Polythionates formation

The sulfite formed would react with excess hydrogen sulfide to produce sulfur directly from the sulfoxylic or thiosulfurous intermediate, Reactions 25 and 26, without polythionate formation. The overall reaction between hydrogen sulfide and sulfite would be ... 

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). 

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. 

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... 

If gaseous sulphur dioxide is passed into a solution of thiosulphate, a yellow solution is formed which on keeping becomes colourless it then yields a precipitate of sulphur when treated with formaldehyde and sodium hydroxide, but no polythionate can be detected. When the colourless solution is neutralised with sodium hydroxide, it is found to contain sulphite and thiosulphate, but sulphur is not precipitated. These results may be due to the formation of an additive compound such as that mentioned in (ii) above.5... 

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... 

Properties.—Trithionic acid is the least stable of the polythionic acids. The aqueous solution of the free acid, which is generally obtained from a cold concentrated solution of the potassium salt by the addition of a suitable acid, such as hydrofluosilicie or perchloric acid, which will remove the metal as a sparingly soluble salt, slowly decomposes, even at the ordinary temperature, with formation of sulphur, sulphur dioxide and sulphuric acid ... 

Oxidising adds such as nitric, chloric and iodic acids induce rapid decomposition of trithionic acid with formation of sulphur and sulphuric acid 2 the presence of other acids, for example hydrochloric, perchloric or dilute sulphuric acid, also hydrogen sulphide, is without any harmful effect.3 Addition of sulphurous acid causes the gradual formation of a mixture of all the polythionic acids. 

Whenever sulphur dioxide, water and nascent sulphur meet, for example in the action of water on sulphur chloride, of mineral acids on a thiosulphate, or of hydrogen sulphide on aqueous sulphur dioxide solution, formation of polythionic acids is likely to occur. Dalton 1 in 1812 demonstrated that the last-named reagents gave rise to an acid liquid, a result which was confirmed later by Thomson 2 in 1846 Wackenroder 3 proved the presence of pentathionic acid in the liquid, since which date the aqueous reaction product has been known as Wackenroder s Solution. ... 

In addition, the further breaking down of these decomposition products results in the formation of polythionates.1... 

Chaudhury and his co-workers 6 showed that the composition of the hydrosol varied according to the method of its formation, but that arsenious acid was usually present. This they considered to be a normal constituent of the sol, and the many irregularities observed in different sols were attributed to interaction of H+-ions and polythionic... 

The average concentrations of reduced inorganic sulfur species in the anoxic zone of the Black Sea measured using a new colorimetric method developed by Volkov [61,62] are summarized in Table 3. Presented elemental sulfur data refer to the stun of elemental sulfur allotropes (zero-valent sulfur) and the zero-valent sulfur derived from some fraction (n - 1) of the original polysulfide S 2. Thiosulfate data in the table represent the total amount of thiosulfate, sulfite, and polythionates. At some stations in the Black Sea, Volkov [61] observed a concentration maximum of elemental sulfur at the oxic/anoxic interface associated with sulfide oxidation by dissolved oxygen and/or Mn oxyhydroxides. Increasing with depth, elemental sulfur concentrations are probably explained by the ongoing process of polysulfide formation... 

This disproportionation reaction follows complex kinetics involving formation of polythionates (S3062-, S4062-, and S5062-) as intermediate products. The initial and rather slow decomposition during the induction period is later accelerated by thiosulfate, which functions as an autocatalyst. After a critical thiosulfate concentration has been reached, sulfur is precipitated, and the acidity increases rapidly. 

Schoon, N.-H. (1962). Kinetics of the formation of thiosulphate, polythionates and sulphate by the thermal decomposition of sulphite cooking liquors. Sven. Papperstidn. 65, 729-754. 

High concentrations of acids and sulfur compounds in crater lakes give rise to a complex chemistry within the waters (Sriwana et al, 2000). Reactions between hydrogen sulfide and sulfur dioxide lead to the formation of polythionates, with 840 , SsOi , and 8506 being the most typical. The initial ratio of 8O2/H28 controls... 

Except in ozone, the alkali-metal ozonates, the unstable O4F2, and a number of organic peroxides and trioxides (e.g. F3C, 000. CF3), the covalent linking of 0 to 0 does not proceed beyond 0=0 or -0—0—. Sulphur, on the other hand, presents a very different picture, a feature of its chemistry being the easy formation of chains of S atoms—in the element itself, in halides S ,X2, polysulphides, and polythionates. 

Thiosulfate Solutions. Aqueous thiosulfate is stable at room temperature for several weeks, but it decomposes within days at 100°C. The reaction products depend on the pH. Our Raman study essentially confirms the formation of products found by earlier authors ( 8, jj). Figure 3 summarizes our results. At high pH thiosulfate prevails at pH<7 two different product groups appear either elemental sulfur and sulfate appear, or polythionates rarely both product groups form simultaneously. At 2[Pg.120]

The formation of polythionates can be rationalized by the reaction shown in Equation VI. 

Figure 9.3-5 is a Pourbaix. predominant-area, diagram for the S-O-HjO system for a total activity of all dissolved sulftir species of 10 1 ( S — 10" ). The only stable sulfiir species are HSOJ. SO2-. H.S. HS". and elemental sulfur. The formation of elemental sulftir films occurs in acid solutions as indicated. In basic solution, during the oxidation of sulfur-bearing compounds, intermediate metastabte solfor species such as thiosulfate, dithionate. and polythionates form. This is a problem previously described in the Sherrill Gordon process. Under acid conditions, during the dissolution of sulfide minerals, elemental sulfur layers often form but metastable solfor intermediates such as thiosulfate and sulfite are not observed. 

Regeneration Step Theory. The reaction of hydrogen sulfide and sulfur dioxide in aqueous solution has been studied extensively as the Wackenroder reaction. The consensus of various workers (9) is that the first stage of the reaction is the formation of an unstable intermediate acid that further reacts to produce the products observed, principally sulfur, thiosulfuric acid, and polythionic acids. The most prominent of the suggested intermediates are sulfoxylic acid (S(OH)2) (10) and thiosulfurous acid (H2S202) (11). Both intermediates have schemes to explain all of the various products formed. The major overall reactions are given below. 

In phase 1, with the higher pH s used, the sulfur formed by Reaction 25 or 26 would be expected to react more readily to give thiosulfate by Reaction 28. Thus, sulfur formation is reduced or eliminated and a greater amount of thiosulfate is formed (12). Also in phase 1, with excess bisulfite, the polythionate chain is not built up as in Reaction 29, but rather tends to be degraded to trithionate and thiosulfate, Reactions 14 and 27. 

Foss (15) has postulated a mechanism for the formation of S8 from polythionates via the unstable sulfanemonosulfonates as intermediates similar to that proposed by Davis (16) for acidified thiosulfate solutions. 

Reaction between sulfanemonosulfonates was also postulated to explain the formation of polythionates (sulfanedisulfonates) as a side product in this system. Two molecules of disulfanemonosulfonate could give pentathionate ... 

Anions of the halides, as well as sulfides, selenides, and tellurides, can be determined by means of anodic waves due to mercury-salt formation. Among the oxygen-containing anions—in addition to those of the metals mentioned above—cathodic reduction waves can be used for determination of bromates, iodates, periodates, sulfites, polythionates, etc. 

Rate-determining reactions between [NaSgOe]" and [OH], and [SgOe] and [H+] are suggested. There is a report of the kinetics of formation and decomposition of the higher polythionic acids. The acid-catalysed hydrolysis of methyl toluene-p-sulphenate, ArS(OMe), has been studied in moist organic solvents ... 

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