The thermal isomerization of 1,1-dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene via 1,5-hydrogen migration

The gas phase isomerization of 1,1-dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene has been studied in a static system. The isomerization is homogeneous and kinetically first order. The rate constants were independent of initial reactant pressure in the range 0.6 to 2 torr and of added nitrogen up to 180 torr. Rate constants determined at 10 temperatures in the range 200 to 254°C fitted the Arrhenius equation k = 10^11.41±0.02 exp (?33,540 ± 47 cal/RT) sec^?1 The low A factor and activation energy are consistent with a concerted 1,5-hydrogen migration via a “tight” cyclic transition complex.     

Study of thermal decomposition of poly(vinyl chloride) type polymers with the use of model substances—III: Gas phase pyrolysis of acetates

The decompositions of the following poly(vinylacetate) models were investigated in the gas phase: 2-acetoxypentane (in the range 323–380°), meso and racem. 2,4-diacetoxypentane (325–375°), 4-acetoxy-1-pentene (302–375°), 4-acetoxy-2-pentene (314–381°), 5-acetoxy-2-hexene (328–391°), and 7-acetoxy-3,5-nonadiene (299–361°). The decompositions are homogeneous unimolecular first-order reactions with rate constants of 1·04 × 10¹³ exp(?45·/RT, 1·63 × 10¹³ exp(?45·4/RT), 1·01 × 10¹³ exp(?44·5/RT), 5sd76 × 10¹² exp(?42·8/RT), 2·01 × 10¹³ exp(?45·5/RT), and 3·29 × 10¹² exp(?41·5/RT) sec^?1, respectively. The two 2,4-diacetoxypentane stereoisomers decompose at almost the same rate. From the course of decomposition of models in the gas phase, possible conclusions about decomposition of polymer are drawn. The role of configuration of sequences, double bonds, their number and geometric isomerism in the macromolecular chains are discussed in connection with elimination of acetic acid from poly(vinyl acetate).     

Kinetics of the reaction of cyclopentane with trichloroethylene

The kinetics of the thermally and radiation initiated chain reaction between trichloroethylene and cyclopentane to produce 1,1-dichlorovinylcyclopentane and hydrogen chloride have been investigated in the temperature range 250–360°C at high pressure in the gas phase. The rate governing step in the chain is (k₃ = 3.3 × 10⁹ exp ?(4800/RT) cc mole^?1 sec ^?1). The rate of the unimolecular decomposition of trichloroethylene is 1.4 × 10¹⁴ exp ?(61,200/RT) sec^?1.     

Thermal decomposition of trimethylene sulfone and 3-methyl sulfolane

Trimethylene sulfone and 3? methyl sulfolane have been pyrolyzed using a modification of the toluene flow method and a comparative rate technique. The main decomposition reactions are where k₁=10^16.1±0.3 exp(?28,100±500/T) sec^?1 and k₂=10^16.1±0.4 exp(?33,200±750/T) sec^?1.     

Temperature dependence of the reaction rate constants for O(3P) atoms with C2H4, C3H6 and NO(M = N2O), determined by a modulation technique

Rate constants for the reaction of O(³P) atoms with C₃H₄, C₃H₆ and NO(M = N₂O) have been measured over the temperature range 300–392°K using a modulation-phase shift technique. The Arrhenius expressions obtained are:C₂H₄, k₂ = 3.37 × 10⁹ exp[?(1270 ± 200)/RT]liter mole^?1 sec^?1,C₃H₆, k₂ = 2.08 × 10⁹ exp[?(0 ± 300)/RT]liter mole^?1 sec^?1,NO(M = N₂O), k₁ = 9.6 × 10⁹ exp[(900 ± 200/RT]liter² mole^?2 sec^?1.These temperature dependencies of k₂ are in good agreement with recent flash photolysis-resonance flourescence measurements, although lower than previous literature values.     

