Rate Constants For Reactions Of Radicals Research Articles

Rate constants for aminyl radical reactions

Rate constants for cyclization of the N-methyl-5,5-diphenyl-4-pentenaminyl radical ( 4) and for reaction of this radical with t-BuSH were determined by direct methods.

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.

Competitive Measurement of Rate Constants for Hydroxyl Radical Reactions Using Radiolytic Hydroxylation of Benzoate.

Hydroxyl radicals were generated from N2O-saturated phosphate-buffered saline solution (pH 7.5) by irradiation with a 3.7 TBq 137Cs source. The radicals attacked benzoate to form highly fluorescent products. The induction of fluorescence was tested in 0.002 to 2mM of benzoate solution; the fluorescence intensity was approximately constant at benzoate concentrations more than 0.1 mM during irradiation, and increased linearly with irradiation dose up to 53 Gy tested. The major primary products detected by high-performance liquid chromatography were three monohydroxybenzoates, 2-, 3- and 4-hydroxybenzoate (HOBZ). The G-values obtained from γ-irradiation for 60 min of a 0.2 mM benzoate solution were G(2-HOBZ)=0.97, G(3-HOBZ)=0.48 and G(4-HOBZ)=0.45. As the fluorescence of irradiated benzoate solution arose mostly from 2- and 3-HOBZ and the intensity of 2-HOBZ is 30 times that of 3-HOBZ, 98% of the fluorescence intensity induced was ascribed to 2-HOBZ. A hydroxyl radical scavenger competed with benzoate for hydroxyl radicals produced, and diminished the fluorescent products. A rate constant for the reaction of a scavenger with hydroxyl radical could be determined from the reduction in fluorescence intensity, using 0.2 mM benzoate and various concentrations of the scavenger. The fluorescence intensity was detectable down to 0.15 μM of 2-HOBZ produced. For various compounds, rate constants obtained in this way were similar to those measured by pulse-radiolysis.

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

AbstractUsing 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[2.2.1.02, 6]heptane), and quadricyclane (quadricyclo[2.2.1.02, 6.03, 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.

Rate constants for the gas‐phase reactions of Cl atoms with a series of hydrofluorocarbons and hydrochlorofluorocarbons at 298 ± 2 K

AbstractA relative rate method has been used to determine rate constants for the gas‐phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH4 of (1.0 ± 0.2) − 10−13 cm3 molecule−1 s−1 at 298 K, the following Cl atom reaction rate constants (in units of 10−15 cm3 molecule−1 s−1) were obtained: CH3F, 340 ± 70; CH3CHF2, 240 ± 50; CH2FCl, 110 ± 25; CHFCl2, 21 ± 4; CHCl2CF3, 14 ± 3; CHFClCF3, 2.7 ± 0.6; CH3CFCl2, 2.4 ± 0.5; CHF2Cl, 2.0 ± 0.4; CH2FCF3, 1.6 ± 0.3; CH3CF2Cl, 0.37 ± 0.08; and CHF2CF3, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.

Gas‐phase reactions of 1,4‐benzodioxan, 2,3‐dihydrobenzofuran, and 2,3‐benzofuran with OH radicals and O3

AbstractThe kinetics of the gas‐phase reactions of 1,4‐benzodioxan, 2,3‐dihydrobenzofuran, and 2,3‐benzofuran with OH radicals and O3 have been studied at 298 ± 2 K and atmospheric pressure of air and the products have also been investigated. 1,4‐Benzodioxan and 2,3‐dihydrobenzofuran were chosen as volatile model compounds for dibenzo‐p‐dioxin and dibenzofuran, respectively. The rate constants, or upper limits thereof, for the O3 reactions were (in cm3 molecule−1 s−1 units): 1,4‐benzodioxan, <1.2 × 10−20; 2,3‐dihydrobenzofuran, <1 × 10−19; and 2,3‐benzofuran, (1.83 ± 0.21) × 10−18. Using a relative rate method, the rate constants for the OH radical reactions (in cm3 molecule−1 s−1 units) were: 1,4‐dibenzodioxan, (2.52 ± 0.38) × 10−11; 2,3‐dihydrobenzofuran, (3.66 ± 0.56) × 10−11; and 2,3‐benzofuran, (3.73 ± 0.74) × 10−11. Salicylaldehyde was observed as a product of the OH radical‐initiated and O3 reactions of 2,3‐benzofuran, with measured formation yields of 0.26 ± 0.05 and 0.13 ± 0.07, respectively.

