The hydroxyl radical reaction rate constant and atmospheric transformation products of 2-butanol and 2-pentanol

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of +2-butanol (2BU, CH₃CH₂CH(OH)CH₃) and 2-pentanol (2PE, CH₃CH₂CH₂CH(OH)CH₃). 2BU and 2PE react with OH yielding bimolecular rate constants of (8.1±2.0)×10⁻¹² cm³molecule⁻¹s⁻¹ and (11.9±3.0)×10⁻¹² cm³molecule⁻¹s⁻¹, respectively, at 297±3 K and 1 atmosphere total pressure. Both 2BU and 2PE OH rate constants reported here are in agreement with previously reported values [1–4]. In order to more clearly define these alcohols' atmospheric reaction mechanisms, an investigation into the OH+alcohol reaction products was also conducted. The OH+2BU reaction products and yields observed were: methyl ethyl ketone (MEK, (60±2)%, CH₃CH₂C((DOUBLEBOND)O)CH₃) and acetaldehyde ((29±4)% HC((DOUBLEBOND)O)CH₃). The OH+2PE reaction products and yields observed were: 2-pentanone (2PO, (41±4)%, CH₃C((DOUBLEBOND)O)CH₂CH₂CH₃), propionaldehyde ((14±2)% HC((DOUBLEBOND)O)CH₂CH₃), and acetaldehyde ((40±4)%, HC((DOUBLEBOND)O)CH₃). The alcohols' reaction mechanisms are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. Labeled (¹⁸O) 2BU/OH reactions were conducted to investigate 2BU's atmospheric transformation mechanism details. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground level ozone-forming potential calculations (incremental reactivity) [5]. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 745–752, 1998     

The hydroxyl radical reaction rate constant and products of methyl isobutyrate

The relative rate technique has been used to measure the rate coefficient for the reaction of the hydroxyl radical (OH) with methyl isobutyrate (MIB, (CH₃)₂ CHC(O) O CH₃) to be (1.7 ± 0.4) × 10⁻¹²cm³molecule⁻¹s⁻¹ at 297 ± 3 K and 1 atmosphere total pressure. To more clearly define MIB's atmospheric degradation mechanism, the products of the OH + MIB reaction were also determined. The observed products and their yields were: acetone (97 ± 1%, (CH₃)₂C(O)) and methyl pyruvate (MP, 3.3 ± 0.3%, CH₃C(O)C(O) O CH₃). The products' formation pathways are discussed in light of current understanding of the atmospheric chemistry of oxygenated organic compounds. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 551–557, 1999     

Kinetic study of the reaction OH + HI by laser photolysis-resonance fluorescence

The gas phase reaction of OH radicals with hydrogen iodide (HI) has been studied using a Laser Photolysis-Resonance Fluorescence (LP-RF) apparatus, recently developed in our group. The measured rate constant at 298 K was (2.7 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. This rate constant is compared with the ones of the reactions OH + HCl and OH + HBr. The role of the reaction OH + HI in marine tropospheric chemistry is discussed. In addition, the LP-RF apparatus was tested and validated by measuring the following rate constants (in cm³ molecule⁻¹ s⁻¹ units): 𝓀(OH + HNO₃) = (1.31 ± 0.06) × 10⁻¹³ at p = 27 and 50 Torr of argon and 𝓀(OH + C₃H₈) = (1.22 ± 0.08) × 10⁻¹². These rate constants are in very good agreement with the literature data.     

Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

Trimethylchlorosilane, (CH3)3SiCl: OH reaction kinetics and infrared spectrum

Rate coefficients for the OH + (CH₃)₃SiCl (trimethylchlorosilane) gas-phase reaction were measured over the temperature range 295–375 K using a pulsed laser photolysis laser-induced fluorescence technique. The room temperature rate coefficient was determined to be k₁(295 K) = (2.51 ± 0.13) × 10⁻¹³ cm³ molecule^–1 s^–1. The Arrhenius expression k₁(T) = (7.06 ± 2.15) × 10⁻¹² exp[–(992 ± 101)/T] cm³ molecule^–1 s^–1, where the quoted uncertainties are 2σ fit precision, describes the measured temperature dependence very well. As part of this work, the infrared spectra of CH₃)₃SiCl was measured.     

