Home > Community > Acid-Catalyzed Alcoholysis of δ-Valerolactone -- Need help with mechanism
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Loren McCune

Acid-Catalyzed Alcoholysis of δ-Valerolactone -- Need help with mechanism

Ali Abdulla  Follow
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The major product should be 5-hydroxypentanoic acid

It isn't, it ethanol it will be ethyl 5-hydroxypentanoate.

The mechanism is the same as the acid-catalysed ester hydrolysis (AAC2), but with ethanol as the nucleophile instead of water.

Your mechanism is OK up until the point where you use ethanol as the nucleophile in an SN2 reaction.

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Dapid Candra  Follow
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Am I correct in assuming that using water in place of the alcohol, the lactone would be hydrolyzed into 5-hydroxypentanoic acid?

Without researching the cited chemistry, I would say the mechanism would be correct, however I don't think your textbook is correct. 5 and 6-membered lactones form very easily. The usual method to isolate the hydroxy acid is to use a base catalyzed opening of the lactone and then a careful neutralization. Excess acid will catalyze lactonization. I think that is the actual chemistry you may find in the literature, but for the purpose of writing the mechanism of an acid catalyzed hydrolysis, it would be fine.

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Dolores C Aquino  Follow
Thank you for your reply. I spoke with my organic chemistry professor. She agrees. So I assume that when the ring breaks, the double bond would form with the hydroxyl group, allowing deprotonation by ethanol? That makes more sense the more I think about it. H+ would be much easier to remove than +CH2CH3. I think my textbook might have mistakenly given the hydrolysis product. Am I correct in assuming that using water in place of the alcohol, the lactone would be hydrolyzed into 5-hydroxypentanoic acid?

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