[nexisrocks]

Hello,

I am attempting to determine the mechanism for the synthesis of p-acetamidobenzenesulfonyl chloride.

The reaction equation is C₆H₅NHCOCH₃ + 2HSO₃Cl --> ClSO₂C₆H₅NHCOCH₃ .  That is, acetanilide plus 2 chlorosulfonic acid produces p-acetamidobenzenesulfonyl chloride.

Because only one chlorosulfonic acid attaches to the acetanilide, I thought perhaps the two chlorosulfonic acids react to form H₂SO₄ and another product.  However, if this is true, I'm not sure what the other product would be.  I made an attempt, below:



But I have this sneaking suspicion that it is incorrect.  If that is so, then I'm really not sure what the mechanism could be.

If someone could help me determine the mechanism (assuming what I have is incorrect), I would greatly appreciate it!

[D|0XIN]

Hi, here's my stab at it :



Seeing chlorosulfonic acid is a very strong acid, it is capable of protonating itself (hence the 2 molar equivs. required). It then loses water, yielding an electrophilic chlorosulfonium species which is then attacked by a pair of pi electrons in the meta-para position of the acyl ring (the acetamido group is ortho-para directing, but due to steric hinderance and other electronic effects (the available resonance forms); directs mainly para).

You obviously got the point about para-directing yourself and were half-way there with the reaction between 2 chlorosulfonic acid molecules, awesome stuff! I am pretty confident that the mechanism I drew works, but please correct me if I'm wrong.

Note that I used ChemDraw Ultra to draw this image and named the product using the structure naming feature, but it is equivalent to p-acetamidobenzenesulfonyl chloride. I also didn't show the deprotonated chlorosulfonic acid conjugate base after protonation of the other equiv. of the acid.

[nexisrocks]

Oh, thank you so much!

What you've done makes a lot of sense.  Thank you very much for your help !