DGP20343
Chemistry of
Petrochemical
Processes
Prepared By:
Donald Anak Juan (GDAJ)
Course Coordinator DGP20343
Jabatan Kejuruteraan Petrokimia (JKPK)
Politeknik Kuching Sarawak (PKS)
Effective:
Session II 2024/2025
Topic 3
Aromatic
Compounds
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Kekulé structure of
aromatic compounds
Kekulé structure of aromatic
compounds
• Benzene exists as C6H6 since 1850’s, but it took a long time
to work out the structure.
• English scientist Michael Faraday discovered it in 1825
from the oily residue left by producing illuminating gas.
One of the models of benzene was put forward by Friedrich
August Kekule in 1865.
Kekulé structure of aromatic
compounds
• Kekulé was the first to suggest a sensible structure
for benzene. The carbons are arranged in a hexagon,
and he suggested alternating double and single bonds
between them. Each carbon atom has a hydrogen attached
to it.
• Benzene belongs to the family of aromatic compounds
with a ring structure. It is the simplest aromatic
hydrocarbon.
• Aromatic refer to the class of compounds that contain
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Benzene and its
derivatives
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Benzene
Benzene
• Benzene
(C6H6)
is
the
most
important
aromatic
hydrocarbon. The IUPAC name for benzene is cyclohexa1,3,5-triene.
• Benzene also precursor for many chemicals that may be
used as end products or intermediates.
• It is used primarily as a solvent in the chemical and
pharmaceutical industries.
• The primary sources of benzene, toluene, and xylenes
are
refinery
streams,
especially
from
catalytic
reforming and cracking, and pyrolysis gasoline from
steam cracking and from coal liquids.
• Benzene is also used in the manufacture of rubber,
lubricants, dyes, detergents, drugs, explosives, and
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Toluene
Toluene
• Toluene
C6H5CH3
also
known
as
methylbenzene,
phenylmethane,
or
toluol)
and
toluene-containing
volatile substances are the most commonly abused
solvents with a demonstrative addictive potential in
humans.
• The application of toluene are:
i. as a solvent (for making
adhesives).
ii.as a gasoline additive.
paint,
rubber,
and
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Xylene
Xylene
• Xylene (CH3)2C6H4 also known as dimethylbenzene or Xylol
was first isolated by French chemist Auguste Cahours in
the year 1850. It is one of the three isomers of
dimethyl benzene.
• Xylene consists of a central benzene ring attached to
two methyl groups as substituents.
• It is found naturally in crude oil around 0.5-1%
depending on the source of crude oil. Xylene also found
in very small quantities of gasoline and aircraft
fuels.
• Xylene is produced by catalytic reforming as well as by
coal carbonization. It also occurs naturally in crude
oil, aircraft fuels, and gasoline.
Xylene
• Xylene (CH3)2C6H4 is an aromatic mixture
three isomers (o-, m-, and p-xylene).
composed of
• It is obtained from catalytic reforming and cracking
units with other C6, C7, and C8 aromatics.
• Phthalic anhydride is mainly produced through catalysed
oxidation of o-xylene. Meanwhile, for the oxidation of
m-xylene produces isophthalic acid and the oxidation of
p-xylene produces terephthalic acid.
• The obtained Xylol contains 40 to 65% of m-xylene and
approximately 20% of o-xylene, 20% of p-xylene and 20%
of ethylbenzene.
• Xylene is also used as a solvent and as an additive for
making fuels, rubber, leather and terephthalic acid
Xylene
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Benzene derivatives
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Mono-substituted
Benzene derivatives
Mono-substituted
Benzene derivatives
• There are TWO (2) systems
monosubstituted benzenes.
are
used
in
naming
• In many simple compounds, benzene is the parent's name
and the substituent is simply indicated by a prefix.
Bromobenzene
Chlorobenzene
Fluorobenzene
Nitrobenzene
Mono-substituted
Benzene derivatives
• For other simple and common compounds, the substituent
and the benzene ring taken together may form a commonly
accepted parent name.
Aniline
Acetophenone
Anisole
(Aminobenzene)
(1-phenylethanone)
(Methoxybenzene)
(Benzeneamine)
(methyl phenyl ketone)
Benzenesulphonic
acid
Mono-substituted
Benzene derivatives
Benzoic acid
Benzaldehyde
Benzonitrile
Benzaldehyde
oxime
Benzamide
Methyl benzoate
Phenol
(Benzenecarboxylic acid)
Sodium benzoate
(Benzoic acid amide)
(Hydroxybenzene)
Mono-substituted
Benzene derivatives
Ethylbenzene
Styrene
(Ethenylbenzene)
(Vinylbenzene)
Toluene
(Methylbenzene)
Propylbenzene
Cumene
(Isopropylbenzene)
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Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
• For di-substituted benzene, there is another unique way
to
indicate
the
relative
position
of
the
two
substituents by using ortho-, meta- and para-.