Interactions of formate ion with triplets of anthraquinone-2-sulfonate, 1,4-naphthoquinone, benzophenone-4-carboxylate and benzophenone-4-sulfonate

The interaction of formate with the triplet states of naphthoquinone (NQ), anthraquinone-2-sulfonate (AQS), benzophenone-4-carboxylate (BC), and benzophenone-4-sulfonate (BS) was studied by laser flash photolysis. Rate constants were determined either by direct measurement of triplet lifetimes or by inhibition of product yields by competitive reactants. Radical products are formed in two stages, direct reduction by formate and efficient secondary reduction by initially formed CO{sub 2}{sup {sm bullet}{minus}} radicals. The quinones react by electron transfer with quenching rate constants k{sub q}(NQ) = 3 {times} 10{sup 9} and k{sub q}(AQS) = 4 {times} 10{sup 8} M{sup {minus}1} s{sup {minus}1}, giving anion radicals with primary yields of {phi}{sub R}(NQ) {approximately} 0.7 and {phi}{sub R}(AQS) {approximately} 0.3. Formic acid quenches {sup 3}AQS much more slowly. The less strongly oxidizing ketone triplets react by H-atom abstraction, k{sub q}(BC) = 1.3 {times} 10{sup 7} and k{sub q}(BS) = 5.3 {times} 10{sup 7} M{sup {minus}1} s{sup {minus}1}, giving protonated ketyl radicals with primary yields {phi}{sub R} {approximately} 0.7. Photoreduction of BC exhibits a deuterium isotope effect, k{sub H}/k{sub D} = 1.6, whereas AQS shows none. A new, short-lived transient, E, is observed in the {sup 3}AQS-formate reaction, which may be an exciplex or adduct. The redox potential, E{degree}{prime}(NQ/NQ{supmore » {sm bullet}{minus}}) = {minus}0.12 V, and rate constants for radical reactions of NQ and O{sub 2} were measured by pulse radiolysis. The results are discussed in terms of pertinent redox potentials, bond strengths, and the nature of the exciplex intermediates.« less

Structure and ESR investigation of plasma‐polymerized film of hexafluoropropene

AbstractThe structure and constitution of plasma‐polymerized film of C3F6 (PPHFP) have been investigated by measuring its ESCA, 19F‐NMR, and IR spectra. It is found that the PPHFP film was a high degree of branching and 57% of quaternary carbons are linked to CF3 groups. It is also found that the constitution of PPHFP film is changed greatly at high power and a large amount of Si and O atoms are linked to the PPHFP chains. Furthermore, using element analysis, ESCA, and theoretical calculation by electronegative model, we found that the nitrogen atoms get into the PPHFP chains when using N2 as plasma gas. Besides, the radical concentration in the film is obtained to be 9.97 × 1019 spins/g and its half‐life is about half a year at room temperature in Ar gas. Having investigated decay process of the radicals in two gases of air and Ar, we calculated the activation energies and rate constants of radical recombination and oxidation reactions at different temperatures.

Phenomenological study of a new flow model of the Belousov–Zhabotinskii reaction

We present a new flow model of the Belousov–Zhabotinskii reaction. The model uses the modified Field and Forsterling set of rate constants and incorporates a set of radical reactions generating bromide ions from HOBr without passing through BrMA. Two separate sets of the radical reaction rate constants are chosen, and the behaviour of each set is examined at different flow rates. Mixed-mode oscillations, chaos and three distinct types of bursting are observed. The trend in complex phenomena is discussed and compared with experimental results.

