → Cl₂ + N₃,k₂₉₅ = (1.78 ± 0.26) × 10^?12 cm³ s^?1 (1σ): N₃ + NO → N₂O + N₂, k₂₉₅ = (1.19 ± 0.31) × 10.^?12 cm³ s^?1 (1σ). A method for determining absolute N₃ radical concentration is reported.     

Alkali‐Metal Ion Catalysis and Inhibition in SNAr Displacement: Relative Stabilization of Ground State and Transition State Determines Catalysis and Inhibition in SNAr Reactivity

We report here the first observation of alkali‐metal ion catalysis and inhibition in S_NAr reactions. The plot of k_obsd versus [alkali‐metal ethoxide] exhibits downward curvature for the reactions of 1‐(4‐nitrophenoxy)‐2,4‐dinitrobenzene with EtOLi, EtONa, and EtOK, but upward curvature for the corresponding reaction with EtOK in the presence of 18‐crown‐6‐ether (18C6). Dissection of k_obsd into the second‐order rate constants for the reactions with the dissociated EtO^? and the ion‐paired EtOM (i.e., k and k_EtOM, respectively) has revealed that the reactivity increases in the order EtOLi<EtONa<EtOK<EtO^?<EtOK/18C6. This indicates that the reaction is inhibited by Li⁺, Na⁺, and K⁺ ions but is catalyzed by 18C6 K⁺ ion. The reactions of 1‐(Y‐substituted‐phenoxy)‐2,4‐dinitrobenzenes have been proposed to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate‐determining step based on the kinetic result that σ^o constants exhibit a much better Hammett correlation than σ^? constants. Alkali‐metal ion catalysis or inhibition has been discussed in terms of differential stabilization of ground‐state and transition‐state complexes through a qualitative energy profile. A π‐complexed transition‐state structure is proposed to account for the kinetic results.     

Determination of propagation and termination rate constants for some methacrylates in their radical polymerizations

Rotating sector determinations of k_p and 2k_t for ten methacrylates undergoing radical polymerization were carried out at 30°C. Ester groups in the monomers were: isopropyl, ethyl, β-cyclohexylethyl, methyl, γ-phenylpropyl, β-phenylethyl, β-methoxyethyl, benzyl, β-chloroethyl, and phenyl. Values of k_p obtained were 121, 126, 1190, 141, 149, 228, 249, 1250, 254, and 411 l./mole-sec., respectively; values of 2k_t × 10^?6 were 4.52, 7.35, 32.8, 11.6, 0.813, 1.88, 9.30, 41.9, 6.71, and 11.9 l./mole-sec., respectively. Omitting the data for the β-cyclohexylethyl and benzyl esters, a Taft correlation, log k_p = (0.70 ± 0.18)σ* + 2.2, was established, where σ* denotes Taft's polar substitutent constants for the above-mentioned ester groups. The steric substituent constants E_s were found to have no influence on k_p. Combination of k_p with r₂ data from copolymerization studies with styrene or methyl methacrylate as M₁ comonomer revealed that the more reactive monomer gave rise to the more reactive polymer radical. Monomer viscosities and molar volumes of the ester groups were found to correlate with 2k_t.     

Determination of absolute rate constants for free radical polymerization of ethyl α-fluoroacrylate and characterization of the polymer

The absolute rate constants for propagation (k_p) and for termination (k_t) of ethyl α-fluoroacrylate (EFA) were determined by means of the rotating sector method; k_p = 1120 and k_t = 4.8 × 10⁸ L/mol.s at 30°C. The monomer reactivity ratios for the copolymerizations with various monomers were obtained. By combining the k_p values for EFA from the present study and those for common monomers with the monomer reactivity ratios, the absolute values of the rate constants for cross-propagations were also evaluated. Reactivities of EFA and poly(EFA) radical, being compared with those of methyl acrylate and its polymer radical, were found to be little affected by the α-fluoro substitution. Poly(EFA) prepared with the radical initiator was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Although the glass transition temperature obtained by DSC for poly(EFA) resembled that of poly(ethyl α-chloroacrylate), its TGA thermogram showed fast chain de polymerization to EFA that was distinct from complicated degradation of poly(ethyl α-chloroacrylate).     

