Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether

Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10^?13 cm³ molecule^?1 s^?1 at 298 K. The primary products and molar yields for the OH reaction with ETBE in the presence of NO_x were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.     

Rates of reaction between the nitrate radical and some aliphatic ethers

Rate coefficients for the reaction of NO₃ with dimethyl ether, diethyl ether, di-n-propyl ether, and methyl t-butyl ether (MTBE) have been determined. Absolute rates were measured at temperatures between 258 and 373 K using the fast flow-discharge technique. Relative rate experiments were also made at 295 K in a reactor equipped with White optics and using FTIR spectroscopy to follow the reactions. The measured rate coefficients (in units of 10^?15 cm³ molecule^?1 s^?1) at 295 K are: 0.26 ± 0.11, 2.80 ± 0.23, 6.49 ± 0.65, and 0.64 ± 0.06 for dimethyl ether, diethyl ether, di-n-propyl ether, and methyl t-butyl ether, respectively. The corresponding activation energies are 21.0 ± 5.0, 17.2 ± 4.0, 15.5 ± 2.1, and 20.1 ± 1.7 kJ mole^?1. The error limits correspond to the 95%-confidence interval. © 1994 John Wiley & Sons, Inc.     

Kinetics and mechanism of the atmospheric oxidation of tertiary amyl methyl ether

Tertiary-amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t-amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction. Values determined for the rate constants for the reaction with OH were 5.48 × 10^?12 (TAME), 1.75 × 10^?12 (t-amyl formate), and 3.85 × 10^?13 cm³ molec^?1 s^?1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t-amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t-amyl alcohol (0.026), 3-methyoxy-3-methyl-butanal (0.044, corrected), t-amyloxy methyl nitrate (0.029), 3-methyoxy-3-methyl-2-butyl nitrate (0.010), and 2-methoxy-2-methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc.     

Kinetics of the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one under simulated atmospheric conditions

Relative rate coefficients for the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one have been determined at 298 K and atmospheric pressure by the relative rate technique. OH radicals were generated by the photolysis of methyl nitrite in synthetic air mixtures containing ppm levels of nitric oxide together with the test and reference substrates. The concentrations of the test and reference substrates were followed by gas chromatography. Based on the value k(OH + cyclohexene) = (6.77 ± 1.35) × 10^?11 cm³ molecule^?1 s^?1, rate coefficients for k(OH + 3‐methyl‐2‐cyclohexen‐1‐one) = (3.1 ± 1.0) × 10^?11 and k(OH + 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one) = (2.4 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1 were determined. To test the system we also measured k(OH + isoprene) = (1.11 ± 0.23) × 10^?10 cm³ molecule^?1 s^?1, relative to the value k(OH + (E)‐2‐butene) = (6.4 ± 1.28) × 10^?11 cm³ molecule^?1 s^?1. The results are discussed in terms of structure–activity relationships, and the reactivities of cyclic ketones formed in the photo‐oxidation of monoterpene are estimated. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 7–11, 2002     

Kinetics and mechanism of the reaction of propylene oxide with chlorine atoms and hydroxy radicals

The kinetics and mechanism of gas‐phase propylene oxide (PPO) reactions were studied in a 142‐L reaction chamber by long‐path Fourier transform infrared spectroscopy at atmospheric pressure and 298 K. Rate coefficients for the reaction of PPO with ozone (O₃), chlorine atoms (Cl), and hydroxyl radicals (OH) were measured using the relative rate technique. Product yields of acetic acid, acetic formic anhydride, formic acid, and carbon monoxide were determined for the following reactions: PPO with Cl both in the presence and absence of NO, PPO with OH and NO, methyl acetate with Cl both in the presence and absence of NO, and ethyl formate with Cl both in the presence and absence of NO. The measured rate coefficients for PPO with O₃, Cl, and OH are <3.5 × 10^?21 cm³ molecule^?1 s^?1, (3.0 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1, and (3.0 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1, respectively. The carbon balance for the products measured ranged from 10% (for OH + PPO) to 100% (for Cl + methyl acetate in the absence of NO). The mechanistic and atmospheric implications of these measurements are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 507–521, 2011     

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.     

Rate constants for the reactions of the OH radical with the propyl and butyl nitrates and 1-nitrobutane at 298 ± 2 k

Using a relative rate method, rate constants for the gas-phase reactions of the OH radical with 1- and 2-propyl nitrate, 1- and 2-butyl nitrate and 1-nitrobutane have been determined in the presence of one atmosphere of air at 298 ± 2 K. Using rate constants for the reactions of the OH radical with propane and cyclohexane of 1.15 × 10^?12 and 7.49 × 10^?12 cm³ molecule^?1 s^?1, respectively, following rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were obtained: 1-propyl nitrate, 0.62; 2-propyl nitrate, 0.41; 1-butyl nitrate, 1.78; 2-butyl nitrate, 0.93; and 1-nitrobutane, 1.35. These rate constants are compared and discussed with the literature data.     

