Synthesizing Phenyl Salicylate: Dehydrate Salicylic Acid

[chem13]

The question asks to suggest a method to synthesize phenyl salicylate.
It's an extension question that I know involves using a method similar to the one used to synthesize aspirin (i.e. dehydrate acetic acid to produce acetic anhydride and then combine that with salicylic acid to form aspirin). The reactants are phenol and salicylic acid.

The thing is, I'm not sure which of those two compounds to dehydrate. I tried dehydrating phenol - which works - but I thought only acids can be dehydrated?

So I basically want to know how salicylic acid can be dehydrated and combined with phenol to make phenyl salicylate. I'm pretty sure this is the answer that my teacher is looking for.

 

[Borek]

I am not sure what your question/problem is, but perhaps this will help: aspirin is an ester. What do you know about esterification?

 

[chem13]

That's true but aspirin is not synthesized using the traditional method of an alcohol+carboxylic acid. Instead, we have to make an acid anhydride first.
My question is how do we apply this method to the synthesis of phenyl salicylate?

 

[Borek]

I have checked my books, using acid anhydride is not listed as a method of preparing phenol esters.

What methods of esterification do you know?

 

[chemisttree]

Borek, using acetic anhydride is the usual method for producing acetyl esters of salicylic acid. It is an ester for the phenol group.

Chem13, see http://www.cerlabs.com/experiments/10534977723.pdf"

 

[Borek]

I have checked Vogel organic recipes (not sure about English title, but you must know the book), making esters of phenol is mentioned in three places - three times they propose to use something different than anhydride.

I am not saying you can't make aspirin with anhydride, I just guess there are reasons to use something else when dealing with phenol.

 

[chemisttree]

No specific reason chemistry-wise except that acetic anhydride is cheap, relatively safe compared to most other methods (excepting the straightforward Fisher synthesis), is really easy to purify, etc.

I'm surprised Vogel wouldn't list acetic anhydride for making acetate esters. It's usually the first thing to try.

 

[Borek]

Hm, perhaps the problem is that I was looking for recipes for making esters of phenol, not of acetic acid. Other end of the problem.

 

[chemisttree]

Ahh, yes. Usually you add relatively simple alcohols to more complex carboxylic acids in an esterification. I can see how that might easily guide you toward more elaborate methods like acid chlorides, carbodiimides and so forth. In this case the situation is reversed... we are adding a very simple carboxylic acid to the more complex alcohol.

Of course the OP's problem is to produce a phenyl ester of salicylic acid leaving the phenol group of the acid unreacted! If you were to activate the carboxylic acid of salicylate you might get self condensation to produce polymeric products. You must find a way to activate the phenol separately before adding it to the salicylic acid in this case. Chem13, are you studying protecting groups?