High-temperature measurements of the reactions of OH with toluene and acetone

The reaction of hydroxyl [OH] radicals with toluene [C6H5CH3] was studied at temperatures between 911 and 1389 K behind reflected shock waves at pressures of approximately 2.25 atm. OH radicals were generated by rapid thermal decomposition of shock-heated tert-butyl hydroperoxide [(CH3)3-CO-OH], and monitored by narrow-line width ring dye laser absorption of the well-characterized R1(5) line of the OH A-X (0,0) band near 306.7 nm. OH time histories were modeled by using a comprehensive toluene oxidation mechanism. Rate constants for the reaction of C6H5CH3 with OH were extracted by matching modeled and measured OH concentration time histories in the reflected shock region. Detailed error analyses yielded an uncertainty estimate of +/-30% at 1115 K for the rate coefficient of this reaction. The current high-temperature data were fit with the lower temperature measurements of Tully et al. [J. Phys. Chem. 1981, 85, 2262-2269] to the following two-parameter form, applicable over 570-1389 K: k3 = (1.62 x 10(13)) exp(-1394/T [K]) [cm3 mol(-1) s(-1)]. The reaction between OH radicals and acetone [CH3COCH3] was one of the secondary reactions encountered in the toluene + OH experiments. Direct high-temperature measurements of this reaction were carried out at temperatures ranging from 982 to 1300 K in reflected shock wave experiments at an average total pressure of 1.65 atm. Uncertainty limits were estimated to be +/-25% at 1159 K. A two-parameter fit of the current data yields the following rate expression: k6 = (2.95 x 10(13)) exp(-2297/T [K]) [cm3 mol(-1) s(-1)].     

High-temperature reactions of OH radicals with benzene and toluene

The rate constants for the reactions of OH radicals with benzene and toluene have been measured directly by a shock tube/pulsed laser-induced fluorescence imaging method at high temperatures. The OH radicals were generated by the thermal decomposition of nitric acid or tert-butyl hydroperoxide. The derived Arrhenius expressions for the rate constants were k(OH + benzene) = 8.0 x 10(-11) exp(-26.6 kJ mol(-1)/RT) [908-1736 K] and k(OH + toluene) = 8.9 x 10(-11) exp(-19.7 kJ mol(-1)/RT) [919-1481 K] in the units of cubic centimeters per molecule per second. Transition-state theory (TST) calculations based on quantum chemically predicted energetics confirmed the dominance of the H-atom abstraction channel for OH + benzene and the methyl-H abstraction channel for OH + toluene in the experimental temperature range. The TST calculation indicated that the anharmonicity of the C-H-O bending vibrations of the transition states is essential to reproduce the observed rate constants. Possible implications to the other analogous H-transfer reactions were discussed.     

Products of the gas-phase OH radical-initiated reactions of 4-methyl-2-pentanone and 2,6-dimethyl-4-heptanone

The gas-phase reactions of the OH radical with 4-methyl-2-pentanone and 2,6-dimethyl-4-heptanone have been investigated in the presence of NO_x. Acetone and 2-methylpropanal were identified and qualified as products of both reactions. The acetone yield from 2,6-dimethyl-4-heptanone increased after addition of NO to reacted mixtures, indicating that acetone is formed through the intermediary of an acyl radical. The acetone and 2-methylopropanal formation yields were determined to be 0.78 ± 0.06 and 0.071 ± 0.011, respectively, from 4-methyl-2-pentanone and 0.68 ± 0.11 and 0.385 ± 0.034, respectively, from 2,6-dimethyl-4-heptanone. The possible reaction mechanisms are discussed and compared with these product data, and it is concluded that the experimental data provide direct evidence for isomerization of the (CH₃)₂CHCH₂C(O)CH₂C(O) (CH₃)₂ alkoxy radical formed from 2,6-dimethyl-4-heptanone. However, the isomerization rates of the alkoxy radicals formed from the ketones depend on whether the H-atom abstracted is on a carbon atom α or β to the >C?O group, with H-atom abstraction from C? H bonds on the β carbon atoms being significantly faster than from C? H bonds on the α carbon atoms. © 1995 John Wiley & Sons, Inc.     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.     