Rate constants for the reactions of conjugated olefins with NO2 in the gas phase

Gas-phase rate constants for the reaction of NO₂ with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono-olefins by factors of 10³–10⁴. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies: k_{1,3-cyclohexadiene} = 5.8 × 10^?14 exp[?(6.1 ± 1.6)/RT] cm³ molecule^?1 s^?1; k_cis-2-butene = 4.68 × 10^?14 exp(?11.2/RT) cm³ molecule^?1 s^?1 [2]. A linear free energy relationship between the reactions of OH and NO₂ with conjugated diolefins was observed.     

High temperature pyrolysis of 1,5-cyclooctadiene and 4-vinylcyclohexene in shock waves

1,5-cyclooctadiene or 4-vinylcyclohexene mixture diluted with argon was heated to temperatures in the range 880–1230 K behind reflected shock waves. Profiles of IR-laser absorption were measured at 3.39 μm. From these profiles, rate constants k₁ and k₂ for the decyclization reactions 1,5-cyclooctadiene → biradical and 4-vinylcyclohexene → biradical were evaluated as k₁ = 5.2 × 10¹⁴ exp(?48.3 kcal/RT) s^?1 and k₂ = 3.5 × 10¹⁴ exp(?55.3 kcal/RT) s^?1, respectively. © 1993 John Wiley & Sons, Inc.     

Anionic polymerization with alkaline earth counterion. III. Aging of oligo- and polystyryl-barium and -strontium in THF

The self-deactivation of polystyryl-barium and polystyryl-strontium in tetrahydrofuran (THF) results essentially from protonation by the solvent. The deactivation constant k_d of this reaction is independent of carbanion concentration, length, and functionality of chains. Relations of k_d with temperature are: polystyryl-barium: k_d = 6.25 × 10⁷ exp(-18,900/RT) sec^?1; polystyryl-strontium: k_d = 4.1 × 10⁶ exp(?16,000/RT) sec^?1. The self-deactivation of α,ω-dicarbanionic oligostyryl-barium is a nonrandomlike reaction. Residual living oligomers are left dicarbanionic even if an important deactivation occurs.     

Thermal decomposition of chlorofluoromethyl peroxynitrates

The thermal decomposition of CCl₃O₂NO₂,CCl₂FO₂NO₂, and CClF₂O₂NO₂ was studied in a temperature-controlled 420 l reaction chamber using in situ detection of peroxynitrates by long-path IR absorption. The temperature dependence of the unimolecular dissociation rate constants was determined at total pressures of 10 and 800 mbar in nitrogen as buffer gas, and the pressure dependence was measured at 273 K between 10 and 800 mbar. In Troe's notation, the data are represented by the following values for the limiting low and high pressure rate constants k₀/[N₂] and k_∞ and the fall-off curvature parameter F_c (in units of cm³ molecule^?1 s^?1, s^?1): CCl₃O₂NO₂,k₀/[N₂] = 6.3 × 10^?3 exp(?85.1 kJ · mol^?1/RT), k_∞ = 4.8 × 10¹⁶ exp(?98.3 kJ · mol^?1/RT), F_c = 0.22; CCl₂FO₂NO₂, k₀/[N₂] = 1.01× 10^?2 exp(?90.3 kJ · mol^?1/RT), k_∞ = 6.6 × 10¹⁶ exp(?101.8 kJ · mol^?1/RT), F_c = 0.28; and CClF₂O₂NO₂, k₀/[N₂] = 1.80 × 10^?3 exp(?87.3 kJ · mol^?1/RT), k_∞ = 1.60 × 10¹⁶exp(?99.7 kJ · mol^?1/RT), F_c = 0.30. From these dissociation rate constants and recently measured rate constants for the reverse reaction (see Caralp, Lesclaux, Rayez, Rayez, and Forst [19]), bond energies (=ΔH) of 100, 103, and 104 kJ/mol were derived for the RO₂–NO₂ bonds in CCl₃O₂NO₂, CCl₂FO₂NO₂, and CClF₂O₂NO₂, respectively. The kinetic and thermochemical parameters of these decomposition reactions are compared with those of the dissociation of other peroxynitrates. Atmospheric implications of the thermal stability of chlorofluoromethyl peroxynitrates are briefly discussed.     

