Polythionic acid

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... 

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 ... 

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... 

Polythioether polymer, 22 40-41 Polythioethers, 23 704 Polythionic acids, 23 641 Polythiophene(s), 22 207t 23 708 conducting, 7 517-520 7 523, 527 electrochromic material, 6 572t, 575, 581t... 

NOTE Typical agents of concern are hydrogen sulfide, amines, chlorides, bromides, iodides, cyanides, fluorides, naphthenic acid and polythionic acid. Other agents affecting elastomer selection include ketones, ethylene oxide, sodium hydroxide, methanol, benzene and solvents. 

Sulphur is applied, commonly in the powdered form or as /lowers of sulphur, to medicinal purposes, and also agriculturally as a dust or dressing to check fungoid diseases of certain plants, ( specially the vine.5 The toxic properties of sulphur have not been fully elucidated and are variously ascribed to reduction to hydrogen sulphide, oxidation to polythionic acids, or to the vapour of the element itself, produced by slow vaporisation.8 If adsorbed pcntathionic acid be removed from... 

Highly dispersed sols, containing up to 0-082 per cent, of sulphur, may be obtained 3 by passing superheated sulphur vapour, free from air, into air-free water. The sols have an acid reaction due to traces of polythionic acids and hydrogen sulphide. They are white and remain stable for several weeks. 

Even in the presence of a large excess of water decomposition only proceeds to the extent of 93-68 per cent., being partly restrained by the presence of the hydrogen chloride formed. The other factor which influences the extent of the action is the sulphur formed by subsequent reaction between the hydrogen sulphide and the sulphur dioxide. Polythionic acids arc formed in solution and the sulphur which separates encloses undecomposed chloride and may also dissolve in it.5... 

This final stage is reached more quickly in the presence of excess of hydrogen sulphide. In the presence of excess of sulphurous acid some polythionic acid is formed.2... 

Formation.—The free acid is exceedingly unstable and, at best, is obtainable only in very dilute solution many of the older methods described for the synthetic production of aqueous solutions of the acid probably yielded only one or more of the polythionic acids.1... 

The decomposition of the polythionic acids (q.v.) in the presence of alkali, the decomposition of hydrosulphites (p. 227) and the hydrolysis of nitrogen sulphide2 by water or aqueous alkali are also processes in which salts of thiosulphuric acid are formed. Certain micro-organisms capable of converting sulphur to thiosulphate have been isolated from soil cultures.3... 

Aqueous solutions of thiosulphuric acid and its salts are not very stable, but tend to decompose, yielding sulphurous and polythionic acids and a deposit of sulphur. The decomposition may take place in at least three different ways 3... 

When acids act on thiosulphates, polythionic acids are formed.5 This is explained by reactions (b) and (c). The fact that the amount of hydrogen sulphide liberated is very small in proportion to the amount of polythionic acid formed is attributed 8 to the fact that reaction (a) is that which normally occurs to the greatest extent when acid acts upon thiosulphate the hydrogen sulphide is thus liberated in the presence of a large amount of sulphurous acid and hence rapidly destroyed. Trithionic acid is thus a primary product of thiosulphate decomposition, and in its turn decomposes as explained on p. 212. 

On the other hand, much stronger evidence is available in favour of the earlier formula,4 which accords well with the relationship between the acid and the polythionic acids.5 The formation of sodium thiosulphate by Spring s synthesis from sodium sulphide and sodium sulphite (p. 194) is definitely favourable to this constitution, as also especially is the fact that an alkali thiosulphate will react with only an equimoleeular proportion of an organic (alkyl) halide,6 the product... 

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