Kinetics of OH radical reactions with a series of ethers

The rate constants for the reactions of OH with dimethyl ether (k₁), diethyl ether (k₂), di-n-propyl ether (k₃), di-isopropyl ether (k₄), and di-n-butyl ether (k₅) have been measured over the temperature range 230–372 K using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique. The temperature dependence of k₁,k₄, can be expressed in the Arrhenius plots form: k₁ = (6.30 ± 0.10) × 10^?12 exp[?(234 ± 34)/T] and k₄ = (4.13 ± 0.10) × 10^?12 exp[(274 ± 26)/T]. The Arrhenius plots for k₂,k₃, and k₅, were curved and they were fitted to the three parameter expressions: k₂ = (1.02 ± 0.08) × 10^?17 T² exp[(797 ± 24)/T], k₃ = (1.84 ± 0.23) × 10^?17T² exp[(767 ± 34)/T], and k₅ = (6.29 ± 0.74) × 10^?18T² exp[(1164 ± 34)/T]. The values at 298 K are (2.82 ± 0.21) × 10^?12, (1.36 ± 0.11) × 10^?11,(2.17 ± 0.16) × 10^?11, (1.02 ± 0.10) × 10^?11, and (2.69 ± 0.22) × 10^?11 for k₁, k₂, k₃, k₄, and k₅, respectively, (in cm³ molecule^?1 s^?1). These results are compared to the literature data. © 1995 John Wiley & Sons, Inc.     

Kinetics of OH and Cl reactions with a series of aldehydes

The rate constants for the reactions of the OH radicals with a series of aldehydes have been measured in the temperature range 243–372 K, using the pulsed laser photolysis‐pulsed laser induced fluorescence method. The obtained data for propanaldehyde, iso‐butyraldehyde, tert‐butyraldehyde, and n‐pentaldehyde were as follows (in cm³ molecule⁻¹ s⁻¹): (a) in the Arrhenius form: (5.3 ± 0.5) × 10⁻¹² exp[(405 ± 30)/T], (7.3 ± 1.9) × 10⁻¹² exp[(390 ± 78)/T], (4.7 ± 0.8) × 10⁻¹² exp[(564 ± 52)/T], and (9.9 ± 1.9) × 10⁻¹² exp[(306 ± 56)/T]; (b) at 298 K: (2.0 ± 0.3) × 10⁻¹¹, (2.6 ± 0.4) × 10⁻¹¹, (2.7 ± 0.4) × 10⁻¹¹, and (2.8 ± 0.2) × 10⁻¹¹, respectively. In addition, using the relative rate method and alkanes as the reference compounds, the room‐temperature rate constants have been measured for the reactions of chlorine atoms with propanaldehyde, iso‐butyraldehyde, tert‐butyraldehyde, n‐pentaldehyde, acrolein, and crotonaldehyde. The obtained values were (in cm³ molecule⁻¹ s⁻¹): (1.4 ± 0.3) × 10⁻¹⁰, (1.7 ± 0.3)10⁻¹⁰, (1.6 ± 0.3) × 10⁻¹⁰, (2.6 ± 0.3) × 10⁻¹⁰, (2.2 ± 0.3) × 10⁻¹⁰, and (2.6 ± 0.3) × 10⁻¹⁰, respectively. The results are presented and discussed in terms of structure‐reactivity relationships and atmospheric importance. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 676–685, 2000     

Determination of acetone, 2-butanone, diethyl ketone and BTX using HSCC-UV-IMS

A combination of a custom-designed ion mobility spectrometer (IMS) with a UV ionization source and a high speed capillary column (HSCC) has been developed as an analytical device for the sensitive detection of volatile organic compounds (VOCs), e.g. 2-propanone (acetone), 2-butanone and 3-pentanone (diethyl ketone) in the gas phase. A fast separation of the three selected substances and benzene, toluene and m-xylene (BTX) - all of which occur in human breath - has been achieved within less than four minutes at a carrier gas flow rate of 4.5 mL x min(-1). Multi-dimensional correlations presented support the interpretation of the acquired spectra of mixtures. Method detection limits were 2.7 microg x L(-1) for acetone and 2-butanone and 3.0 microg x L(-1) for diethyl ketone in nitrogen, respectively. The assay linear dynamic range is 4-320 microg x L(-1).     

