Oxidation by hydroxyl radicals

The most reliable kinetic data are for atmospheric oxidation by hydroxyl radicals. These data are usually reported as second-order rate constants applied to the concentration of the chemical and the concentration of hydroxyl radicals (usually of the order of 10s radicals per cm3). The product of the assumed hydroxyl radical concentration and the second-order rate constant is a first-order rate constant from which a half-life can be deduced. 

Table 2. Chemical species those are able to be oxidized by hydroxyl radicals [36]...

All cresol isomers can be rapidly removed from environmental media. The dominant removal mechanism in air appears to be oxidation by hydroxyl radical during the day and nitrate radical at night, with half-lives on the order of a day. In water under aerobic conditions, biodegradation will be the dominant removal mechanism half-lives will be on the order of a day to a week. Under anaerobic conditions, biodegradation should still be important, but half-lives should be on the order of weeks to months. In soil under aerobic conditions, biodegradation is also important, but half-lives are less certain, although probably on the order of a week or less. 

The mechanism that accounts for the oleofinic oxidation by hydroxyl radicals is the hydrogen abstraction. Moreover Cl radicals may also be an important mechanism for chlorinated organics. When the C-Cl bond is broken by photolysis, a Cl radical is released and can initiate additional oxidation reactions through a chain mechanism as follows ... 

Indirect photolysis rate constant, usually with oxidant specified e.g., kHO for oxidation by hydroxyl radical... 

Oxidation of DMDS by OH Radical Dimethyl disulfide is oxidized by hydroxyl radicals (50-53) according to the reaction ... 

Oxidation rate constant k, for gas-phase second order rate constants, kOH for reaction with OH radical, kNG3 with N03 radical and kG3 with 03 or as indicated, data at other temperatures see reference k0H(calc) = 1.8 x to 12 cm3 molecule-1 s 1 at room temp. (SAR, Atkinson 1987) tropospheric lifetime x(calc) = 8-17 d, based on kOH(calc.) = (1.4 - 2.9) x io 12 cm3 molecule-1 s 1 for dichlorobiphcnyls at room temp. (Atkinson 1987) koH.(aq.) = 7.9 x 109 dm3 mol-1 s-1, PCB in Aroclor 1242 mixture, oxidized by hydroxyl radicals generated with Fenton s reagent in aqueous solutions at 25°C, half-lives range from 4-l 1 d in freshwater systems, 0.1-10 d in cloud water, > 1000 d in oceans for PCBs with as many as 8 chlorines (relative rate method, Sedlak Andren 1991) tropospheric lifetime x(calc) = 3.4-7.2 d, based on the experimentally determined gas-phase reaction kOH(exptl) = (2.0-4.2) x io-12 cm3 molecule-1 s-1, and the calculated kOH(calc) = (1.4 - 3.1) x io-12 cm3 molecule-1 s 1 at room temp. (Kwok et al. 1995)... 

In the case of water splitting, this process takes place, in most cases, through oxidation by hydroxyl radicals formed when the photogenerated holes interact with adsorbed water in the following way (Figure 2.11) [48,49] ... 

L7. Leeuwenburgh, C., Hansen, P., Shaish, A., Holloszy, J. O., and Heinecke, J. W., Markers of protein oxidation by hydroxyl radical and reactive nitrogen species in tissues of aging rats. Am, J. Physiol. 274, R453-R461 (1998). 

Molecular hydrogen is assumed to be well mixed in the troposphere, with a mixing ratio of 0.4 to 0.6 ppm [Junge (128) and Scholz, Ehhalt, Heidt, and Martell (219)]. Koyama (142) found that swamps and paddies are very small natural sources. Levy (153) proposed both an atmospheric source (photodissociation of formaldehyde) and an atmospheric sink (oxidation by hydroxyl radical). From daily average number densities for the hydroxyl radical and a daily average hydrogen production rate,... 

---