Room temperature rate constants for the reaction of OH with selected chlorinated and oxygenated hydrocarbons

A study was conducted to measure the hydroxyl radical rate constants using a relative rate procedure in which the photolysis of methyl nitrite was the source of OH. During the course of this study, the OH rate constant was measured for a number of chlorinated solvents for which measurements have not previously been reported or for which there are few reliable measurements. Room temperature OH rate constants are presented for six chlorinated hydrocarbons (allyl chloride, benzyl chloride, chlorobenzene, epichlorohydrin, trichloroethylene, and vinylidene chloride) and four oxygenated hydrocarbons (acrolein, methacrolein, methyl ethyl ketone, and propylene oxide). Also included are OH rate constants for alkanes (ethane, propane, isobutane, and cyclohexane), alkenes (trans?2-butene and isoprene), and aromatic hydrocarbons (benzene, toluene, o^?, m^?, and p-xylene). Rate constants for compounds not previously reported include vinylidene chloride (1.49 ± 0.21 × 10^?11 cm³ molecule^?1 s^?1) and benzyl chloride (2.96 ± 0.15 × 10^?12 cm³ molecule^?1 s^?1). The analysis for chlorinated hydrocarbons included a correction for possible chlorine atom reactions.     

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.     

Ketone photolysis in the presence of oxygen: A useful source of OH for flash photolysis kinetics experiments

Previous studies have shown a significant OH yield from the reaction of RCO radicals (generated from the photolysis of corresponding ketone) with oxygen below total pressures of 200 Torr. The potential of these reactions as a source of OH radicals for flash photolytic kinetic studies is investigated. The viability of the method was tested by measuring rate coefficients for the reaction of OH with ethanol using both acetone/O₂ mixtures and t‐butyl hydroperoxide photolysis. The results (with statistical errors at the 2σ level) are in excellent agreement with each other (k_EtOH(acetone) = (5.87 ± 0.34) × 10^?18 T² exp((515 ± 21)K/T) cm³ molecule^?1 s^?1 and k_EtOH (t‐butyl hydroperoxide) = (5.27 ± 0.34) × 10^?18 T² exp((557 ± 20)K/T) cm³ molecule^?1 s^?1) and with the IUPAC recommendation. The reaction of OH with methyl ethyl ketone (2‐butanone) has also been investigated using a similar technique. The results show a strong non‐Arrhenius temperature dependence, k = (3.84 ± 0.12) × 10^?24× T⁴ × exp((1038 ± 11)/t). The merits of the ketone/oxygen OH source are contrasted with other established precursors. A major advantage of the technique is the ability to cleanly generate OD without the potential for isotopic scrambling prior to photolysis. © 2008 Wiley Periodicals, Inc. 40: 504–514, 2008     

Rate constants of the gas‐phase reactions of OH radicals with trans‐2‐hexenal,trans‐2‐octenal,and trans‐2‐nonenal

The rate constants of the gas‐phase reaction of OH radicals with trans‐2‐hexenal, trans‐2‐octenal, and trans‐2‐nonenal were determined at 298 ± 2 K and atmospheric pressure using the relative rate technique. Two reference compounds were selected for each rate constant determination. The relative rates of OH + trans‐2‐hexenal versus OH + 2‐methyl‐2‐butene and β‐pinene were 0.452 ± 0.054 and 0.530 ± 0.036, respectively. These results yielded an average rate constant for OH + trans‐2‐hexenal of (39.3 ± 1.7) × 10^?12 cm³ molecule^?1 s^?1. The relative rates of OH+trans‐2‐octenal versus the OH reaction with butanal and β‐pinene were 1.65 ± 0.08 and 0.527 ± 0.032, yielding an average rate constant for OH + trans‐2‐octenal of (40.5 ± 2.5) × 10^?12 cm³ molecule^?1 s^?1. The relative rates of OH+trans‐2‐nonenal versus OH+ butanal and OH + trans‐2‐hexenal were 1.77 ± 0.08 and 1.09 ± 0.06, resulting in an average rate constant for OH + trans‐2‐nonenal of (43.5 ± 3.0) × 10^?12 cm³ molecule^?1 s^?1. In all cases, the errors represent 2σ (95% confidential level) and the calculated rate constants do not include the error associated with the rate constant of the OH reaction with the reference compounds. The rate constants for the hydroxyl radical reactions of a series of trans‐2‐aldehydes were compared with the values estimated using the structure activity relationship. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 483–489, 2009     

