Dithionic acid

HIO3 iodic acid H2S2S4 dithionic acid... 

HNO4 peroxonitric acid H2S2O4 dithionous acid... 

Sulfuric acid, H2SO4, the most important commercial sulfur compound (see Sulfuric acid and sulfur trioxide), and peroxymonosulfuric acid [7722-86-3] (Caro s acid), H2SO, are discussed elsewhere (see Peroxides and peroxide compounds, inorganic). The lower valent sulfur acids are not stable species at ordinary temperatures. Dithionous acid [15959-26-9] H2S2O4, sulfoxyHc acid [20196-46-7] H2SO2, and thiosulfuric acid [13686-28-7] H2S2O2 are unstable species. A discussion of efforts to isolate and characterize the unstable sulfur acids is given (330). 

Dithionites. Although the free-dithionous acid, H2S2O4, has never been isolated, the salts of the acid, in particular zinc [7779-86-4] and sodium dithionite [7775-14-6] have been prepared and are widely used as industrial reducing agents. The dithionite salts can be prepared by the reaction of sodium formate with sodium hydroxide and sulfur dioxide or by the reduction of sulfites, bisulfites, and sulfur dioxide with metallic substances such as zinc, iron, or zinc or sodium amalgams, or by electrolytic reduction (147). 

In dithionic acid and dithionates, 8205 , the oxidation state of the 2 8 atoms has been reduced from VI to V by the formation of an 8-8 bond (Table 15.18, p. 705). The free acid has not been obtained pure, but quite concentrated aqueous solutions can be prepared by treatment of the barium salt with the stoichiometric amount of H28O4 ... 

The chromic acid oxidation of dithionic acid is independent of oxidant concentration and its rate is equal to that of the acid-catalysed hydrolysis to sulphite and sulphate, which must therefore constitute the rate-determining process . ... 

One of the unstable oxyacids of sulfur is dithionous acid, H2S204, which contains sulfur in the +3... 

The dithionate ion is a good coordinating ion that forms stable chelates. In addition to dithionic acid,... 

Dithionous acid, 23 669 Dithiopolyesters, 23 739 Dithiozone extraction method, silver analysis via, 22 651 Dithizone, molecular formula, 5 713t Ditins, 24 826... 

By adding sulphuric acid to a solution of the baric dithio-note, baric sulphate is preoipitated and dithionic acid remains in solutions—... 

Sodium hydrosulfite Dithionous acid, disodium salt (8,9) (7775-14-6)... 

The term polythionic acids covers a group of acids 3 of the general formula HgS Oj, where x may range from 2 to 6, the various members of the group being distinguished by the names dithionic acid, trithionic acid, etc. 

Dithionic Acid, H2S2O0, is obtained only in aqueous solution. If sulphur dioxide is passed into an aqueous suspension of ferric hydroxide at 0° C., a red solution of ferric sulphite is first produced, which then changes to a pale green solution of ferrous sulphite and ferrous dithionate 4... 

By the addition of barium hydroxide to the solution, a solution of barium dithionate can be obtained which, on treatment with the necessary quantity of sulphuric acid, yields a dilute solution of dithionic acid this can be concentrated to some extent by evaporation at the ordinary temperature, but if the concentration is carried too far, decomposition ensues, with formation of sulphur dioxide and sulphuric acid. If so desired, the barium dithionate itself may be isolated by removing the excess of barium hydroxide with a current of carbon dioxide and then allowing the solution to evaporate until crystallisation occurs. 

The process by which Gay-Lussac and Welter 5 discovered dithionic acid was the oxidation of sulphurous acid with manganese dioxide the reaction is frequently represented as... 

The aqueous solution is odourless, but possesses an acid taste its electrical conductivity shows that dithionic acid is to be classed amongst the strong acids.4 The heat of formation5 of aqueous dithionic acid relative to its elements and the solvent is represented by the equation ... 

Dithionic acid solutions are remarkably resistant to oxidation the cold solutions withstand the attack of hypochlorite, hypobromite and permanganic acid, although on boiling, these reagents become reduced by the sulphur dioxide liberated in the decomposition of the dithionic acid sodium peroxide effects a partial oxidation in the cold.2... 

The Dithionates or Hyposulphates.—These salts, like the nitrates, are all soluble in water only normal salts are known.4 They may be obtained by neutralising dithionic acid solution with the hydroxide of the base, and also by double decomposition between barium dithionate solution and the sulphate of the base, or between manganese dithionate solution and the hydroxide of the base 5 also by methods on pp. 206-8. 

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