Q2P - Organic Chemistry (Mcmurry)

Question

Propose a mechanism for the electrophilic fluorination of benzene with $\mathbf{F}\mathbf{-}\mathbf{TEDA}\mathbf{-}{\mathbf{BF}}_{\mathbf{4}}$.

Step-by-Step Solution

Answer

Formation of fluorobenzene

Step1: Electrophilic substitution

In electrophilic aromatic substitution reactions, the hydrogen atom present in the aromatic ring is replaced by an electrophile.

The pi-electron of benzene attacks the fluorine of $\mathbf{F}\mathbf{-}\mathbf{TEDA}\mathbf{-}{\mathbf{BF}}_{\mathbf{4}}$and the non-aromatic intermediates losses – H to give the fluorinated product. 

Step 2: Mechanism

The mechanism begins with the aromatic ring attacking the fluorine atom bound to nitrogen in $\mathrm{F}-\mathrm{TEDA}-{\mathrm{BF}}_4$. This is because this fluorine is the most electrophilic atom. With this attack, we generate structure 2 which upon reacting with base rearomatizes to give the final product, fluorobenzene. The mechanism is as follows:

Formation of fluorobenzene