Hydroxyl radical reaction rate constants

The C—H bond energies vary from 423 kJ for a primary C—H 410 kJ for a secondary bond and 402 kJ mol for a tertiary bond. Thus for a reaction involving hydrogen abstraction one would predict that tertiary C—H bonds would be most susceptible and that the overall reaction rate would depend on both the number and type of C—H bonds. An empirical structure-activity relation for predicting rates of hydroxyl radical reactions has been developed based on this assumption. The rate constant for a given compound is expressed as a function of the number of each type of bond and the adjacent functional groups as follows ... 

The dominant transformation process for trichloroethylene in the atmosphere is reaction with photochemically produced hydroxyl radicals (Singh et al. 1982). Using the recommended rate constant for this reaction at 25 °C (2.36x10 cm /molecule-second) and a typical atmospheric hydroxyl radical concentration (5x10 molecules/cm ) (Atkinson 1985), the half-life can be estimated to be 6.8 days. Class and Ballschmiter (1986) state it as between 3 and 7 days. It should be noted that the half-lives determined by assuming first-order kinetics represent the calculated time for loss of the first 50% of trichloroethylene the time required for the loss of the remaining 50% may be substantially longer. 

No systematic studies of a number of compoimds have yet appeared to discover correlations suggestive of mechanism. This paper presents the fractional conversions and reaction rates measured under reference conditions (50 mg contaminants/m ) in air at 7% relative humidity (1000 mg/m H2O), for 18 compounds including representatives of the important contaminant classes of alcohols, ethers, alkanes, chloroethenes, chloroalkanes, and aromatics. Plots of these conversions and rates vs. hydroxyl radical and chlorine radical rate constants, vs. the reactant coverage (dark conditions), and vs. the product of rate constant times coverage are constructed to discern which of the proposed mechanistic suggestions appear dominant. 

Figure 3a presents the maximum conversion and the initial rate of each compoimd versus the literatme second order rate constant for contaminant reaction with hydroxyl radicals. The conversion increases with increasing values of koH, but with considerable scatter. 

Anbar, M. and Neta, P. (1967). A compilation of specific biomolecular rate constants for the reaction of hydrated electrons, hydrogen atoms and hydroxyl radicals with inorganic and organic compounds in aqueous solutions. Int. J. Appl. Radiat. Isot. 18, 493-497. 

The principal pathway leading to degradation of acrylonitrile in air is believed to be photooxidation, mainly by reaction with hydroxyl radicals (OH). The rate constant for acrylonitrile reaction with OH has been measured as 4.1 x 10" cm /molecule/second (Harris et al. 1981). This would correspond to an atmospheric half-life of about 5 to 50 hours. This is consistent with a value of 9 to 10 hours measured in a smog chamber (Suta 1979). 

DeMore, W.B., Bayes, K.D.(1999) Rate constants for the reactions of hydroxyl radical with several alkanes, cycloalkanes, and dimethyl ether. J. Phys. Chem. A, 103, 2649-2654. 

Jolly, G.S., Paraskevopoulos, G., Singleton, D.L. (1985) Rate of OH radical reactions. XII. The reactions of OH with c-C3H6, c-C5H10, and c-C7H14. Correlation of hydroxyl rate constants with bond dissociation energies. Int. J. Chem. Kinet. 17, 1-10. 

Winer, A.M., Lloyd, A.C., Damall, KR., Pitts, Jr., J.N. (1976) Relative rate constants for the reaction of the hydroxyl radical with selected ketones, chloroethenes, and monoterpene hydrocarbons. J. Phys. Chem. 80, 1635-1639. 

Kwok, W.S.C., Atkinson, R. (1995) Estimation of hydroxyl radical reaction rate constants for gas-phase organic compounds using a structure reactivity relationship an update. Atmos. Environ. 29, 1685-1695. 

Ohta, T., Ohyama, T. (1985) A set of rate constants for the reactions of hydroxyl radicals with aromatic hydrocarbons. Bull. Chem. Soc. Jpn. 58, 3029-3030. 

Oxidation rate constant k, for gas-phase second order rate constants, koH for reaction with OH radical, kNC,3 with N03 radical and krj, with 03 or as indicated, data at other temperatures see reference photooxidation tA = 1111-38500 h, based on measured rate constant for reaction with hydroxyl radical in water (Radding et al. 1976 quoted, Howard et al. 1991) k(aquatic) fate rate of 50 L mol 1 s 1 with t,A = 1600 d (Callahan et al. 1979)... 