The gas phase reactions of hydroxyl radicals with a series of aliphatic ethers over the temperature range 240–440 K

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of linear aliphatic ethers using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for dimethylether (k₁), diethylether (k₂), and dipropylether (k₃) were used to derive the Arrhenius expressions and At 296 K, the measured rate constants (in units of 10^?13 cm³ molecule^?1 s^?1) were: k₁ = (24.9 ± 2.2), k₂ = (136 ± 9), and k₃ = (180 ± 22). Room temperature rate constants for the OH reactions with several other aliphatic ethers were also measured. These were (in the above units): di-n-butylether, (278 ± 36); di-n-pentylether, (347 ± 20); ethyleneoxide, (0.95 ± 0.05); propyleneoxide, (4.95 ± 0.52); and tetrahydrofuran, (178 ± 16). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.     

Über die Si-N-bindung: XLI. Kinetische untersuchungen zur hydrolyse von trimethylsilylurethanen des typs Me3Si(p-XC6H4)NCOOEt

Hydrolysis reactions of silylurethanes Me₃Si(p-XC₆H₄)NCOOEt (I) with X = Cl, H or Me in aqueous buffer solutions, with pH values from 1.94 to 10.00 were studied.The catalytic rate constants for the acid and base catalysed reactions and for the “non-catalysed” reaction k(H₃O⁺), k(CH₃COO^?), k(H₂PO₄^?), k(HPO₄^2?), k(NH₃), k(OH^?) and k₀ were evaluated from the pseudo first-order rate constants k_exp determined by UV spectroscopy.The Brönsted coefficients for the base-catalysed reactions were obtained from the catalytic rate constants found and the known constants of dissociation K(HB⁺).The ρ values of the reactions could be derived from the σ constants given by Jaffé.The kientical results obtained are interpreted mechanistically and are believed to also have model character for other nucleophilic substitution reactions with silicon compounds.     

The gas phase reactions of hydroxyl radicals with a series of aliphatic alcohols over the temperature range 240–440 K

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of aliphatic alcohols using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for methanol (k₁), ethanol (k₂), and 2-propanol (k₃) were used to derive the Arrhenius expressions and At 296 K, the measured rate constants (in units of 10^?13 cm³ molecule^?1 s^?1) were: k₁ = (8.61 ± 0.47), k₂ = (33.3 ± 2.3), and k₃ = (58.1 ± 3.4). Room temperature rate constants for the OH reactions with several other aliphatic alcohols were also measured. These were (in the above units): 1-propanol, (53.4 ± 2.9); 1-butanol, (83.1 ± 6.3) and 1-pentanol, (108 ± 11). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.     

Atmospheric chemistry of di-tert-butyl ether: Rates and products of the reactions with chlorine atoms,hydroxyl radicals,and nitrate radicals

The rate constants for the gas-phase reactions of di-tert-butyl ether (DTBE) with chlorine atoms, hydroxyl radicals, and nitrate radicals have been determined in relative rate experiments using FTIR spectroscopy. Values of k_(DTBE+CI) = (1.4 ± 0.2) × 10⁻¹⁰,k_(DTBE+OH) = (3.7 ± 0.7) × 10⁻¹², and k_(DTBE+N03) = (2.8 ± 0.9) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ were obtained. Tert-butyl acetate was identified as the major product of both Cl atom and OH radical initiated oxidation of DTBE in air in the presence of NO_x. The molar tert-butyl acetate yield was 0.85 ± 0.11 in the Cl atom experiments and 0.84 ± 0.11 in OH radical experiments. As part of this work the rate constant for reaction of Cl atoms with tert-butyl acetate at 295 K was determined to be (1.6 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The stated errors are two standard deviations (2σ). © 1996 John Wiley & Sons, Inc.     

