Benzene is an organic chemical compound with the molecular formula C6H6. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point

1. Welcome to the
presentation on
benzene
Prepared by
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2. What is BENZENE?

3. Resonance Energy of BENZENE:

4. Br2/
CCl4
• No
Reaction
Cold
KMnO4
• No
Reaction
H2O /
H+
• No
Reaction
BENZENE does not behave like Alkenes or Alkynes:

5. Molecular Structure of BENZENE:

6. Kekule’s structure of BENZENE:

7. Aromaticity
Aromaticity is a property of the sp2 hybridized planar
rings in which the p-orbital, one on each atom, allow
cyclic delocalization of π electrons.
CRITERIA:
RULE 1: An aromatic compound is cyclic and planar
RULE 2: Each atom in an aromatic ring has a p-orbital which
is parallel so that a continuous overlap is possible around the
ring
RULE 3: The cyclic pi-molecular orbital formed by overlap of p-
orbital must contain ( 4n+2) pi electrons.

8. Cycloheptatriene
• Cyclic & Planar
• Has a 3 double bonds & 6 pi-electrons
• 1 saturated Carbon without a p-orbital
Cyclooctatetriene
• Cyclic & Planar
• Has a p-orbital on each atom of the ring
• Huckel Rule not satisfied
Benzene
• Cyclic & Planar
• Has a p-orbital on each atom of the ring
• Obeys Huckel Rule

9. PHYSICAL PROPERTIES
1. Benzene is a colorless liquid of boiling point
80.10C, melting point 5.50C
2. It is immiscible with water but miscible with
alcohol, ether and chloroform
3. Benzene itself is a good solvent for many organic
and inorganic substance
4. Its vapour is highly toxic; inhalation over a
period of time leads to anemia.
5. It burns with a luminous, sooty flame
6. Benzene and its derivatives shows characteristics IR
spectrum

10. Method of Preparation of BENZENE:
Large scale preparation (From Petroleum):

11. Small scale preparation:
• By passing Acetylene through red hot tube at 5000C
• By heating Phenol with Zinc dust

12. Principle types of reactions of BENZENE:
• Electrophilic Substitution reaction
• Addition reactions
• Oxidation reactions

13. Electrophilic Substitution Reaction:
General mechanism:
+ E
+
H
E
H
+slow, rate
determining
Step 1:
Step 2:
E
H
+
fast
+ H
+
E
Electro-
phile
Resonance-stabilized
cation intermediate

14. Comparison between Alkene & Benzene:
Alkene Benzene
The Carbonium ion produced from the
Alkene usually combines with a
Nucleophile to give the overall addition
product.
Whereas in Benzene the Nucleophile
removes a proton from the Carbonium ion
intermediate. The loss of proton allows the
electrons from the C-H bond to go back
into the ring & re-generate the aromatic pi-
system.
Both are sucseptible to Electrophilic attack because of their exposed pi-electrons.

15. Chemical Reactions:
+
Benzenesulfonic acid
Sulfonation:
H S O 3 HS O 3
H 2 S O 4
++
An alkylbenzene
Alkylation:
RR X
A l X 3
H X
++
Acylation:
An acylbenzene
H R C X
A l X 3 H X
O
C R
O
H

16. + +
Chlorobenzene
Halogenation:
H ClCl2
Fe Cl3
HCl
++
Nitrobenzene
Nitration:
H N O2HN O3
H2 SO4
H2 O
Friedel-Crafts alkylation:
Cl
AlCl3
HCl+
Benzene 2-Chloropropane
(Isopropyl chloride)
Cumene
(Isopropylbenzene)
+

17. Friedel-Crafts Alkylation
Step 1: formation of an alkyl cation as an ion pair.
Step 2: attack of the alkyl cation on the ring.
Step 3: proton transfer regenerates aromaticity.
R Cl ClAl
Cl
Cl
R Cl
Cl
Cl
Al Cl R+
AlCl4
-
An ion pair containing
a carbocation
+
-
+
A molecular
complex
+ R+
R
H
R
H
R
H
A resonance-stabilized cation
+
+
+
H
R
Cl AlCl3 R AlCl3 HCl+ ++

18. Addition Reactions:
Addition of Hydrogen:
Addition of Halogens:
The above two reactions involve a Free Radical Mechanism

19. Uses:
• Benzene is an important industrial solvent and precursor in the
production of drugs, plastics, synthetic rubber, and dyes.
• It is a natural constituent of crude oil, and may be synthesized from
other compounds present in petroleum.
•Benzene is widely used in the United States; it ranks in the top 20
chemicals for production volume.
•Some industries use benzene to make other chemicals which are used to
make plastics, resins, and nylon and synthetic fibers.
•Benzene is also used to make some types of rubbers, lubricants, dyes,
detergents, drugs, and pesticides.
•Natural sources of benzene include volcanoes and forest fires.
•Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.

20. Summary:

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