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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Darkstar on September 07, 2004, 08:52:43 PM

Title: Benzaldehyde + Ac2O
Post by: Darkstar on September 07, 2004, 08:52:43 PM

Benzaldehyde + acetyl anhydride in the presence of NaOAc. What kind of reaction is this? Just a common carbonyl alpha-substitution or something else? What do we get?

Title: Re:Benzaldehyde + Ac2O
Post by: movies on September 08, 2004, 12:49:28 AM

It's not an alpha substitution, there are no alpha protons in benzaldehyde.  I think that those are acylation conditions.  Sort of like Friedel-Crafts, but without a metal Lewis acid.  I think that you would get 3-formyl acetophenone.

Title: Re:Benzaldehyde + Ac2O
Post by: falcon on September 08, 2004, 05:07:22 AM

 :o
It`s classic Perkin condensation! Synthesis  of cinnamic (3-phenyl-2-propenoic) acids. Acetate anion
tears off the proton from acetic anhydride, this anion attack carbonyl group in benzaldehyde, further follows migration negative charge, leading to cinnamic acid.

Title: Re:Benzaldehyde + Ac2O
Post by: Darkstar on September 08, 2004, 06:28:06 AM

That's right... thanks, I see now.

Title: Re:Benzaldehyde + Ac2O
Post by: movies on September 08, 2004, 12:04:05 PM

Really?  But the acetate anion isn't nearly a strong enough base to remove that proton!

Title: Re:Benzaldehyde + Ac2O
Post by: movies on September 08, 2004, 01:11:08 PM

I stand corrected.  Falcon was right on.  Here is a link with some references if anyone is interested:

http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR300.htm