Sulfuric acid reaction with hydroxyl radicals

Once sulfur dioxide has escaped into the atmosphere, it undergoes a series of reactions by which it is converted to sulfuric acid. Those reactions are somewhat complex and may follow at least three different courses. In the first of these reaction sequences, sulfur dioxide reacts with hydroxyl radicals in the atmosphere in the presence of some metallic catalyst (M) to form the bisulfite radical (HSO3 ) ... 

They also found that, depending on the electrolyte composition, the organics were oxidized on both the electrode surface by reaction with hydroxyl radicals and in the bulk of the solution by inorganic oxidants electrogenerated on the BDD anodes, such as peroxodisulfuric acid from sulfuric acid oxidation ... 

The atomic oxygen thus produced can react with molecular oxygen to form ozone. Acid rain results from the reaction of NO2 and SO3 with hydroxyl radical and water vapor in the air to form nitric acid (HNO3) and sulfuric acid (H2SO4). The acids dissolve in water and return to the earth in the rain. 

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. 

Figure 4-13 shows an example from a three-dimensional model simulation of the global atmospheric sulfur balance (Feichter et al, 1996). The model had a grid resolution of about 500 km in the horizontal and on average 1 km in the vertical. The chemical scheme of the model included emissions of dimethyl sulfide (DMS) from the oceans and SO2 from industrial processes and volcanoes. Atmospheric DMS is oxidized by the hydroxyl radical to form SO2, which, in turn, is further oxidized to sulfuric acid and sulfates by reaction with either hydroxyl radical in the gas phase or with hydrogen peroxide or ozone in cloud droplets. Both SO2 and aerosol sulfate are removed from the atmosphere by dry and wet deposition processes. The reasonable agreement between the simulated and observed wet deposition of sulfate indicates that the most important processes affecting the atmospheric sulfur balance have been adequately treated in the model. 

Other than water, protein is the major constituent of meat averaging nearly 21% in heef or chicken meat, with fat varying fiom 4.6 to 11.0% in beef and fiom 2.7 to 12.6% in chickoi. The principal radiolytic reactions of aqueous solutions of aliphatic amino acids are reductive deamination and decarboxylation. Alanine yields NH3, pyruvic add, acetaldehyde, propionic acid, CO2, H2, and ethylamine (6). Sulfur-containing amino adds are espedally sensitive to ionizing radiation. Cysteine can be oxidized to cystine by the hydroxyl radical or it can react with the hydrated electron and produce... 

The reaction reaches equilibrium rapidly if the hydroxyl group is attached to a reactive radical, as in tertiary alcohols. In such cases, excess of the halogen acid is shaken with the alcohol, and the mono-halogen compound is separated. With primary and secondary alcohols, equilibrium is reached more slowly, and a catalyst (such as zinc chloride in the case of hydrochloric acid, and sulfuric acid in the case of hydrobromic acid) is used. On account of its cost, hy-driodic acid is not used, but iodine and phosphorus, which react as follows ... 

Calvert (2 ) has pointed out that gas-phase reactions of SO2 with ozone (O3), hydroxyl radical (OH ), and hydroperoxyl radical (HOp ) are too slow to account for the aforementioned rates of sulfate production. Consequently, the catalytic autoxidation of SO2 in deliquescent haze aerosol and hydrometeors has been proposed as a viable non-photolytic pathway for the rapid formation of sulfuric acid in humid atmospheres (30-35). In addition, hydrogen peroxide and ozone have been given serious consideration as important aqueous-phase oxidants of dissolved SO2 as discussed by Martin (35). Oxidation by H2O2 seems to be most favorable under low pH conditions (pH < 4) because of a rapid rate of reaction anc[ a negative pH-dependence that favors the facile conversion of HSO3 to sulfate. 

Hatakeyama, S., Okuda, M., Akimoto, H. Formation of sulfur dioxide and methanesulfonic acid in the photooxidation of dimethyl sulfide in the air. Geophys. Res. Lett. 9, 583-586 (1982) Hatakeyama, S., Washida, N., Akimoto, H. Rate constants and mechanisms for the reaction of hydroxyl (OD) radicals with acetylene, propyne, and 2-butyne in air at 297 2 K. J. Phys. Chem. 90, 173-178 (1986)... 

Protonated Amino Radicals. The reac.tion of hydroxyl amine with TiCl, in aqueous, acidic methanol results in the formation of the simplest protonated amino radical, NH,T. This radical added readily to butadiene and to simple olefins to form products which were the result of coupling of the intermediate B-aminoalkyl radicals ( ). The addition reactions of protonated di-alkylamino radicals were described in a series of elegant papers by Neale and his co-workers (5-10). The radicals were generated from the appropriate N-chloroamines in presence of the unsaturated system. The most effective acid solvent combination was found to be 4M sulfuric acid in glacial acetic acid, but other acid/solvent combinations were also used. The reactions proceeded by chain mechanisms, which were initiated by light or by... 

The alkylperoxyl radical can be expected to react with sulfur amino acids by mechanisms similar to those for HOO- and HO-. Reactions of the hydroxyl and hydroperoxyl radicals have been more extensively studied because of their importance in radiation biochemistry. Thus, for cysteine, glutathione, and sulfhydryl proteins,... 

The reaction is self-catalyzed and irradiation can be cut off after the process has started. Free radicals can be produced by UV light (with optional water), ozone, X- or y-ray, and acetic anhydride or chlorine. The main intermediates are thus sulfur dioxide in its triplet state ( SOp alkyl, R hydrogenosulfonyl, HSO alkanesulfonyl, RSO alkanepersulfonyl, RSOj-O-O alkanesulfony-loxy, RS02-0 and hydroxyl, OH radicals and alkaneperoxysulfonic acid. Since RSO is the most stable free radical, the most probable chain rupture reaction is ... 

The added hydroxyl function may, of course, also be removed by externally available protons, for example, in highly acidic solutions. In this case the sulfur-centered radical cation will, however, not couple with the nitrogen but associate with the sulfur of an unoxidized molecule to form the dimeric (>S Sradical cation, reaction (69b). 

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