Relative rate constant measurements for the gas-phase reactions of hydroxyl radicals with 4-methyl-2-pentanone,trans-4-octene,and trans-2-heptene

The relative OH reaction rates from the simulated atmospheric oxidation of 4-methyl-2-pentanone, trans-4-octene, and trans-2-heptene have been measured. Reactions were carried out at 297 ± 2 K in 100-liter FEP Teflon®-film bags. The OH radicals were produced from the photolysis of methyl nitrite. The measured rate constants (×10¹¹ cm³ molecule^?1 s^?1) were as follows: 6.77 ± 0.50 for trans-4-octene, 1.40 ± 0.07 for 4-methyl-2-pentanone, and 6.70 ± 0.23 for trans-2-heptene using an absolute rate constant of 2.63 × 10¹¹ cm³ molecule^?1 s^?1 for the reaction of OH with propene; the principal reference organic. © John Wiley & Sons, Inc.     

Kinetic study of the reactions of Cl atoms with CF3CH2CH2OH, CF3CF2CH2OH, CHF2CF2CH2OH, and CF3CHFCF2CH2OH

The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF(3)CH(2)CH(2)OH (1), CF(3)CF(2)CH(2)OH (2), CHF(2)CF(2)CH(2)OH (3), and CF(3)CHFCF(2)CH(2)OH (4), were studied in the gas phase over the temperature range of 273-363 K by using very low-pressure reactor mass spectrometry. The absolute rate coefficients were given by the expressions (in cm(3) molecule(-1) s(-1)): k(1) = (4.42 +/- 0.48) x 10(-11) exp(-255 +/- 20/T); k(1)(303) = (1.90 +/- 0.17) x 10(-11), k(2) = (2.23 +/- 0.31) x 10(-11) exp(-1065 +/- 106/ T); k(2)(303) = (6.78 +/- 0.63) x 10(-13), k(3) = (8.51 +/- 0.62) x 10(-12) exp(-681 +/- 72/T); k(3)(303) = (9.00 +/- 0.82) x 10(-13) and k(4) = (6.18 +/- 0.84) x 10(-12) exp(-736 +/- 42/T); k(4)(303) = (5.36 +/- 0.51) x 10(-13). The quoted 2sigma uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis mechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and the end products were the corresponding aldehydes (R(F)-CHO; R(F) = -CH(2)CF(3), -CF(2)CF(3), -CF(2)CHF(2), and -CF(2)CHFCF(3)), providing a strong experimental indication that the primary reactions proceed mainly via the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and ionization potentials for the title compounds were determined by density functional theory calculations, which also suggest that the alpha-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of room-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated C2-C5 ethers and C2-C4 alcohols, is good with an average deviation of a factor of 2, and is given by the expression log(k) (in cm(3) molecule(-1) s(-1)) = (5.8 +/- 1.4) - (1.56 +/- 0.13) x (ionization potential (in eV)).     

Fragmentation reactions of the enolate ions of 2-pentanone

The reaction of [OH]^? with 2-pentanone produces two enolate ions, [CH₃CH₂CH₂COCH₂]^? and [CH₃COCHCH₂CH₃]^?, by proton abstraction from C(1) and C(3), respectively. Using deuterium isotopic labelling the fragmentation reactions of each enolate have been delineated for collisional activation at both high (8 keV) and low (5–100 eV) collisional energies. The primary enolate ion fragments mainly by elimination of ethene. Two mechanisms operate: elimination of C(4) and C(5) with hydrogen migration from C(5), and elimination of C(3) and C(4) with migration of the C(5) methyl group. Minor fragmentation of the primary enolate also occurs by elimination of propane and elimination of C₂H₅; the latter reaction involves specifically the terminal ethyl group. The secondary enolate ion fragments mainly by loss of H₂ and by elimination of CH₄; for the latter reaction four different pathways are operative. Minor elimination of ethene also is observed involving migration of a C(5) hydrogen to C(3) and elimination of C(4) and C(5) as ethene.     

