I've mastered MOST aromatic substitution reactions, but I found one in my book that perplexes me. (Unfortunately the answer isn't at the back of the book.)

 

In the reaction below, one might think that two products will form in a substituon reaction: an OH group in the ortho and para positions, relative to fluorine - since it is the least deactivating of the two substituents. However, something tells me that electrophillic substitution will occur since this is an acid-catalyzed reaction and it is carried out under warm condition. Therefore, the SO3H group will be replaced with a hydrogen, yielding simply, fluorobenzene. Can anyone enlighten me about which mechanism/product to expect? Thanks so much in advance! I really want to understand this so I can do well on next week's big exam, yet importantly become a good researcher someday!

i can't think of a way in which the SO3h group can just be replaced by a hydrogren... there's no nucleophillic group to replace it.

 

possibly, if its a substitution the acid will protonate an oxygen on the sulfur, turning it into a better leaving group. Then the water can attack, ultimately forming an alcohol.

 

If the question is about directing effects, then maybe you should looking towards that answer, though I can't think of one. I can't think of a mechanism off the top of my head and my orgo book is in my car.

 

H20 isn't going to add onto a benzene via an acid catalyst.

sulphonation is reversible so this is not a particularly unusual reaction

I found a video on YouTube about electrophilic aromatic substitution

 

It is an analogy of this reaction and Homer Simpson and doughnuts. Hope this is helpful!