What is toluene used for? Preparation and Properties

Toluene Formula and Structure

Toluene is an aromatic hydrocarbon. Toluene is a colourless liquid and water-insoluble liquid. It is smell like paint thinners. Toluene IUPAC systematic name is Methylbenzene. Toluene was first derived from reagent named Tolu Balsam. Hence it was named toluene. Toluene formula is C₆H₅CH₃.

Preparation of Toluene

Benzene

Benzene: toluene can be made from benzene by a Friedel–Crafts reaction.

C₆H₆ + CH₃Cl → C₆H₅CH₃ + HCl

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Bromobenzene

Bromobenzene: Toluene is obtained when sodium is reacted with an analogous mixture of bromobenzene and bromomethane in ethereal solution.

C₆H₅Br + 2Na + BrCH₃ → C₆H₅CH₃ + 2NaBr

Similarly, toluene is also obtained by the action of chlorobenzene and methyl chloride from sodium. This reaction is called Wurtz Fittig Reaction.

Read More about Wurtz Fittig Reaction – Click Here

Sodium Toluate

Sodium Toluate: Toluene can be obtained by heating a mixture of sodium toluate and soda lime.

C₆H₄(CH₃)COONa + NaOH → C₆H₅CH₃ + Na₂CO₃

Grignard Reagent

Grignard Reagent: toluene is obtained by reaction of phenylmagnesium chloride, bomomide or iodide with methyl chloride, bromide or iodide.

C₆H₅MgBr + CH₃Br → C₆H₅CH₃ + MgBr₂

Coal tar

It is obtained from the efficient distillation of Coal tar in commercial quantities.

When distillation of Coal tar at 170°C a fractional liquid obtained. It is called light oil. It is lighter than water.

In addition to benzene, toluene and xylene, basic substances like pyridine and acidic substances like phenol and cresol are present. To remove them, light oil is first reacted with sodium hydroxide, which removes acidic impurities.

After this, its diluents are reacted with H₂SO₄, which results in the separation of basic substances such as pyridine.

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Now the light oil is washed with water. Due to which acidic elements are removed. In this way, efficient distillation of purified oil is done, which gives the following effect.

90% benzoyl (80 – 110°C) – 90% benzoyl means that distillation of 100 ml at 100°C gives 90 ml distillate. It contains 70% benzene and the rest toluene and xylene.

50% benzoyl (110 – 140°C): 50% benzoyl means that distillation of 100 ml at 100°C gives 50 ml distillate, it contains 45% benzene and the remaining toluene, xylene and other hydrocarbons.

Solvent naphtha or benzoic 140 – 170°C – It is used in dissolving dyes, rubber and resins, on re-effecting distillation of the above constituents, benzene at 80°C gives toluene at 110°C and xylene at 135°C.

Petroleum

Petroleum: In commercial quantities it is obtained from aromatization of n-heptane obtained from petroleum.

It’s C₆ – C₈ component is heated at high pressure and high temperature in the presence of appropriate catalysts to form benzene, toluene and xylene from petroleum. In this action, benzene, toluene and xylene are obtained as a result of aromatisation of aliphatic and alicyclic hydrocarbons. This action is called catalytic reforming or plat forming. Its ingredients are separated by Fractional distillation from a mixture of benzene, toluene and xylene.

Toluene Physical Properties

• Toluene is a colourless liquid.
• Its boiling point is 110.
• Its smell is similar to benzene
• It is insoluble in water but soluble in alcohol, ether and benzene.
• It is itself a good solvent for many organic compounds.
• Toluene Formula: C7H8

Toluene Chemical Properties

Replacement of hydrogen atoms of benzene ring: In the absence of sunlight and in the presence of a halogen carrier such as Fe and FeCl₃, it reacts with the halogens to form the replacement product.

The methyl group is ortho and para is the director group. Therefore, in this reaction, hydrogen atoms of ortho and para positions of methyl group are displaced by halogen atoms.

Example: A mixture of ortho and para substitution products is obtained from mono chlorination of toluene.

Replacement of hydrogen atoms of methyl group: On flowing chlorine in boiling toluene in the presence of sunlight, hydrogen atoms of methyl group are displaced by chlorine atoms and the side chain substitution product is obtained.

Nitration

Nitration: A mixture of e-nitro-toluene and p-nitro-toluene is obtained from the reaction of concentrated HNO₃ with toluene in the presence of concentrated H₂SO₄.

2,4,6 tri-nitro-toluene(T.N.T.) is obtained by heating toluene at about 50°C with mild nitric acid and mild sulphuric acid. Which is a strong explosive substance.

Sulphonation

Sulphonation: A mixture of n- and p-toluenesulfonic acid is obtained by heating toluene with concentrated sulfuric acid or by replicating with dilute sulfuric acid.

Friedel–Crafts reaction

Friedel–Crafts reaction: A mixture of ortho and para xylene is obtained when the toluene is replicated with methyl chloride in the presence of anhydrous AlCl₃.

This reaction is similar to CH₃COCl in the presence of anhydrous AlCl₃ of toluene and a mixture of ortho and para substitution products is obtained.

Addition of Hydrogen: In the presence of nickel or platinum, methyl cyclohexane is obtained as a result of high pressure and the addition of toluene and hydrogen at about 250°C temperature.

Oxidation: (i) It is benzaldehyde oxidized by chromyl chloride. This reaction takes place in two steps.

C₆H₅OH₃ + 2CrO₂Cl₂ → C₆H₅CH(OCrOHCl₂)₂ → C₆H₅CHO

This reaction is called etard’s reaction. Oxidation of toluene from CrO₃ and acetic anhydride also gives benzaldehyde.

benzaldehyde is also obtained by oxidation of toluene by an acidic solution of magazine dioxide at 350°C. Oxygen of toluene by oxidation of air in the presence of vanadium pentoxide (V₂O₅) also gives benzaldehyde.

It is benzoic acid oxidized by acidic KMnO₄ or acidic K₂Cr₂O₇.

C₆H₅OH + 3O → C₆H₅COOH + H₂O

Important Notes: If a lateral chain (-CH3, -C2H5, -CH=CH2) is present in an aromatic compound, the entire lateral chain is converted into the -COOH group upon oxidation of that compound by acidic KMnO₄ or acidic K₂Cr₂O₇.

The oxidation of tertiary butyl benzene is a consequence of the above general trend of aromatic compounds. The main product of oxidation by its acidic KMnO₄ or acidic K₂Cr₂O₇ is not benzoic acid. In this reaction, the product formed by fission of benzene ring is the main product.

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Toluene Uses

It is used in making many other aromatic compound, which are used as pigments, pigments, explosives and other useful substances. Of these, T N T and securin are the two main and useful substances obtained from toluene.

It is used as oil fat rubber and some other substances.

It is also used in dry cleaning of clothes.

Toluene can be used as fuel in moter cars in combination with petrol.