Sulfite, sodium, reduction mechanism

Isocyanates and isothiocyanates are reduced to methylamines on treatment with LiAlH4. LiAIH4 does not usually reduce azo compounds622 (indeed these are the products from LiAIH4 reduction of nitro compounds, 9-67), but these can be reduced to hydrazo compounds by catalytic hydrogenation or with diimide623 (see 5-9). Diazonium salts are reduced to hydrazines by sodium sulfite. This reaction probably has a nucleophilic mechanism.624... 

Addition of osmium tetroxide to norbornene 2 followed by reductive cleavage with sodium sulfite gives the exo,exo diol 3. The same reaction sequence carried out on 7,7-dimethylnorbornene 4 gives endo,endo diol 5. From these results deduce the mechanism of the addition and facial selectivity for these two substrates. 

The naphthylamines may be prepared by reduction of the corresponding nitro compound, but they are readily accessible from naphthois by the Bucherer reaction The naphthol is heated, preferably under pressure in an autoclave, with ammonia and aqueous sodium hydrogen sulfite solution, when an addition-elimination sequence occurs. The detailed mechanism is not completely elucidated, but the Bucherer reaction is restricted to those phenols that show a tendency to tautomerize to the keto form, such as the naphthois and 1,3-dihydroxybenzene (resorcinol). Using 1-naphthol for illustration, the first step is addition of the hydrosulfite across the 3,4-double bond of either the enol or keto tautomer (Scheme 12.9). Nucleophilic attack by ammonia at the carbonyl group... 

The exact mechanism of toxicity has not been elucidated, although there is a lot of information on how sulfur-based compounds are detoxified by the liver. Sodium sulfite is a mild reducing agent that would most likely cause burning or irritation at the site of exposure or application by altering oxidation-reduction potential and pH. 

The prevention of iron-oxide-induced corrosion can be accomplished by mechanical filtration of iron oxide, by the use of additives (iron oxide dispersants), and by adding inhibitors for corrosion. Standard procedures for reduction of corrosion in boilers include deaeration of the feedwater and the use of additives such as sodium sulfite. 

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