Collision-theory calculations of rate constants for some atmospheric radical reactions over the temperature range 10-600 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCollision-theory calculations of rate constants for some atmospheric radical reactions over the temperature range 10-600 KL. F. PhillipsCite this: J. Phys. Chem. 1990, 94, 19, 7482–7487Publication Date (Print):September 1, 1990Publication History Published online1 May 2002Published inissue 1 September 1990https://doi.org/10.1021/j100382a033RIGHTS & PERMISSIONSArticle Views194Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (839 KB) Get e-Alerts

Rate constants for the gas-phase reactions of OH and NO 3 radicals and O 3 with sabinene and camphene at 296±2 K

The rate constants for the gas-phase reactions of sabinene and camphene, two monoterpenes emitted from vegetation, with OH and NO 3 radicals and O 3 have been determined at 296±2 K and one atmosphere total pressure of air. The OH and NO 3 radical reaction rate constants were determined using relative rate techniques. Using rate constants of k(OH + isoprene) = 1.01 × 10 −10 cm 3 molecule −1 s −1, k(NO 3 + trans-2-butene) = 3.87 × 10 −13 cm 3 molecule −1 s −1 and k(NO 3 + 2-methyl-2-butene) = 9.33 × 10 −12 cm 3 molecule −1 s −1, the following OH and NO 3 radical reaction rate constants (in cm 3 molecule −1 s −1 were obtained: OH radical reaction; sabinene, 1.17 × 10 −10 and camphene, 5.33 × 10 −11; NO 3 radical reaction; sabinene, 1.01 × 10 −11, and camphene, 6.54 × 10 −13. The absolute O 3 reaction rate constants determined were (in cm 3 molecule −1 s −1 units): sabinene, 8.07 × 10 −17, and camphene, 9.0 × 10 −19. These rate constants are compared to literature data for other structural-related alkenes and monoterpenes.

ChemInform Abstract: Kinetics of CH Radical Reactions with N2O, SO2, OCS, CS2, and SF6

Pulsed laser photolysis/laser-induced fluorescence (LIF) is utilized to measure absolute rate constants of CH radical reactions as a function of temperature and pressure. Multiphoton dissociation of CHBr3 at 266 nm is employed for the generation of CH (X2Π) radicals. The CH radical relative concentration is monitored by exciting fluorescence on the R1(2) line of the (A2Δ – X2Π) transition at 429.8 nm. A resistively heated cell allows temperature studies to be performed from room temperature to ≈670 K. The following Arrhenius equations are derived: With the exception of SF6, the reactions of sulfur containing species proceed at rates that are near the theoretical gas kinetic collision frequency. Additionally, these reactions all have activation energies that are near zero or slightly negative. These observations are consistent with an insertion-decomposition mechanism being dominant under these conditions.

Kinetics of CH radical reactions with N2O, SO2, OCS, CS2, and SF6

AbstractPulsed laser photolysis/laser‐induced fluorescence (LIF) is utilized to measure absolute rate constants of CH radical reactions as a function of temperature and pressure. Multiphoton dissociation of CHBr3 at 266 nm is employed for the generation of CH (X2Π) radicals. The CH radical relative concentration is monitored by exciting fluorescence on the R1(2) line of the (A2Δ – X2Π) transition at 429.8 nm. A resistively heated cell allows temperature studies to be performed from room temperature to ≈︂670 K. The following Arrhenius equations are derived: With the exception of SF6, the reactions of sulfur containing species proceed at rates that are near the theoretical gas kinetic collision frequency. Additionally, these reactions all have activation energies that are near zero or slightly negative. These observations are consistent with an insertion‐decomposition mechanism being dominant under these conditions.

Kinetics of the gas‐phase reactions of the OH radical with (C2H5)3PO and (CH3O)2P(S)Cl at 296 ± 2 K

AbstractThe kinetics of the gas‐phase reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl and of the reactions of NO3 radicals and O3 with (CH3O)2P(S)Cl have been studied at room temperature. Using a relative rate technique, the rate constants determined for the reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl at 296 ± 2 K and 740 torr total pressure of air were (5.53 ± 0.35) × 10−11 and (5.96 ± 0.38) × 10−11 cm3 molecule−1 s−1, respectively. Upper limits to the rate constants for the NO3 radical and O3 reactions with (CH3O)2P(S)Cl of <3 × 10−14 cm3 molecule−1 s−1 and <2 × 10−19 cm3 molecule−1 s−1, respectively, were obtained. These data are compared and discussed with previous literature data for organophosphorus compounds.