Temperature dependence of the reactions of HO2 with NO and NO2

Mixtures of N₂O, H₂, O₂, and trace amounts of NO and NO₂ were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H₂). HO₂ radicals are produced from the photolysis and they react as follows: Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k_1a/k₃^1/2 = 6.4 × 10^?6 exp { z?(1400 ± 500)/RT} cm^3/2/sec^1/2. If k₃ is taken to be 3.3 × 10^?12 cm³/sec independent of temperature, k_1a = 1.2 × 10^?11 exp {?(1400 ± 500)/RT} cm³/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k_2b/k₁ = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k_1a given above leads to k_2b = 4.2 × 10^?13 cm³/sec, which is assumed to be independent of temperature. The intermediate HO₂NO₂ is unstable and induces the dark oxidation of NO through reaction (?2b), which was found to have a rate coefficient k_?2b = 6 × 10¹⁷ exp {?26,000/RT} sec^?1 based on the value of k_1a given above. The intermediate can also decompose via Reaction (10b) is at least partially heterogeneous.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5-trioxane between 290 and 600 K

Absolute rate constants are measured for the reactions: OH + CH₂O, over the temperature range 296–576 K and for OH + 1,3,5-trioxane over the range 292–597 K. The technique employed is laser photolysis of H₂O₂ or HNO₃ to produce OH, and laser-induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH₂O) = (1.66 ± 0.20) × 10^?11 exp[?(170 ± 80)/RT] cm³ s^?1 and k(1,3,5-trioxane) = (1.36 ± 0.20) × 10^?11 exp[?(460 ± 100)/RT] cm³ s^?1. The transition-state theory is employed to model the OH + CH₂O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH₂O) = 1.2 × 10^?18 T^2.46 exp(970/RT) cm³ s^?1. An estimate of 91 ± 2 kcal/mol is obtained for the first C? H bond in 1,3,5-trioxane by using a correlation of C? H bond strength with measured activation energies.     

The Gas-phase thermal unimolecular isomerization of n-propylidenecyclopropylamine to 5-ethyl-1-pyrroline

The gas-phase thermal isomerization of N-propylidenecyclopropylamine has been studied in the temerature range of 573° to 635°K. The reaction is homogeneous and kinetically first order and yields 5-ethyl-1-pyrroline as the sole product. The rate constants are independent of pressure in the range of 2.5 to 55 torr and fit the Arrhenius relationship log k(sec^?1) = (14.05 ± 0.06) - (47.77 ± 0.16)/θ where θ = 2.303 RT in units of kcal/mole, or log k(sec^?1) = (14.05 ± 0.06) - (199.9 ± 0.7)/θ, where θ = 2.303RT in kJ/mole. From considerations of a biradical pathway it is concluded that the resonance stabilization energy of the substituted 2-aza-allyl radical is very similar to that of the methallyl radical.     

Neighboring olefinic double-bond participation in gas phase pyrolysis of some alkenyl chlorides

4-Chloro-1-butene, 5-chloro-1-pentene, and 6-chloro-1-hexene have been shown to decompose, in a static system, mainly to hydrogen chloride and the corresponding alkadienes. In packed and unpacked clean Pyrex vessels the reactions were significantly heterogeneous. However, in a vessel seasoned with allyl bromide these reactions were homogeneous, unimolecular, and follow a first-order law. The working temperature range was 389.6–480.0°C and with a pressure range of 53–221 Torr. The rate constants for the homogeneous reactions were expressed by the following Arrhenius equations: 4-chloro-1-butene: logk(sec^?1) = (13.79 ± 0.17) – (223.8 ± 2.1)kJ/mole/2.303RT; 5-chloro-1-pentene: logk(sec^?1) = (14.25 ± 1.20) – (238.4 ± 12.7)kJ/mole/2.303RT; and 6-chloro-1-hexene: logk(sec^?1) = (12.38 ± 0.22) – (209.6 ± 2.9)kJ/mole/2.303RT. The olefinic double bond has been found to participate in the rate of dehydrohalogenation of 4-chloro-1-butene. The insulation of the CH₂?CH in chlorobutene by one or two methylene chains to the reaction center does not indicate neighboring group participation. The three-membered conformation is the most favored structure for anchimeric assistance of the double bond in gas phase pyrolysis of alkenyl chlorides. The heterolytic nature of these eliminations is also supported by the present work.     

