The determination of the arrhenius parameters for the reaction Cl + C2F5I → ICl + C2F5 using a competitive method

The reactions have been studied competitively over the range of 28–182°C by photolysis of mixtures of Cl₂ + C₂F₅I+ CH₄. We obtain where θ = 2.303RT J/mol. The use of published data on reaction (2) leads to log (k₁cm³/mol sec) = (13.96 ± 0.2) ? (11,500 ± 2000)/θ.     

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.     

The oxidation of methyl radicals at room temperature

Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k₁ is in the fall-off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10^?12 cm³/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10^?31 cm⁶/molec² · sec with N₂ as third body and (1.5 ± 0.8) × 10^?30 with neopentane; we cannot differentiate between k_2a and k_2c and we conclude k_2a + (k_2c) = (3.05 ± 0.8) × 10^?13 cm³/molec · sec and k_2b = (1.6 ± 0.4) × 10^?13 cm³/molec · sec; k₃ = (6.0 ± 1.0) × 10^?11 cm³/molec · sec.     

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.     

The gas-phase kinetics of the reaction of 1,1-difluoroiodoethane with hydrogen iodide: The C–I bond dissociation energy in 1,1-difluoroiodoethane

The kinetics of gas-phase reaction of CH₃CF₂I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism: A least squares treatment of the data gave where θ = 2.303 RT kcal/mole. The observed activation energy E₁ was combined with E₂ = 0 ± 1 kcal/mole to yield The result, combined with data for several C? I bond dissociation energies, leads us to conclude that the C(sp³)? I bond is relatively insensitive to F for H substitution and that the C(sp²)–I bond has considerable double-bond character.     

Thermal stability of intermediate sized acetylenic compounds and the heats of formation of propargyl radicals

4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are In combination with previous results, rate expressions for propargyl C? C bond cleavage are related to that for the alkanes by the expression These results yield a propargyl resonance energy of D(nC₃H₇-H) – D(C₃H₃-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH₃C≡CCH₂-H) – D(C₃H₃-H) = 0.6 ± 3 kJ, D(sC₄H₉-H) – D(iC₃H₇-H) = 0 ± 3 kJ, D(iC₄H₉-H) – D(nC₃H₇-H) = 2 ± 3 kJ, and D(nC₃H₇-H) – D(iC₃H₇-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.     

Rate constants and kinetic isotope effects for hydrogen/deuterium abstraction by chlorine atoms from the chloromethyl group in CH2ClCH2Cl,CD2ClCD2Cl,CH2ClCHCl2, and CH2ClCDCl2

The abstraction of hydrogen and deuterium from 1,2-dichloroethane, 1,1,2-trichloroethane, and two of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigatedin the temperature range 0–95°C using methane as a competitor. Rate constants and their temperature coefficients are reported for the following reactions Over the temperature range of this investigation an Arrhenius law temperature dependence was observed in all cases. Based on the adopted rate coefficient for the chlorination of methane [L.F. Keyser, J. Chem. Phys., 69 , 214 (1978)] which is commensurate with the present temperature range, the following rate constant values (cm³ s^?1) are obtained: The observed pure primary, and mixed primary plus α- and β3-secondary kinetic isotope effects at 298 K are k₃/k₆ = 2.73 ± 0.08, and k₁/k₂ = 4.26 ± 0.12, respectively. Both show a normal temperature dependence decreasing to k₃/k₆ = 2.39 ± 0.06 and k₁/k₂ = 3.56 ± 0.09 at 370 K. Contrary to some simple theoretical expectations, the kinetic isotope effect for H/D abstraction decreases with increasing number of chlorine substituents in the geminal group in a parallel manner to the trend established previously for C1-substitution in the adjacent group. The occurrence of a β-secondary isotope effect, k₄/k₅, is established; this effect suggests a slight inverse temperature dependence.     

Chain ion molecular mechanism of ascorbic acid oxidation with hydrogen peroxide. Cu3+ ion as a chain carrier

The kinetics and mechanism of ascorbic acid (DH₂) oxidation have been studied under anaerobic conditions in the presence of Cu²⁺ ions. At 10^?4 ≤ [Cu²⁺]₀ < 10^?3M, 10^?3 ≤ [DH₂]₀ < 10^?2M, 10^?2 ≤ [H₂O₂] ≤ 0.1M, 3 ≤ pH < 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ₂ (25°C) = (6.5 ± 0.6) × 10^?3 sec^?1. The effective activation energy is E₂ = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu⁺ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu⁺ initiation in the Cu²⁺ reaction with ascorbic acid by the expression where C is a function of pH and of H₂O₂ concentration. The rate equation where k₁(25°C) = (5.3 ± 1) × 10³M^?1 sec^?1 is true for the steady-state catalytic reaction. The Cu⁺ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu²⁺–DH₂–H₂O₂ system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu⁺ with H₂O₂, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme. Initiation: Propagation: Termination:      

