What is Toluene?
Toluene is a transparent, colourless liquid with an odour similar to benzene. Toluene's chemical formula is C6H5CH3.
The chemical compound toluene is naturally occurring and mainly derived from petroleum or petrochemical processes. The toluene chemical is present in gasoline, glues, and paints. The liquid toluene smells like paint thinners, is colourless and insoluble in water. It's a mono-substituted colourless liquid that has a CH3 group attached to a phenyl group.
The Properties of Toluene
In comparison with benzene, toluene is more electrophilic. It reacts in the same position with normal fragrance due to the greater percentage of methyl group than electron-releasing properties. Chlorotoluene undergoes sulfonation to produce p-toluene sulfonic acid, which then undergoes chlorination by Cl2 in the presence of FeCl3 to yield ortho and para isomers.
Structure of Toluene
Paints and glues are both manufactured with toluene as a solvent. Toluene is used extensively as a chemical raw material.
Production of Toluene
As a by-product of gasoline production, toluene can also be found naturally in crude oil. Toluene is also produced as a by-product of coal cooking.
Toluene can be produced at a low cost at industrial levels. There are several ways to synthesise it. Toluene is obtained from the reaction between benzene and methyl chloride in the presence of Lewis acid.
C6H5H + CH3Cl → C6H5CH3 + HCl
Chemical Properties
Toluene exhibits electrophilic aromatic substitution reactions similar to those of normal aromatic hydrocarbons. Toluene has a greater capacity for releasing electrons than hydrogen atoms in the same position because of the methyl group present in it. Compared to benzene, methyl is more electrophilic. In the presence of FeCl2, it is chlorinated by Cl2 with sulfonation to give chlorotoluene sulfonic acid, and by sulfonation to give para- and ortho-isomers of chlorotoluene.
A significant factor affecting toluene's oxidative capacity is its methyl side chain. Benzaldehyde is produced by combining the compound with potassium permanganate and chromyl chloride. This is known as the Étard reaction.
The methyl group is halogenated in the presence of free radicals. As an example, N-Bromosuccinimide (NBS) yields benzyl bromide in the presence of AIBN when heated with toluene. Bromination of toluene with HBr and H2O2 is also possible by using light and HBr.
C6H5CH3 + Br2 → C6H5CH2Br + HBr
C6H5CH2Br + Br2 → C6H 5CHBr2 + HBr
A strong base will deprotonate the methyl group; the pKa is estimated to be around 41. The methylcyclohexane is formed by hydrogenation. Hydrogen pressure and a catalyst are required.
Uses of Toluene
Benzene can be synthesised from toluene. Toluene reacts with hydrogen gas according to the chemical equation below.
C6H5CH3 + H2 → C6H6 + CH4
In contrast, benzene and xylene are used for the second most common application.
Chemicals that are Produced from Toluene
Benzene and xylene are synthesised using toluene as well as the following chemical reactions:
Foam polyurethane
Trinitrotoluene – Explosive
TNT
Synthetic Drugs.
The Use of Toluene as a Solvent
Solvents commonly made with toluene include:
Glues
Paints
Paint Thinners
Printing Ink
Rubber
Leather Tanners
Silicone Sealants
Chemical Reactants
Lacquers
Disinfectants.
Toluene's Other Applications
Internal combustion engines can run on it as gasoline fuel.
Toluene's Niche Applications
Carbon nanomaterials, nanotubes, and whole rods are dissolved in it.
Commercial Preparation of Toluene
From Coal Tar:
Light oil fraction of coal tar is the primary source of commercial production of toluene. The light oil fraction is washed with conc. H2SO4 in order to remove the bases present in it, then with NaOH to remove acidic substances and finally with water.
It is subjected to fractional distillation. The vapours collected between 80 – 110oC is 90% benzol it contains 70 - 80% benzene and 14 - 24% toluene. 90% benzol is again distilled, and the part distilling between 108 – 1100C is collected as toluene.
Preparation of Toluene from Methylcyclohexane and N-Heptane
It is also obtained by cyclization of n-heptane followed by an aromatization.
Reactions of Toluene
1. Oxidation of Toluene
As toluene is an aromatic compound, it is less susceptible to an oxidation reaction. The methyl group of toluene is a side chain in the aromatic ring structure and is oxidised to the carboxyl group in the presence of a strong oxidising agent.