Kinetic studies of the self‐reaction and reaction with HO2 of a tertiary β‐brominated peroxy radical between 298 and 393 K

The kinetics of reactions of the tertiary β‐brominated peroxy radical BrC(CH₃)₂C(CH₃)₂O₂ (2‐bromo‐1,1,2‐trimethylpropylperoxy) have been studied using the laser flash photolysis technique, photolysing HBr at 248 nm in the presence of O₂ and 2,3‐dimethylbut‐2‐ene. At room temperature, a rate constant of (2.0 ± 0.8) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ was determined for the BrC(CH₃)₂C(CH₃)₂O₂ self‐reaction. The reaction of BrC(CH₃)₂C(CH₃)₂O₂ with HO₂ was investigated in the temperature range 306–393 K, yielding the following Arrhenius expression: k(BrC(CH₃)₂C(CH₃)₂O₂ + HO₂) = (2.04 ± 0.25) × 10⁻¹² exp[(501 ± 36)K/T] cm³ molecule⁻¹ s⁻¹, giving by extrapolation (1.10 ± 0.13) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 298 K. These results confirm the enhancement of the peroxy radical self‐reaction reactivity upon β‐substitution, which is similar for Br and OH substituents. In contrast, no significant effect of substituent has been observed on the rate constant for the reactions of peroxy radicals with HO₂. The global uncertainty factors on rate constants are equal to nearly 2 for the self‐reaction and to 1.35 for the reaction with HO₂. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 41–48, 2001     

A study of the self reaction of CH2ClO2 and CHCl2O2 radicals at 298 K

A low‐pressure discharge‐flow system equipped with laser‐induced fluorescence (LIF) detection of NO₂ and resonance‐fluorescence detection of OH has been employed to study the self reactions CH₂ClO₂ + CH₂ClO₂ → products (1) and CHCl₂O₂ + CHCl₂O₂ → products (2), at T = 298 K and P = 1–3 Torr. Possible secondary reactions involving alkoxy radicals are identified. We report the phenomenological rate constants (k_obs) k_1obs = (4.1 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k_2obs = (8.6 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and the rate constants derived from modelling the decay profiles for both peroxy radical systems, which takes into account the proposed secondary chemistry involving alkoxy radicals k₁ = (3.3 ± 0.7) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k₂ = (7.0 ± 1.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ A possible mechanism for these self reactions is proposed and QRRK calculations are performed for reactions (1), (2) and the self‐reaction of CH₃O₂, CH₃O₂ + CH₃O₂ → products (3). These calculations, although only semiquantitative, go some way to explaining why both k₁ and k₂ are a factor of ten larger than k₃ and why, as suggested by the products of reaction (1) and (2), it seems that the favored reaction pathway is different from that followed by reaction (3). The atmospheric fate of the chlorinated peroxy species, and hence the impact of their precursors (CH₃Cl and CH₂Cl₂), in the troposphere are briefly discussed. HC(O)Cl is identified as a potentially important reservoir species produced from the photooxidation of these precursors. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 433–444, 1999     

1,1,1,3,3,-pentafluorobutane (HFC-365mfc): atmospheric degradation and contribution to radiative forcing

