Acetal Formation from Benzaldehyde and Ethanol

Acetal Formation from Benzaldehyde and Ethanol THE OVERALL REACTION  

Steps 1-3 Acid-catalyzed nucleophilic addition of 1 mole of ethanol to the carbonyl group. The details of these 

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 from hydronium ion to the hydroxyl oxygen of the hemiacetal. 

Step 5 Loss of water from the protonated hemiacetal gives an oxygen-stabilized carbocation. Of the resonance structures shown, the more stable contributor satisfies the octet rule for both carbon and oxygen. 

Step 6 Nucleophilic attack of ethanol on the oxygen-stabilized carbocation 

Step 6 Nucleophilic addition of ethanol to the oxygen-stabilized carbocation 

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FIGURE 17 9 The mechanism of acetal formation from benzaldehyde and ethanol... 

Problem 17.8 asked you to write details of the mechanism describing formation of benzaldehyde diethyl acetal from benzaldehyde and ethanol. Write a stepwise mechanism for the acid hydrolysis of this acetal. 

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