Transformations of Sulfur

The stable form of sulfur under moderately strong reducing conditions (pe —3) is hydrogen sulfide, H2S, which is readily soluble and under non-acid conditions 

There may be a cycling of S compounds of different oxidation state between anaerobic and aerobic zones in the soil, such as at the soil—floodwater interface. In reduced lake and marine sediments this leads to accumulation of insoluble sulfides as S04 carried into the sediment from the water above is immobilized. Such deposits function as sinks for heavy metals. Plants absorb S through their roots as S04 H2S is toxic to them. Therefore HS must be oxidized to S04 in the rhizosphere before it is absorbed. 

The initial increase occurs because 864 sorbed on variable charge clays and oxides is desorbed as the pH increases. The rate of subsequent reduction will be 

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Reproduced with permission from R. J. Charlson, W. L. Chameides, and D. Kley (1985). The transformations of sulfur and nitrogen in the remote atmosphere. In "The Biogeochemical Cycling of Sulfur and Nitrogen in the Remote Atmosphere" (J. N. Galloway, R. J. Charlson, M. O. Andreae and H. Rodhe, eds), pp. 67-80, D. Reidel Publishing Company, Dordrecht.)... 

Fig. 13-2 The chemical and physical transformations of sulfur in the atmospheric cycle. Circles are chemical species, the box represents cloud-liquid phase. DMS = CH3SCH3, DMDS = CH3SSCH3, Siv = (S02)aq + HSOi" + SO3 + CH20HS03, and MSA (methane sulfonic acid) = CH3SO3H. The chemical transformations are as... 

Gonzalez JM, Kiene RP, Moran MA (1999) Transformation of sulfur compounds by an abundant lineage of marine bacteria in the a-subclass of the Proteobacteria. Appl Environ Microbiol 65 3810-3819... 

The principal cause of acid rain is the combustion of fossil fuels that produce sulfur and nitrogen emissions. The primary sources are electrical power plants, automobiles, and smelters. Power plants produce most of the sulfur emissions and automobiles most of the nitrogen emissions. Other sources of acid rain include nitrogen fertilizers, jet aircraft, and industrial emissions. Just as in our discussion of ozone, numerous reactions are involved in the formation of acid rain. The process can be understood by considering the transformation of sulfur and nitrogen oxides into their respective acidic forms sulfuric acid and nitric acid. Sulfur, present up to a few percent in fuels such as coal, is converted to sulfur dioxide when the fuel is burned. The sulfur dioxide reacts with water to produce sulfurous acid, H,SO ,, that is then oxidized to sulfuric... 

Products of the LOX pathway or compounds formed by autoxidation of fatty acids (Scheme 7.2) are also important for leek aroma [31, 163]. Volatile compounds of the LOX pathway are not pronounced in the aroma profile of freshly cut leeks owing to a high content of thiosulfinates and thiopropanal-S-oxide [30]. In processed leeks that have been stored for a long time (frozen storage), however, these aliphatic aldehydes and alcohols have a greater impact on the aroma profile owing to volatilisation and transformations of sulfur compounds [31, 165]. The most important volatiles produced from fatty acids and perceived by GC-O of raw or cooked leeks are pentanal, hexanal, decanal and l-octen-3-ol (Table 7.5) [31, 35, 148, 163, 164]. 

Studies of sulfur-containing organic compounds in coal provide information on the origin of organic sulfur and the transformation of sulfur compounds during coal maturation. The distribution and types of organic sulfur compounds in coal have profound implications for desulfurization processes. 

J. W. Gall, presented at "Physico-Chemical Transformation of Sulfur Compounds in the Atmosphere and the Formation of Acid Smogs," Mainz (1967). 

Sulfoxidation. This is a faidy common transformation of sulfur-containing pesticides such as aldicarh (6) (eq. 8) and EPTC (19). 

Figure 17 shows schematically the major transformations of sulfur in aquatic systems and their related isotopic fractionations. Processes that do not significantly fractionate sulfur isotopes include (i) weathering of sulfide and sulfate minerals, (ii) adsorption-desorption interactions with organic matter, and (iii) isotopic exchange between S04 and HS or H2S in low-temperature environments. Precipitation of sulfate minerals is accompanied by only slight isotopic fractionation, and the precipitates are generally... 

Swider, K.T. Makin, J.E. (1989) Transformations of sulfur compounds in marsh-flat sediments. Geochim. Cosmochim. Acta 53, 2311-23. 

Microbial transformation of sulfur gases play an important role in S exchange between atmosphere and biosphere ... 

Figure 13-2 summarizes the chemical and physical transformations of sulfur compounds that occur in the atmosphere. Most of the chemical transformations involve the oxidation of sulfur. The key oxidizing agents are thought to be the OH radical. 

The sulfur compounds, except the sulfate of sea salt particles, are released into the atmosphere in gaseous form. In spite of this fact the majority of atmospheric sulfur in clean air is found in particulate matter as sulfate (see later). Thus, the aim of studies on transformations of sulfur compounds is to determine the nature and rate of oxidation processes leading to sulfate formation. 

Schematic representation of the transformation of sulfur compounds in the atmosphere according to Kellogg et al. (1972). (Copyright 6.2.1979 by the American Association for the Advancement of Science...

Development of microbial strains for desulfurization of petroleum crude, transformation of sulfur compounds like dibenzothiophene (dbt) exhibiting enhanced specificity, and improved reaction rates on changed nutritional inputs making progress - genes encoding enzymes associated with the transformation of dbt into a fluorescent metabolite are marked in E. coli and Rhodococcus sp. 

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