Polythionate

HNO3 nitric acid H2S3O4 polythionic acid... 

Certain of the above reactions are of practical importance. The oxidation of hydrogen sulfide in a flame is one means for producing the sulfur dioxide required for a sulfuric acid plant. Oxidation of hydrogen sulfide by sulfur dioxide is the basis of the Claus process for sulfur recovery. The Claus reaction can also take place under mil der conditions in the presence of water, which catalyzes the reaction. However, the oxidation of hydrogen sulfide by sulfur dioxide in water is a complex process leading to the formation of sulfur and polythionic acids, the mixture known as Wackenroeder s Hquid (105). 

In solution, the hydrogen sulfide and sulfur dioxide [7446-09-5] thus formed react to producing polythionic acids and elemental sulfur. 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Thiosulfuric Acid. Thiosulfuiic acid [14921 -76-7] is relatively unstable and thus cannot be recovered from aqueous solutions. In laboratory preparation, a lead thiosulfate [26265-65-6] solution is treated with H2S to precipitate PbS, or a concentrated solution of sodium thiosulfate [7772-98-7] is treated with HCl and cooled to — 10°C to crystalline NaCl. Aqueous solutions of thiosulfuric acid spontaneously decompose to yield sulfur, SO2, and polythionic acids, H2S O. Thiosulfuric acid is a strong acid comparable to sulfuric acid. Dissociation constants, = 0.25, = 0.018, have been... 

These three methods are employed commercially. In addition, decomposition of polythionates in alkaline solution or their reaction with sulfide or sulfite gives thiosulfates ... 

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. 

Both S2F2 and SSF2 are rapidly hydrolysed by pure water to give Sg, HF and a mixture of polythionic acids H2S Oe (n 4-6), e.g. ... 

H2S, SO2, H2SO3, H2SO4 and the polythionic acids H2SxOe. Oxidation of SCI2 yields thionyl chloride (OSCI2) and sulfuryl chloride (O2SCI2) (see Section 15.2.4). Reaction with F2 produces SF4 and SFe (p. 686), whereas fluorination with NaF is accompanied by some disproportionation ... 

Attempts to prepare thiosulfuric acid by acidification of stable thiosulfates are invariably thwarted by the ready decomposition of the free acid in the presence of water. The reaction is extremely complex and depends on the conditions used, being dominated by numerous redox interconversions amongst the products these can include sulfur (partly as cyclo-Sf,), SO2, H2S, HiS,. H2SO4 and various polythionates In the absence of water, however, these reactions are avoided and the parent acid is more stable it decomposes quantitatively below 0° according... 

Anhydrous polythionic acids can be made in ether solution by three general routes ... 

Poly-morphie, /. polymorphism, polymorphy, -nom, n. polynomial, -saure, f. poly add. -schwefelwasserstoff, m. hydrogen persulfide (either H2S2 or HaSa). -sUiciumsaure,/. polysilicic acid, -styrol, n. polystyrene, -thion s ure, /. polythionic acid, -zimtsaure, /. polycinnamic acid, polyzyklisch, a. polycyclic. 

Austenitic stainless steels Chloride (and other halide) ion Polythionic acids High-temperature water Hydrogen sulfide (aqueous)... 

Nickel alloys Sfiong alkali Polythionic acids Chloride ion... 

Alloy 800 Polythionic acids IG Stabilise material against intergranular corrosion... 

Fig. 1-19. The sulfur Ka spectrum from a series of compounds containing sulfur at different valences. The triplet in all the polythionates results from the superposition of the al, a2 doublets of sulfur at two different valences. (Courtesy of Faessler and Goehring, N aturwissenschaften, 39, 169.)...

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