Sulfur chemistry

Sulfur chemistry is important both in combustion and in the petrochemical industry. Most fossil fuels contain sulfur, and also biofuels and household waste have a sulfur content. As a consequence sulfur species are often present in combustion processes. Knowledge of gas-phase sulfur chemistry occurring in combustion has bearing on pollutant emissions and on system corrosion. Air pollution by SO2 still constitutes a major environmental concern and search for control techniques has motivated research also on high-temperature homogeneous sulfur chemistry. However, more recent work on sulfur chemistry has been concerned mainly with the effect of sulfur on other pollutant emissions, such as NO and CO, and with the SO3/SO2 ratio, which is important for the corrosive potential of the flue gas and for formation of sulfur containing aerosols. 

The speciation of the gas-phase sulfur depends on the parent fuel and the reaction conditions [204]. The sulfur-containing compounds occurring in combustion range from simple species such as H2S in natural gas and produced from gasification of solid fuels to com- 

In the petrochemical industry, gas-phase sulfur chemistry is important in the Claus pro-cess[141], which is used to remove sulfur from acid gas streams generated in oil and gas operations. In this process a high-temperature furnace (1200-1500 K) is used to oxidize about a third of the H2S in the acid gas to SO2. Subsequently the remaining H2S reacts with the SO2 over a catalyst (440-640 K) to form free sulfur. The process can be described in terms of the overall reactions 

The gas-phase sulfur chemistry occurring in the front-end furnace of the Claus process is presumably similar to reactions occurring under fuel-rich conditions in combustion. However, in both systems the chemistry is quite complex and involves a number of unresolved issues. 

The chemistry of sulfur in flames has received considerable attention [79]. Results from various combustion systems indicate that the initial speciation of the gas phase sulfur is of minor importance, both for its interaction with fuel oxidation and nitrogen chemistry and for the SO3/SO2 ratio in the flue gas. This is fortuitous, since even for the simplest sulfur compounds, such as H2S, knowledge of its oxidation chemistry is incomplete. However, in flames the oxidation is believed to proceed by the overall sequence 

Northern Hemisphere. The natural sources include volcanoes, plants, soil and biogenic activity in the oceans. In terms of photochemistry the major sulfur oxide, sulfur dioxide (SO2) does not photodissociate in the troposphere (cf. NO2), i.e. 

The solubility of SO2 is related to the pH of the aqueous phase, decreasing at lower values of pH. The oxidation of sulfur (IV) to sulfur (VI) is a complex process dependent on many physical and chemical factors. The main oxidants seem to be O2 (catalysed/uncatalysed), O3, H2O2, the oxides of nitrogen and free-radical reactions in clouds and fogs. For example, H2O2 is highly soluble in solution so even at relatively low gas-phase concentrations (typically ca. 1 ppbv) there is a 

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Synthesis and Properties. The synthesis of (21) follows a very straightforward route based on readily accessible starting materials and on some novel reactions ia organo—inorganic sulfur chemistry (83—85), as well as on polycondensation chemistry analogous to that utilized ia the preparation of poly(alkyl/arylphosphazenes). One preparation of (21) is as follows ... 

Metal Ion-Promoted Reactions of Thiols. Metal ion-promoted reactions of thiols have been reviewed (53). The bulk of the coverage concerns metal ion promoted aspects of sulfur chemistry. The main topics of interest are the formation of sulfenamides, sulfides, and disulfides using metal-mediated reactions. 

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing... 

Wachtershanser has also suggested that early metabolic processes first occurred on the surface of pyrite and other related mineral materials. The iron-sulfur chemistry that prevailed on these mineral surfaces may have influenced the evolution of the iron-sulfur proteins that control and catalyze many reactions in modern pathways (including the succinate dehydrogenase and aconitase reactions of the TCA cycle). 

F. Jellinek, Sulfides, Chap. 19 in G. Nickless (ed.). Inorganic Sulfur Chemistry, pp. 669-747, Elsevier, Amsterdam, 1968. A comprehensive review with 631 references. 

S. Wolfe, in Organic Sulfur Chemistry, Theoretical and Experimental Advances (Eds. F. Bernardi, I. G. Csizmadia and A. Mangini), Elsevier, Amsterdam, 1985, pp. 133-190. 

C. Y. Meyers, in Topics in Organic Sulfur Chemistry (Ed. M. Tisler), University Press, Ljubljana, Yugoslavia, 1978, pp. 207-260. 

M. Cinquini, F. Cozzi and F. Montanari, in Organic Sulfur Chemistry, Theoretical and... 

Dae S. Organic Sulfur Chemistry Structure and Mechanism, CRC Press, London, 1991. 

For a review of nitrogen ylids, see Musker, W.K. Fortschr. Chem. Forsch., 1970,14, 295. For a monograph on sulfur ylids, see Trost, B.M. Melvin Jr, L.S. Sulfur Ylids Academic Press NY, 1975. For reviews, see Fava, A. in Bemardi Csizmadia Mangini Organic Sulfur Chemistry Elsevier NY, 1985, p. 299 Belkin, Yu.V. Polezhaeva, N.A. Russ. Chem. Rev., 1981, 50,481 Block, E. in Stirling The Chemistry of the Sulphonium Group,... 

For reviews of sulfur-containing carbanions, see Oae, S. Uchida, Y. in Patai Rappoport Stirling The Chemistry ofSulphones and Sulphoxides, Wiley NY, 1988, p. 583 Wolfe, S. in Bemardi Csizmadia Mangini Organic Sulfur Chemistry Elsevier, NY, 1985, p. 133 Block, E. Reactions ofOrganosulfur Compounds Academic Press NY, 1978, p. 42 Durst, T. Viau, R. Intra-Sci. Chem. Rep., 1973, 7 (3), 63. For a review of selenium-stabilized carbanions, see Reich, H.J. in Liotta Organoselenium Chemistry Wiley NY, 1987, p. 243. For support for this theory, see Wolfe, S. LaJohn, L.A. Bemardi, F Mangini, A. Tonachini, G. Tetrahedron Lett., 1983, 24, 3789 Wolfe, S. Stolow, A. LaJohn, L.A. Tetrahedron Lett., 1983, 24, 4071. 

With the availability of sophisticated computational methods, combined with the ever increasing speed of computers and the latest parallel computing technology, quantum chemical calculations with chemical accuracy for larger systems are now readily available. Thus, computational chemistry will play a major role in solving many of the unresolved and challenging problems in sulfur chemistry. 

B. Meyer, Elemental Sulfur Chemistry and Physics, Interscience, New York, 1965 with Chapters on the following topics ... 

S. Oae, T. Okuyama (Eds.), Organic Sulfur Chemistry Biochemical Aspects,... 

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