Dimethyl sulfide reactions atmosphere

Direct Kinetic and Mechanistic Study of the OH-Dimethyl Sulfide Reaction Under Atmospheric Conditions... 

Atmosphere—Water Interaction. Although water is a very minor component of the atmosphere, less than 10 vol % of the atmosphere consisting of water, many important reactions occur ki the water droplets of cloud, fog, and rain. The atmosphere is an oxic environment ki its water phase, gigantic quantities of reductants, such as organic substances, Fe(II), SO2, CH SCH (dimethyl sulfide), and nitrogen oxides, are oxidized by oxidants such as oxygen, OH radicals, H2O2, and Fe(III). 

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. 

The vast majority of sulfur at any given time is in the lithosphere. The atmosphere, hydrosphere, and biosphere, on the other hand, are where most transfer of sulfur takes place. The role of the biosphere often involves reactions that result in the movement of sulfur from one reservoir to another. The burning of coal by humans (which oxidizes fossilized sulfur to SO2 gas) and the reduction of seawater sulfate by phytoplankton which can lead to the creation of another gas, dimethyl sulfide (CH3SCH3), are examples of such processes. 

Sulfides and disulfides can be produced by bacterial reactions in the marine environment. 2-Dimeth-ylthiopropionic 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). Further details are given in Chapter 11, Part 2. Methyl sulfide can also be produced by biological methylation of sulfide itself (HS ). Carbon radicals are not the initial atmospheric products from organic sulfides and disulfides, and the reactions also provide an example in which the rates of reaction with nitrate... 

While investigating the potential for an instrument to measure atmospheric dimethyl sulfide (DMS) [69], discussed below, Hills et al. investigated the possibility of adding H2 to the reaction cell to provide chemical amplification of the chemiluminescence signal via the catalytic chain reaction ... 

Wallington, T. J., T. Ellermann, and O. J. Nielsen, Atmospheric Chemistry of Dimethyl Sulfide UV Spectra and Self-Reaction Kinetics of CH3SCH2 and CH3SCH202 Radicals and Kinetics of the Reactions CH,SCH2 + 02 -> CH3SCH202 and CH,SCH202 + NO -> CH,SCH20 + N02, J. Phys. Chem., 97, 8442-8449 (1993). 

Treatment of a-iodo lactone (45) with triethylborane under oxygen atmosphere gives the corresponding a-hydroxy lactone (46), via a-lactone radical species. This reaction comprises of SH2 reaction by Ef on the iodine atom of a-iodo lactones, reaction of the formed a-lactone radical with molecular oxygen, and subsequent hydrogen-atom abstraction from the solvent to form alkyl hydroperoxide (ROOH). Finally, by the addition of dimethyl sulfide for the reduction of the peroxide, the corresponding a-hydroxy lactone is obtained (eq. 2.24) [58]. 

The oxidized dimer, [Fe2(TPA)20(0Ac)]3+, 41, was shown to be an efficient catalyst for cyclohexane oxidation using tert-BuOOH as a source of oxygen (69). This catalyst reacts in CH3CN to yield cyclohexanol (9 equiv), cyclohexanone (11 equiv), and (tert-butylperoxy)cyclohexane (16 equiv) in 0.25 h at ambient temperatures and pressures under an inert atmosphere. The catalyst is not degraded during the catalytic reaction as determined by spectroscopic measurements and the fact that it can maintain its turnover efficiency with subsequent additions of oxidant. Solvent effects on product distribution were significant benzo-nitrile favored the hydroxylated products at the expense of (tert-butyl-peroxy)cyclohexane, whereas pyridine had the opposite effect. Addition of the two-electron oxidant trap, dimethyl sulfide, to the catalytic system completely suppressed the formation of cyclohexanol and cyclohexanone, but had no effect on the production of (tert-butylper-oxy)cyclohexane. These and other studies suggested that cyclohexanol and cyclohexanone must arise from an oxidant different from that responsible for the formation of (tert-butylperoxy)cyclohexane. Thus, two modes of tert-BuOOH decomposition were postulated a heterolytic... 

A widespread marine source of S02 is required to explain these observations. In Section 10.2 it was shown that the oceans release hydrogen sulfide and dimethyl sulfide, and that both are rapidly oxidized in the atmosphere by reaction with OH radicals. The processes convert hydrogen sulfide fully to S02, whereas dimethyl sulfide yields primarily methanesulfonic acid, and S02 accounts for only 25% of all products. Let us see whether the oxidation of these compounds suffices to explain the S02 mixing ratios observed in marine air. For this purpose we assume steady-state conditions and use the lifetimes for H2S and DMS given in Table 10-2. The mixing ratio for S02 at the ocean surface then is... 

Wallington, T. J., Ellermann, T., and Nielsen, O. J. (1993) Atmospheric chemistry of dimethyl sulfide-UV spectra and self-reaction kinetics of CH3SCH2 and CH3SCH2O2 radicals and kinetics of the reactions CH3SCH2 + 02—> CH3SCH202 and CH3SCH202+NO—>CH3SCH20 + N02, /. Phys. Chem. 97, 8442-8449. 

Dimethyl sulfide (DMS), CH SCH, is the largest natural contributor to the global sulfur flux (see Section 2.2.1). The DMS-OH rate constant, approximately 5 X 10 cm molecule s at 298 K, exceeds that of DMS-NO, by a factor of 4. (In contrast, the reactions of H2S and CH,SH with NO, are, respectively, 6000 and 40 times slower than that with OH.) The DMS lifetime in the marine atmosphere as a result of both OH and NO, reactions is on the order of one to several days, with the majority of the path occurring by OH at low latitudes and by NO, in colder, darker regions. Because of the photochemical source of OH, DMS removal by OH occurs only during daytime, leading to a pronounced diel cycle in DMS concentration. 

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