The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k(OH+CF₃CH₂CF₂CH₃)=2.0×10⁻¹²exp(−1750±400/T) cm³ molecule⁻¹ s⁻¹ based on k(OH+CH₃CCl₃)=1.8×10⁻¹² exp (−1550±150/T) cm³ molecule⁻¹ s⁻¹ for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF₃CH₂CF₂CH₃)=(1.1±0.3)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The chlorine initiated photooxidation of CF₃CH₂CF₂CH₃ was investigated from 273–330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF₂O and CO₂, with smaller amounts of CF₃O₃CF₃. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH₂(SINGLE BOND) and (SINGLE BOND)CH₃ groups in CF₃CH₂CF₂CH₃, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF₃CH₂CCl₂F and CF₃CH₂CF₃ were also determined at 298 K k(OH+CF₃CH₂CCl₂F)=(8±3)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(OH+CF₃CH₂CF₃)=(3.5±1.5)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(Cl+CF₃CH₂CCl₂F)=(3.5±1.5)×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹]; k(Cl+CF₃CH₂CF₃)<1×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The results indicate that the most probable site for H-atom abstraction from CF₃CH₂CF₂CH₃ is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF₃CH₂CF₂CH₃, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO₂ are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.     

Rate coefficients for the reactions of OH with butanols from 298 K to temperatures relevant for low-temperature combustion

Rate coefficients for the reactions of OH with n, s, and iso-butanol have been measured over the temperature range 298 to ∼650 K. The rate coefficients display significant curvature over this temperature range and bridge the gap between previous low-temperature measurements with a negative temperature dependence and higher temperature shock tube measurements that have a positive temperature dependence. In combination with literature data, the following parameterizations are recommended: k_{1,OH + n-butanol}(T) = (3.8 ± 10.4) × 10⁻¹⁹T^{2.48 ± 0.37}exp ((840 ± 161)/T) cm³ molecule⁻¹ s⁻¹ k_{2,OH + s-butanol}(T) = (3.5 ± 3.0) × 10⁻²⁰T^{2.76 ± 0.12}exp ((1085 ± 55)/T) cm³ molecule⁻¹ s⁻¹ k_{3,OH + i-butanol}(T) = (5.1 ± 5.3) × 10⁻²⁰T^{2.72 ± 0.14}exp ((1059 ± 66)/T) cm³ molecule⁻¹ s⁻¹ k_{4,OH + t-butanol}(T) = (8.8 ± 10.4) × 10⁻²²T^{3.24 ± 0.15}exp ((711 ± 83)/T) cm³ molecule⁻¹ s⁻¹ Comparison of the current data with the higher shock tube measurements suggests that at temperatures of ∼1000 K, the OH yields, primarily from decomposition of β-hydroxyperoxy radicals, are ∼0.3 (n-butanol), ∼0.3 (s-butanol) and ∼0.2 (iso-butanol) with β-hydroxyperoxy decompositions generating OH, and a butene as the main products. The data suggest that decomposition of β-hydroxyperoxy radicals predominantly occurs via OH elimination.     

The hydroxyl radical reaction rate constant and atmospheric transformation products of 2‐propoxyethanol

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of 2‐propoxyethanol (2PEOH, CH₃CH₂CH₂OCH₂CH₂(OH)). 2PEOH reacts with OH with a bimolecular rate constant of (21.4 ± 6.0) × 10⁻¹² cm³molecule⁻¹s⁻¹ at 297 ± 3 K and 1 atm total pressure, which is a little larger than previously reported [1]. Assuming an average OH concentration of 1 × 10⁶ molecules cm⁻³, an atmospheric lifetime of 13 h is calculated for 2PEOH. In order to more clearly define this hydroxy ether's atmospheric reaction mechanism, an investigation into the OH + 2PEOH reaction products was also conducted. The OH + 2PEOH reaction products and yields observed were: propyl formate (PF, 47 ± 2%, CH₃CH₂CH₂OC(O)H), 2 propoxyethanal (CH₃CH₂CH₂OCH₂C(O)H 15 ± 1%), and 2‐ethyl‐1,3‐dioxolane (5.4 ± 0.4%). The 2PEOH reaction mechanism is discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground‐level ozone‐forming potential calculations (incremental reactivity) [2]. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 315–322, 1999     

Rate coefficients for the reactions of chlorine atoms with methanol and acetaldehyde