• Although this o-, m-, p- system is the common naming
system for benzene derivatives, they have been applied
broadly in books and literatures.
Ortho- OR o-
Meta- OR m-
Para- OR p-
OR 1,2-
OR 1,3-
OR 1,4-
EXAMPLE
3.1.1
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
ortho-dibromobenzene
meta-dibromobenzene
para-dibromobenzene
o-dibromobenzene
m-dibromobenzene
p-dibromobenzene
1,2-dibromobenzene
1,3-dibromobenzene
1,4-dibromobenzene
EXAMPLE
3.1.2
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
ortho-dichlorobenzene
meta-dichlorobenzene
para-dichlorobenzene
o-dichlorobenzene
m-dichlorobenzene
p-dichlorobenzene
1,2-dichlorobenzene
1,3-dichlorobenzene
1,4-dichlorobenzene
EXAMPLE
3.1.3
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
ortho-difluorobenzene
meta-difluorobenzene
para-difluorobenzene
o-difluorobenzene
m-difluorobenzene
p-difluorobenzene
1,2-difluorobenzene
1,3-difluorobenzene
1,4-difluorobenzene
EXAMPLE
3.1.4
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
ortho-dimethylbenzene
meta-dimethylbenzene
para-dimethylbenzene
o-dimethylbenzene
m-dimethylbenzene
p-dimethylbenzene
1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene
OR
ortho-xylene
meta-xylene
para-xylene
o-xylene
m-xylene
p-xylene
1,2-xylene
1,3-xylene
1,4-xylene
EXAMPLE
3.1.5
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
ortho-nitrobenzoic acid
meta-nitrobenzoic acid
para-nitrobenzoic acid
o-nitrobenzoic acid
m-nitrobenzoic acid
p-nitrobenzoic acid
2-nitrobenzoic acid
3-nitrobenzoic acid
4-nitrobenzoic acid
EXAMPLE
3.1.6
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
para-ethylmethylbenzene
ortho-bromonitrobenzene
para-chlorobenzaldehyde
p−ethylmethylbenzene
o-bromonitrobenzene
p-chlorobenzaldehyde
4-ethyl-1-methylbenzene
2-bromo-1-nitrobenzene
4-chlorobenzaldehyde
EXAMPLE
3.1.7
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
meta-chloroperoxybenzoic acid
ortho-toluic acid
m-chloroperoxybenzoic acid
o-toluic acid
3-chloroperoxybenzoic acid
2-methylbenzoic acid
EXAMPLE
3.1.8
Di-substituted
Benzene derivatives
Di-substituted
Benzene derivatives
para-nitrophenol
para-cresol
p-nitrophenol
p-cresol
4-nitrophenol
4-methylphenol
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More than two
substituted Benzene
derivatives
More than two
substituted Benzene derivatives
1,2,3-trichlorobenzene
2,4-dichlorophenol
2,5-dimethylphenol
1,2,4-tribromobenzene
1,3,5-trimethylbenzene
(Cumene)
4-bromo-1-chloro-2-nitrobenzene
4-bromo-1,2-dimethylbenzene
EXAMPLE
3.2.1
More than two
substituted Benzene
derivatives
More than two
substituted Benzene derivatives
1-bromo-2,5-difluorobenzene
1,2-diamino-4,5-difluorobenzene
1,2-dibromo-4,5-difluorobenzene
1,4-dichloro-2,5-difluorobenzene
1,2,4,5-tetrabromo-3,6-difluorobenzene
hexachlororobenzene
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Physical properties
of Benzene and its
derivatives
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Physical properties
of Benzene
Physical properties of Benzene
• Benzene is a closed ring of six carbon atoms linked by
bonds that alternate between single and double bonds.
Each carbon atom is bound by a single hydrogen atom.
• The physical properties of benzene are as follows:
i. It is a colourless liquid and has an aromatic odour.
ii.It has a moderate boiling point 80°C and a high
melting point 55°C.
𝑔
0.87 3 , i t
𝑐𝑚
iii.It has a density of
is lighter than
water.
iv.Insoluble in water and miscible with alcohol, ether
and chloroform.
v. It is highly flammable and burns with a sooty flame.
