The Chemistry of Sulfur

Sulfur obtained from underground deposits by the Frasch process. 

About 60% of the sulfur produced in the United States comes from the underground deposits of elemental snlfnr found in Texas and Louisiana. This sulfur is recovered by using the Frasch process developed by Herman Frasch in the 1890s. Superheated water is pumped into the deposit to melt the sulfur (mp = 113°C), which is then forced to the surface by air pressure (Fig. 20.21). The remaining 40% of snlfur produced in the United States either is a by-prodnct of the purification of fossil fuels before combustion to prevent pollntion or comes from the sulfur dioxide (SO2) scrubbed from the exhaust gases when snlfnr-containing fnels are burned. 

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The scrubbing of sulfur dioxide from exhaust gases was discussed In Section S.10. 

Sulfur bums in air with a bright blue flame to give sulfur dioxide (S02 , a colorless gas with a pungent odor, which condenses to a liquid at 10°C and 1 atm. Sulfur dioxide is a V-shaped molecule, which is a very effective antibacterial agent often used to preserve stored fruit. 

In contrast to oxygen, elemental sulfur exists as S2 molecules only in the gas phase at high temperatures. Because sulfur atoms form much stronger a bonds than ir bonds, S2 is less stable at 25°C than larger aggregates such as S6 and Sg rings and S chains (Fig. 19.17). The most stable form of sulfur at 25°C and 1 atm is called rhombic sulfur [see Fig. 19.18(a)], which contains stacked Ss rings. If rhombic sulfur is melted and heated to 120°C, it forms 

The Frasch method for recovering sulfur from underground deposits. 

From its position below oxygen in the periodic table, we might expect the simplest stable oxide of sulfur to have the formula SO. However, sulfur monoxide, which can be produced in small amounts when gaseous sulfur dioxide (S02) is subjected to an electrical discharge, is very unstable. The difference in the stabilities of the 02 and SO molecules probably reflects the much 

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In contrast to oxygen, elemental sulfur exists as S2 molecules only in the gas phase at high temperatures. Because sulfur atoms form much stronger a bonds than tt bonds, S2 is less stable at 25°C than larger aggregates such as 

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R. P. Sharma and R. D. Vetma, Recent Developments in the Chemistry of Sulfur-Nitrogen Compounds Sulfur-Nitrogen Cyclic Anions, J. Sci. Ind. Res., 40, 34 (1981). 

Groups. Supplement S The Chemistry of Sulfur-Containing Functional Groups (S. Patai and Z. Rappoport, eds.), p. 659. Wiley, New York, 1993. 

Reviews and Monographs on the Chemistry of Sulfur-Rich Compounds... 

Bond Energy Terms in the Chemistry of sulfur. Selenium and Tellurium... 

Z. B. Alfassi (Ed.), The Chemistry of Sulfur Radicals, Wiley, Chichester, 1999. 

The literature is covered up to the beginning of the year 2003. A list of useful previous reviews and monographs related to the chemistry of sulfur-rich compounds including elemental sulfur is available on-line as suplementary material to these Volumes. 

An outline of the chemistry of sulfur dyes, which is not well established, is presented in Chapter 6. 

The chemistry of sulfur is a broad area that includes such chemicals as sulfuric acid (the compound prepared in the largest quantity) as well as unusual compounds containing nitrogen, phosphorus, and halogens. Although there is an extensive chemistry of selenium and tellurium, much of it follows logically from the chemistry of sulfur if allowance is made for the more metallic character of the heavier elements. All isotopes of polonium are radioactive, and compounds of the element are not items of commerce or great use. Therefore, the chemistry of sulfur will be presented in more detail. 

The use of six equivalents of dihydrogen peroxide leads to a clean conversion of the dithiolate complex to the disulfonate compound. Earlier studies on oxidation of nickel thiolates showed that oxidations with dioxygen stop at monosulfinates. Our observation and the characterization of the first chelating bis-sulfonato nickel complex formed from the direct oxidation of a mononuclear nickel dithiolate, may also provide new insight into the chemistry of sulfur-rich nickel-containing enzymes in the presence of oxygen. 

