Acetal Formation from Benzaldehyde and Ethanol THE OVERALL REACTION: Benzaldehyd

Question

Acetal Formation from Benzaldehyde and Ethanol THE OVERALL REACTION: Benzaldehyde Benzaldehyde diethyl acetal Water THE MECHANISM Steps 1-3: Acid-catalyzed nucleophilic addition of 1 mole of ethanol to the carbonyl group. The details of these three steps are analogous to the three steps of acid catalyzed hydration in Mechanism 18.2. The product of thése three steps is a hemiacetal. +CH3CH2OH CH3 Benzaldehyde Ethanol ethyl hemiacetal Step 4: Steps 4 and 5 are analogous to the two steps in the formation of carbocations in acid-catalyzed reactions of alcohols. Step 4 is proton transfer to the hydroxyl oxygen of the hemiacetal + H Conjugate acid ethyl hemiacetel Step 5: Loss of water from the protonated hemiacetal gives an oxygen-stabilized carbocation. Of the resonan?e structures shown, the more stable contributor satisfies the octet rule for both carbon and oxygern OCH,CH More stable contnbutor Less stable ceatribator ethyl bemuiacetal Step 6 Nucleophilic addition of ethanol to the oxygen- stabilized carbocation CH CH + Conjugate acid of benzaldehyde diethyl apetal Step 7 Proton transfer from the conjugate acid of the product to ethanol Canj gate acid af benaaldchyde diethyl acetal diehyl acetal acid of ethanol

Explanation / Answer

2.a)step1 here only protonation occurs to carbonyl oxygen.

3.A)2

4.b)combination of (b)

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