OH radical reaction rate constants for polycyclic alkanes: Effects of ring strain and consequences for estimation methods

Using a relative rate method, rate constants for the gas-phase reactions of the OH radical with trans-pinane [(1R, 2R)-2, 6, 6-trimethylbicyclo[3.1.1]heptane], tricyclene (1, 7, 7-trimethyltricyclo[2.2.1.0^{2, 6}]heptane), and quadricyclane (quadricyclo[2.2.1.0^{2, 6}.0^{3, 5}]heptane) of (1.34 ± 0.29) × 10^?11 cm³ molecule^?1 s^?1, (2.86 ± 0.62) × 10^?12 cm³ molecule^?1 s^?1 and (1.83 ± 0.41) × 10^?12 cm³ molecule^?1 s^?1, respectively, have been determined at 296 ± 2 K. These rate constants are compared with values calculated from an empirical estimation method and used to refine this estimation technique for the calculation of OH radical reaction rate constants for polycyclic systems. © John Wiley & Sons, Inc.     

Kinetics of the reaction of OH radicals with a series of esters under simulated conditions at 295 K

The rate constants of the isopropyl acetate, n-propyl acetate, isopropenyl acetate, n-propenyl acetate, n-butyl acetate, and ethyl butyrate reactions with OH radicals were determined in purified air under atmospheric conditions, at 750 torr and (295 ± 2) K. A relative rate experimental method was used; n-heptane, n-octane, and n-nonane were the reference compounds, with, respectively, rate constants for the reaction with OH of 7.12 × 10⁻¹², 8.42 × 10⁻¹², and 9.70 × 10⁻¹² molecule⁻¹ cm³s⁻¹. The following rate constants were obtained in units of 10⁻¹² molecule⁻¹ cm³s⁻¹; isopropyl acetate, (3.12 ± 0.29); n-propyl acetate, (1.97 ± 0.24); isopropenyl acetate, (62.53 ± 1.24); n-propenyl acetate, (24.57 ± 0.24); n-butyl acetate, (3.29 ± 0.35); and ethyl butyrate, (4.37 ± 0.42). Tertiary butyl acetate has a low reactivity with OH radicals (<1 × 10⁻¹² molecule⁻¹ cm³s⁻¹). © 1996 John Wiley & Sons, Inc.     

Kinetics of the reaction of OH radicals with a series of ethers under simulated atmospheric conditions at 295 K

Ethers are being increasingly used as motor fuel additives to increase the octane number and to reduce CO emissions. Since their reaction with hydroxyl radicals (OH) is a major loss process for these oxygenated species in the atmoshpere, we have conducted a relative rate study of the kinetics of the reactions of OH radicals with a series of ethers and report the results of these measurements here. Experiments were performed under simulated atmospheric conditions; atmospheric pressure (? 740 torr) in synthetic air at 295 K. Using rate constants of 2.53 × 10^?12, and 1.35 × 10^?11 cm³ molecule^?1 s^?1 for the reaction of OH radicals with n-butane and diethyl ether, the following rate constants were derived, in units of 10^?11 cm³ molecule^?1 s^?1: dimethylether, (0.232 ± 0.023); di-n-propylether, (1.97 ± 0.08); di-n-butylether, (2.74 ± 0.32); di-n-pentylether, (3.09 ± 0.26); methyl-t-butylether, (0.324 ± 0.008); methyl-n-butylether, (1.29 ± 0.03); ethyl-n-butylether, (2.27 ± 0.09); and ethyl-t-butylether, (0.883 ± 0.026). Quoted errors represent 2σ from the least squares analysis and do not include any systematic errors associated with uncertainties in the reference rate constants used to place our relative measurements on an absolute basis. The implications of these results for the atmospheric chemistry of ethers are discussed.     

A laser flash photolysis/IR diode laser absorption study of the reaction of chlorine atoms with selected alkanes

A high‐resolution IR diode laser in conjunction with a Herriot multiple reflection flow‐cell has been used to directly determine the rate coefficients for simple alkanes with Cl atoms at room temperature (298 K). The following results were obtained: k(Cl + n‐butane) = (1.91 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐pentane) = (2.46 ± 0.12) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + iso‐pentane) = (1.94 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + neopentane) = (1.01 ± 0.05) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐hexane) = (3.44 ± 0.17) × 10^?10 cm³ molecule^?1 s^?1 where the error limits are ±1σ. These values have been used in conjunction with our own previous measurements on Cl + ethane and literature values on Cl + propane and Cl + iso‐butane to generate a structure activity relationship (SAR) for Cl atom abstraction reactions based on direct measurements. The resulting best fit parameters are k_p = (2.61 ± 0.12) × 10^?11 cm³ molecule^?1 s^?1, k_s = (8.40 ± 0.60) × 10^?11 cm³ molecule^?1 s^?1, k_t = (5.90 ± 0.30) × 10^?11 cm³ molecule^?1 s^?1, with f( ? CH₂^? ) = f (? CH₂^? ) = f (?C?) = f = 0.85 ± 0.06. Tests were carried out to investigate the potential interference from production of excited state HCl(v = 1) in the Cl + alkane reactions. There is some evidence for HCl(v = 1) production in the reaction of Cl with shape n‐hexane. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 86–94, 2002     

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.     