The reaction of OH with NO2 and the deactivation of O(1D) by CO

NO₂ was photolyzed with 2288 Å radiation at 300° and 423°K in the presence of H₂O, CO, and in some cases excess He. The photolysis produces O(¹D) atoms which react with H₂O to give HO radicals or are deactivated by CO to O(³P) atoms The ratio k₅/k₃ is temperature dependent, being 0.33 at 300°K and 0.60 at 423°K. From these two points, the Arrhenius expression is estimated to be k₅/k₃ = 2.6 exp(?1200/RT) where R is in cal/mole – °K. The OH radical is either removed by NO₂ or reacts with CO The ratio k₂/k^α is 0.019 at 300°K and 0.027 at 423°K, and the ratio k₂/k⁰ is 1.65 × 10^?5M at 300°K and 2.84 × 10^?5M at 423°K, with H₂O as the chaperone gas, where k^α = k₁ in the high-pressure limit and k⁰[M] = k₁ in the low-pressure limit. When combined with the value of k₂ = 4.2 × 10⁸ exp(?1100/RT) M^?1sec^?1, k^α = 6.3 × 10⁹ exp (?340/RT)M^?1sec^?1 and k⁰ = 4.0 × 10¹²M^?2sec^?1, independent of temperature for H₂O as the chaperone gas. He is about 1/8 as efficient as H₂O.     

Study of the reactions of oxygen atoms with carbonothioicdichloride,carbonothioicdifluoride, and tetrafluoro-1,3-dithietane

The reactions of ground-state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro-1,3-dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast-flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants are??(O + C₂CS) =(3.09 ± 0.54) × 10^?11 exp(+115 ± 106 cal/mol/RT),??(O + F₂CS) = (1.22 ± 0.19) × 10^?11 exp(-747 ± 95 cal/mol/RT), and??(O + F₄C₂S₂) = (2.36 ± 0.52) × 10^?11 exp(-1700 ± 128 cal/mol/RT) cm³/molec˙sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy-rich adduct which then decomposes by C-S bond cleavage.     

The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2

The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO₂ to determine rate constants k₁ and k₂ in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k₁(sec^?1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k₂ ≈ 5 × 10⁴M^?1· sec^?1. The disproportionation/recombination ratio k_7b/k_7a = 0.30 ± 0.05 was also determined: When O₂ was added to DMP mixtures containing NO₂, relative rate constants k₁₂/k_7a were obtained over the temperature range of 396–442°K: A review of literature data produced k_7a = 10^9.8±0.5M^?1·sec^?1, giving log k₁₂(M^?1·sec^?1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.     

Ozone–olefin reactions in the gas phase 1. Rate constants and activation energies

Reactions of ozone with simple olefins have been studied between 6 and 800 mtorr total pressure in a 220-m³ reactor. Rate constants for the removal of ozone by an excess of olefin in the presence of 150 mtorr oxygen were determined over the temperature range 280 to 360° K by continuous optical absorption measurements at 2537 Å. The technique was tested by measuring the rate constants k₁ and k₂ of the reactions (1) NO + O₃ → NO₂ + O₂ and (2) NO₂ + O₃ rarr; NO₃ + O₂ which are known from the literature. The results for NO, NO₂, C₂H₄, C₃H₆, 2-butene (mixture of the isomers), 1,3→butadiene, isobutene, and 1,1 -difluoro-ethylene are 1.7 × 10^{?1 4} (290°K), 3.24 × 10^?17 (289°K), 1.2 × 10^{?1 4} exp (–4.95 ± 0.20/RT), 1.1 × 10^{?1 4} exp (–3.91 ± 0.20/RT), 0.94 × 10^{?1 4} exp ( –2.28 ± 0.15/RT), 5.45 ± 10^{?1 4} exp ( –5.33 ± 0.20/RT), 1.8 ×10^?17 (283°K), and 8 × 10^?20 cm³/molecule ·s(290°K). Productformation from the ozone–propylene reaction was studied by a mass spectrometric technique. The stoichiometry of the reaction is near unity in the presence of molecular oxygen.     

Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K

The kinetics of the gas-phase reaction of Cl atoms with CF₃I have been studied relative to the reaction of Cl atoms with CH₄ over the temperature range 271–363 K. Using k(Cl + CH₄) = 9.6 × 10^?12 exp(?2680/RT) cm³ molecule^?1 s^?1, we derive k(Cl + CF₃I) = 6.25 × 10^?11 exp(?2970/RT) in which E_a has units of cal mol^?1. CF₃ radicals are produced from the reaction of Cl with CF₃I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C₂F₅I)/k(Cl + CF₃I) = 11.0 ± 0.6 and k(Cl + C₂F₅I)/k(Cl + C₂H₅Cl) = 0.49 ± 0.02. The reaction of CF₃ radicals with Cl₂ was studied relative to that with O₂ at pressures from 4 to 700 torr of N₂ diluent. By using the published absolute rate constants for k(CF₃ + O₂) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k₀(CF₃ + O₂) = (4.8 ± 1.2) × 10^?29 cm⁶ molecule^?2 s^?1; k_∞(CF₃ + O₂) = (3.95 ± 0.25) × 10^?12 cm³ molecule^?1 s^?1; F_c = 0.46. The value of the rate constant k(CF₃ + Cl₂) was determined to be (3.5 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 at 296 K. The reaction of Cl atoms with CF₃I is a convenient way to prepare CF₃ radicals for laboratory study. © 1995 John Wiley & Sons, Inc.     

Rate constants for the gas‐phase reactions of chlorine atoms with 1,4‐cyclohexadiene and 1,5‐cyclooctadiene at 298 K

Rate constants for the reactions of Cl atoms with two cyclic dienes, 1,4‐cyclohexadiene and 1,5‐cyclooctadiene, have been determined, at 298 K and 800 Torr of N₂, using the relative rate method, with n‐hexane and 1‐butene as reference molecules. The concentrations of the organics are followed by gas chromatographic analysis. The ratios of the rate constants of reactions of Cl atoms with 1,4‐cyclohexadiene and 1,5‐cyclooctadiene to that with n‐hexane are measured to be 1.29 ± 0.06 and 2.19 ± 0.32, respectively. The corresponding ratios with respect to 1‐butene are 1.50 ± 0.16 and 2.36 ± 0.38. The absolute values of the rate constants of the reaction of Cl atom with n‐hexane and 1‐butene are considered as (3.15 ± 0.40) × 10^?10 and (3.21 ± 0.40) × 10^{? 10} cm³ molecule^?1s^?1, respectively. With these, the calculated values are k(Cl + 1,4‐cyclohexadiene) = (4.06 ± 0.55) × 10^?10 and k(Cl + 1,5‐cyclooctadiene) = (6.90 ± 1.33) × 10^?10 cm³ molecule^?1 s^?1 with respect to n‐hexane. The rate constants determined with respect to 1‐butene are marginally higher, k(Cl + 1,4‐cyclohexadiene) = (4.82 ± 0.80) × 10^{? 10} and k(Cl + 1,5‐cyclooctadiene) = (7.58 ± 1.55) × 10^{? 10} cm³ molecule^?1 s^?1. The experiments for each molecule were repeated three to five times, and the slopes and the rate constants given above are the average values of these measurements, with 2σ as the quoted error, including the error in the reference rate constant. The relative rate ratios of 1,4‐cyclohexadiene with both the reference molecules are found to be higher in the presence of oxygen, and a marginal increase is observed in the case of 1,5‐cyclooctadiene. Benzene is identified as one major product in the case of 1,4‐cyclohexadiene. Considering that the cyclohexadienyl radical, a product of the hydrogen abstraction reaction, is quantitatively converted to benzene in the presence of oxygen, the fraction of Cl atoms that reacts by abstraction is estimated to be 0.30 ± 0.04. The atmospheric implications of the results are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 431–440, 2011