Brandt and van Eldik30 review of the chemistry of sulfur(IV) oxidation, with emphasis on the catalytic role of metal ions such as Fe2+. We consider here only a simplified summary of the principal atmospheric oxidation processes. It is likely that oxidation is effected primarily through the action of hydrogen peroxide or ozone in water droplets in clouds, through the photochemical effect of ultraviolet light, or by heterogeneous catalysis of the S02-02 reaction by dust particles 9,30,31... 

In view of the remarkably swift development of the chemistry of sulfur heterocycles, an extension of quantum-chemical calculations to various additional physical properties as well as a more systematic approach in both experimental and theoretical studies can be expected in the near future. Even though it is not possible to put forward responsibly an optimum unique set of HMO empirical parameters, Model B (8S = 1, 3C(a) = 0.1, pcs = 0.7) may perhaps be recommended for the beginning of a systematic treatment. As for other parameters, the set given by Streitwieser4 can be recommended the value 0.5 has proved suitable for p8S. It is quite obvious, however, that such studies should develop simultaneously with application of more sophisticated methods, above all the configuration interaction method.42... 

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... 

Recent Progress in the Chemistry of Sulfur-containing Heterocyclic Compounds N. Lozac h, Ind. Chim. Belg., 1961, 26, 1130-1139. 

The chemistry of sulfur in fossil fuels is of both practical and academic interest. The behavior of sulfur during processing high-sulfur crude oils, coals and natural gas to make environmentally acceptable fuels poses special... 

Removal of sulfur compounds from fuel oils is usually accomplished at the refinery. Although most of the sulfur in oil is in the high boiling fraction, some middle distillates have high sulfur contents. A better understanding of the chemistry of sulfur compounds in oil will also facilitate their efficient removal. 

The chemistry of sulfur compounds is replete with beautiful examples of regioselectivity inversions,28 but unfortunately not all of them can be explained by FO theory. 

The technology of sulfur vulcanisation of unsaturated elastomers has evolved since Goodyear s invention in 1839. Scientific studies into the chemistry of sulfur vulcanisation started to appear in the late 1950s (for reviews see References [14-18]). Two experimental approaches can be distinguished the analysis of rubber vulcanisates themselves and the so-called low-molecular-weight model studies. 

In the following we present an application of laser induced fluorescence to a study of the chemistry of sulfur in rich hydrogen/oxygen/nitrogen (H2/O2/N2) flames and demonstrate a simple rationale for taking quench effects into account. Fluorescence measurements for S2, SH, S02, SO, and OH along with measurements of flame temperature and H-atom (in sulfur free flames) have been employed to develop a kinetic model for the highly coupled flame chemistry of sulfur. The kinetic aspects of the study already have been presented in considerable detail (6). 

This chapter describes the chemistry of sulfur, selenium, and tellurium. Polonium will be mentioned only briefly in keeping with the fact that all of the isotopes of the element are radioactive. As a result, the chemistry of such an element is too specialized for inclusion in a survey book of this type. The plan followed in this chapter will be to discuss some of the topics of sulfur chemistry separately from those of selenium and tellurium because in several regards sulfur is somewhat different from the other two elements. 

The discussion up to this point has been aimed at putting sulfur chemistry in its historical and economic perspective. In some ways, the chemistry of sulfur and its compounds has been of paramount importance for centuries, a trend that continues to the present time. 

Several important halogen derivatives of sulfuric acid are produced from S03. Some of these will be described in the next section, and some are discussed with the chemistry of sulfuric acid. 

That this emerging technology deserves more scrutiny, as was detailed in the recently published report by Corma (20) outlining the chemistry of sulfur removal during FCC operations. A better understanding of the process chemistry and the role of specific catalysts should allow the FCC unit itself to contribute to a lowering of the sulfur in the gasoline pool. 

The redox processes involved in the chemistry of sulfur and iron can be simulated on a computer. The feasibility of such simulations is supported by the good agreement between computer results and field data on the corresponding system of interest as shown by the example of roll-type uranium deposits. 

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