Rate coefficients have been measured for the reactions of Cl atoms with methanol (k₁) and acetaldehyde (k₂) using both absolute (laser photolysis with resonance fluorescence) and relative rate methods at 295 ± 2 K. The measured rate coefficients were (units of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹): absolute method, k₁ = (5.1 ± 0.4), k₂ = (7.3 ± 0.7); relative method k₁ = (5.6 ± 0.6), k₂ = (8.4 ± 1.0). Based on a critical evaluation of the literature data, the following rate coefficients are recommended: k₁ = (5.4 ± 0.9) × 10⁻¹¹ and k₂ = (7.8 ± 1.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ (95% confidence limits). The results significantly improve the confidence in the database for reactions of Cl atoms with these oxygenated organics. Rate coefficients were also measured for the reactions of Cl₂ with CH₂OH, k₅ = (2.9 ± 0.6) × 10⁻¹¹ and CH₃CO, k₆ = (4.3 ± 1.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, by observing the regeneration of Cl atoms in the absence of O₂. Based on these results and those from a previous relative rate study, the rate coefficient for CH₃CO + O₂ at the high pressure limit is estimated to be (5.7 ± 1.9) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 776–784, 1999     

The hydroxyl radical reaction rate constant and products of ethyl 3-ethoxypropionate

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of ethyl 3-ethoxypropionate (EEP, CH₃CH₂(SINGLE BOND)O(SINGLE BOND)CH₂CH₂C(O)O(SINGLE BOND)CH₂CH₃). EEP reacts with OH with a bimolecular rate constant of (22.9±7.4)×10⁻¹² cm³ molecule⁻¹s⁻¹ at 297±3 K and 1 atmosphere total pressure. In order to more clearly define EEP's atmospheric reaction mechanism, an investigation into the OH+EEP reaction products was also conducted. The OH+EEP reaction products and yields observed were: ethyl glyoxate (EG, 25±1% HC((DOUBLE BOND)O)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (2-formyl) acetate (EFA, 4.86±0.2%, HC((DOUBLE BOND)O)(SINGLE BOND)CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (3-formyloxy) propionate (EFP, 30±1%, HC((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl formate (EF, 37±1%, HC((DOUBLE BOND)O)O(SINGLE BOND)CH₂CH₃), and acetaldehyde (4.9±0.2%, HC((DOUBLE BOND)O)CH₃). Neither the EEP's OH rate constant nor the OH/EEP reaction products have been previously reported. The products' formation pathways are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. © 1997 John Wiley & Sons, Inc.     

Temperature dependence of the reaction of NO with CFCl2CH2O2 and CH3CFClO2 radicals

The reaction of NO with the peroxy radical CFCl₂CH₂O₂, and with CH₃CFClO₂ was investigated at 8(SINGLEBOND)20 torr and 263(SINGLEBOND)321 K by UV flash photolysis of CFCl₂CH₃/O₂/NO gas mixtures. The kinetics were determined from observations of the growth rate of the CFCl₂CH₂O radical and the decay rate of NO by time-resolved mass spectrometry. The temperature dependence of the bimolecular rate coefficients, with their statistical uncertainties, can be expressed as (2.9 ± 0.7) e^(435±96)/T × 10⁻¹² cm³ molecule ⁻¹s⁻¹, or (1.3 ± 0.2) (T/300)^{&minus(1.5±0.2)} × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for NO + CFCl₂CH₂O₂, and (3.3 ± 0.6)e^(516±73)/T × 10⁻¹² cm³ molecule⁻¹ s⁻¹, or (2.0 ± 0.3) (T/300)^{&minus(1.8±0.3)} × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for NO + CH₃CFClO₂. No pressure dependence of the rate coefficients could be detected over the 8(SINGLEBOND)20 torr range investigated. © 1996 John Wiley & Sons, Inc.     

