Give appropriate reagents for this transformation.

Question

BlackTom AI · Accepted Answer

Let’s break down what reaction is happening to acetone (a carbonyl compound) when it’s treated with methanol under acidic conditions.
Option 1: H2O / CH3I. This combination would be appropriate for converting an alcohol to a methyl ether via SN2 in some contexts, or for hydrolysis and iodination steps, but it’s not the standard method to form acetals from a ketone. It does not promote acetal formation from acetone with methanol.
Option 2: CH3MgBr / H3O+. A Grignard reagent (CH3MgBr) would attack the carbonyl carbon of acetone to yield a tertiary alcohol after workup, not the acetal or ether product depicted. This pathway adds a methyl group to the carbonyl, giving a different product entirely.
Option 3: excess CH3OH / H+. Under acidic conditions, methanol acts as both solvent and alcohol source, and the excess methanol promotes formation of the acetal (dimethyl acetal) from acetone. This is the classic acetalization reaction, converting the ketone carbonyl into an acetal with methoxy substituents, which matches a typical acetone + methanol under acid scenario.
Option 4: 1 equivalent CH3OH / H+. With only one equivalent of methanol, the reaction tends not to push to complete acetal formation and may give partial or reversible intermediates, but the controlled, standard protocol for forming the acetal from a ketone uses excess alcohol to drive the equilibrium toward acetal formation.
In summary, Option 3 (excess CH3OH / H+) aligns with the conventional method to convert a ketone like acetone into its acetal using methanol under acidic catalysis, whereas the other options describe pathways that do not lead to the depicted product.

Give appropriate reagents for this transformation.单项选择题

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