[kape1one]

Hey Chemical Forums,

I am a new member. I have a question regarding Friedel Crafts Alkylation. The question involves the reaction between Benzene, Tert-butyl chloride, and FeBr3.
The question is asking about a new product that forms between the FeBr3 and t-butyl chloride.
What is it? It has to be an alkyl halide.

Also, how does t-butyl chloride by itself make HCl?

Thank you!
http://i1251.photobucket.com/albums/hh560/kape1one/Chemistry.jpg

[Fluorine]

Welcome!

According to forum rules before anyone can help you must first show an attempt at solving the problem. If you have absolutely no idea how to approach this read in your book, notes, or wikipedia about Friedel-Crafts alkylation.

[kape1one]

Thank you for letting me know!

This is what I have tried so far:

The chloride from the t-butyl will react with the FeBr3, forming a bond between Iron and Chloride. The Cl will have a positive charge and the Iron will have a negative charge. After that, I want to "kick out" the Cl-FeBr3 and end up with the carbocation of t-butyl. That is where I am stuck. Can one of the bromines from the FeBr3 react with the carbocation? Or will the carbocation react with the benzene?

For the second question. I think that the HCl comes from an Elimination reaction, but I am not 100% sure. I am thinking of 2 t-butyl chrlorides reacting. One becomes the carbocation after the Cl leaves. The second t-butyl will take a Hydrogen from the carbocation, and form a double bond (elimination), thus forming HCl.Am I on the right track?

Thanks!

[Fluorine]

You've got the right idea in some of the parts. The catalyst will help the chloride off leaving the t-butyl as a carbocation. After this forms it will react with the benzene ring as you thought. One of the double bonds will open up and attack the carbocation, "alkylating" the ring. The reaction isn't over yet though, so far we have;



How can we restore aromaticity from here?

Edit: The catalyst should be FeBr₃Cl, I drew FeCl₄ - sorry.

[Nomeru]

Thank you for letting me know!

This is what I have tried so far:

The chloride from the t-butyl will react with the FeBr3, forming a bond between Iron and Chloride. The Cl will have a positive charge and the Iron will have a negative charge. After that, I want to "kick out" the Cl-FeBr3 and end up with the carbocation of t-butyl. That is where I am stuck. Can one of the bromines from the FeBr3 react with the carbocation? Or will the carbocation react with the benzene?

For the second question. I think that the HCl comes from an Elimination reaction, but I am not 100% sure. I am thinking of 2 t-butyl chrlorides reacting. One becomes the carbocation after the Cl leaves. The second t-butyl will take a Hydrogen from the carbocation, and form a double bond (elimination), thus forming HCl.Am I on the right track?

Thanks!

Thats more like it! Lets see, as far as I know, chlorine will not make 2 bonds (So no t-bu-Cl-FeBr3). You're right next though, the chlorine leaves you with a carbocation. tBu+ and Cl-AlBr3- are what are present at this stage, we agree. Your second paragraph isn't quite right-Consider only 1 benzene, tBuCl, and FeBr3. Have you looked at any other reactions with aromatics as of yet? From here, it's going to be very similar to halogenation of an aromatic if that helps. What do we want to happen between these products? Consider benzene for a moment. It has 6 delocalized electrons, and we have a carbocation who isnt too happy having a positive charge.