Rate coefficients for the reactions of OH with n‐propanol and iso‐propanol between 237 and 376 K

The rate coefficients for the reaction OH + CH₃CH₂CH₂OH → products (k₁) and OH + CH₃CH(OH)CH₃ → products (k₂) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k₁ and k₂ are as follows: k₁ = (6.2 ± 0.8) × 10^?12 exp[?(10 ± 30)/T] cm³ molecule^?1 s^?1, with k₁(298 K) = (5.90 ± 0.56) × 10^?12 cm³ molecule^?1 s^?1, and k₂ = (3.2 ± 0.3) × 10^?12 exp[(150 ± 20)/T] cm³ molecule^?1 s^?1, with k₂(298) = (5.22 ± 0.46) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10^?19 and (1.90 ± 0.10) × 10^?18 cm² molecule^?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010     

Kinetics and mechanism for the oxidation of 1,1,1-trichloroethane

The reaction mechanisms for oxidation of CH₃CCl₂ and CCl₃CH₂ radicals, formed in the atmospheric degradation of CH₃CCl₃ have been elucidated. The primary oxidation products from these radicals are CH₃CClO and CCl₃CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH₃CCl₃ have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH₃CCl₃) = (5.4 ± 3) 10^?12 exp(?3570 ± 890/RT) cm³ molecule^?1 s^?1. A value of this rate constant of 1.3 × 10^?14 cm³ molecule^?1 s^?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH₃ CCl₃ reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH₃CCl₃) = (1.09 ± 0.35) × 10^?14, ??(OH + CH₃CClO) = (0.91 ± 0.32) × 10^?14, ??(OH + CCl₃CHO) = (178 ± 31) × 10^?14, ??(OH + CCl₂O) < 0.1 × 10^?14; all in units of cm³ molecule^?1 s^?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed.     

Gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH2C(CH3)C(O)OONO2

The gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH₂ ? C(CH₃)C(O)OONO₂ (MPAN) has been studied at 298 ± 2 K and atmospheric pressure. The OH-MPAN reaction rate constant relative to that of OH + n-butyl nitrate is 2.08 ± 0.25. This ratio, together with a literature rate constant of 1.74 × 10^?12 cm³ molecule^?1 s^?1 for the OH + n-butyl nitrate reaction at 298 K, yields a rate constant of (3.6 ± 0.4)× 10^?12 cm³ molecule^?1 s^?1 for the OH-MPAN reaction at 298 ± 2 K. Hydroxyacetone and formaldehyde are the major carbonyl products. The yield of hydroxyacetone, 0.59 ± 0.12, is consistent with preferential addition of OH at the unsubstituted carbon atom. Atmospheric persistence and removal processes for MPAN are briefly discussed. © 1993 John Wiley & Sons, Inc.     

Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals,the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

The rate constant for the reaction of CH₃OCH₂ radicals with O₂ (reaction (1)) and the self reaction of CH₃OCH₂ radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k₁ was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# → CH₂OCH₂O₂H^# → 2HCHO + OH (k_prod) CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# + M → CH₃OCH₂O₂ + M (k_RO2) k = k_RO2 + k_prod, where k_RO2 is the rate constant for peroxy radical production and k_prod is the rate constant for formaldehyde production. The k₁ values obtained at 296K together with the available literature values for k₁ determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: k_RO2,0 = (9.4 ± 4.2) × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k_RO2,∞ = (1.14 ± 0.04) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_prod,0 = (6.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, where k_RO2,0 and k_RO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH₃OCH₂O₂ radicals and k_prod,0 represents the bimolecular rate constant for the reaction of CH₃OCH₂ radicals with O₂ to yield formaldehyde in the limit of low pressure. k_RO2,∞ = (1.07 ± 0.08) × 10⁻¹¹ exp(−(46 ± 27)/T) cm³ molecule⁻¹ s⁻¹ was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k₅ = (4.1 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and at 18 bar total pressure over the temperature range 296–523K, k₅ = (4.7 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. As a part of this study the decay rate of CH₃OCH₂ radicals was used to study the thermal decomposition of CH₃OCH₂ radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH₃OCH₂ radicals were consistent with the literature value of k₂ = 1.6 × 10¹³exp(−12800/T)s⁻¹. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.     

