Elimination, direction sulfur dioxide

The reaction products from the fuel must be gaseous so that they can be directly vented to the air. This eliminates the requirement for hardware to collect, store and return the spent solid or liquid reaction products. The product of the reaction of hydrogen with oxygen, from the air, is water. There is no carbon so no un-bumed hydrocarbons or toxic carbon monoxide is produced. All fossil fuels contain some amount of sulfur compounds. These are converted to sulfur dioxide when the fuel is burned. Most processes under consideration for the production of hydrogen are free from sulfur or any other harmful contaminants. Thus, unlike fossil fuel hydrocarbons, hydrogen combustion products will not be contaminated with sulfur compounds. 

Cycloaddition of thiophene dioxides with alkenic dienophiles often directly leads to the formation of a benzene ring. This can be attained by extrusion of sulfur dioxide from the initial adducts, followed by 1) elimination of a small molecule, 2) an intramolecular hydrogen transfer, and 3) (accidental) oxidative dehydrogenation under applied conditions. 

Sulfur dioxide is undesirable if the concentration is above a few parts per million. The delicate color of the fruit is impaired and in some cases the metal of the can is corroded. Direct consumption cane sugars produced by the sulfitation process are usually undesirable for canning but the supply is limited to one section of the country. Sulfur dioxide is used in processing beet sugars but not as a bleach as was the practice earlier in the industry. It is now recognized that a few parts per million of sulfur dioxide added before the evaporation of the thin juice act as an inhibitor to the nonenzymatic browning and result in a sugar with less than 1 p.p.m. of sulfur. In the same manner the starch-conversion producers have been able to eliminate the objectionable hydroxymethyl furfural, an undesirable side reaction product in starch conversion. 

Diels-Alder cycloaddition of thiophene 1,1-dioxides with alkynic dienophiles leads to the formation of benzene derivatives directly via elimination of a sulfur dioxide. 

The most used analytical technique for SO2 monitoring is based on fluorescence. Excitation of sulfur dioxide molecules by ultraviolet radiation (UV) in the 190-230 nm region gives an emitting fluorescent radiation, whose wavelength and intensity are directly proportional to the concentration of sulfur dioxide. The main interfering compound is represented by polycyclic aromatic hydrocarbons to eliminate their effect, the analyzers are equipped with a permeation device which selectively removes hydrocarbon molecules from the gas sample. ... 

The basis of the lead chamber process was, therefore, to combine sulfur dioxide with the oxygen in air in the presence of a relatively small amount of niter. Some details of the process development are summarized in Table 2.1 and a typical lead chamber plant is shown in Figure 2.1. Despite this conclusion, many UK producers continued to operate the process in batches until as late as 1820. The fact that it was difficult to transport sulfuric acid meant that many small, onsite plants supplied users directly. This, of course, eliminated competition and delayed technical developments. Even after the eventual introduction of the contact process during the 1920s, the lead chamber process was still widely... 

The a-exomethylene-y-lactone framework has been successfully constructed via two electrosynthetic pathways, that is, both by the direct and by the concerted decarboxylation processes as mentioned earlier [Eq. (45)] [151]. The electrodecarboxylation of XCa is probably initiated by a one-electron oxidation of the sulfur atom, giving first the cation radical (XCb) and subsequently a concerted elimination of the thiyl radical and carbon dioxide to LXXXIX. On the other hand, the electrochemical decarboxylation of LXXXVIIIa involves an El-type elimination of a proton from the cation intermediate (LXXXVIIIb) generated from direct two-electron oxidation of the carboxyl group. The latter method generally requires a higher oxidation potential than that required for the concerted method. Therefore, the concerted electrodecarboxylation method becomes more advantageous, especially when the substrates or products are unstable under oxidative conditions. 

Molten salt from the reducer is next processed to convert sulfides back to carbonates for recycle to the absorber. This is accomplished in a regeneration column, which operates at about 800°F and uses a mixture of carbon dioxide and water vapor to displace hydrogen sulfide gas from the molten salt. The hydrogen sulfide-rich gas stream from this step is fed directly into a Claus type sulfur plant. Work on the process was terminated after a small demonstration unit developed mechanical problems, including plugging of a mist eliminator at the absorber outlet and corrosion in some lines carrying hot molten salt. 

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