The product formed with Vanillin and Acetic Anhydride in acid based reaction.

[hellomister]

Hey all

 

I was wondering what the expected product should be in this reaction, everywhere i looked says it will be the same product as for the base reaction, but I dont think that is right. The product I predicted was having an acyl group on the anhydride substitute for the hydrogen on the aldehyde part of Vanillin.

 

Can anyone tell me if this is correct?

 

thank you.

[UC]

acid reaction? base reaction?

 

So, you are saying that the hydrogen on the aldehyde would be replaced by the O from an acetate group? But, in changing a the carbon-hydrogen bond to a carbon-oxygen bond, you've oxidized the vanillin. What got reduced? Now, being attached to a carbonyl carbon, that hydrogen is decently acidic, but there is one much more acidic hydrogen on the vanillin molecule that will react instead. In order for the reaction to occur, the electrophilic carbonyl carbons on the acetic anhydride need a nucleophile from vanillin. The only thing nucleophilic on vanillin are the oxygens and the phenol oxygen has electrons being given to it from that hydrogen. The carbonyl oxygen only has it's two lone pairs and a little electron density from the carbon.

 

Keep in mind that the general scheme of carboxylic acid anhydride reactions is:

 

[ce] (RCO)2O + R[/ce]'[ce]OH -> RCOOR[/ce]'[ce] + RCOOH [/ce]

 

(anhydride + alcohol -> ester + acid)

[hellomister]

Thank you very much, I ended up doing the reaction for a base catalyzed reaction and while drawing the mechanism I realized I could also do something else at the anhydride part of the molecule. I think I have figured it out since it corresponds to my NMR data.