Can Propagation Reaction in Carbocationic Polymerization and Copolymerization of Styrene be Diffusion Controlled ?

Summary: The reactivity ratios r₁ and r₂ in copolymerizations of styrene and parasubstituted styrenes, for which r₁ = 1/r₂, are in contradiction with diffusion control for their propagation reactions. The cross propagation rate constants k_12copol in copolymerization of styrene with p-chlorostyrene, p-methylstyrene and p-methoxystyrene have been shown to increase with their nucleophilicity parameter N. This is also not compatible with diffusion controlled cross propagation and propagation, but agrees with similar rate constants of propagation for these monomers. The capping rate constants k_12capp of reactions of poly(p-methylstyrene)^± and poly(p-methoxystyrene)^± with π-nucleophiles also increase with N, but with a much larger selectivity. This shows that k_12copol and k_12capp are not identical. The k, from 10⁹ to 6 10⁹ L mol⁻¹ s⁻¹, obtained with p-chlorostyrene, styrene and p-methylstyrene by the Diffusion Clock (DC) method are not consistent with those derived from the ionic species concentration (ISC method) for indene, 2,4,6-trimethylstyrene and p-methoxystyrene of the order of 10⁴ – 10⁵ L mol⁻¹ s⁻¹, also measured for living polymerization. These last values are in agreement with those measured previously in nonliving systems, and with an approximate compensation between the reactivity of a monomer and that of the corresponding carbocation.     

The gas phase reactions of hydroxyl radicals with a series of carboxylic acids over the temperature range 240–440 K

The temperature dependencies of the rate constants for the gas phase reactions of OH radicals with a series of carboxylic acids were measured in a flash photolysis resonance fluorescence apparatus over the temperature range 240–440 K. The data at total pressures (using Ar diluent gas) between 25–50 torr for acetic acid (k₁), propionic acid (k₂), and i-butyric acid (k₃) were used to derive the Arrhenius expressions and At 298 K, the measured rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were: k₁ = (0.74 ± 0.06), k₂ = (1.22 ± 0.12), and k₃ = (2.00 ± 0.20). In addition a rate constant of (0.37 ± 0.04), in the above units, was determined for the reaction of OH with formic acid. The error limits cited above are 2σ from the linear least squares analyses. These results are discussed in terms of the mechanisms for these reactions and are compared to literature data.     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

Kinetics of Chlorohydrination of Allyl Chloride

The chlorohydrination of allyl chloride with chlorine in water was studied at 20–80°C. The effect of the concentration of chloride ions within the range 0–3.6 mol/l on the selectivity of formation of glycerol dichlorohydrins was studied. An equation that relates the selectivity and the concentration of Cl^–was derived, which adequately describes experimental data. The schemes of parallel and consecutive reactions occurring in the system were suggested. The ratios between the rate constants of the following reactions were found: the reactions of chlorine with water and allyl chloride dissolved in water (k ₁/k ₄= 4.1 × 10^–4), the reaction of allyl chloride with hypochlorous acid and the decomposition of hypochlorous acid (k ₂/k ₃= 1.7 × 10³), and the reactions of the allyl chloride–chlorine complex with a water molecule and Cl^–(k ₅/k ₆= 2.9 × 10^–2).     

Arrhenius parameters for the reactions CH3. + C4H10 → CH4 + C4H9. and C2H5. + C4H10 → C2H6 + C4H9.

Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions and of the Arrhenius parameters of the reactions Established data for k₁/k₂ allow estimation of k₁ for 951°K and this, with recent thermochemical data, yields the result log k_?1 (l.mole s^?1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k₃k₄ (l.²mole^?2s^?2) is found to be associated with the Arrhenius parameters log (A₃A₄) = 21.90 ± 0.6 and (E₃ + E₄) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A₄ = 10.5 ± 0.4 (l.mole^?1s^?1) and E₄ = 20.1 ± 1.7 kcal/mole, hence log A₃ = 11.4 ± 0.8 (l.mole^?1s^?1) and E₃ = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical–alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.     