Rate constants for the gas-phase reactions of the OH radical with a series of aromatic hydrocarbons at 296 ± 2 K

Using a relative rate method, rate constants have been determined at 296 ± 2 K for the gas-phase reactions of the OH radical with toluene, the xylenes, and the trimethylbenzenes. Using the recommended literature rate constant for the reaction of OH radicals with propene of (2.66 ± 0.40) × 10^?11 cm³ molecule^?1 s^?1, the following rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were obtained: toluene, 5.48 ± 0.84; o-xylene, 12.2 ± 1.9; m-xylene, 23.0 ± 3.5; p-xylene, 13.0 ± 2.0; 1,2,3-trimethylbenzene, 32.7 ± 5.3; 1,2,4-trimethylbenzene, 32.5 ± 5.0; and 1,3,5-trimethylbenzene, 57.5 ± 9.2. These data are compared with the literature values.     

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     

The temperature dependence of the OH radical reactions with some aromatic compounds under simulated tropospheric conditions

The temperature dependence of the rate coefficients for the OH radical reactions with toluene, benzene, o-cresol, m-cresol, p-cresol, phenol, and benzaldehyde were measured by the competitive technique under simulated atmospheric conditions over the temperature range 258–373 K. The relative rate coefficients obtained were placed on an absolute basis using evaluated rate coefficients for the corresponding reference compounds. Based on the rate coefficient k(OH + 2,3-dimethylbutane) = 6.2 × 10^?12 cm³ molecule^?1s^?1, independent of temperature, the rate coefficient for toluene k_OH = 0.79 × 10^?12 exp[(614 ± 114)/T] cm³ molecule^?1 s^?1 over the temperature range 284–363 K was determined. The following rate coefficients in units of cm³ molecule^?1 s^?1 were determined relative to the rate coefficient k(OH + 1,3-butadiene) = 1.48 × 10^?11 exp(448/T) cm³ molecule^?1 s^?1: o-cresol; k_OH = 9.8 × 10^?13 exp[(1166 ± 248)/T]; 301–373 K; p-cresol; k_OH = 2.21 × 10^?12 exp[(943 ± 449)/T]; 301–373 K; and phenol, k_OH = 3.7 × 10^?13 exp[(1267 ± 233)/T]; 301–373 K. The rate coefficient for benzaldehyde k_OH = 5.32 × 10^?12 exp[(243 ± 85)/T], 294–343 K was determined relative to the rate coefficient k(OH + diethyl ether) = 7.3 × 10^?12 exp(158/T) cm³ molecule^?1 s^?1. The data have been compared to the available literature data and where possible evaluated rate coefficients have been deduced or updated. Using the evaluated rate coefficient k(OH + toluene) = 1.59 × 10^?12 exp[(396 ± 105)/T] cm³ molecule^?1 s^?1, 213–363 K, the following rate coefficient for benzene has been determined k_OH = 2.58 × 10^?12 exp[(?231 ± 84)/T] cm³ molecule^?1 s^?1 over the temperature range 274–363 K and the rate coefficent for m-cresol, k_OH = 5.17 × 10^?12 exp[(686 ± 231)/T] cm³ molecule^?1 s^?1, 299–373 K was determined relative to the evaluated rate coefficient k(OH + o-cresol) = 2.1 × 10^?12 exp[(881 ± 356)/T] cm³ molecule^?1 s^?1. The tropospheric lifetimes of the aromatic compounds studied were calculated relative to that for 1,1,1-triclorethane = 6.3 years at 277 K. The lifetimes range from 6 h for m-cresol to 15.5 days for benzene. © 1995 John Wiley & Sons, Inc.     

Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane

The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k₁ = (1.17 ± 0.15) × 10^?16 T^3/2 exp[?(1037 ± 87) kcal mol^?1/RT] cm³ molecule^?1 s¹ and k₂ = (5.06 ± 0.57) × 10^?16 T^3/2 exp[?(228 ± 78) kcal mol^?1/RT] cm³ molecule^?1 s^?1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure-reactivity correlations involving kinetic and energetic parameters.