Hydroxyl radical reaction with carbonate

Further reaction of carbon monoxide with hydroxyl radical yields carbon dioxide (equation 8.35), whereas reaction of carbon monoxide with carbine yields ketene (equation 8.36) [14], Atomic hydrogen, in turn, converts carbon monoxide to formaldehyde (equations 8.37-8.38), which in principle may be a substrate for prebiotic... 

The reaction of carbon monoxide with hydroxyl radicals is a very important reaction in the lower atmosphere. It oxidizes CO, a highly toxic gas... 

PROBABLE FATE photolysis, could be important, only identifiable transformation process if released to air is reaction with hydroxyl radicals with an estimated half-life of 8.4 months oxidation, has a possibility of occurring, photooxidation half-life in air 42.7 days-1.2 yrs hydroiysis too slow to be important, first-order hydrolytic half-life 275 yrs voiatilization likely to be a significant transport process, if released to water or soil, volatilization will be the dominant environmental fate process, volatilization half-life from rivers and streams 43 min-16.6 days with a typical half-life being 46 hrs sorption adsorption onto activated carbon has been demonstrated bioiogicai processes moderate potential for bioaccumulation, biodegradation occurs in some organisms, in aquatic media where volatilization is not possible, anaerobic degradation may be the major removal process other reactions/interactions may be formed from haloform reaction after chlorination of water if sufficient bromide is present... 

Much more significant is reaction with hydroxyl radicals, which are themselves formed photolytically, but many other molecules, and free radicals are involved. The decomposition of Carbon Tetrachloride (and F 11 and F 12), which are the only halogenated compounds which reach the stratosphere in any quantity, is initiated there by direct photolytic production of a chlorine atom some of the other... 

Hydroxyl groups are always protected prior to reaction with bromine radicals, and derived esters have proved suitable. Benzoates are particularly useful and are preferable to acetates, which are susceptible to methyl-group bromination, particularly when the acetoxyl groups are bonded to carbon atoms in the -relationship to carbon radicals. Conceivably, this susceptibility can be accounted for as follows. 

The formation of scavenger substances can also retard removal efficiency and kinetic reaction rates. Scavengers are ions such as bicarbonate, carbonate, chloride, and humic acid, etc. These scavengers subsequently react with hydroxyl radicals produced during the degradation process. Therefore, the removal efficiency will be reduced significantly. In the presence of scaveng-... 

Bonifacic M, Schafer K, Mockel H, Asmus K-D (1975b) Primary steps in the reactions of organic disulfides with hydroxyl radicals in aqueous solution. J Phys Chem 79 1496-1502 Bonifacic M, Armstrong DA, Carmichael I, Asmus K-D (2000a) p-Fragmentation and other reactions involving aminyl radicals from amino acids. J Phys Chem B 104 643-649 Bonifacic M, Hug GL, Schoneich C (2000b) Kinetics of the reactions between sulfide radical cation complexes,[S.. S]+ and [S. N]+, and superoxide or carbon dioxide radical anions. J Phys Chem A 104 1240-1245... 

Organic radicals formed in these reactions may further react with oxygen (in an aerated medium as in water treatment) to yield organic peroxyl radicals that can eventually react with compounds present in the medium to release the superoxide ion radical (see route through 5 in Fig. 6 see also the work of von Sonntag and Schuchmann [122] for more details about peroxyl radical reactions). In these cases, compounds that react with the hydroxyl radical are known to be promoters of ozone decomposition because the superoxide ion radical consumes ozone at a fast rate [see reaction (63) above]. On the contrary, if the reaction between hydroxyl radical and compound M does yield inactive radicals, M is known as a scavenger or inhibitor of ozone decomposition (see route to 4 in Fig. 6). Many natural substances such as humic substances and carbonates are known to possess such a role [121]. However, the case of carbonate ion is rather special because it reacts with hydroxyl radicals to yield the carbonate ion radical ... 

The peroxyl radicals M-0-0 thus formed undergo a variety of molecular rearrangements and/or elimination reactions until the final oxidation products are formed. In reality, these oxidation products are interfering with hydroxyl radical attack on M and hence they are complicating the product spectrum considerably. Additionally, the bicarbonate and carbonate radicals may introduce selective oxidation reactions into the degradation cycle (Fig. 6-16). 

Ab initio molecular orbital theory is utilized to study the hydrogen abstraction reaction of n-bromopropane with hydroxyl radical and chlorine atom. The stability of the trans and gauche isomers of n-bromopropane is explored. The potential energy surface of both reactions is characterized by pre- and post-reactive complexes, as well as transition state structures in both trans and gauche isomeric forms. The importance of these two reactions relies on the ultimate product distribution from both reactions. Differences in the reactivity of 1-bromopropane toward OH and Cl are observed. The reaction of n-bromopropane with OH radical favors the abstraction of hydrogen atoms while the reaction with Cl atoms favors the abstraction of hydrogen atoms at the a and p carbon sites. 

Whether or not CO can affect an increase in the oxidation rate of NO in the presence of hydrocarbons depends on the relative rates of these competing reactions. For a highly reactive hydrocarbon such as mesity-lene, the reaction of the hydrocarbon with hydroxyl radicals is so fast that the reaction of CO with OH cannot compete even at high CO-hydrocarbon ratios. For less reactive hydrocarbons such as ethylene and 1-butene, CO competes with the hydrocarbon for the OH radicals and, in systems containing these hydrocarbons, a carbon monoxide effect is possible. The rate constant for the reaction of ethylene with hydroxyl radicals has been measured to be 3.6 X 10 1/mole-sec 15). This is forty times greater than the rate constant of 8.9 X 10 1/mole-sec (JO) for the reaction of OH with CO. Therefore, a CO effect should be possible at CO-ethylene ratios of 40 or greater. Experimentally, an increase in the NO oxidation rate for this system was observed at a CO—hydrocarbon ratio of 50. 

J.V. Goldstone, M.J. Pullin, S. Bertilsson, B.M. Voelker (2002). Reactions of hydroxyl radical with humic substances Bleaching, mineralization, and production of bioavail-able carbon substrates. Environ. Sci. Technol, 36,364-372. 

An example in which formation of a carbon radical is not the initial reaction is provided by the atmospheric reactions of organic sulfides and disulfides. They also provide an example in which rates of reaction with nitrate radicals exceed those with hydroxyl radicals. 2-dimethylthiopropionic acid is produced by algae and by the marsh grass Spartina alternifolia, and may then be metabolized in sediment slurries under anoxic conditions to dimethyl sulfide (Kiene and Taylor 1988), and by aerobic bacteria to methyl sulfide (Taylor and Gilchrist 1991). It should be added that methyl sulfide can be produced by biological methylation of sulfide itself (HS ) (Section 6.11.4). Dimethyl sulfide — and possibly also methyl sulfide — is oxidized in the troposphere to sulfur dioxide and methanesulfonic acids. 

Carbon disulfide reacts with hydroxyl radicals in the troposphere to produce carbonyl sulfide (Cox and Sheppard 1980). The lifetime of carbon disulfide in the troposphere, assuming a reaction rate constant of 4.3 x 10"13 cm3 molecule 1, is 73 days (uncertain) other estimates (assuming different reaction rate constants) range from less than 1 week to more than 10 weeks (Cox and Sheppard 1980 EPA 1978a ... 

Atkinson R, Perry RA, Pitts JN Jr. 1978. Rate constants for the reaction of hydroxyl radicals with carbonyl sulfide, carbon disulfide and dimethyl thioether over the temperature range 299-430 K. Chem Phys Lett 54 14-18. 

---