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#1 2009-02-26 18:44:07


2-hydroxytetrahydrofuran (hemiacetal chemistry) hydrolysis

Yahoo!Answers in chemistry wrote:

Trace acid will take your reaction in one direction whereas aqueous acid will take your reaction in the opposite direction. Draw the skeletal structure of the indicated species.

For me, this is not a good example to try to resolve. These reactions are reversible and governed by Le Chatelier's principle. The conditions do not specify which conditions should be which as specifically as I would like if I were trying to get my students to understand this reaction.

In either case, an acid will protonate either sp3-oxygen nearly the same. This gives two possible intermediates. They can open in the directions indicated. If the protonation reaction were performed under dehydrative conditions (catalytic acid I presume, I have saved on space by letting hydronium be the acid for both), then no addition of water will occur. A deprotonation with water will regenerate the hydronium ion and the dihydrofuran product (top).

In the alternate case, loss of the oxonium ion gives the open chain aldehyde (red box). The only problem is this product is undoubtedly unstable and cyclizes to the starting material. I presume this is the dilute acid conditions. Since the hemiacetal is given as the starting material, I am presuming that the open chain product should be considered as the product of this reaction. Too bad, that should have been the starting material and a better problem would be to predict the product of the dehydration of it by going through the hemiacetal.



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