Which reagent is used to form the cyanohydrin from acetaldehyde?

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Multiple Choice

Which reagent is used to form the cyanohydrin from acetaldehyde?

Cyanohydrin formation from aldehydes occurs by nucleophilic attack of cyanide on the carbonyl carbon, followed by protonation of the resulting alkoxide to give the hydroxyl group. Hydrogen cyanide is the reagent here because it supplies the cyanide ion to attack the carbonyl and, in the same molecule, donates the proton needed to convert the alkoxide into the cyanohydrin. Starting from acetaldehyde (CH3CHO), the cyanide adds to the carbonyl carbon and, after proton transfer, yields the cyanohydrin CH3CH(OH)CN. Using a cyanide source like NaCN would provide CN−, but you’d need a separate proton source to form the cyanohydrin; water could protonate but wouldn’t supply the cyanide itself; ammonia doesn’t supply cyanide. Thus, hydrogen cyanide is the appropriate reagent.

Cyanohydrin formation from aldehydes occurs by nucleophilic attack of cyanide on the carbonyl carbon, followed by protonation of the resulting alkoxide to give the hydroxyl group. Hydrogen cyanide is the reagent here because it supplies the cyanide ion to attack the carbonyl and, in the same molecule, donates the proton needed to convert the alkoxide into the cyanohydrin. Starting from acetaldehyde (CH3CHO), the cyanide adds to the carbonyl carbon and, after proton transfer, yields the cyanohydrin CH3CH(OH)CN.

Using a cyanide source like NaCN would provide CN−, but you’d need a separate proton source to form the cyanohydrin; water could protonate but wouldn’t supply the cyanide itself; ammonia doesn’t supply cyanide. Thus, hydrogen cyanide is the appropriate reagent.

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