Oxidation photooxidation t,/2 = 0.32-3.2 h estimated, based on estimated rate constant for the reaction with hydroxyl radicals in air (Atkinson 1987 quoted, Howard et al. 1991) photooxidation t,/2(aq.) = 1,57 - 157 yr estimated, based on measured rate constant for the reaction with singlet oxygen in benzene (Stevens et al. 1974 quoted, Howard et al. 1991). 

Photooxidation l/2 = 1608-16082 h based on estimated rate constant for the reaction with hydroxyl radical in air (Atkinson 1987 quoted, Howard et al. 1991). 

Peroxyl radicals with a strong oxidative effect along with ROOH are continuously generated in oxidized organic compounds. They rapidly react with ion-reducing agents such as transition metal cations. Hydroxyl radicals react with transition metal ions in an aqueous solution extremely rapidly. Alkyl radicals are oxidized by transition metal ions in the higher valence state. The rate constants of these reactions are collected in Table 10.5. 

Various hydroxyl and amino derivatives of aromatic compounds are oxidized by peroxidases in the presence of hydrogen peroxide, yielding neutral or cation free radicals. Thus the phenacetin metabolites p-phenetidine (4-ethoxyaniline) and acetaminophen (TV-acetyl-p-aminophenol) were oxidized by LPO or HRP into the 4-ethoxyaniline cation radical and neutral V-acetyl-4-aminophenoxyl radical, respectively [198,199]. In both cases free radicals were detected by using fast-flow ESR spectroscopy. Catechols, Dopa methyl ester (dihydrox-yphenylalanine methyl ester), and 6-hydroxy-Dopa (trihydroxyphenylalanine) were oxidized by LPO mainly to o-semiquinone free radicals [200]. Another catechol derivative adrenaline (epinephrine) was oxidized into adrenochrome in the reaction catalyzed by HRP [201], This reaction can proceed in the absence of hydrogen peroxide and accompanied by oxygen consumption. It was proposed that the oxidation of adrenaline was mediated by superoxide. HRP and LPO catalyzed the oxidation of Trolox C (an analog of a-tocopherol) into phenoxyl radical [202]. The formation of phenoxyl radicals was monitored by ESR spectroscopy, and the rate constants for the reaction of Compounds II with Trolox C were determined (Table 22.1). 

Rate Constants for the Reaction of Hydroxyl Radical with Flavonoids and Related Compounds (Pulse-Radiolytic Experiments)... 

Laser magnetic resonance, which has already been used to detect the free hydroxyl, methynyl (CH), hydroperoxy, formyl (HCO), and amino radicals in low-pressure gases and could be used to determine rate constants for the reactions of the smaller free radicals. 

The aromatic-hydroxyl radical reaction has been studied by Davis et They reported rate constants for benzene and toluene and concluded that hydroxyl additions to the aromatic ring compete favorably with the abstraction of hydrogen atom from the alkyl substituent. Doyle et al recently published hydroxyl reaction rate constants for a series of alkylbenzenes. 

FIGURE 3-13 Relations between conversion of nitric oxide to nitrogen dioxide and ozone, atomic oxygen, and hydroxyl-radical reaction rate constants. Reprinted with permission from Grosjean. ... 

Chemical/Physical. In the gas phase, cycloate reacts with hydroxyl and NO3 radicals but not with ozone. With hydroxy radicals, cleavage of the cyclohexyl ring was suggested leading to the formation of a compound tentatively identified as C2H5(Cff0)NC(0)SC2H5. The calculated photolysis lifetimes of cycloate in the troposphere with hydroxyl and NO3 radicals are 5.2 h and 1.4 d, respectively. The relative reaction rate constants for the reaction of cycloate with OH and nitrate radials are 3.54 x lO " and 3.29 x 10 cm /molecule-sec, respectively (Kwok et al., 1992). 

CASRN 544-40-1 molecular formula CsHisS FW 146.29 ChemicaPPhysical. MacLeod et al. (1984) studied the reaction of hydroxyl radicals ( limiting reagent ) with dibutyl sulfide in a discharge flow reactor. The rate constants for this reaction at 20,... 

Haag, W.R. and Yao, D.C.C. Rate constants for the reaction of hydroxyl radicals with several drinking water contaminants. 

Niki, H., Maker, P.D., Savage, C.M., and Breitenbach, L.P. Relative rate constants for the reaction of hydroxyl radical with aldehydes, 7 Phys. Chem., 82(2) 132-134, 1978. 

Hodson J. 1988. The estimation of the photodegradation of organic compoundsby hydroxyl radical reaction rate constants obtained from nuclear magneticresonance spectroscopy chemical shift data. Chemosphere 17 2339- 2348. 

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