Mechanism and kinetics of the reaction between hydrogen iodide and ozone

The reaction between hydrogen iodide and ozone at 295 K has been investigated by the resonance fluorescence method applied to the detection of iodine atoms. A chain mechanism is suggested for this reaction. The chain initiation rate constant is k ₁ = (5.45 ± 1.80) × 10^?17 cm³/s, and the chain propagation rate constant is k ₃ = (1.1 ± 0.4) × 10^?12 cm³/s.     

Absolute rate constants for the gas‐phase ozonolysis of isoprene and methylbutenol

The reactions of the biogenic organic compounds isoprene and 2‐methyl‐3‐buten‐2‐ol (MBO) with ozone have been investigated under controlled conditions for pressure (atmospheric pressure) and temperature (293 ± 2 K), using FTIR spectrometry. CO was added to scavenge hydroxyl radical formation during the ozonolysis experiments. Reaction rate constants were determined by absolute rate technique, by measuring both ozone and the organic compound concentrations. The measured values were k₁ = (1.19 ± 0.09) × 10^?17 cm³ molecule^?1 s^?1 for the reaction between ozone and isoprene and k₂ = (8.3 ± 1.0) × 10_?18 cm³ molecule^?1 s^?1 for the reaction between ozone and MBO. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 152–156 2004     

Gas‐Phase Reaction of Monomethylhydrazine with Ozone: Kinetics and OH Radical Formation

The gas‐phase reaction of monomethylhydrazine (CH₃NH? NH₂; MMH) with ozone was investigated in a flow tube at atmospheric pressure and a temperature of 295 ± 2 K using N₂/O₂ mixtures (3–30 vol% O₂) as the carrier gas. Proton transfer reaction–mass spectrometry (PTR‐MS) and long‐path FT‐IR spectroscopy served as the main analytical techniques. The kinetics of the title reaction was investigated with a relative rate technique yielding k_MMH+O3 = (4.3 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1. Methyldiazene (CH₃N?NH; MeDia) has been identified as the main product in this reaction system as a result of PTR‐MS analysis. The reactivity of MeDia toward ozone was estimated relative to the reaction of MMH with ozone resulting in k_MeDia+O3 = (2.7 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1. OH radicals were followed indirectly by phenol formation from the reaction of OH radicals with benzene. Increasing OH radical yields with increasing MMH conversion have been observed pointing to the importance of secondary processes for OH radical generation. Generally, the detected OH radical yields were definitely smaller than thought so far. The results of this study do not support the mechanism of OH radical formation from the reaction of MMH with ozone as proposed in the literature.     

Kinetics of the I2-catalyzed isomerization of allyl chloride to cis- and trans-1-chloro-1-propene. The stabilization energy of the chloroallyl radical

The I₂-catalyzed isomerization of allyl chloride to cis- and trans- l-chloro-l-propene was measured in a static system in the temperature range 225–329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M^?1 sec^?1] = (10.5 ± 0.2) ?; (18.3 ± 10.4)/θ, where θ is 2.303RT in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH⁰ (CH₂CHCHCl? H) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH⁰ (CH₂CHCHF? H) = 88.6 ± 1.1 and DH⁰ (CH₂CHCHBr? H) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the C? H bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α-halogen atoms than from differences in the unsaturated systems.     

A laser flash photo lysis-resonance fluorescence kinetic study: Reaction of O(3P) with O3

The laser flash photolysis of ozone at ≈ 6000 Å has been used to generate a clean kinetic source of ground state atomic oxygen, O(³P). The decay of O(³P) due to reaction with O₃ was monitored via resonance fluorescence at 1300 Å, under static reaction cell conditions. Over the temperature range of 220–353°K, the bimolecular rate constant, k₁, could be expressed in Arrhenius form as: k₁ = (2.02 ± 0.19) × 10^?11 exp[-(4522 ± 210 kcal/mole)/RT]. Units are in cm³molec^?1 sec^-1. A comparison of the results from this work with other recent investigations, indicates that the reliability of k₁ is now probably as good as 10–15% over nearly 300 degrees.     

