HSbF6

[mr.mechanics]

i came acroos a reaction of phenol with Br2 in the presencs of HSbF6.

the answer was m-bromophenol.

could someone explain me the mechanism?

please?

also, could anyone tell me the properties of this reagent?

and about any similar reagents?

please help me out...

[John Cuthber]

I think you need to know 2 things about HSbF6; it's a very strong acid and its conjugate base is a very poor nucleophile.

[UC]

That would be an electrophilic aromatic substitution, as described here: http://www.cem.msu.edu/~reusch/VirtualText/benzrx1.htm

 

The HSbF6 is fluoroantimonic acid, the strongest superacid known. It is powerful enough to protonate simple alkanes, so phenol and bromine should be pretty easy.

 

[ce] Ph-OH + HSbF6 -> [Ph-OH2]^+[sbF6]^- [/ce]

 

The phenylhydronium ion there would behave like a nitro group, explained in the reference I linked you above. Therefore, substitution would occur preferably on the 3 position. Since HSbF6 is such a strong acid, you can safely assume that virtually all of the phenol is protonated all the time.

 

The bromine is also probably protonated on on end of the dimer, which induces a dipole moment and drives the electrophilic aromatic substitution reaction.

 

As for safety (from wiki): HF-SbF5 is rapidly and explosively decomposed by water. It reacts with virtually all known solvents.

 

If you're even vaguely considering working with this stuff, don't.

[mr.mechanics]

thanks very much for your help.

i didn't know anything about that acid.

 

and don't you worry, i'm just a high school student, preparing for the iit jee 2009; i won't think of dealing with such dangerous stuff.

by the way, do there exist stuffs like 'super bases'?

 

could you name a few?

 

and could you please let me know about some more unconventional reagents, or links to places where i could get something?

 

that would be a very great help.

[UC]

thanks very much for your help.

i didn't know anything about that acid.

 

and don't you worry, i'm just a high school student, preparing for the iit jee 2009; i won't think of dealing with such dangerous stuff.

by the way, do there exist stuffs like 'super bases'?

 

could you name a few?

 

and could you please let me know about some more unconventional reagents, or links to places where i could get something?

 

that would be a very great help.

 

superbases? try wikipedia

 

by definition, they are all water reactive.