Electrophilic Substitution Lab 1

Chemical reactions in which an electrophile displaces a group in a compound, typically but not always hydrogen.

Electrophile? An electrophile is an atom, ion, molecule or even a compound that has an affinity for electrons positive charged. It act as electron acceptors during a chemical reaction to make a new covalent bond

 Electrophilic aromatic substitution  Electrophilic aliphatic substitution

Is reaction in which an electrophile replace one of the hydrogen atoms of the ring.  Type of electrophilic aromatic reaction;  Nitration  Halogenation  Sulfonation  Acylation and alkylating Friedel-Crafts reactions.

Step 1(key step) Arenium ions (nonaromatic cyclohexadienyl cation)

Step 2 Mechanism of EAS: arenium ions The proton is removed by any of the bases, for example by the anion derived from the electrophile

 Benzene does not react with Br 2 or Cl 2 unless a Lewis acid is present in mixture  Lewis acid is an electron-pair acceptor  Lewis acid is used to make halogen a stronger electrophile.  Lewis acids are:  FeCl3  FeBr3  AlCl3

Benzene sulfonic acid

benzene nitrobenzene

 Nitration are usually carried out at comparatively low temperatures 50-55C  At high temperature may loss of material because of oxidizing action of nitric acid

Step 1 Step 2 NO 2 + (electrophile)

Step 3 Step 4 Arenium ions The nitronium ion is the actual electrophile in nitration ; it reacts with benzene to form a resonance-stabilized arenium ion The arenium ion then loses a proton to a Lewis base and becomes nitrobenzene

acetyl group benzoyl group  Friedel-Crafts Acylation reaction is mean introducing an acyl group into aromatic ring  Two common acyl groups are acetyl group and benzoyl group