Elemental sulfur oxidation

The complexes [MoO(S2)(S2CNR2)2l are effective catalysts for the episulfurization of ( )-cycloalkenes by elemental sulfur. Oxidation of the same complex by 3-chloroperoxybenzoic acid, or reaction of [Mo203(S2CNEt2)4l or [MoO(S2CNEt2)2l with S2O sources, afforded the pentagonal-bipyramidal [MoO(S20-iS,iS )(S2CNEt2)2] which contains axial Mo=0 and equatorial /< -S20. ... 

In the Maumee Chemical [60] plan for saccharin, there is a curiosity with respect to the oxidation number of the sulfur atom in the source material as shown in step 1 of the following scheme. It conld be either sodium sulfide (oxidation number = -2) or elemental sulfur (oxidation number = 0). In this case, the arithmetic mean of these valnes was nsed as the oxidation number of the sulfur atom in the starting material (oxidation number = -1) which, by the way, corresponds to the oxidation number of sulfur in disodium disulfide that is generated in situ from sodium sulfide and elemental sulfur. 

Surface oxidation of sulfide minerals has been reviewed recently by Smart et al. [78]. Studies of the physical and chemical forms of oxidation products by SAM, XPS, STM. AFM, SEM and ToF-SIMS have revealed several different proces.ses of oxidation. The seminal work of Buckley et al. (e.g., [79,80)) was the first to identify the process of formation of oxyhydroxide products on underlying metal-deficient, sulfur-rich layers of similar forms to those described in Section 4.3. Other oxidation products have been observed directly, such as polysulfides, elemental sulfur, oxidized fine sulfide particles, colloidal hydroxide particles and flocculated aggregates, as well as continuous surface layers of... 

Although thiosulfate is one of the few reducing titrants not readily oxidized by contact with air, it is subject to a slow decomposition to bisulfite and elemental sulfur. When used over a period of several weeks, a solution of thiosulfate should be restandardized periodically. Several forms of bacteria are able to metabolize thiosulfate, which also can lead to a change in its concentration. This problem can be minimized by adding a preservative such as Hgl2 to the solution. 

Reduction of metal oxides with hydrogen is of interest in the metals refining industry (94,95) (see Metallurgy). Hydrogen is also used to reduce sulfites to sulfides in one step in the removal of SO2 pollutants (see Airpollution) (96). Hydrogen reacts directiy with SO2 under catalytic conditions to produce elemental sulfur and H2S (97—98). Under certain conditions, hydrogen reacts with nitric oxide, an atmospheric poUutant and contributor to photochemical smog, to produce N2 ... 

Through reaction with sulfide or elemental sulfur at 215°C, lignosulfonates can also be used in the commercial production of dimethyl sulfide and methyl mercaptan (77). Dimethyl sulfide produced in the reaction is further oxidized to dimethyl sulfoxide (DMSO), a useful industrial solvent (see Sulfoxides). 

In addition to the materials shown in Table 1, other organic materials find a minor portion of their use in mbber processing, such as waxes and fatty acids. Also, the mbber industry uses modest amounts of inorganic compounds, notably elemental sulfur, zinc oxide, magnesium oxide, and sodium bicarbonate. 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Silver Thiosulfate. Silver thiosulfate [23149-52-2], Ag 2 y is an insoluble precipitate formed when a soluble thiosulfate reacts with an excess of silver nitrate. In order to minimize the formation of silver sulfide, the silver ion can be complexed by haUdes before the addition of the thiosulfate solution. In the presence of excess thiosulfate, the very soluble Ag2(S203) 3 and Ag2(S203) 3 complexes form. These soluble thiosulfate complexes, which are very stable, are the basis of photographic fixers. Silver thiosulfate complexes are oxidized to form silver sulfide, sulfate, and elemental sulfur (see Thiosulfates). 

Another process, which also generates elemental sulfur as a by-product, has been patented by Envirotech Research Center in Salt Lake City (29). In the Electroslurry process, a ball mill finely grinds a chalcopyrite concentrate, which reacts with an acidic copper sulfate solution for iron removal. The Hquor is electrolyzed and the iron is oxidized to the ferric form. This latter step leaches copper from the copper sulfide for deposition on the cathode. Elemental sulfur is recovered at the same time. 

Oxidation. Disulfides are prepared commercially by two types of reactions. The first is an oxidation reaction uti1i2ing the thiol and a suitable oxidant as in equation 18 for 2,2,5,5-tetramethyl-3,4-dithiahexane. The most common oxidants are chlorine, oxygen (29), elemental sulfur, or hydrogen peroxide. Carbon tetrachloride (30) has also been used. This type of reaction is extremely exothermic. Some thiols, notably tertiary thiols and long-chain thiols, are resistant to oxidation, primarily because of steric hindrance or poor solubiUty of the oxidant in the thiol. This type of process is used in the preparation of symmetric disulfides, RSSR. The second type of reaction is the reaction of a sulfenyl haUde with a thiol (eq. 19). This process is used to prepare unsymmetric disulfides, RSSR such as 4,4-dimethyl-2,3-dithiahexane. Other methods may be found in the Hterature (28). 

Barium sulfide solutions undergo slow oxidation in air, forming elemental sulfur and a family of oxidized sulfur species including the sulfite, thiosulfate, polythionates, and sulfate. The elemental sulfur is retained in the dissolved bquor in the form of polysulfide ions, which are responsible for the yellow color of most BaS solutions. Some of the mote highly oxidized sulfur species also enter the solution. Sulfur compound formation should be minimized to prevent the compounds made from BaS, such as barium carbonate, from becoming contaminated with sulfur. 

By-product processing Hydrogen sulfide Conversion to elemental sulfur or sulfuric acid by liquid absorption, wet oxidation to elemental sulfur, combustion to SO2... 

The dissolved hydrogen sulfide is oxidized to form a mixture of elemental sulfur and hydro-quinone. The solution is injected with air or oxygen to oxidize the hydro-quinone back to quinone. The solution is then filtered or centrifuged to remove the sulfur and the quinone is then reused. 

Some of the elemental sulfur produced in the regeneration step remains in the bed. After several cycles this sulfur will cake over the ferric oxide, decreasing the reactivity of the bed. Typically, after 10 cycles the bed must be removed from the vessel and replaced with a new bed. 

Direct conversion processes use chemical reactions to oxidize H2S and produce elemental sulfur. These processes are generally based either on the reaction of H2S and O2 or H2S and SO2. Both reactions yield water and elemental sulfur. These processes are licensed and involve specialized catalysts and/or solvents. A direct conversion process can be ii.scd directly on the produced gas stream. Where large flow rates are encoLui tered. ii is more common to contact the produced gas stream with a chemical or physical solvent and use a direct conversion proce.ss on the acid cas liberated in the regeneration step. 

This process is used to treat gas streams containing high concentrations of H2S. The chemistry of the units involves partial oxidation of hydrogen sulfide to sulfur dioxide and the catalytically promoted reaction of hh.S and SO2 to produce elemental sulfur. The reactions are staged and arc. is lollows ... 

Displacement of the sulfhydryl group in primary thiols, like L cysteine and 2-diethylaminoethanethiol, requires elemental fluorine, the most active oxidant Elemental sulfur is the major by-product in those reactions [7] (equation 2)... 

Type B (redox) reactions are more complex. Sulfide in this reaction is converted into some other oxidation state of sulfur. For example, sulfides can be converted to a zero oxidation state of elemental sulfur by oxygen ... 

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