A kinetic study of the reactions of the hydrogen atom with the cyclohexadiene isomers in the gas phase

Absolute values of the rate constants for the reaction of hydrogen atoms with cyclic olefins in the gas phase have been measured in a discharge-flow system under 3.5, 16, and 22 torr Ar at 23°C. The attenuation of hydrogen atom concentration in the reaction tube in the presence of a large excess of olefin was measured with an ESR spectrometer, and the products were analyzed by gas chromatography. Cyclic C₆ hydrocarbons were the only significant products obtained when the hydrogen atom concentration was 2.6 × 10^?10 mole/1., the olefin concentration was in the range of 9 to 22 × 10^?8 mole/1., and the pressure was 16 torr Ar. The values for the rate constants for reaction with cyclohexadiene-1,3, cyclohexadiene-1,4, and cyclohexene are, respectively, (9 ± 2) × 10⁸, (12 ± 1) × 10⁸, and (6 ± 1) × 10⁸ l./mole-sec, and they are not changed significantly by a sixfold change in total pressure. The fraction of the total interaction that proceeds by addition is 84% in the cyclohexadiene-1,3 system, but only 18% in the cyclohexadiene-1,4 system, and the cyclohexadienyl radical is therefore the dominant radical species in the latter system. The pattern of interaction between the hydrogen atom and the cyclohexadienyl radical was determined, and comprises 65% of disproportionation, and 13% and 23% of combination to yield cyclohexadiene-1,3 and cyclohexadiene-1,4, respectively. These results are consistent with the general patterns of reactivity emerging from studies of the reactions between free radicals and olefins in related systems.     

The dissociation of 3-chloro-1-butene and the resonance energy of the chloro-allyl radical

Methane is a primary product of pyrolysis of 3-chloro-l-butene at temperatures in the range 776–835°K, and from its rate of formation values have been obtained for the limiting high-pressure rate constant of the reaction These may be represented by the expression log [(k₁)_∞/sec^?1] = (16.7 ± 0.3) ? (71.5 ± 1.5)/θ, where θ = 2.303RT kcal/mole. Assuming a zero activation energy for the reverse reaction and that over the experimental temperature range the rates at which a methyl radical adds on to chlorobutene are comparable to those at which it abstracts hydrogen, the activation energy for the dissociation reaction leads to a value of 83.2 ± 1.9 ckal/mole for D(H? CHClCH:CH₂) at 298°K. Taking D(H? CHClCH₂CH ₃) = 95.2 ± 1.0 kcal/mole a value of 12.0 ± 2.1 kcal/mole is obtained for the resonance energy of the chloroallyl radical. This value in conjunction with resonance energies obtained in earlier work indicates that substitution of a hydrogen atom on the carbon atom adjacent to the double bond in the allyl radical leads to no significant variation in the allylic resonance energy.     

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.     

Decomposition of meta- and para-phenylphenol during ozonation process

The decomposition of meta-phenylphenol (m-PP) and para-phenylphenol (p-PP) in a heterogeneous gas-liquid system using ozone was investigated. The influence of different reaction parameters such as ozone and PP isomers concentration as well as pH and temperature of the reaction mixture on the PP decay rate was determined. The second-order rate constants for the direct reaction of molecular ozone, determined in a homogeneous system, were (5.85 ± 0.35) × 10² M^?1 s^?1 and (8.90 ± 0.33) × 10² M^?1 s^?1 for m-PP and p-PP, respectively. The rate constants for the reaction of m-PP and p-PP with ozone increased with increasing pH. The reaction rate constants with ozone were found to be (1.75 ± 0.02) × 10⁹ M^?1 s^?1 and (1.86 ± 0.02) × 10⁹ M^?1 s^?1 for m-PP and p-PP anions, respectively.     

The kinetics of complex formation between Ti(IV) and hydrogen peroxide

The kinetics of the formation of the titanium‐peroxide [TiO²⁺₂] complex from the reaction of Ti(IV)OSO₄ with hydrogen peroxide and the hydrolysis of hydroxymethyl hydroperoxide (HMHP) were examined to determine whether Ti(IV)OSO₄ could be used to distinguish between hydrogen peroxide and HMHP in mixed solutions. Stopped‐flow analysis coupled to UV‐vis spectroscopy was used to examine the reaction kinetics at various temperatures. The molar absorptivity (ε) of the [TiO²⁺₂] complex was found to be 679.5 ± 20.8 L mol^?1 cm^?1 at 405 nm. The reaction between hydrogen peroxide and Ti(IV)OSO₄ was first order with respect to both Ti(IV)OSO₄ and H₂O₂ with a rate constant of 5.70 ± 0.18 × 10⁴ M^?1 s^?1 at 25°C, and an activation energy, E_a = 40.5 ± 1.9 kJ mol^?1. The rate constant for the hydrolysis of HMHP was 4.3 × 10^?3 s^?1 at pH 8.5. Since the rate of complex formation between Ti(IV)OSO₄ and hydrogen peroxide is much faster than the rate of hydrolysis of HMHP, the Ti(IV)OSO₄ reaction coupled to time‐dependent UV‐vis spectroscopic measurements can be used to distinguish between hydrogen peroxide and HMHP in solution. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 457–461, 2007     

