OH radicals, reactions

Anderson PN, RA Hites (1996) OH radical reactions the major removal pathway for polychlorinated biphenyls from the atmosphere. Environ Sci Technol 30 1756-1763. 

Kwok ESC, R Atkinson, J Arey (1995) Rate constants for the gas-phase reactions of the OH radical with dichlorobiphenyls, 1-chlorodibenzo-p-dioxin, 1,2-dimethoxybenzene, and diphenyl ether estimation of OH radical reaction rate constants for PCBs, PCDDs, and PCDFs. Environ Sci Technol 29 1591-1598. 

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. 

Yim et al. (2002) studied the sonlytic degradation of diethyl phtahalate in aqueous solution. Degradation followed pseudo-first-order kinetics. Monoethyl phthalate, a hydrolysis product of diethyl phthalate, was approximately 3.3 times higher at pH 12 than at pH 7. The investigators concluded that the reaction was affected by pH of the solution. In the presence of ultrasound, the OH radical reaction, thermal reaction, and hydrolysis were all involved during the reaction. 

Atkinson, R. Estimation of OH radical reaction rate constants and atmospheric lifetimes for polychlorinated biphenyls, dibenzo-/rdioxins, and dibenzofmans. Environ. Sci Technol, 21(3) 305-307, 1987a. 

Overend, R. and Paraskevopoulos, G. Rates of OH radical reactions. 4. Reactions with methanol, ethanol, 1-propanol, and 2-propanol at 296 K, J. Phys. Chem., 82(12) 1329-1333, 1978. 

De, AK Chaudhuri, B Bhattaehaijee, S Dutta, BK. Estimation of OH radical reaction rate eonstants for phenol and ehlorinated phenols using UV/H2O2 photo-oxidation. Journal of Hazardous Materials, 1999 64 (1), 91-104. 

Jolly, G. S., G. Paraskevopoulos, and D. L. Singleton, Rates of OH Radical Reactions. XII. The Reactions of OH with c-C3H, c-C Hl(l, and c-C7Hu. Correlation of Hydroxyl Rate Constants with Bond Dissociation Energies, Int. J. Chem. Kinet., 17, 1-10... 

Dhanya, S., and R. D. Saini, Rate Constants of OH Radical Reactions in Gas Phase with Some Fluorinated Compounds A Correlation with Molecular Parameters, Int. J. Chem. Kinet., 29, 187-194 (1997). 

It should be noted that (R23) is a chain-propagating reaction, converting H atoms to HO2 radicals. However, because HO2 is much less reactive than H, O, and OH radicals, reaction (R23) acts in effect as a chain-terminating step. In addition to the gas-phase chainterminating steps, radicals may be deactivated at the walls of the vessel... 

For the 03/UV process Prengle (1975) has recommended the use of stirred photochemical tanks (STPR) to obtain better mass transfer. Simultaneous ozone contacting and irradiation was found to be more successful than in sequence due to the need for good ozone transfer to sustain the OH-radical reaction. A promising alternative to the STPR may be the... 

Although it is possible that Taube s results could also be explained by the formation of OH radicals, reactions (34) and (38) are consistent when allowance is made for deactivation of the HO-OH complex by solvent in the aqueous solution. 

The rate constants for 8 and 9 were determined by pulse radiolysis by adding known amounts of excess acid or H20-2 and measuring the pseudo-first order decay of hydrated electron absorption (15, 25). The rate constant for recombination of OH radicals (Reactions 19) was deter-... 

OH radical reaction rate constants for phenol were estimated by De et al. (1999). 

De, A.K., Chaudhuri, B., Bhattacharjee, S., Dutta, B.K., Estimation of OH radical reaction rate constants for phenol and chlorinated phenols using UV/H202 photo-oxidation, /. Haz. Mat., 64, 91-104, 1999. 

Moorthy PN, Hayon E (1975) Free-radical intermediates produced from the one-electron reduction of purine, adenine and guanine derivatives in water. J Am Chem Soc 97 3345-3350 Mori M, Teshima S-l, Yoshimoto H, Fujita S-l, Taniguchi R, Hatta H, Nishimoto S-l (2001) OH Radical reaction of 5-substituted uracils pulse radiolysis and product studies of a common redox-ambivalent radical produced by elimination of the 5-substituents. J Phys Chem B 105 2070-2078 Morin B, Cadet J (1995) Chemical aspects of the benzophenone-photosensitized formation of two lysine - 2 -deoxyguanosine cross-links. J Am Chem Soc 117 12408-12415 Morita H, Kwiatkowski JS,TempczykA(1981) Electronic structures of uracil and its anions. Bull Chem Soc Jpn 54 1797-1801... 

Vieira AJSC, Steenken S (1987a) Pattern of OH radical reaction with 6- and 9-substituted purines. Effect of substituents on the rates and activation parameters of unimolecular transformation reactions of two isomericOH adducts. J PhysChem 91 4138-4144 Vieira AJSC, Steenken S (1987b) Pattern of OH radical reaction with N6,N6-dimethyladenosine. Production of three isomeric OH adducts and their dehydration and ring opening reactions. J Am Chem Soc 109 7441-7448... 

