Dithionate ion

Sodium hydrosulfite or sodium dithionate, Na2S204, under alkaline conditions are powerful reducing agents the oxidation potential is +1.12 V. The reduction of -phenylazobenzenesulfonic acid with sodium hydrosulfite in alkaline solutions is first order with respect to -phenylazobenzenesulfonate ion concentration and one-half order with respect to dithionate ion concentration (135). The SO 2 radical ion is a reaction intermediate for the reduction mechanisms. The reaction equation for this reduction is... 

Sflf-Test 1S.4A What is the oxidation number of sulfur in (a) the dithionate ion, S2062 (b) the thiosulfate ion, S2032- ... 

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

Pyrolusite, in oxidation of sulfurous acid to dithionate ion, 2 168 Pyrophosphates, determination of, in mixtures of phosphates, 3 93 Pyrophosphoric acid, 3 96, 97 Pyrosulfites, alkali metal, 2 162 Pyrosulfuryl chloride, 3 124, 126... 

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

The improvement over the existing Japanese processes can be made by developing a more efficient ferrous chelate such that it can provide better absorption efficiency for NO, faster reaction rates between NO and S02> and better stability for the ferrous chelate toward oxidation, compared to Fe +(EDTA) or Fe +(NTA) employed in Japanese processes. The development of an efficient and cost-effective method for the reduction of ferric chelate to ferrous chelate without producing dithionate ions could make the process attractive. In addition to these areas, the study of several alternative approaches and novel ideas could develop into a much more efficient and cost-effective scrubber system employing metal chelate additives. 

It is of interest that there are reducing agents that may be oxidized to one product by two-electron oxidants and to a different product by one-electron oxidants. One of the simolest of these is SOI , which is oxidized to S024 by T1+8, JOr, or Br2. However, when MnOt> Ce(IV), Co(III), or Fe(III) is used as an oxidant, the dithionate ion, SaOjj" is formed, and may be made to predominate. The dithionate almost certainly results from the dimerization of the SOj radical ion, formed in an initial one-electron transfer ... 

The oxidation state of sulfur in H2S206 is formally +5. This acid is not obtained as a pure compound, although a sizable number of dithionate salts are known. The structure of the dithionate ion is... 

Toward transition metals, the dithionate ion behaves as a bidentate ligand, and it forms a large number of complexes. 

X-ray diffraction shows the dithionate ion to consist of two triangular pyramids joined at their apices (Fig. 188). In the trithionate ion the third sulphur atom lies between the other two with an S—S—S angle of 103° (Fig. 189). In the tetrathionate and pentathionate ions the additional sulphur atoms are attached to one another in simple chains (Fig. 190). 

Fig. 10.07. The structures of some polynuclear sulphur oxy-ions. (<2) The dithionate ion, So062. (b) The trithionate ion, S3062-. (c) The perdisulphate ion, S2082-. (d) The metabisulphite ion, S2052. ...

The S-S distances of 2 15 A in the trithionate ion (and also of 2 01 A in the dithionate ion) are in reasonably satisfactory agreement with the S-S distance of 2 04 A in the S8 molecule of elementary sulphur, in which, also, the sulphur atoms are linked by single covalent bonds. 

Figure 15.17a shows the presence of a long S—S bond the anion possesses a staggered conformation in the solid state. The dithionate ion can be prepared by controlled oxidation of [803] (equations 15.97 and 15.98), but not by the reduction of [804] (equation 15.99). The [8205] can be isolated as the soluble salt Ba820g, which is easily converted into salts of other cations. 

Dithionate salts may be prepared by oxidizing acidic sulfite solutions with manganese dioxide, as shown in Equation (17.20). The dithionate ion, 820, is stable in solution and is useful as a moderately large counteranion to precipitate similarly sized cations. The free dithionic acid, H2S2O6, can be prepared by treating dithionate solutions with acid, as represented in Equation (17.21) ... 

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