The reaction of a carbonyl compound with sodium hydrogen sulphite gives a crystalline adduct that is useful for
Correct answer: B. separating and purifying the carbonyl compound, since the adduct can be decomposed to regenerate it
- A. measuring the pH of the compound
- B. separating and purifying the carbonyl compound, since the adduct can be decomposed to regenerate it
- C. converting the compound into an alkane
- D. detecting the presence of a benzene ring
Explanation
The bisulphite adduct crystallises out and can be filtered off, and treating it with dilute acid or alkali releases the original aldehyde or ketone in a pure state. Only aldehydes, methyl ketones and a few cyclic ketones form the adduct, because larger groups hinder the approach of the bulky nucleophile. It is therefore a purification method and, incidentally, a structural test.
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About Nucleophilic Addition Reactions
Nucleophilic addition occurs at the polar carbonyl group of aldehydes and ketones, where a nucleophile attacks the electron-deficient carbon atom. Reactions with hydrogen cyanide, sodium bisulfite, alcohols and Grignard reagents are explained through tetrahedral intermediates, acid or base catalysis, and the different reactivity of aldehydes and ketones.
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