Vieira AJSC, Steenken S (1990) Pattern of OH radical reaction with adenine and its nucleosides and nucleotides. Characterization of two types of isomeric OH adduct and their unimolecular transformation reactions. J Am Chem Soc 112 6986-6994 Vieira AJSC, Steenken S (1991) Pattern of OH radical reaction with N6,N6,9-trimethyladenine. Dehy-droxylation and ring-opening of isomeric OH-adducts. J PhysChem 95 9340-9346 Vieira AJSC, Candeias LP, Steenken S (1993) Hydroxyl radical induced damage to the purine bases of DNA in vitro studies. J Chim Phys 90 881-897... 

Estimation Methods for OH Radical Reaction Rate Constants... 

Based on direct spectroscopic measurements of OH radical concentrations at close to ground level, peak daytime OH radical concentrations are typically (3-10) x 106 molecule cm-3 (see, for example, Brauers et al., 1996 Mather et al., 1997 Mount et al., 1997). A diur-nally, seasonally, and annually averaged global tropospheric OH radical concentration has been derived from the emissions, atmosphere concentrations, and OH radical reaction rate constant for methyl chloroform (CH3CC13), resulting in a 24-hr average OH radical concentration of 9.7 x 10s molecule cm 3 (Prinn et al., 1995). 

For the majority of gaseous organic compounds, the potential loss or transformation processes in the troposphere are wet and dry deposition, photolysis, reaction with OH radicals, reaction with N03 radicals, and reaction with 03. The overall lifetime, xoverall, of a chemical present in the gas phase is then given by ... 

For the majority of gas-phase organic chemicals present in the troposphere, reaction with the OH radical is the dominant loss process (Atkinson, 1995). The tropospheric lifetime of a chemical is the most important factor in determining the relative importance of transport, to both remote regions of the globe and to the stratosphere, and in determining the possible buildup in its atmospheric concentration. Knowledge of the OH radical reaction rate constant for a gas-phase organic compound leads to an upper limit to its tropospheric lifetime. 

To date, OH radical reaction rate constants have been measured for 500 organic compounds (Atkinson, 1989, 1994, 1997). However, many more organic chemicals are emitted into the atmosphere, or formed in situ in the atmosphere from photolysis or chemical reactions of precursor compounds, for which OH radical reaction rate constants are not experimentally available. Thus the need to reliably calculate OH radical reaction rate constants for those organic compounds for which experimental data are not currently available. 

The method is based on the observations that gas-phase OH radical reactions with organic compounds proceed by four reaction pathways, assumed to be additive H-atom abstraction from C-H and O-H bonds, OH radical addition to >C=C< and -C=C-bonds, OH radical addition to aromatic rings, and OH radical "interaction" with N-, S-, and P-atoms and with more complex structural units such as ->P=S, >NC(0)S- and >NC(0)0- groups. The total rate constant is assumed to be the sum of the rate constants for these four reaction pathways (Atkinson, 1986). The OH radical reactions with many organic compounds proceed by more than one of these pathways estimation of rate constants for the four pathways follow. Section 14.3.5 gives examples of calculations of the OH radical reaction rate constants for the "standard" compounds lindane (y-hexachlorocyclohexane), trichloroethene, anthracene, 2,6-di-ferf-butylphenol, and chloropyrofos. 

The OH radical reactions with a number of nitrogen-, sulfur- and phosphorus-containing organic compounds appear to proceed, at least in part, by an initial addition reaction (Atkinson, 1989,1994 Kwok et al., 1996), although the products observed may in some cases be those expected from H-atom abstraction. Note that the recent study of Talukdar et al. (1997) indicates that the reactions of the OH radical with alkyl nitrates proceed only by H-atom abstraction, and Table 14.1 gives the applicable substituent group factors for alkyl nitrates. 

As examples of the calculation of OH radical reaction rate constants using the method discussed above (Kwok and Atkinson, 1995), the OH radical reaction rate constants for lindane [y-hexachlorocyclohexane cyclo-(-CHCl-)6], trichloroethene (CHC1=CC12), 2,6-di-tert-butylphenol, and chloropyrofos appear below. As the section dealing with OH radical addition to aromatic rings mentions, at present the rate constant for the reaction of the OH radical with anthracene (and other PAH) cannot be estimated with the method of Kwok and Atkinson (1995). In carrying out these calculations, one first must draw the structure of the chemical (the structures are shown in the appendix to Chapter 1). Then one carries out the calculations for each of the OH radical reaction pathways which can occur for that chemical. 

The stereochemical conformation of hexachlorocyclohexane (i.e., whether the Cl atoms are axial or equatorial) has no effect on the estimated rate constant for the OH radical reaction. For the purposes of the calculation, all six carbon atoms are therefore equivalent, with each carbon atom being bonded to two carbon atoms (each with substituent H and Cl atoms) and to one H atom and one Cl atom [i.e., (-CHCl-)6]. The rate constant therefore is given by ... 

To date, no experimentally measured OH radical reaction rate constant for lindane at room temperature is available in the literature for comparison. 

The OH radical reaction occurs at the >C=C< bond, and H-atom abstraction from the vinyl C-H bond is neglected. There are three Cl atom substituents around the >C=C< bond, and the "base" structural unit is the -CH=C< group (Table 14.2). The effects of the three Cl atom substituents are taken into account using the C(-Cl) value from Table 14.3. The rate constant, ktotal, for trichloroethene is given by ... 

The OH radical reaction rate constant for 2,6-di-ferf-butylphenol is given by ... 

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