Tunable diode laser studies of the reaction of Cl atoms with CH3CHO

The reaction Cl + CH₃CHO → HCl + CH₃CO (1) was studied using flash photo‐lysis / tunable diode laser absorption spectroscopy to monitor the production of HCl. The rate coefficient, k₁, was measured to be (7.5 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 298 K. HCl (v = 0) and HCl^† (v = 1) were measured directly in this study and the yields of HCl (v = 0, 1, >1) for the reaction of Cl with CH₃CHO were determined to be 0.44 ± 0.15, 0.56 ± 0.15, and <0.04, respectively. The rate coefficient for the quenching of HCl^† (v = 1) by CH₃CHO was k_17e = (4.8 ± 1.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 766–775, 1999     

Rate constants for the gas-phase reaction of the hydroxyl radical with a series of dimethylbenzaldehydes and trimethylphenols at atmospheric pressure

Rate constants for three dimethylbenzaldehydes and two trimethylphenols have been determined for the OH reactions at 298±2 K and atmospheric pressure using a relative rate method. The OH reaction rate constants were placed on an absolute basis using the literature rate constant for 1,2,4-trimethylbenzene of (3.25±0.5)×10⁻¹¹ cm³ molecule⁻¹s⁻¹). The measured rate constants were (in units of cm³ molecule⁻¹ s⁻¹) 2,4-dimethyl-benzaldehyde, (4.32±0.67)×10⁻¹¹; 2,5-dimethylbenzaldehyde, (4.37±0.68)×10⁻¹¹; 3,4-dimethylbenzaldehyde, (2.14±0.34)×10⁻¹¹; and 2,3,5- trimethylphenol, (12.5±1.9)×10⁻¹¹, 2,3,6-trimethylphenol, (11.8±1.8)×10⁻¹¹. Using an average OH concentration of 8.7×10⁵ molecule cm⁻³, the estimated atmospheric lifetimes are ca. 7.5 h for 2,4- and 2,5-dimethylbenzaldehydes, ca. 15 h for 3,4-dimethylbenzaldehyde, ca. 2.5 h for 2,3,5- and 2,3,6-trimethylphenols. The reactivities of the trimethylphenols exceed those of the dimethyl-benzaldehydes by more than a factor of 3. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 523–525, 1997.     

Gas‐phase reaction of dichlorvos,carbaryl, chlordimeform,and 2,4‐D butyl ester with OH radicals

Widespread use of pesticides has caused serious environmental concern. In order to evaluate the fate of organic pesticides in the atmosphere, rate constants for gas phase reactions of OH radicals with dichlorvos, carbaryl, chlordimeform, and 2,4‐D butyl ester were measured using the relative rate method at ambient temperature and 101 kPa total pressure. On‐line FTIR spectroscopy was used to monitor the concentrations of pesticides as a function of time. The reaction rate constants with OH radicals (in units of cm³ molecule⁻¹ s⁻¹) have been determined as (2.0 ± 0.4) × 10⁻¹¹ for dichlorvos, (3.3 ± 0.5) × 10⁻¹¹ for carbaryl, (3.0 ± 0.7) × 10⁻¹⁰ for chlordimeform, and (1.5 ± 0.2) × 10⁻¹¹ for 2,4‐D butyl ester. These rate constants agree well with those estimated based on the structure–activity relationship. The group rate constant for NC group (k_(NC)) was estimated as 2.7 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Dimethyl phosphite has been tentatively identified as a product of the reaction of dichlorvos with OH radicals. Atmospheric lifetimes due to the reactions with OH radicals were also estimated (in units of h): 14 ± 3 for dichlorvos, 8 ± 1 for carbaryl, 1.0 ± 0.3 for chlordimeform, and 19 ± 3 for 2,4‐D butyl ester. These short atmospheric lifetimes indicate that the four organic pesticides degrade rapidly in the atmosphere, and they themselves are unlikely to cause persistent pollution. Further studies are needed to identify the potential hazard of their degradation products. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 755–762, 2005