Which of the following gases when passed through warm dilute solution of H2SO4 in presence of HgSO4 gives acetaldehyde
Correct answer: D. C2H2
- A. CH4
- B. C2H6
- C. C2H4
- D. C2H2
Explanation
Ethyne reacts with dilute H2SO4 in the presence of HgSO4 by acid-catalysed hydration, initially forming an enol that rearranges to acetaldehyde, CH3CHO. Ethene would form an alcohol under hydration conditions, not acetaldehyde. Students may choose C2H4 because it is the nearest lower unsaturated hydrocarbon, but an alkyne is required for this reaction.
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About Preparation of Aldehydes and Ketones
Aldehydes and ketones are prepared mainly by controlled oxidation or dehydrogenation of primary and secondary alcohols, respectively. The topic also includes ozonolysis of alkenes, hydration of alkynes and preparation through acyl derivatives, with attention to why primary alcohols can give aldehydes whereas secondary alcohols give ketones.
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