Sciencemadness Discussion Board

p-Terphenyl from p-dichlorobenzene and benzene

TheChemiKid - 26-7-2014 at 17:36

Could I use a modified version of the Friedel–Crafts alkylation to form p-Terphenyl from p-Dichlorobenzene and Benzene with Anhydrous Aluminum Chloride?
My idea would be to use 1 mole of p-Dichlorobenzene, 2 moles of Benzene, and 2 equivalents of Anhydrous Aluminum Chloride. Is this possible? I have never seen any literature like this.

FireLion3 - 26-7-2014 at 18:56

I know one way it could be prepared is in a cross coupling reaction between a halobenzene and dihalobenzene, in which the halogens are different so that the catalyst only activates one or the other and so that the activated substrate can only react what it is supposed to react with.

If your reaction could work, or the one above I just wrote about, there is always the inevitability of homo coupling side-products.

About your reaction, I imagine it may work at first, assuming the Aluminum Chloride could activate the dichlorobenzene, to which if not you would need to use a different halogen. Even if it does work, I don't think it will be viable since your product is far more nucleophilic and conjugated than benzene and will react much more quickly with the electrophilic halobenzene than with benzene itself.

UnintentionalChaos - 26-7-2014 at 22:31

Quote: Originally posted by TheChemiKid  
Could I use a modified version of the Friedel–Crafts alkylation to form p-Terphenyl from p-Dichlorobenzene and Benzene with Anhydrous Aluminum Chloride?
My idea would be to use 1 mole of p-Dichlorobenzene, 2 moles of Benzene, and 2 equivalents of Anhydrous Aluminum Chloride. Is this possible? I have never seen any literature like this.


Nope. There's a reason you've never seen any literature like it. You can't do FC alkylations with aryl or vinyl halides. The resulting carbocation would be far too unstable.

You are looking to do a cross coupling. Pd is best and it still won't do what you want with those reactants. If you used chlorobenzene and copper powder, you might be able to manage an Ullman reaction. The yield is not great and you'd still have to sort the desired productout from biphenyl and other sideproducts.

TheChemiKid - 27-7-2014 at 04:36

Thanks for the help guys, I am still relatively new to Org. chem, so everything helps.
Edit: Typo fixed

[Edited on 7-27-2014 by TheChemiKid]

UnintentionalChaos - 27-7-2014 at 11:53

Quote: Originally posted by TheChemiKid  
Thanks for the help guys, I am still relatively new to Org. chem, so everything helps.
Edit: Typo fixed


I too, own a jar of p-dichlorobenzene that I have never used...

It's really pretty useless. It's resistant to any sort of electrophilic aromatic substitution because the chlorines are deactivating. Nitration requires fuming nitric acid to get even a single nitro on. I'm not even sure if it's any good for grignards. And even then, what would you make with para-substitution?

If monodechlorination was possible, I'd do that because chlorobenzene is a pain in the butt to make.

subsecret - 13-8-2014 at 11:56

Is Friedel-Crafts impossible in this case because of the benzene ring's pi cloud?