Stereo‐dynamics of the F + HCl → HF + Cl reaction

We present a quasi‐classical trajectory (QCT) study on product polarization for the reaction F(²P) + HCl(v = 0, j = 0) → HF + Cl(²P) on a recently computed 1² A′ ground‐state surface reported by Deskevich et al. J Chem Phys, 2006, 124, 224303. Four polarization dependent generalized differential cross‐sections (2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t), (2π/σ)(dσ₂₂₊/dω_t), and (2π/σ)(dσ_21?/dω_t) were calculated in the center‐of‐mass frame at four different collision energies. The obtained P(θ_r), P(?_r), and P(θ_r, ?_r), which denote respectively the distribution of angles between k and j′, the distribution of dihedral angle denoting k‐k′‐j′ correlation and the angular distribution of product rotational vectors in the form of polar plots, indicate that the degree of rotational alignment of the product HF molecule is strong and the degree of the rotational alignment decreases as collision energy increases. The product rotational angular momentum vector j′ is not only aligned, but also oriented along the y‐axis, and the molecular rotation of the product prefers an in‐plane reaction mechanism rather than the out‐of‐plane mechanism. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Secondary hydrogen isotope effect for the transition from olefin to free radical

Secondary kinetic isotope effects occur in radical additions to deuterated olefins. Substitution of a deuterium at a carbon undergoing an sp² to sp³ hybridization-change during reaction, C_β in eq. (1), leads to an inverse isotope effect of 3–5% (k_H/k_D = 0.95–0.97). The effect at a carbon going from an olefinic to a radical center, C_α in eq. (1), generally has been assumed to be negligible, since a nominal sp² hybridization is maintained throughout reaction. Using new, sensitive instrumentation for radioactivity determination and a recently developed quench correction technique, we now find that there is a small, normal isotope effect (k_H/k_T 1) associated with a change from olefin to radical. Specifically, when R· is the polystyryl radical, X is phenyl, and the α-C bears a tritium, k_H/k_T = 1.04. This result is discussed in relation to recent data on cycloaddition reactions.     

Kinetics of the gas‐phase reactions of CHXCFX (X = H,F) with OH (253–328 K) and NO3 (298 K) radicals and O3 (236–308 K)

Rate constants for the reactions of OH and NO₃ radicals with CH₂?CHF (k₁ and k₄), CH₂?CF₂ (k₂ and k₅), and CHF?CF₂ (k₃ and k₆) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k₁ = (1.20 ± 0.37) × 10^?12 exp[(410 ± 90)/T], k₂ = (1.51 ± 0.37) × 10^?12 exp[(190 ± 70)/T], and k₃ = (2.53 ± 0.60) × 10^?12 exp[(340 ± 70)/T] cm³ molecule^?1 s^?1. The rate constants for NO₃ radical reactions at 298 K were k₄ = (1.78 ± 0.12) × 10^?16 (CH₂?CHF), k₅ = (1.23 ± 0.02) × 10^?16 (CH₂?CF₂), and k₆ = (1.86 ± 0.09) × 10^?16 (CHF?CF₂) cm³ molecule^?1 s^?1. The rate constants for O₃ reactions with CH₂?CHF (k₇), CH₂?CF₂ (k₈), and CHF?CF₂ (k₉) were determined by means of an absolute rate method: k₇ = (1.52 ± 0.22) × 10^?15 exp[?(2280 ± 40)/T], k₈ = (4.91 ± 2.30) × 10^?16 exp[?(3360 ± 130)/T], and k₉ = (5.70 ± 4.04) × 10^?16 exp[?(2580 ± 200)/T] cm³ molecule^?1 s^?1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH₂?CHF, CH₂?CF₂, and CHF?CF₂ with respect to reaction with OH radicals, NO₃ radicals, and O₃ were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010