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Topic: The mechanism of esterification (of anhydride + alcohol)  (Read 2879 times)

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Offline Natalia_Poland

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The mechanism of esterification (of anhydride + alcohol)
« on: November 22, 2015, 07:41:14 AM »
Hi!
Could someone help me write mechanism of esterification of this compounds?
I need it for laboratory classes at the university.
t-butyl alcohol + acetic anhydride ---(zinc chloride as catalyst)---> t-butyl acetate + water

I found such a mechanism (picture), but I do not use in the process of hydrochloric acid and do not know how the end of reaction will look like.

Offline orgopete

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #1 on: November 22, 2015, 08:47:50 AM »
This mechanism is incorrect. It has been written as an uncatalyzed reaction (and chloride is not the most basic agent).

The zinc can coordinate with electrons in the same manner as a proton.
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Offline Natalia_Poland

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #2 on: November 22, 2015, 09:06:41 AM »
So how should look this mechanism properly? ???

Offline Babcock_Hall

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #3 on: November 22, 2015, 12:28:32 PM »
Welcome to the forum.  You may wish to read over the forum rules, so that you can better understand what it is that we do and do not do here.  It is up to you to write the mechanism out, and then we can give you pointers.

Offline orgopete

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #4 on: November 22, 2015, 02:37:25 PM »
If the reaction were acid catalyzed, then it must be used in writing the mechanism. Hint, start with a protonation step by the acid. Zinc chloride is probably acting similarly. The actual species that must be protonated is not the actual most basic compound (ROH).
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline Natalia_Poland

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #5 on: November 23, 2015, 07:52:16 AM »
I do not know how the end of the mechanism will look like. According to the instructions I have water as a product.

Offline orgopete

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Re: The mechanism of esterification (of anhydride + alcohol)
« Reply #6 on: November 23, 2015, 08:51:34 AM »
Water is the by-product for a Fischer esterification, acetic acid is the by-product here. In your mechanism, you might want to "transfer" the zinc to an oxygen of the acetate mid-stage. Then it can be the weakest base. Why isnt the protonated alcohol the leaving group? Isn't it the weakest base?
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

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