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Author Topic: Friedel Crafts mechanism problem help  (Read 1224 times)

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michaelaaaaa

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Friedel Crafts mechanism problem help
« on: March 16, 2012, 07:21:13 PM »

http://26.media.tumblr.com/tumblr_m10jt7PUmr1qzof18o1_500.png

Ok so the problem is written at the top its a benzene with a och3 on it, you use reagents:
1. ch3co2coch3, AlCl3, CS2
2. HCl, H2O
to get the product (sorry the picture is so small)

my problem is I got the product before using the second step reagents (HCl, and H2O) so what is the function of the HCl and H2O?

Anyone?
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Potla

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Re: Friedel Crafts mechanism problem help
« Reply #1 on: March 20, 2012, 09:23:28 PM »

my problem is I got the product before using the second step reagents (HCl, and H2O) so what is the function of the HCl and H2O?
I think HCl and H2O means dil. H+, which acts as a catalyst for the process. In case of anhydrides, I think two moles of AlCl3 is required, one mole is used for liberating the acid chloride from the anhydride:
R-CO-O-CO-R + AlCl3 --> RCOCl +RCOOAlCl2.
The second mole, forms the sigma complex with C6H6OMe and then the O-Al-Cl3 might take H+ and liberate one mole of HCl. Then the complex may lose a proton to regain aromaticity, followed by which the Cl may (intramolecular) attack the -AlCl2, causing breakage of O-Al bond and C-Cl bond through a 4-membered transition state.
This may be possible. I don't really know if all of this is correct or not, since I am a beginner. Hope I could be of some help. :)
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