Lab 1
Electrophilic Substitution
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)
E
E
E
E
A
H
H
H
Arenium ions
(nonaromatic cyclohexadienyl cation)
Mechanism of EAS: arenium ions
Step 2
E
E
+ H A
H
:A-
The proton is removed by any of the
bases, for example by the anion derived
from the electrophile
 Benzene does not react with Br2 or Cl2
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
Br
+ Br2
FeBr3
heat
+ HBr
Bromobenzene (75%)
Benzene sulfonic acid
+ HNO3 + H2SO4
50-55 oC
NO2
+ H3O+ + HSO4-
(85%)
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
NO2+ (electrophile)
Step 3
Arenium ions
The nitronium ion is the actual electrophile in nitration ; it reacts
with benzene to form a resonance-stabilized arenium ion
Step 4
The arenium ion then loses a proton to a Lewis base and
becomes nitrobenzene
 Friedel-Crafts Acylation reaction is
mean introducing an acyl group into
aromatic ring
 Two common acyl groups are acetyl
group and benzoyl group
benzoyl group
acetyl group