Cage reactions in the photolysis of 2,2,4,4-tetramethyl-3-pentanone

The product quantum yields in the photolysis of 2,2,4,4-tetramethyl-3-pentanone have been measured in homogeneous solvents of different viscosities, in micellar solutions of cetyltrimethylammonium chloride and sodium dodecyl sulfate, and in dioctadecyl ammonium chloride vesicles. The product quantum yield in n-heptane was found to be 1. This value decreases to 0.5 in paraffin oil as a consequence of geminate recombination. In the presence of free radical scavengers, the extent of geminate disproportionation can be evaluated from the yields of isobutene and 2,2-dimethyl propionaldehyde. From these yields and the geminate recombination yields the total amount of geminate processes and the disproportionation-to-combination ratio for caged radicals are estimated. It is found that micelles provide the most efficient cages. In these media only about 10% of the radicals avoid cage processes. The disproportionation-to-combination ratio of tert-butyl and pivaloyl radicals was found to be extremely media dependent. The measured values ranged from about 0.2 in paraffin oil to 0.8 in cetyltrimethylammonium chloride micelles.     

Rate constants for the gas-phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K

Rate constants for the gas-phase reactions of O₃ with the sesquiterpenes α-cedrene, α-copaene, β-caryophyllene, α-humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α-phellandrene, and α-terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10^?17 cm³ molecule^?1 s^?1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α-phellandrene, 298 ± 105; α-terpinene, 2110 ± 770; α-cedrene, 2.78 ± 0.71; α-copaene, 15.8 ± 5.6; β-caryophyllene, 1160 ± 430; α-humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O₃ reactions with the sesquiterpenes, of 0.67 for α-cedrene, 0.35 for α-copaene, 0.06 for β-caryophyllene, and 0.22 for α-humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O₃ are calculated. © 1994 John Wiley & Sons, Inc.     

Kinetics of the reactions of O3 and OH radicals with a series of dialkenes and trialkenes at 294 ± 2 K

Rate constants for the gas phase reactions of O₃ and OH radicals with 1,3-cycloheptadiene, 1,3,5-cycloheptatriene, and cis- and trans-1,3,5-hexatriene and also of O₃ with cis-2,trans-4-hexadiene and trans -2,trans -4-hexadiene have been determined at 294 ± 2 K. The rate constants determined for reaction with O₃ were (in cm³ molecule^-1s^?1 units): 1,3-cycloheptadiene, (1.56 ± 0.21) × 10^-16; 1,3,5-cycloheptatriene, (5.39 ± 0.78) × 10^?17; 1,3,5-hexatriene, (2.62 ± 0.34) × 10^?17; cis?2,trans-4-hexadiene, (3.14 ± 0.34) × 10^?16; and trans ?2, trans -4-hexadiene, (3.74 ± 0.61) × 10^?16; with the cis- and trans-1,3,5-hexatriene isomers reacting with essentially identical rate constants. The rate constants determined for reaction with OH radicals were (in cm³ molecule^?1 s^?1 units): 1,3-cycloheptadiene, (1.31 ± 0.04) × 10^?10; 1,3,5-cycloheptatriene, (9.12 × 0.23) × 10^?11; cis-1,3,5-hexatriene, (1.04 ± 0.07) × 10^?10; and trans 1,3,5-hexatriene, (1.04 ± 0.17) × 10^?10. These data, which are the first reported values for these di- and tri-alkenes, are discussed in the context of previously determined O₃ and OH radical rate constants for alkenes and cycloalkenes.     

