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Toluene-Preparation, Physical Properties, Chemical Properties, Electrophilic Aromatic Substitution, Applications and uses, Practice Problems & FAQs

During World War II, the cities of Hiroshima and Nagasaki were destroyed by American forces with the help of two atomic bombs. Do you know that each of those bombs was equivalent to about 20,000 tonnes of T.N.T?

T.N.T. (Tri-nitrotoluene) is a widely known explosive material. It is prepared by the tri-nitration of toluene.


Toluene undergoes an electrophilic aromatic substitution reaction to form trinitrotoluene.

TABLE OF CONTENT

What is Toluene?

Toluene is also known as toluol in some cases. It is an aromatic hydrocarbon. It's a benzene derivative with a monosubstituted methyl group. In the IUPAC system, toluene is referred to as methylbenzene. Toluene is primarily employed as a feedstock and a solvent in industry. Toluene-based inhalants are also used recreationally. Unfortunately, toluene has the ability to harm our bodies' neurological systems.

Structure of Toluene


Preparation of Toluene

There are various methods for the preparation of toluene which are as follows.

  • Friedel Craft Alkylation of Benzene

Benzene reacts with methyl chloride in the presence of Lewis Acid(anhydrous AlCl3) results in the formation of Toluene as a major product.


Toluene is also formed when benzene reacts with dimethyl sulfate.


  • Aromatization of n-heptane

  • Synthesis from Ethyne

When acetylene is passed through propyne in a red hot copper tube, toluene is formed as a result of cyclic polymerization.


  • Wurtz-Fittig Reaction

When a mixture of chlorobenzene and methyl chloride reacts with sodium metal in the presence of dry ether solution yields Toluene as a major product.

It follows a free radical mechanism.


  • Decarboxylation of Toluic acid

When a sodium salt of (o, m, p)-toluic acid is heated in the presence of soda lime, toluene is formed.


  • From Cresol

When ortho, meta, or para cresol is distilled with zinc dust, toluene is obtained.


  • From Toluidine

When p-toluidine is treated with nitrous acid and then with ethanol, toluene is obtained.


  • From Grignard Reagent

When phenyl magnesium bromide is treated with methyl bromide, toluene is formed.


Physical Properties of Toluene

  • Toluene is a clear and colourless liquid.
  • It has a benzene-like smell.
  • Its chemical formula is C7H8
  • Toluene is insoluble in water but soluble in alcohol, benzene, and ether.
  • Boiling Point of Toluene is 111C
  • Melting Point of Toluene is -95C
  • Molecular Weight of Toluene is 92.141 gmol-1
  • Density of toluene is 0.87 gmL-1

Chemical Reactions of Toluene

The Toluene molecule contains both aromatic and aliphatic parts. So it shows the properties of both parts.


Electrophilic Aromatic Substitution

Toluene gives Electrophilic Aromatic Substitution reaction more readily than benzene because it contains a -CH3 group that is electron releasing in nature, it activates the benzene nucleus and gives EAS reaction.

The attached -CH3 group is an ortho and para directing group. On substitution, it gives a mixture of ortho and para derivatives.


  • Halogenation of Toluene

In the presence of Lewis Acid(FeCl3 or AlCl3), toluene reacts with chlorine or bromine to give a mixture of o- and p-derivatives.


  • Nitration of Toluene 

A mixture of ortho and para nitrotoluene is formed when toluene is treated with conc. HNO3 and conc. H2SO4


  • Sulphonation of Toluene 

A mixture of ortho and para toluene sulphonic acid is formed when toluene is treated with conc. H2SO4


  • Benzylic Bromination of Toluene

For the bromination of benzylic hydrogen, a selective brominating agent is used i.e., N-Bromosuccinimide(NBS).


  • Side Chain Halogenation of Toluene

It proceeds through a Free Radical mechanism and forms Benzyl Chloride.

It is also a free radical substitution reaction.


Oxidation Reaction

  • When Toluene is treated with hot acidic KMnO4, Na2Cr2O7 or conc. HNO3, methyl group attached to the benzene ring is oxidized to -COOH group, Benzoic Acid is formed.

  • Toluene is converted to benzaldehyde when treated with acidic manganese dioxide or chromyl chloride in CCl4 solution.

Addition Reaction

Methylcyclohexane is formed when vapours of toluene and hydrogen are heated at 200C in the presence of Nickel catalyst.


Ozonolysis of Toluene


Application and Uses of Toluene

  • In industries and laboratories, it is generally used as a solvent.
  • It's also utilized to raise the octane level of gasoline, which is a critical combustible in aviation. 
  • It's used to make coatings, paints, and resins.
  • The disproportionation of toluene to a mixture of xylene and benzene is the second-best use.
  • Toluene is required for the manufacture of dinitrotoluene, which is required for the manufacture of toluene diisocyanate, which is used to generate polyurethane foams.
  • It's also used as a precursor in substitution and oxidation reactions to make regularly used or other precursors.
  • The manufacturing of trinitrotoluene explosives necessitates the use of toluene. Toluene is nitrated twice, once to dinitrotoluene and then to trinitrotoluene.
  • Because they are universal solvents, they can be used to dissolve paint thinners, paints, rubber, silicone sealants, disinfectants, various chemical reactants, leather tanners, adhesives (glues), lacquers, and printing ink, among other things.

Practice Problems

Q1. How to distinguish between Benzene and Toluene?

Solution: By Oxidation reaction.

Toluene is oxidized to benzaldehyde by using chromyl chloride and benzoic acid using hot concentrated Potassium permanganate


Benzene is stable, it does not undergo oxidation reactions easily.

Q2. Write the reaction for the conversion of toluene to benzene.

Solution: Toluene is first oxidized to Benzoic acid and then Decarboxylation of benzoic acid gives Benzene.


Q3. Calculate the number of sigma bonds and pi bonds in toluene.

Solution: There are 15 sigma bonds and 3 pi bonds in toluene


Q4. Write the reaction for the conversion of benzamide to toluene.

Solution:

Benzamide undergoes Hoffmann bromamide degradation reaction i.e., is treated with Bromine in the presence of NaOH to give Aniline.

Aniline formed is treated with nitrous acid at low temperature forms Benzene diazonium chloride which on treated with H3PO4 forms Benzene.

The Formed benzene undergoes Friedel Crafts Alkylation reaction gives Toluene.


Frequently Asked Questions - FAQ

Q 1. What happens when the combustion of toluene takes place?
Answer: Toluene in the presence of oxygen burns with a smoky flame.


Q 2. How is trinitrotoluene(TNT) prepared from toluene?
Answer: TNT is prepared from toluene by nitration. On mononitration, nitrotoluene is formed and on further nitration dinitrotoluene and trinitrotoluene are formed.

Q 3. How is Toluene commercially prepared?
Answer: Toluene is commercially prepared from light oil fraction of coal-tar and in large quantities, it is obtained from catalytic dehydrogenation of petroleum products.

Q 4. What is the color of Toluene?
Answer: Toluene is clear, colorless liquid with a benzene-like smell.

Related Topics

Chlorination

Friedel-crafts reaction 

Electrophilic Aromatic Substitution reactions of benzene

Wurtz reaction

Chemical Reactions of Alkynes

Alkanes

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