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I was wondering if there is a decent and non-complex way to predict the outcome of mixing two chemicals together.

I know that molecular dynamics is used in computational chemistry to understand some of these types of problems, but in many cases I have noticed that they seem to be restricted to classical physics and therefore cannot accurately predict any real reactions.

My point in asking is such that I can have a broader understanding of this; However, at the moment, I am interested in the difference between this reaction:

and the same reaction while replacing the triflic acid ($\ce{CF3SO3H}$) with chlorosulfonic acid.

Would there be any differences if these two superacids were switched?

The paper from which I obtained this reaction from is here:

Klumpp, Douglas A., Rendy Rendy, Yun Zhang, Alma Gomez, and Aaron McElrea. "Dicationic Intermediates Involving Protonated Amides: Dual Modes of Reactivity Including the Acylation of Arenes." Organic Letters 6, no. 11 (2004): 1789-1792.

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I don't know for sure, but I suspect these two reagents would lead to the same product. They are both superacids, and extremely harsh.

Whichever is a better Bronsted acid (proton donor) in benzene probably leads to a faster reaction, or better conversion. But who knows? Maybe the reactions are so acidic (two plus charges in a small organic molecule!) that they are just about the same.

There may be some superacid expert lurking on chemistry.se who knows this answer, but I think the only way to know is to do the reaction.

You may also want to write the corresponding author of the paper. They may already know the answer. Or, they might be flattered and may find the question interesting enough to go to the lab and do the experiment.

(I don't think computational chemistry will help here.)

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  • $\begingroup$ Thanks Eric! That's a great answer, but why do you believe that computational chemistry will not help in this instance? Is it just too complex? $\endgroup$
    – chase
    Jun 2 '13 at 2:40
  • $\begingroup$ @chase I think it's too complicated. The conjugate base may complex with the dication in some peculiar, solvent-separated ion pair. These just aren't easy to model. $\endgroup$
    – Eric Brown
    Jun 2 '13 at 3:40
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Reactivity of these acids is very different, triflic acid shows mainly acidic properties, while chlorosulfonic is also strong oxidant and electrophile, and also chlorinating and dehydrating agent, which makes it unsuitable for using instead of triflic in your case.

It's not a good idea to even use benzene as solvent for chlorosulfonic acid, because it can get chlorosulfonated (see this question) and substrates in these reactions are more reactive than benzene. In condensation reaction water is created and $\ce{HSO3Cl}$ would gradually hydrolyse, even if it worked properly.

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