High-temperature kinetics of the reactions of SO2 and SO3 with atomic oxygen

A nozzle-beam-skimmer sampling system is used to measure species concentration profiles for a lean one-dimensional premixed CO? O₂? Ar flame, into which small amounts of sulfur dioxide are introduced. The net formation rate for sulfur trioxide is obtained from the flux fraction profile for this species. The kinetic scheme is then utilized, along with the measured temperature profiles, to evaluate the rate coefficients k₁ and k₂ over the temperature range of 1435–1850 K. The most satisfactory agreement between the measured net formation rate for SO₃ and that calculated on the basis of reactions (1) and (2) is obtained with the rate coefficients Reactions (1) and (2) are found to be nearly balanced in a substantial region of the flame. Here the data are more sensitive to the difference in activation energies, as opposed to a particular value for either. Implications of this observation on the uncertainty of the deduced temperature dependence for each reaction are discussed, as are some of the procedures used in the data analysis.     

Rate constants for the gas-phase reaction of OH radicals with a series of ketones at 299 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of ketones have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of hydroxyl radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³ molecule^?1 s^?1, the rate constants obtained are (× 10¹² cm³ molecule^?1 s^?1): 2-pentanone, 4.74 ± 0.14; 3-pentanone, 1.85 ± 0.34; 2-hexanone, 9.16 ± 0.61; 3-hexanone, 6.96 ± 0.29; 2,4-dimethyl-3-pentanone, 5.43 ± 0.41; 4-methyl-2-pentanone, 14.5 ± 0.7; and 2,6-dimethyl-4-heptanone, 27.7 ± 1.5. These rate constants indicate that while the carbonyl group decreases the reactivity of C? H bonds in the α position toward reaction with the OH radical, it enhances the reactivity in the β position.     

Mechanism of OH radical reactions with HCN and CH3CN: OH regeneration in the presence of O2

A theoretical study on the mechanism of the OH reactions with HCN and CH(3)CN, in the presence of O2, is presented. Optimum geometries and frequencies have been computed at BHandHLYP/6-311++G(2d,2p) level of theory for all stationary points. Energy values have been improved by single-point calculations at the above geometries using CCSD(T)/6-311++G(2d,2p). The initial attack of OH to HCN was found to lead only to the formation of the HC(OH)N adduct, while for CH(3)CN similar proportions of CH(2)CN and CH(3)C(OH)N are expected. A four-step mechanism has been proposed to explain the OH regeneration, experimentally observed for OH + CH(3)CN reaction, when carried out in the presence of O2. The mechanism steps are as follows: (1) OH addition to the C atom in the CN group, (2) O2 addition to the N atom, (3) an intramolecular H migration from OH to OO, and (4) OH elimination. This mechanism is in line with the one independently proposed by Wine et al. for HCN. The results obtained here suggest that for the OH + HCN reaction, the OH regeneration might occur even in larger extension than for OH + CH(3)CN reaction. The agreement between the calculated data and the available experimental evidence on the studied reactions seems to validate the mechanism proposed here.     

Kinetic measurements of methyl and ethyl nitrate reactions with OH radicals

Reaction rate coefficients of methyl and ethyl nitrates with OH radicals were determined by the relative rate method in 1 atmosphere of oxygen. Reactions were initiated by the photochemical formation of OH radicals utilizing the reaction: H₂O+O(¹D)→2OH. O(¹D) was obtained through a stationary photolysis of excess ozone in an experimental system under black light irradiation. Measurements were carried out for various combinations with different reference materials. Rate coefficients obtained were (0.30±0.032 (2σ)×10⁻¹³ cm³molecule⁻¹s⁻¹ (Temp.: 304–310 K) for methyl nitrate and (2.0±0.70)× 10⁻¹³ cm³molecule⁻¹s⁻¹ (298–310 K) for ethyl nitrate. For methyl nitrate, this data indicates the preference of a smaller rate coefficient between the two values reported in the literature [1,2], which have shown large discrepancies of more than one order of magnitude. For ethyl nitrate, only one measurement has been reported [2]. However, the present result suggests that the reported value was overestimated by a factor of more than two. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 933–941, 1997.     

Syntheses and reactions of alkylacetylenic alcohols and ketones of the thiophene series

The reaction of thiophene-2-carbaldehyde and 5-ethylthiophene-2-carbaldehyde with alkylethynylmagnesium halides has given thienyl acetylenic alcohols, and these have been oxidized to the corresponding ketones. The reactions of the latter with hydrazine and their hydrogenation have been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 894–897, July, 1970.