Atmospheric reactions of chloroethenes with the OH radical

AbstractThe kinetics and products of the homogeneous gas‐phase reactions of the OH radical with the chloroethenes were investigated at 298 ± 2 K and atmospheric pressure. Using a relative rate technique and ethane as a scavenger for the chlorine atoms produced in these OH radical reactions, rate constants (in units of 10−12 cm3 molecule−1s−1) of 8.11 ± 0.24, 2.38 ± 0.14, and 1.80 ± 0.03 were obtained for 1,1‐dichloroethene, cis‐1, 2‐dichloroethene and trans‐1,2‐dichloroethene, respectively. Under these conditions, the major products observed by long pathlength FT‐IR absorption spectroscopy were HCHO and HC(O)Cl from vinyl chloride; HC(O)Cl from cis‐ and trans‐1,2‐dichloroethene; HCHO and COCl2 from 1,1‐dichloroethene; HC(O)Cl and COCl2 from trichloroethene; and COCl2 from tetrachloroethene. In the absence of a Cl atom scavenger, significant yields of the chloroacetyl chlorides, CHxCl3−xC(O)Cl, were observed from 1,1‐dichloro‐, trichloro‐ and tetrachloroethene, indicating that these products resulted from reactions involving chlorine atoms. The yields of all of these products are reported and the mechanisms of these gas‐phase reactions discussed. In addition, OH radical reaction rate constants were redetermined, in the presence of a Cl atom scavenger, for cis‐ and trans‐1,3‐dichloropropene and 3‐chloro‐2‐chloromethyl‐1‐propene, being (in units of 10−12 cm3 molecule−1 s−1) 8.45 ± 0.41, 14.4 ± 0.8, and 33.5 ± 3.0, 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.

ChemInform Abstract: A Structure‐Activity Relationship for the Estimation of Rate Constants for the Gas‐Phase Reactions of OH Radicals with Organic Compounds.

AbstractThe structure‐activity relationship published by the author (1986) is further updated and extended to allow OH radical reaction rate constants for organic compounds containing ‐NH2, =NH, and =N‐ groups and S atoms to be calculated at room temp. and atmospheric pressure of air.

Determination of sulfite radical (SO.3-) reaction rate constants by means of competition kinetics.

The sulfite radical anion (SO.3-) was found to react rapidly with the flavonoid quercetin (k = 2.5 x 10(8) dm3mol-1s-1) and the carotenoids crocin (k = 1.0 x 10(9) dm3mol-1s-1) and crocetin (k = 1.5 x 10(9) dm3mol-1s-1). The reactions can easily be monitored due to the strong absorptions of the substrates and, in the case of quercetin, the formation of a strongly absorbing transient species. Using these substances, we determined by means of competition kinetics rate constants of SO.3- reactions with nucleic acid components, polyunsaturated fatty acids, and glutathione.

A structure‐activity relationship for the estimation of rate constants for the gas‐phase reactions of OH radicals with organic compounds

AbstractA previous technique for the calculation of rate constants for the gas‐phase reactions of the OH radical with organic compounds has been updated and extended to include sulfur‐ and nitrogen‐containing compounds. The overall OH radical reaction rate constants are separated into individual processes involving (a) H‐atom abstraction from CH and OH bonds in saturated organics, (b) OH radical addition to >CC< and CC unsaturated bonds, (c) OH radical addition to aromatic rings, and (d) OH radical interaction with NH2, >NH, >N, SH, and S groups. During its development, this estimation technique has been tested against the available database, and only for 18 out of a total of ca. 300 organic compounds do the calculated and experimental room temperature rate constants disagree by more than a factor of 2. This suggests that this technique has utility in estimating OH radical reaction rate constants at room temperature and atmospheric pressure of air, and hence atmospheric lifetimes due to OH radical reaction, for organic compounds for which experimental data are not available. In addition, OH radical reaction rate constants can be estimated over the temperature range ca. 250–1000 K for those organic compounds which react via H‐atom abstraction from CH and OH bonds, and over the temperature range ca. 250–500 K for compounds containing >CC< bond systems.