Heterogeneous oxidation reaction of gas‐phase ozone with anthracene in thin films and on aerosols by infrared spectroscopic methods

In this paper, a real‐time laboratory study of the heterogeneous oxidation reaction of gas‐phase ozone with anthracene on surface substrates by using infrared spectroscopy in two distinctly different experimental configurations is reported. One set of kinetic measurements was made by attenuated total internal reflection infrared (ATR‐IR) spectroscopy using approximately 75‐nm films of anthracene adsorbed on ZnSe, for which the reactive uptake coefficient was determined to be (2.0 ± 1.1) × 10^?7. Using an aerosol flow tube coupled to an infrared spectrometer (AFT‐IR), similar measurements were made on (NH₄)₂SO₄ (ammonium sulfate) aerosols coated with a 0.1‐μm film of anthracene. The aerosol kinetic results as a function of the ozone concentration are consistent with a Langmuir–Hinshelwood‐type mechanism, for which the ozone‐partitioning coefficient was K = (1.4 ± 1.7) × 10^?16 cm³ molecule^?1, and the maximum pseudo‐first‐order rate coefficient was k^I_max = (0.035 ± 0.016) s^?1. Infrared spectroscopic and mass spectrometric analysis of the ozonolysis reaction in the bulk phase identified the main ozonolysis products as dihydroxyanthrones, 9,10‐endoperoxide–anthracene, 9,10‐anthraquinone, and anthrone. Larger products were also seen in the mass spectra, most likely the result of secondary product and oligomer formation. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 694–707, 2011     

Rate constants for the gas-phase reactions of Ozone with unsaturated Aliphatic Alcohols

The gas-phase reaction of ozone with unsaturated alcohols in air has been investigated at atmospheric pressure and ambient temperature (288–291 K). Cyclohexane was added to scavenge the hydroxyl radical which forms as a product of the ozone–unsaturated alcohol reaction. The reaction rate constants, in units of 10^?18 cm³ molecule^?1 s^?1, are 16.2 ± 0.7 for (±) 3-buten-2-ol, 17.9 ± 1.8 for 1-penten-3-ol, 10.0 ± 0.3 for 2-methyl-3-buten-2-ol, 169 ± 25 for cis-2 penten-1-ol, and 251 ± 41 for 2-buten-1-ol (mixture of isomers). Substituent effects on reactivity are discussed. The reactivity of unsaturated alcohols towards ozone is similar to that of their alkene structural homologues. Implications of these results with respect to the atmospheric persistence of unsaturated alcohols are briefly discussed. © 1994 John Wiley & Sons, Inc.     

Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acid

The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm^?3 hydrochloric acid. The reaction proceeds with the formation of an ion‐pair between peroxydisulphate and chloride ion as the Michealis–Menten plot was linear with intercept. The ion‐pair thus formed oxidizes AuCl₂^? in a slow two‐electron transfer step without any formation of free radicals. The ion‐pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm^?3 mol^?1 and 5.0 ± 1.0 × 10^?2 dm³ mol^?1 s^?1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl₂, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm³ mol^?1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589–594, 2002     

Rate coefficient for the reaction of CCl3 radicals with ozone

The rate coefficient for the reaction of CCl₃ radicals with ozone has been measured at 303 ± 2 K. The CCl₃ radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl₃ concentration was monitored with a photoionization mass spectrometer. Addition of the O₃–O₂ mixture to this system caused a decay of the CCl₃ concentration because of the reactions of CCl₃ + O₃ → products (5) and CCl₃ + O₂ → products (4). The decay of signals from the CCl₃ radical was measured in the presence and absence of ozone. In the absence of ozone, the O₃–O₂ mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl₃ + O₂ could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10^?13 cm³ molecule^?1 s^?1 and was also found to be independent of the total pressure (253–880 Pa of N₂). This result shows that the reaction of CCl₃ with O₃ cannot compete with its reaction with O₂ in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003     

