Other Addition Reactions Additions of Cyanide and Bisulfite

Many other addition reactions follow the pattern of carbonyl hydration. Two typical examples are c ohydrin formation and bisulfite addition. Both of these reactions are generally base catalyzed. Because of an understandable and widespread aversion to working with the volatile and notorious HCN, cyanide additions are generally carried out with cyanide ion. Potassium cyanide (K CN) is certainly poisonous, but it s not volatile, and one knows where it is at all times, at least as long as basic conditions are maintained. 

Cyanide ion is a good nucleophile and attacks the electrophilic carbonyl compound to produce an alkoxide (Fig. 16.35). This alkoxide is protonated by solvent, often water, to give the final product, a cyanohydrin. The cyanohydrin is often not stable under basic conditions and reverses to the carbonyl compound and cyanide. 

PROBLEM 16.9 Why does acetaldehyde in aqueous solution form an excellent yield of cyanohydrin even though acetaldehyde is substantially hydrated in water K 1) Might it not be argued that, because about one-half of the aldehyde is present in hydrated form at equilibrium, no more than about 50% cyanohydrin can be formed. Why is this argument wrong Hint. See Rgure 16.34. 

Bisulfite addition to an aldehyde or ketone is similar to cyanide addition, although the nucleophile in this case is sulfur. Sodium bisulfite adds to many aldehydes and ketones to give an addition product, often a nicely isolable solid (Rg. 16.36). 

The reactions we have seen so far have all been simple additions of a generic HX to the carbon-oxygen bond of a carbonyl group. Now we move on to related reactions in which there is one more dimension. In these new reactions, addition of HX is accompanied by the loss of some other group. 

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Other Addition Reactions Additions of Cyanide and Bisulfite... 

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