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AlCl3 reacting with benzene

CH3Cl + C6H6 (with AlCl3) makes C6H5CH3 + HCl

But, why doesn't C6H5AlCl2 form?

Surely the delocalised e- in the benzene ring would be more attracted to the d+ Al, than the d+ C in the polarised CH3Cl molecule?
Original post by Pigster
CH3Cl + C6H6 (with AlCl3) makes C6H5CH3 + HCl
But, why doesn't C6H5AlCl2 form?
Surely the delocalised e- in the benzene ring would be more attracted to the d+ Al, than the d+ C in the polarised CH3Cl molecule?

Please ignore.
———
The reaction is
CH3Cl + AlCl3 -> AlCl4- + CH3 radical.
The CH3 radical reacts with benzene
(edited 1 month ago)
Original post by BankaiGintoki
The reaction is
CH3Cl + AlCl3 -> AlCl4- + CH3 radical.
The CH3 radical reacts with benzene

No, there are no radicals involved. It is a Friedel-Crafts reaction using a Lewis acid catalyst.

The electron deficient aluminium accepts a lone pair from the chlorine:

Cl-Cl: ==> AlCl3

This produces a complex with the exterior chlorine having a positive (or slightly positive charge). There is a negative charge on the aluminium.

Hence the positive exterior chlorine becomes an electrophile and attracts the electron pair from the benzene ring.

+Cl----Cl--AlCl3

C6H6 + +Cl----Cl--AlCl3 ==> C6H5Cl + HCl + AlCl3

The aluminium chloride is regenerated - it is a catalyst
Original post by Pigster
CH3Cl + C6H6 (with AlCl3) makes C6H5CH3 + HCl
But, why doesn't C6H5AlCl2 form?
Surely the delocalised e- in the benzene ring would be more attracted to the d+ Al, than the d+ C in the polarised CH3Cl molecule?

The aluminium has a negative (or partial) negative charge after accepting the lone pair from the chlorine.
Reply 4
Original post by charco
The aluminium has a negative (or partial) negative charge after accepting the lone pair from the chlorine.

Aye, but before that, before it attracts the CH3Cl, it has a hefty d+ on the AlCl3, which surely has to be bigger than the d+ on the C of the complex.

So why doesn't the the benzene ring just cut out the middle man and attack the AlCl3, forming the broken ring, just like in the normal mechanism, i.e. C6H5 with the broken ring, with a bond to H and a bond to AlCl3^-, then break one of the three Al-Cl bonds, which both e- going to the Cl.

I know it doesn't happen, but I am just curious why it doesn't.

My suspicion is that it is down to the Al-Cl bond strength, causing the whole process to have too high an Ea.
Original post by charco
No, there are no radicals involved. It is a Friedel-Crafts reaction using a Lewis acid catalyst.
The electron deficient aluminium accepts a lone pair from the chlorine:
Cl-Cl: ==> AlCl3
This produces a complex with the exterior chlorine having a positive (or slightly positive charge). There is a negative charge on the aluminium.
Hence the positive exterior chlorine becomes an electrophile and attracts the electron pair from the benzene ring.
+Cl----Cl--AlCl3
C6H6 + +Cl----Cl--AlCl3 ==> C6H5Cl + HCl + AlCl3
The aluminium chloride is regenerated - it is a catalyst

Thank you.
Original post by Pigster
Aye, but before that, before it attracts the CH3Cl, it has a hefty d+ on the AlCl3, which surely has to be bigger than the d+ on the C of the complex.
So why doesn't the the benzene ring just cut out the middle man and attack the AlCl3, forming the broken ring, just like in the normal mechanism, i.e. C6H5 with the broken ring, with a bond to H and a bond to AlCl3^-, then break one of the three Al-Cl bonds, which both e- going to the Cl.
I know it doesn't happen, but I am just curious why it doesn't.
My suspicion is that it is down to the Al-Cl bond strength, causing the whole process to have too high an Ea.

Maybe the large chlorine atoms sterically hinder any attack as the aluminium ...

... or maybe it does in a reversible equilibrium that cannot go anywhere.

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