Synthesis of aspirin

[mahdiking]

in the Synthesis of aspirin, what is the reason for attacking OH function group in acid salicylic to CO function group inanhydride acid
and
what is the reason for not attacking COOH function group in acid salicylic to CO function group in anhydride acid

 

[BabcockHall]

Suppose you formed the mixed anhydride. Could it react with anything?

[Elite Engineer]

in the Synthesis of aspirin, what is the reason for attacking OH function group in acid salicylic to CO function group inanhydride acid

and

what is the reason for not attacking COOH function group in acid salicylic to CO function group in anhydride acid

 

The single OH groups retains more electron density to itself making it more strongly polar, and therefore more prone to an electrophilic attack. The OH on the carbonyl group has less electron density from the carbon, because some of it is shared with the double bonded oxygen (R=O). You will have some product where the C=O group is attacked, but it is a minor product.

 

~EE

Edited October 14, 2016 by Elite Engineer

[hypervalent_iodine]

I think the question is worded a bit funny. I think the fact that you don't get the anhydride is taken as a given. The question is why you get that regioselectivity. The reason is simply that the anhydride that would form if the carboxylate reacts with the acetic anhydride is less stable than the ester that forms when the phenoxide reacts. Under basic conditions the phenoxide is also going to be a stronger base and more likely to react with the anhydride.