Carbonyl group sulfite addition

Methods of preventing browning could consist of measures intended to slow reaction rates, such as control of moisture, temperature, or pH, or removal of an active intermediate. Generally, it is easier to use an inhibitor. One of the most effective inhibitors of browning is sulfur dioxide. The action of sulfur dioxide is unique and no other suitable inhibitor has been found. It is known that sulfite can combine with the carbonyl group of an aldose to give an addition compound ... 

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... 

Bisulfite Addition Products and the Bucherer Reaction. The addition of sodium bisulfite to aldehydes and some ketones superficially appears to involve the addition of the elements Na and HS03 to the carbonyl group. Kinetic studies, however, indicate that the reaction is complicated and probably involves sulfite rather than bisulfite ion.10 One possible mechanism is the following ... 

This reaction has many implications for foodstuffs. For example, aroma components possessing a carbonyl group become involatile and do not contribute anymore to the overall flavor. Other nucleophilic reactions include the cleavage of S-S bonds in proteins and addition to C=C bonds of a,(l-unsaturated carbonyl compounds. Control of nonenzymatic browning is based on this latter reaction (McWeeny et al., 1974). A key intermediate of the Maillard reaction, i.e., 3,4-deoxyhexulos-3-ene, is efficiently blocked by a fast reaction with sulfite, leading to formation of 3,4-dideoxy-4-sulfohexosulose, which is much less reactive and in which sulfite is irreversibly bound. 

Although simple isocyanates are not electrophilic enough to add to alkenes, electron-deficient isocyanates will add to alkenes. Chlorosulfonyl isocyanate is the most reactive and most commonly used isocyanate105-107. It undergoes stereospecific syn addition to alkenes. The carbonyl group adds to the most nucleophilic end of the double bond. The chlorosulfonyl group can be reductively hydrolyzed with sodium sulfite. Asymmetric induction will result from addition to... 

Formation of addition compounds from species containing carbonyl groups has been exploited for the determination of organic compounds reacting with hydrogen sulfite ion in the presence of acetone, methanol, or acetic acid. Primary amines can be determined alone and in mixtures with secondary and tertiary amines by condensation with aldehydes such as salicylaldehyde and 4-dimethylaminocinnamalde-hyde. 

Sodium hydrogen sulfite also adds to aldehydes and some ketones to form hydroxysulfonic acids (22) (Scheme 20). The nucleophilic addition generally goes well with aldehydes and methyl ketones of the type RCOMe, where R is a primary alkyl group. Since the water soluble products are readily converted back to the carbonyl compounds by treatment with dilute acid, the reaction provides a useful method for purification of carbonyl compounds from non-carbonyl impurities. 

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