Rate constants for the gas-phase reaction of C5?C10 alkenes with ozone

The gas-phase reaction of ozone with C₅? C₁₀ alkenes(eight 1-alkenes, four 1,1-disubstituted alkenes, and cyclohexene) has been investigated at atmospheric pressure and ambient temperature (285–293 K). Cyclohexane was added to scavenge the hydroxyl radical, which forms as a product of the ozone-alkene reaction. The reaction rate constants, in units of 10^?18 cm³ molecule^?1 s^?1, are 9.6±1.6 for 1-pentene, 9.7±1.4 for 1-hexene, 9.4±0.4 for 1-heptene, 12.5±0.4 for 1-octene, 8.0±1.4 for 1-decene, 3.8±0.6 for 3-methyl-1-pentene, 7.3±0.7 for 4-methyl-1-pentene, 3.9±0.9 for 3,3-dimethyl-1-butene, 13.3±1.4 for 2-methyl-1-butene, 12.5±1.1 for 2-methyl-1-pentene, 10.0±0.3 for 2,3-dimethyl-1-butene, 13.7±0.9 for 2-ethyl-1-butene, and 84.6±1.0 for cyclohexene. Substituent effects on alkene reactivity are examined. Steric effect appear to be important for all 1,1-disubstituted alkenes as well as for those 1-alkenes that bear s-butyl and t-butyl groups. The results are briefly discussed with respect to the atomospheric persistence of the alkenes studied. © 1995 John Wiley & Sons, Inc.     

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.     

Reaction of tetramethyl-1,2-dioxetane with triphenylphosphine: Activation parameters for the formation of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane

The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d₆ produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS^≠ = ?28 eu; k_30° = 1.8 m^?1sec^?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS^≠ = ?24 eu, k_30° = 1.3 M^?1sec^?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS^≠ = ?29 eu, k_30° = 4.9 M^?1 sec^?1.     

Oxidative decomposition of oxalate ion with ozone in aqueous solution

The oxidation of oxalate ions with ozone in aqueous solution has been studied, and the effects of pH, temperature, and reactant concentrations on the reaction rate and efficiency have been estimated. The oxidative decomposition is most effective in alkaline medium (pH ≥ 10) at 50°C. Under these conditions, the consumption of ozone is 0.6±0.1 g per gram of oxalate or 1.1±0.1 mol per mole of oxalate, which corresponds to the stoichiometry (COO^–)₂ + O₃ + H₂O → 2CO₃^2– + O₂ + 2H⁺.     

A flash photolysis–resonance fluorescence kinetics study of the reactions of ground-state sulfur atoms. V. Rate parameters for the reaction of S(3P)with cis-2-butene and tetramethylethylene

Rate parameters for the reaction of ground-state atomic sulfur, S(³P), with the olefins cis-2-butene and tetramethylethylene have been determined over a temperature range of ∽280°K. A major finding of this study was that the rate constants for both reactions showed negative temperature dependencies. When k is expressed in the form of an Arrhenius equation, this necessarily leads to negative activation energies: k₁ = (4.68 ± 0.70) × 10^?12 exp ^{(+0.23 ± 0.09 kcal/mole)/RT} (219°-500°K) k₂ = (4.68 ± 1.70) × 10^?12 exp ^{(+1.29 ± 0.23 kcal/mole)/RT} (252°-500°K) Units are cm³ molec^?1s^?1. When a threshold energy of 0.0 kcal/mole is assumed for reaction (2), the temperature dependence of the preexponential term has a value of T^?2. Making the usual simplifying assumptions, neither collision theory nor transition state theory leads to a preexponential factor with a strong enough negative temperature dependence. A comparison of these results with those derived from studies of the reactions of atomic oxygen, O(³P), with the same olefins shows that in both studies simple bimolecular processes were being examined. Also discussed are the possible experimental and theoretical ramifications of these new results.     

Different effects of active minor admixtures on hydrogen and methane ignitions

The methane combustion inhibitor CCl₄ exerts no effect on the first ignition limit of hydrogen; therefore, the role of hydrogen atoms in hydrocarbon oxidation consists at least of participating in longer reaction chains than are observed in hydrogen oxidation. The upper limits of the rate constants of the reactions of hydrogen atoms with propylene and isobutylene molecules were estimated by the self-ignition limit method to be (1.0 ± 0.3) × 10^?11 exp(?1450 ± 400/T) and (0.8 ± 0.3) × 10^?11 exp(?550 ± 200/T) cm³ molecule^?1 s^?1, respectively, in the temperature range of 840–950 K. These data are evidence that the stronger inductive effect of the two methyl groups in isobutylene lowers the energy barrier to the H + iso-C₄H₈ reaction. It has been demonstrated experimentally that chemiluminescence in the hydrocarbon flame front at atmospheric pressure precedes heat evolution. Throughout the pressure and temperature ranges examined (5–750 Torr, 298–950 K), the chain mechanism determines the basic laws of combustion.