[Chemistry Class Notes] on Benzene – Physical and Chemical Properties Pdf for Exam

The word ‘Benzene’ is derived from the name of Gum Benzoin, which is an Aromatic form of Resin. Michael Faraday first discovered Benzene in some illuminating gas, and it was named so by Mitscherich, a German Chemist. Benzene is an Organic Compound with the Chemical formula of C₆H₆. It is also widely known as the father of the Aromatic Compounds. Benzene is the simplest HydroCarbon and has a very sweet Aroma.

Benzene Chemical Structure and Detailed Description

C₆H₆ is the Chemical formula of Benzene. It is a form of Cyclic HydroCarbon, i.e., each of its Carbon atoms is arranged in a ring of 6 members, and is only bonded with 1 Hydrogen atom. There are two resonance structures available in Benzene.

It is an Aromatic PetroChemical and crude oil’s natural element. Having an odour just like Gasoline, the Liquid is colourless, Highly Toxic, and Carcinogenic. It naturally occurs in the Environment and forms in volcanic eruptions and forest fires. It is also produced in industries using coal and oil.

Benzene Preparation and Properties

For the preparation of Benzene, the following methods are carried out.

1. Benzene Preparation from Alkynes

With the help of Cyclic polymerization, Benzene can be prepared from Ethyne. In this method, Ethyne passes from a tube of red-hot iron at 873K, the molecules of Ethyne then goes through Cyclic polymerization for the formation of Benzene.

2. Benzene Preparation from Aromatic Acids

Benzene can also be prepared from the Aromatic acids by a Decarboxylation Reaction. In this method, the Sodium Salt of Benzoic Acid heats with Soda Lime for the formation of Benzene and Sodium Carbonate.

3. Benzene Preparation from Phenol

Benzene can be prepared from the Reduction of Phenols. In this method, the vapours of Phenol pass over the heated dust of Zinc. The dust then reduces the vapour for the formation of Benzene.

4. Benzene Preparation from Sulphonic Acids

Benzene can be prepared through the Hydrolysis of Sulphonic Acids. In this method, the acid is exposed to heated steam, and this leads to the formation of Benzene.

[ C_{6} H_{5} + SO_{3}H + H_{2}O rightarrow C_{6}H_{6} + H_{2}SO_{4}]

Benzene is a naturally occurring substance that has the capability of Chemical production. It is also used in the industries for serving various needs. Here, we will describe the properties of Benzene.

Now, let us discuss Benzene physical and Chemical properties.

Physical Properties of Benzene:

1. Benzene is a colourless Compound, and the physical state of Benzene is liquid.

2. Benzene melts at 5.5 °C, and it boils at 80.1 °C.

3. Benzene is not miscible in water and is soluble in organic solvents.

4. It has an Aromatic odour.

5. The density of Benzene is 0.87 gm/cm³ and is lighter than water.

6. Benzene exhibits resonance.

7. It is inflammable, and its combustion produces sooty flames.

Chemical Properties of Benzene and its Derivatives:

The Chemical composition of Benzene is C₆H₆ , i.e., it is made of 6 Carbon atoms and 6 Hydrogen atoms.

1. Nitration of Benzene

At 323-333K, Benzene reacts with nitric acid in the presence of sulphuric acid for the formation of nitroBenzene. 

2. Sulfonation of Benzene

It is a process in which Benzene is heated with fuming sulphuric acid, i.e. H₂SO₄ + SO₃ for the formation of Benzene sulphuric acid. It is a reversible reaction.

3. Halogenation of Benzene

In the presence of Lewis acids (FeCl₂, FeBr₂), Benzene reacts with the halogens for forming the aryl halides.

4. Friedel Craft’s Alkylation Reaction

Benzene gets treated with an alkyl halide in the presence of any Lewis acid for the formation of alkylBenzene.

5. Friedel Craft’s Acylation Reaction

Benzene is treated with an acyl halide in the presence of any Lewis acid for the formation of acyl Benzene.

6. Addition Reaction

Adding chlorine to Benzene in the presence of UV rays leads to the formation of Benzene hexachloride, also known as gammaxene.

7. Combustion of Benzene

During the combustion of Benzene, it burns with a sooty flame and evolves CO₂.

[ C_{6}H_{6} + O_{2} rightarrow CO_{2} + H_{2}O]

Benzene Uses

Benzene serves many industrial needs, like the manufacturing of lubricants, rubbers, plastics, dyes, etc. Other than these, Benzene also has some other uses in non-industrial matters. However, the toxic nature of Benzene limits its usage, and there are only a few uses are listed below.

1. It is used for preparing Phenol. It also helps in the preparation of Aniline, which is used in dyes. Also, it is used in the manufacture of detergents.

2. Earlier, Benzene also helped in the degreasing activity of metals.

3. It is used for the manufacture of nylon fibers.

4. Benzene is used for effective formation of other Chemicals, like cumene, alkylBenzene, ethylBenzene, nitroBenzene, etc.