The oxidation of toluene forms benzaldehyde which can further be oxidised to form benzoic acid. There are many oxidising agents like potassium permanganate.
2. Bromination of Toluene
The reaction of toluene with bromine is known as bromination of toluene. The bromination of it can take place either on the side chain or an aromatic ring.
Both bromination reactions occur with a different mechanism. Generally, side chain by free radical mechanism and aromatic bromination follows electrophilic substitution mechanism.
3. Nitration of Toluene
Introduction of a nitro group into toluene forms ortho-toluene & para-toluene and the reaction is called nitration of toluene.
The reaction follows the electrophilic substitution mechanism, and the mixture of concentrated sulfuric and nitric acid behaves as a nitrating agent.
In this case, concentrated sulfuric acid acts as a catalyst and generates a nitronium ion which behaves as an electrophile.
Nitronium ions attack on aromatic rings, majorly at ortho and para positions which further form ortho and para-products.
Due to the presence of a methyl group on the ring of toluene, the nitration of toluene is around twenty-five times faster than benzene. As the methyl group is activating towards the -ortho and -para directing groups, hence the nitration of toluene gives poly substituted nitro-products.
However, the use of low temperature can prevent the substitution of more than one nitro group on the aromatic ring.
Note:
Under normal conditions, toluene gives all three isomers, out of which ortho-derivative forms around 63 % and 34% of para-product and 3% of meta-product is formed.
High yield of ortho products can be explained by the resonating structure of the arenium ion which forms as an intermediate.
FAQs on Toluene
1. What exactly is Toluene and what is its chemical formula?
Toluene is a common aromatic hydrocarbon. It's known as a clear, colorless liquid that doesn't dissolve in water and has a distinct, sharp smell, similar to paint thinners. Structurally, it is a benzene ring where one hydrogen atom is replaced by a methyl group (-CH₃). The chemical formula for Toluene is C₇H₈.
2. What is the official IUPAC name for Toluene?
The official IUPAC (International Union of Pure and Applied Chemistry) name for Toluene is Methylbenzene. While this is its systematic name, the common name 'Toluene' is also officially recognised and widely used in chemistry.
3. Can you describe the structure of a Toluene molecule?
The structure of Toluene is made of two key parts:
- A benzene ring, which is a flat, six-carbon ring with alternating double bonds.
- A methyl group (-CH₃), which is attached to one of the carbons in the benzene ring.
4. What are some common uses of Toluene in industry and everyday products?
Toluene is widely used as a solvent. You can find it in many common products, including:
- Paints and paint thinners
- Adhesives and glues
- Nail polish removers
- Permanent markers
5. What are the main physical properties of Toluene?
The key physical properties that help identify Toluene are:
- Appearance: It is a clear and colorless liquid.
- Odor: It has a distinctive sweet, pungent odor.
- Solubility: It is insoluble in water but mixes well with other organic solvents like ether and alcohol.
- Boiling Point: It has a boiling point of about 111°C.
6. How is Toluene different from Benzene?
While both are aromatic hydrocarbons, the main difference lies in their structure. Benzene (C₆H₆) is the fundamental aromatic ring. Toluene (C₇H₈) is a benzene ring with an added methyl (-CH₃) group. This small addition makes Toluene generally less toxic than Benzene and also makes it more reactive in certain chemical reactions, like electrophilic substitution.
7. Why doesn't Toluene dissolve in water?
Toluene does not dissolve in water because of their different molecular polarities. Water is a polar molecule, with distinct positive and negative ends. Toluene, on the other hand, is a non-polar molecule. A core principle in chemistry is that "like dissolves like." This means polar substances mix with other polar substances, and non-polar substances mix with other non-polar ones. Since their polarities are mismatched, they do not mix.
8. Is Toluene considered a harmful or dangerous chemical?
Yes, Toluene can be harmful if not handled correctly. Inhaling its fumes can cause short-term effects like dizziness and headaches. Long-term exposure to high concentrations can pose serious health risks, including damage to the nervous system, kidneys, and liver. Due to these risks, its use is often regulated, and it should always be handled in a well-ventilated space with appropriate safety gear.
