Disulfite ion

Figure 1532 Structure of (a) the disulfite ion 8265 in (NH4)2S20s, and (b) the dithionite ion 8264 Na2S204.2H20.

Due to the fact that the sulfate and selenate oxyanions have the same spatial configuration, the corresponding rare earth compounds are isostructural with only a few exceptions. Their physical and chemical properties are also largely similar. On the other hand, the relationship between rare earth sulfites and selenites is not as close as one would expect. Besides the larger size of the selenite ion, possible factors leading to structural and other differences between the sulfites and selenites include the different relative stabilities of the tetra- and hexavalent states and the lower stability of the selenium-selenium bond compared to the sulfur-sulfur bond. The first factor is responsible for the different observed thermal decomposition mechanisms while the latter contributes, for instance, to the formation of a diselenite ion which has an oxygen-bridged structure. This is much different from the disulfite ion, which is nonsymmetrical and contains a sulfur-sulfur bond. 

Most sulfites (except those of the alkali metals and ammonium) are rather insoluble as indicated above such solutions contain the HSOi ion predominantly, but attempts to isolate M HSOs tend to produce disulfites (p. 720) by dehydration" ... 

Sheppard (1988) examined the chemical mechanisms that underlie the bronchoconstrictive effect of sulfur dioxide. Sulfur dioxide dissolves in water to form bisulfite ion, sulfite ion, and hydrogen ion. The bisulfite ion is a nucleophile that can disrupt disulfite bonds. It has been postulated that bisulfite... 

B. J. Johnson, Sulfite-disulfite equilibrium on an ion chromatography column, J. Chromatogr.. 508,271,1990. 

The mechanism of the nucleophilic attack in this reaction is not completely known it is still not clear whether species responsible for cleavage of the cystine are the sulfite (S03") or bisulfite (HS03 ) or disulfite (S2O5") ions. Products of the reaction are a free thiol residue and a cysteine—S—sulfonate residue, also known as Bunte salt. Though totally ionized at pH values above 1, Bunte salts are capable of a number of reactions, including reformation of disulfide bonds. 

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