Sulfides and Disulfides

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 

Appreciation of interactive processes that have been outlined has been able to illuminate discussion of mechanisms for reactions as diverse as the acidification of water masses, climate alteration, ozone formation and destruction, and the possible enviromnental roles of trichloroacetic acid and nitroarenes. 

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Originally, vulcanization implied heating natural rubber with sulfur, but the term is now also employed for curing polymers. When sulfur is employed, sulfide and disulfide cross-links form between polymer chains. This provides sufficient rigidity to prevent plastic flow. Plastic flow is a process in which coiled polymers slip past each other under an external deforming force when the force is released, the polymer chains do not completely return to their original positions. 

Sweetening. Another significant purification appHcation area for adsorption is sweetening. Hydrogen sulfide, mercaptans, organic sulfides and disulfides, and COS need to be removed to prevent corrosion and catalyst poisoning. They ate to be found in H2, natural gas, deethanizer overhead, and biogas. Often adsorption is attractive because it dries the stream as it sweetens. 

Two undesirable aspects of FCC naphtha quaUty are that it may contain unacceptably high amounts of foul smelling mercaptans, and that its thermal stabiUty may be too low. Mercaptans are usually found in the light FCC naphtha and may be removed or converted to sulfides and disulfides by a sweetening process such as Merox, developed by UOP. Thermal stabiUty is improved in sweetening processes through removal of cresyUc and naphthenic acids. It may be further improved by clay treating and by addition of oxidation inhibitors such as phenylene diamine. 

Direct splitting requires temperatures above 977°C. Yields of around 30% at 1127°C are possible by equiUbrium. The use of catalysts to promote the reaction can lower the temperature to around the 327—727°C range. A number of transition metal sulfides and disulfides are being studied as potential catalysts (185). Thermal decomposition of H2S at 1130°C over a Pt—Co catalyst with about 25% H2 recovery has been studied. 

Fluorinated and Ghlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The Hterature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl haHdes, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal haHde catalysts, such as... 

The main by-products of this type of process are sulfides and disulfides. The disulfides are formed by the inclusion of an oxidizing agent (generally oxygen) that may be present in the reaction mixture or upon purification. Some of the sulfides formed in this fashion are useful as intermediates for the production of antioxidants. Other mercaptopropionates can be made in similar fashion, if the alkyl acrylate is available. 

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 in crude oils is mainly present in the form of organosulfur compounds. Hydrogen sulfide is the only important inorganic sulfur compound found in crude oil. Its presence, however, is harmful because of its corrosive nature. Organosulfur compounds may generally be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols (mercap-tans). Thiophene, sulfides, and disulfides are examples of non-acidic sulfur compounds found in crude fractions. Extensive research has been carried out to identify some sulfur compounds in a narrow light petroleum fraction.Examples of some sulfur compounds from the two types are ... 

Sulfur-containing amino acids, such as methionine and cystine, are probably the precursors of the mercaptans, sulfides, and disulfides.3 Dimethyl sulfide yields dimethyl sulfoxide and its oxidized product dimethyl... 

Chang and co-workers isolated strain Nocardia sp. CYKS2 from a dyeing industry wastewater using DBT as the sole sulfur source [27]. This strain also desulfurized DBT to the same product 2-HBP however, it had broader substrate specificity and was reported to desulfurize thiophenes, sulfides, and disulfides (Table 3) in addition to DBT. However, it did not desulfurize trithiane, thianthrene and 4,4 -thiodiphenol. The desulfurization experiments were conducted in batch with the rate reported as 0.279 mg-sulfur/L dispersion/h for DBT conversion. 

During the chain oxidation of hydrocarbons, sulfides and disulfides terminate chains by reacting with peroxyl radicals [40,42,44], which, as opposed to phenols, are weak inhibitors (see Table 17.6). The mechanism and stoichiometry of the termination reaction by sulfides remain yet unclear. Since sulfenic acid is an efficient scavenger of free radicals, the oxidation of tetralin in the presence of dialkylsulfoxide occurs only if the initiation rate v > vimin is proportional to the concentration of sulfoxide [5], so that the rate of oxidation is... 

Rate Constants of Reactions of Peroxyl Radicals with Sulfides and Disulfides in Hydrocarbon Solutions (Experimental Data)... 

The significant role of intermediates of conversion of sulfides and disulfides should be highlighted. Thus, sulfenic acid is formed by sulfoxide decomposition and terminates chains by reacting with R02 and, on the other hand, initiates chains by reacting with hydroperoxide. 

The ideas developed here are largely based on the concept of the coordination at the (hydr)oxide interface the ideas apply equally well to silicates. Somewhat modified concepts for the surface chemistry of carbonate, phosphate, sulfide and disulfide minerals have to be developed. 

Structure, acidity and basicity 100 Oxidation of sulfinic acids 101 Disproportionation 102 Reactions with alkyl sulfides and disulfides 103 Desulfonylation 106... 

Methanethiol Methyl Mercaptan Thiols, Mercaptans Thiols, Sulfides, and Disulfides Thorium Tin... 

A number of volatile aliphatic compounds that contain nitrogen or sulfur atoms are important aroma constituents. Alkyl thiols, dialkyl sulfides and disulfides, and alkyl thiocyanates belong to this group. They occur widely in foods and spices and determine the odor of, for example, onions, garlic, and mustard. Because of their potent smell, they are used in high dilution and are often produced only in small quantities. The same is true for the following ... 

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