Consider the reaction of ethanoyl chloride with methanol shown below. What product(s) may you expect to be formed from the reaction?

Question

BlackTom AI · Accepted Answer

Nucleophilic acyl substitution gives methyl acetate (product A). Relevant concepts: acyl chlorides are highly reactive toward nucleophiles; alcohols (MeOH) attack the carbonyl to give esters under acid catalysis; formation of acetals (geminal dialkoxy compounds) requires an aldehyde/ketone, not an acyl chloride; symmetric anhydride formation requires a carboxylate nucleophile, not an alcohol.

Step-by-step mechanism and reasoning:
1) Protonation (acid catalysis) increases the electrophilicity of the ethanoyl chloride carbonyl.  
2) Methanol acts as a nucleophile and attacks the carbonyl carbon, forming a tetrahedral (hemiacetal-like) intermediate: O– attached to C, with –Cl and –OCH3 substituents present.  
3) Collapse of the tetrahedral intermediate expels chloride (a very good leaving group), regenerating the carbonyl and giving methyl acetate (CH3COOCH3) and HCl as byproduct. This is the classic nucleophilic acyl substitution pathway for acyl chlorides with alcohols.

Why product A is correct:
- Acyl chlorides react rapidly with alcohols to give esters; methyl acetate (A) is the expected and major product under these conditions.

Why B and C are incorrect:
- B (a geminal dimethyl acetal-type structure) would arise from addition of two methoxy groups to an aldehyde/ketone (acetal formation). Ethanoyl chloride cannot directly form that structure because acyl chlorides do not equilibrate to an aldehyde under these conditions; acetal formation requires a free carbonyl (aldehyde/ketone) and typically excess alcohol with acid catalyst.  
- C (acetic anhydride) would require nucleophilic attack by acetate (carboxylate) on an acyl chloride. In the presence of methanol and acid, alcoholysis to the ester is far faster and more favorable than formation of the anhydride; there is no source of free acetate nucleophile to form C in the described reaction.

Conclusion: The reaction of ethanoyl chloride with methanol under acid catalysis yields methyl acetate only (Product A), matching the provided answer (b. Product A only).

Consider the reaction of ethanoyl chloride with methanol shown below. What product(s) may you expect to be formed from the reaction?Single choice

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