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Physical properties
of Toluene
Physical properties of Toluene
• Toluene is used as a solvent, in aviation gasoline, and
in
making
chemicals,
perfumes,
medicines,
dyes,
explosives and detergents.
• The physical properties of toluene are as follows:
i. It is a clear, colourless liquid and has a sweet,
strong odour.
ii.It has a boiling point 111°C and a melting point 95°C.
𝑔
iii.It has a density of 0.87 3 , i t is lighter than
𝑐𝑚
water.
iv.Insoluble in water and miscible with ethanol,
diethyl
ether,
acetone,
acetic
acid,
carbon
disulphide and chloroform.
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Physical properties
of Xylene
Physical properties of Xylene
• Xylene are an important petrochemical produced by catalytic
reforming and also by coal carbonisation in the manufacture of
coke fuel.
• The physical properties of xylene are as follows:
i. It is a clear, colourless liquid and has a sweet, strong
odour.
ii. It has a boiling point of 144°C
m−xylene and 138°C of p−xylene.
of
o−xylene,
139°C
of
iii.It has a melting point of -26°C of o−xylene, -48°C of
m−xylene and 13°C of p−xylene.
iv. It
has
a
density
of
𝑔
𝑔
0.88 3 𝑜𝑓o−xylene, 0.86 3 𝑜𝑓m−xylene and p − xylene. It is lighter
𝑐𝑚
𝑐𝑚
than water.
v. Insoluble in water and miscible with alcohol, ether and
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Chemical properties
of Benzene and its
derivatives
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Chemical properties
of Benzene
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Chlorination of
Benzene
Chlorination of Benzene
• Chlorination
of
benzene
is
an
electrophilic
substitution reaction in which Cl+ serves as the
electrophile.
• The reaction occurs in the presence of a Lewis acid
catalyst such as FeCl3.
• Chlorination of benzene produce chlorobenzene. This
chlorobenzene has TWO (2) application which are:
i. as an intermediate production of commodities such as
rubber, dyestuffs and herbicides.
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Nitration of
Benzene
Nitration of Benzene
• Similar to the alkylation and the chlorination of
benzene, the nitration reaction of benzene is an
electrophilic substitution of a benzene hydrogen (a
proton) with a nitronium ion (NO2+).
• The liquid-phase reaction occurs in presence of both
concentrated nitric and concentrated sulphuric acids as
well as the operating temperature 50–55°C:
• Nitration of benzene produce nitrobenzene. Nitrobenzene
is used to produce aniline, lubricating oils, dyes and
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Oxidation of
Benzene
Oxidation of Benzene
• The oxidation of benzene
produce maleic anhydride.
is
the
oldest
method
to
• The catalytic oxidation reaction of benzene occurs at
approximately 450-500°C and atmospheric pressure when
vapours of benzene and air are passed over vanadium
pentoxide, V2O5/MO3.
• The
oxidation
of
benzene
produce
maleic
anhydride.
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Chemical properties
of Toluene
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Chlorination of
Toluene
Chlorination of Toluene
• There are TWO (2) reactions involve in chlorination of
toluene:
i. free radical reaction.
Side chain chlorination of toluene will produce
benzal chloride.
The hydrolysis of benzal chloride at 100°C will
produce benzaldehyde.
Toluene
Benzyl
Benzal
chloride
chloride
Benzaldehyde
Chlorination of Toluene
ii.chlorination with Lewis acid.
In the presence of Lewis acid (FeCl3 or AlCl3),
toluene reacts with chlorine to give a mixture of oand p- derivatives.
Toluene
o-chlorotoluene
p-chlorotoluene
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Nitration of
Toluene
Nitration of Toluene
• Toluene reacts about 25 times faster than benzene under
the same conditions. For nitration of toluene, it
occurs with an electrophilic substitution of nitronium
ions.
Toluene
is
activated
toward
electrophilic
aromatic substitution and that the methyl group is an
activating group.
• Nitration of toluene gives a mixture of products,
primarily those resulting from substitution at the
ortho and para positions.
Toluene
o-nitrooluene
m-nitrooluene
p-nitrooluene
(60%)
(4%)
(36%)
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Oxidation of
Toluene
Oxidation of Toluene
• Oxidation of toluene will produce benzoic acid. This
oxidation can occur under FOUR (4) catalyst such as
cobalt
acetate,
sodium
dichromate,
potassium
permanganate and concentrated nitric acid.
• The reaction occurs at 173-300°C and 10 atm with yield
conversion over 90%.
Toluene
Benzoic acid