Incorporating glycidyl methacrylate into block copolymers using poly(methacrylate‐ran‐styrene) macroinitiators synthesized by nitroxide‐mediated polymerization

Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder^®) to yield methacrylate rich copolymers with polydispersities _w/ _n = 1.23–1.46. k_pK values (k_p = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k_pK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight _n = 12.9–33.5 kg mol^?1) resulted in slightly broader molecular weight distributions with _w/ _n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher _w/ _n = 2.01–2.48. P(XMA/S) macroinitiators ( _n = 4.9–8.9 kg mol^?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with _w/ _n ～ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (～20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009     

The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br₂]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br₂[(2.7–13.6) × 10^?3M], H⁺ (0.03–2.0M), and Br^? (up to 0.6M). The mechanism with k₁ = 20.2 ± 1.2 M^?1 sec^?1, pK₂ = 3.76, pK₃ = ?1.20, accounts for all experimental observations. Br₃^? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.     

Kinetics of the gas phase reaction of OH radicals with pyrrole and thiophene

Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k₁) and thiophene (k₂) have been measured over the temperature ranges 298–440 and 274–382 K, respectively, using the flash photolysis-resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25–100 torr andwere fit by the Arrhenius expressions and with rate constants at 298 ± 2 K of k₁ = (1.03 ± 0.06) × 10^?10 cm³ molecule^?1 s^?1 and k₂ = (8.9 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.     

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 photochlorination of perfluorocyclopentene

The gas-phase photochlorination of perfluorocyclopentene under continuous and intermittent illumination with 4360-Å radiation was studied between 10° and 60°C. The rate constants for the reactions. (3) (4) were measured as k₃ = (1.20 + 0.58) × 10⁸ exp (?6.430 ± 177/RT) l·(mole sec) and k₄ = (1.86 ± 0.76) × 10⁷ l·(mole sec).     

The reactions of alkoxy radicals with O2. II. n-C3H7O radicals

n-C₃H₇ONO was photolyzed with 366 nm radiation at ?26, ?3, 23, 55, 88, and 120°C in a static system in the presence of NO, O₂, and N₂. The quantum yields of C₂H₅CHO, C₂H₅ONO, and CH₃CHO were measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?₁ = 0.38 ± 0.04 independent of temperature. The n-C₃H₇O radicals can react with NO by two routes The n-C₃H₇O radical can decompose via or react with O₂ via Values of k₄/k₂ ? k_4b/k₂ were determined to be (2.0 ± 0.2) × 10¹⁴, (3.1 ± 0.6) × 10¹⁴, and (1.4 ± 0.1) × 10¹⁵ molec/cm³ at 55, 88, and 120°C, respectively, at 150-torr total pressure of N₂. Values of k₆/k₂ were determined from ?26 to 88°C. They fit the Arrhenius expression: For k₂ ? 4.4 × 10^?11 cm³/s, k₆ becomes (2.9 ± 1.7) × 10^?13 exp{?(879 ± 117)/T} cm³/s. The reaction scheme also provides k_4b/k₆ = 1.58 × 10¹⁸ molec/cm³ at 120°C and k_8a/k₈ = 0.56 ± 0.24 independent of temperature, where      

Reactions of alkoxy radicals with O2. I. C2H5O radicals

C₂H₅ONO was photolyzed with 366 nm radiation at ?48, ?22, ?2.5, 23, 55, 88, and 120°C in a static system in the presence of NO, O₂, and N₂. The quantum yield of CH₃CHO, Φ{CH₃CHO}, was measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?_1a = 0.29 ± 0.03 independent of temperature. The C₂H₅O radicals can react with NO by two routes The C₂H₅O radical can also react with O₂ via Values of k₆/k₂ were determined at each temperature. They fit the Arrhenius expression: Log(k₆/k₂) = ?2.17 ± 0.14 ? (924 ± 94)/2.303 T. For k₂ ? 4.4 × 10^?11 cm³/s, k₆ becomes (3.0 ± 1.0) × 10^?13 exp{?(924 ± 94)/T} cm³/s. The reaction scheme also provides k_8a/k₈ = 0.43 ± 0.13, where      

BrNO—thermodynamic properties,the ultraviolet/vis spectrum,and the kinetics of its formation

The equilibrium has been studied between 275°and 363°K. Third-law calculations lead to ΔH°₂₉₈(1) = -11.50 ±0.17 kcal/mol, from which Absorption bands of BrNO in the ultraviolet with e (γ_max = 215 nm) = 1.84±0.17 × 10⁴ 1/mol·cm, and in the red with e (γ_max = 708 nm) = 7.7±1.9 1/mol·cm at 298°K have been investigated. The rate of formation of BrNO has also been measured between 275°and 363°K.     

