Rate Constants For Reactions Of Hydroxyl Radicals Research Articles

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.

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.

Free-Radical Kinetics at High Pressure: A Mathematical Analysis of the Flow Reactor

Highly accurate reaction rate constants may be extracted from data obtained in well-developed (laminar or turbulent) diffusive flow over a wide range of experimental conditions. In many cases, data obtained in the core of such a flow may be treated as if the flow were one dimensional, leaving only a small correction for radial diffusion. This correction factor is derived analytically and presented in terms of easily observed quantities. The correction is robust; experimental and theoretical evidence is presented showing that it is insensitive to assumed axial symmetry and remains small so long as the interaction between the core and wall of a flowtube falls within well-defined bounds. The major limitations to accuracy in our high-pressure flow kinetics system (HPFS) are discussed in conjunction with observations of bimolecular reaction rate constants made over a very wide range of experimental conditions for the reactions OH + ethane → products and OH + cyclohexane → products. In the current experiment, accuracy for hydroxyl radical reactions is limited to roughly 12% for pressures of nitrogen ranging from 2 to 600 Torr. The accuracy in the measured ratio of two hydroxyl radical reaction rate constants is roughly 6%. Accuracy is currently limited primarily by absolute velocity measurements and by radical detection sensitivity. Strategies for further improving the accuracy of the high-pressure flow (HPF) technique are discussed.

Estimation of hydroxyl radical reaction rate constants for gas-phase organic compounds using a structure-reactivity relationship: An update

The structure-reactivity approach proposed by Atkinson (1986, Chem. Rev. 86, 69-201) and extended by Atkinson (1987, Int. J. Chem. Kinet. 19, 799-828) for the calculation of rate constants for the gas-phase reactions of the OH radical with organic compounds has been re-investigated using the presently available database. Substituent group factors for several new groups are derived, including those for fluorinated eithers. Using a large fraction of the available database to derive the parameters needed to calculate the OH radical reaction rate constants, the 298 K rate constants of ∼90% of approximately 485 organic compounds are predicted to within a factor of 2 of the experimental values. Disagreements between calculated and experimental rate constants most commonly occur for halogen-containing compounds, and in particular for haloalkanes, haloalkenes and halogenated ethers. Disagreements also arise for ethers, especially for polyethers and cycloethers. The present estimation technique is reasonably reliable when used within the database used in its derivation, but extrapolation to organic compounds outside of this database results in a lack of assurance of its reliability, and its use for organic compounds which belong to classes other than those used in its development is discouraged.

Kinetics of the reactions of OH radicals with selected acetates and other esters under simulated atmospheric conditions

AbstractThe relative hydroxyl radical reaction rate constants from the simulated atmospheric oxidation of selected acetates and other esters have been measured. Reactions were carried out at 297 ± 2 K in 100‐liter FEP Teflon®‐film bags. The OH radicals were generated from the photolysis of methyl nitrite in pure air. Using a rate constant of 2.63 × 10−11 cm3 molecule−1 s−1 for the reaction of OH radicals with propene, the principal reference organic compound, the rate constants (×1012 cm3 molecule−1 s−1) obtained for the acetates and esters used in this study are: n–propyl acetate 3.42 ± 0.87 n–butyl acetate 5.71 ± 0.94 n–pentyl acetate 7.53 ± 0.48 2–ethoxyethyl acetate 10.56 ± 1.31 2–ethoxyethyl isobutyrate 13.56 ± 2.32 2–ethoxyethyl methacrylate 27.22 ± 2.06 4–pentene‐1‐yl acetate 43.40 ± 3.85 3–Ethoxyacrylic acid ethyl ester 33.30 ± 1.22 Error limits represent 2σ from linear least‐squares analysis of data.A linear correlation was observed for a plot of the measured relative rate constants vs. the number of CH2 groups per molecule of the following acetates: methyl acetate, ethyl acetate, n‐propyl acetate, butyl acetate, and pentyl acetate. © 1993 John Wiley & Sons, Inc.

Oxidation of atrazine in water by ultraviolet radiation combined with hydrogen peroxide

The oxidation of atrazine in water by means of direct photolysis at 254 mm and with hydrogen peroxide combined with a u.v. radiation has been studied. The influence of bicarbonate/carbonate ions and a commercial humic substance on the oxidation rate has been observed. Depending on the initial atrazine concentration conversions higher than 99% can be achieved from both types of oxidation in less than 15 min. The oxidation rate is especially fast with the combination of hydrogen peroxide and u.v. radiation. The humic substance applied slows down the rates of both types of processes because it absorbs radiation and scavenges hydroxyl radicals. There is an optimum initial concentration of hydrogen peroxide, about 0.01 M, above which the oxidation rate of atrazine decreases. The quantum yield and hydroxyl radical reaction rate constant of atrazine were found to be 0.05 mol photon −1 and 1.8 × 10 20 M −1 s −1, respectively.

The estimation of the photodegradation of organic compounds by hydroxyl radical reaction rate constants obtained from nuclear magnetic resonance spectroscopy chemical shift data

The use of nuclear magnetic resonance chemical shift data for predicting the rate of photodegradation of organic chemicals in air, due to reaction with hydroxyl radicals, has been critically examined. Relationships between the average 13C or 1H chemical shift and the hydroxyl radical rate constant have been studied for a wide range of compounds. Recommendations regarding the utility of the procedure are made.