Sulphite ions

However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

Although sulphur dioxide, as a gas, is a reducing agent in the sense that it unites with oxygen, free or combined (for example in dioxides or peroxides) most of its reducing reactions in aqueous solution are better regarded as reactions of sulphurous acid (in acid solution), or the sulphite ion (in alkaline solution). 

The sulphite ion, SO3, has a pyramidal structure and the short S—O bond length suggests the presence of double bonding, i.e. 

In the presence of strong reducing agents the sulphite ion acts as an oxidising agent some examples are ... 

Evaporation and crystallisation of the sodium sulphite solution gives crystals of the heptahydrate NajSOj.THjO. However, on evaporation of the hydrogensulphite solution, the solid obtained is chiefly sodium pentaoxodisulphate(IV) ( metabisulphite ) Na2S20j, and contains little if any of the hydrogensulphite. However, the hydrogen sulphite ion is obtained when the solid redissolves in water ... 

Further reaction between hydrogen sulphide and the sulphite ion yields sulphur together with thionic acids) ... 

General corrosion damage was the cause of failure of an A1 alloy welded pipe assembly in an aircraft bowser which was attacked by a deicing-fluid — water mixture at small weld defects . Selective attack has been reported in welded cupro-nickel subjected to estuarine and seawater environments . It was the consequence of the combination of alloy element segregation in the weld metal and the action of sulphate reducing bacteria (SRB). Sulphide-coated Cu-enriched areas were cathodic relative to the adjacent Ni-rich areas where, in the latter, the sulphides were being continuously removed by the turbulence. Sulphite ions seemed to act as a mild inhibitor. 

This procedure emphasises the overall division of oxidants into one-equivalent and two-equivalent types defined in terms of how many equivalents of reducing species, e.g. electrons or hydrogen atoms, are taken up by the oxidant in the primary act, as deduced from the behaviour of the oxidant towards either hydrazine , sulphite ion or captive ligand according to the schemes (a)-(c) respectively. 

The rate of oxidation of sulphite ion by tetrabromoaurate is pH-dependent and analysis of the kinetic data leads to the rate law... 

The determination of formaldehyde, a substance of great interest on account of its toxicity and high significance to the resin, fertilizer and explosive manufacturing industries, among others, entails the use of rapid, convenient, safe methods. One sensor developed for this purpose uses the manifold shown in Fig. 4.6 to handle the reagents involved, viz. / -rosaniline (PRA) and sulphite. The instability of sulphite ion calls for on-line mixing with PRA dissolved in 0.4 M HCl prior to injection of the sample. After the... 

A sensitive colour test for sulphite ions consists in adding, drop by drop, a 0-01 per cent, solution of Fast Blue R crystals, shaking after each addition, until the violet coloration disappears and a yellow solution is produced the test is sensitive to one part of sulphurous acid in about 175,000. Thiosulphates and polythionates do not interfere, but sulphides and hydroxides must be absent.1... 

The direct replacement of the hydroxyl group in simple phenols by an amino or substituted amino group requires drastic conditions and the method is not suitable for laboratory preparations. With the polyhydric phenols, and more particularly with the naphthols, such replacements occur more readily. Thus 2-naphthol is converted into 2-naphthylamine by heating with ammoniacal ammonium sulphite solution at 150°C in an autoclave. The reaction (the Bucherer reaction) depends upon the addition of the hydrogen sulphite ion to the keto form of the naphthol and the subsequent reaction with ammonia. 

The mechanism of this reduction probably involves the initial addition of a sulphite ion to the diazonium group to give an azosulphonate which undergoes further conjugate (1,4-) addition of the nucleophilic sulphite ion. The resulting intermediate is protonolytically cleaved on heating under acidic conditions ... 

The results of this calculation for the above-mentioned decomposition experiment are given in Fig. 6.14 by the continuous lines. The crosses illustrate the variation of the concentration of dithionite and sulphite in solution obtained by titration of samples taken at fixed times. It can be seen that the concentrations obtained by calculation from the experimental currents (continuous line) are in good agreement with the ones obtained by titration (crosses). Note also that the increase of the concentration of sulphite is twice as high as the drop of the sodium dithionite concentration. Indeed, for each dithionite ion that is decomposed, two sulphite ions are... 

Visible and NMR spectra (Crampton, 1967) indicate that, in aqueous dimethyl sulphoxide, the sulphite ion adds to the 3-position of 2,4,6-... 

B. L. Wedzicha and M. T. Kaputo, Melanoidins from glucose and glycine Composition, characteristics and reactivity towards sulphite ion, Food Chem., 1992, 63, 359-367. 

Sulphite ion has been successfully used to replace halogen in 4-chloro-l-naphthol743,744,... 

Sulphur dioxide, S02, and sulphurous acid H2S03 Sulphur dioxide gas, when dissolved in water, forms sulphurous acid. It is a strong reducing agent, its action is based on the transformation of sulphite ion to sulphate. The oxidation number of sulphur changes from +4 to +6, hence 2 electrons are released during the process ... 

Note that the thioantimonate SbSO ion is the derivative of the antimonate ion Sb04- (and has nothing whatsoever to do with the sulphite ion SO2-). 

The precipitate dissolves if sulphite ions are added in excess Ag2S03j+S02- 2[AgS03]-... 

The precipitate dissolves on prolonged passage of the gas, due to the formation of hydrogen sulphite ions ... 

Plot the absorbance of die standard solutions against the concenhation of sulphite ion, and read off the concenhation in the sample. 

The normal urinary concenhation of sulphite ion is less than 6 Lig/ml. The estimated lethal dose of sulphurous acid is 10 g. 

Other reactions involving this aldehyde include the following (1) combination with sulphite ion, which substantially increases the proportion of bound sulphite in wine (2) formation of addition compounds with some polyphenols such as tannins and procyanidins, where it acts as a bridging molecule (Haslam and Lilley 1998) and (3) chemical oxidation to acetic acid, which only occurs to a small extent and has little influence on wine composition and quality. 

---