Reactions of alkoxy radicals with O2. III. i-C4H9O radicals

i-C₄H₉ONO was photolyzed with 366-nm radiation at ?8, 23, 55, 88, and 120°C in a static system in the presence of NO, O₂, and N₂. The quantum yield of i-C₃H₇CHO, Φ{i-C₃H₇CHO}, was measured as a function of reaction of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?₁ = 0.24 ± 0.02 independent of temperature. The i-C₄H₉O radicals can react with NO by two routes The i-C₄H₉O radical can decompose via or react with O₂ via Values of k₄/k₂ ? k_4b/k₂ were determined to be (2.8 ± 0.6) × 10¹⁴, (1.7 ± 0.2) × 10¹⁵, and (3.5 ± 1.3) × 10¹⁵ molec/cm³ at 23 55, and 88°C, respectively, at 150-torr total pressure of N₂. Values of k₆/k₂ were determined from ?8 to 120°C. They fit the Arrhenius expression: For k₂ ? 4.4 × 10¹¹ cm³/s, k₆ becomes (3.2 ± 2.0) × 10^?13 exp{?(836 ± 159)/T} cm³/s. The reaction scheme also provides k_4b/k₆ = 3.59 × 10¹⁸ and 5.17 × 10¹⁸ molec/cm³ at 55 and 88°C, respectively, and k_8b/k₈ = 0.66 ± 0.12 independent of temperature, where      

Mechanism of catalytic ascorbic acid oxidation system Cu2+–ascorbic acid–O2

Analysis is made of reported results on the kinetics and mechanism of ascorbic acid oxidation with oxygen in the presence of cupric ions. The diversities due to methodological reasons are cleared up. A kinetic study of the mechanism of Cu²⁺ anaerobic reaction with ascorbic acid (DH₂) is carried out. The true kinetic regularities of catalytic ascorbic acid oxidation with oxygen are established at 2.7 ≤ pH < 4, 5 × 10^?4 ≤ [DH₂] ≤ 10^?2M, 10^?4 ≤ [Cu²⁺] ≤ 10^?3M, and 10^?4 ≤ [O₂] ≤ 10^?3M: where??₁ (25°C) = 0.13 ± 0.01 M^?0.5˙sec^?1. The activation energy for this reaction is E₁ = 22 ± 1 kcal/mol. It is found by means of adding Cu⁺ acceptors (acetonitrile and allyl alcohol) that the catalytic process is of a chain nature. The Cu⁺ ion generation at the interaction of the Cu²⁺ ion with ascorbic acid is the initiation step. The rate of the chain initiation at [Cu²⁺] ± 10^?4M, [DH₂] ± 10^?2M, 2.5 < pH < 4, is where??_i,1 (25°C) = (1.8 ± 0.3)M^?1˙sec^?1, E_i,1 = 31 ± 2 kcal/mol. The reaction of the Cu⁺ ion with O₂ is involved in a chain propagation, so that the rate of catalytic ascorbic acid oxidation for the system Cu²⁺? DH₂? O₂ is where??₁ (25°C) = (5 ± 0.5) × 10⁴ M^?1˙sec^?1. The Cu⁺ ion and a species interacting with ascorbate are involved to quadratic chain termination. By means of photochemical and flow electron spin resonance methods we obtained data characteristic of the reactivities of ascorbic acid radicals and ruled out their importance for the catalytic chain process. A new type of chain mechanism of catalytic ascorbic acid oxidation with oxygen is proposed: .     

Pyrolysis of 1-chloro-1,1-difluoroethane in the absence and in the presence of CCl4 and mixtures of CCl4 + HCl

The thermal dehydrochlorination CF₂ClCH₃ → CF₂ ? CH₂ + HCl has been studied in a static system between 637 and 758 K. It is a homogeneous, molecular first-order reaction and its rate constant is given by This reaction has also been studied in the presence of CCl₄ and mixtures of CCl₄ and HCl between 585 and 662 K. It is then accelerated and the initial rate increase is given by with log₁₀ (k′, L^½ /mol^½ · s) = ?(41,650 ± 180)/4.576T + (10.84 ± 0.06) and log₁₀ k″ = (7900 ± 180)/4.576T ? (0.59 ± 0.06). A radical chain mechanism is shown to be consistent with these latter results.     

Kinetics of the thermal decomposition of bis-pentafluorosulfur trioxide(SF5O3SF5) in the presence of carbon monoxide

The thermal decomposition of SF₅O₃SF₅ in the presence of CO has been investigated between -9.8°C and + 9.9°C. Besides traces of S₂F₁₀, equimolecular amounts of SF₅O₂SF₅ and CO₂ are formed. The reaction is homogeneous. Its rate is proportional to the pressure of the trioxide and in dependent of the total pressure, the pressure of inert gases and of carbon monoxide: where k = k_1∞ = 10^16.32±0.40 exp(?25,300 ± 500 cal)/RT sec^?1. Consequently, In the presence of oxygen a sensitized CO₂ formation is observed. A mechanism is given which explains the experimental results.