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Topic: Anhydride+AlCl3  (Read 11151 times)

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Offline Rutherford

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Anhydride+AlCl3
« on: January 21, 2013, 12:30:56 PM »
How do anhydrides activate AlCl3? I see this first time and I need to finish this scheme.

Offline discodermolide

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Re: Anhydride+AlCl3
« Reply #1 on: January 21, 2013, 12:36:10 PM »
This is just a normal Friedel-Crafts acylation.
Look on this page for the Haworth reaction
http://en.wikipedia.org/wiki/Friedel–Crafts_reaction
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Offline Rutherford

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Re: Anhydride+AlCl3
« Reply #2 on: January 21, 2013, 12:59:16 PM »
From looking at the scheme I tried to work out the mechanism, is it okay?
In the mechanism I wrote that the second C atom got the acyl group attached to it, but it could be any of the C atoms. How should I know which one it is?

Offline discodermolide

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Re: Anhydride+AlCl3
« Reply #3 on: January 21, 2013, 01:08:39 PM »
I don't really like the acylcarbocation, but I suppose it may be stabilised by the Al.
Alkyl groups on the benzene ring are ortho/para directors, so I guess you will get some para substitution product.
Don't forget that when the pi electrons of the aromatic ring attack the acylcation you generate a cation in the benzene ring which is resonance stabilised.
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Offline Rutherford

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Re: Anhydride+AlCl3
« Reply #4 on: January 21, 2013, 01:30:01 PM »
"Don't forget that when the pi electrons of the aromatic ring attack the acylcation you generate a cation in the benzene ring which is resonance stabilised."

Knew that but didn't know how to draw it. Thanks very much for the help. I got one last question. In the Haworth reaction on the wikkipedia link you posted, the product is reduced and then H+ is added so the R-COOH group cyclizated to form a cyclic ketone. How is this possible?

Offline discodermolide

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Re: Anhydride+AlCl3
« Reply #5 on: January 21, 2013, 01:33:02 PM »
Similar mechanism protonate on of the acid and cyclisation via the pi electrons as usual.
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