H₂SO₄ + HNO₃ + C₆H₆ | Nitration of Benzene

When benzene is heated with concentrated sulfuric acid ( H₂SO₄) and concentrated nitric (HNO₃) acid, nitrobenzene is given as the product. A hydrogen atom of benzene is replaced by a nitro group (-NO₂) in this reaction.

In this tutorial, we will learn followings.

1. Benzene nitration and characteristics of the reaction
2. Nitration at different temperatures
3. Mechanism of benzene nitration and uses of benzene nitration in chemical industries
4. Nitration of other benzene compounds

Nitration of benzene

The replacement of a hydrogen atom in the benzene ring by a nitro group (-NO₂) is called nitration. Benzene is heated with concentrated nitric acid and sulfuric acid about 330K temperature to obtain nitrobenzene. Water is given as a by-product.

This reaction is a very dangerous reaction because benzene nitration is an exothermic reaction (reaction releases large heat to the outside environment. . Heat of the reaction is -117 kJ/mol.

Nitrating mixture

Concentrated H₂SO₄ and HNO₃ acids mixture is called as a nitrating mixture.

Nitrobenzene

Here we study some characteristics of nitrobenzene.

• A yellowish, oily, aromatic nitro-compound with an almond-like odor with C₆H₅NO₂ molecular formula.
• -NO₂ is a deactivating group
• Nitrobenzene is used to prepare aniline.

Concentrated H₂SO₄ and HNO₃ acids

Concentrated H₂SO₄ acid behaves as a proton donator and HNO₃ acid accepts that electron. After the reaction, H₂SO₄ is generated again to show catalyst properties.

• Sulfuric acid shows acidic properties while nitric acid behaves as a base.

Benzene nitration at different temperatures

At higher temperature, there is a chance to give different substitutes of nitro (can join more than two -NO₂ groups).

Nitrobenzene is a deactivator. So furthermore nitration is hard. So we have to heat the nitration mixture more than benzene nitration. For nitration of nitrobenzene, temperature should be around, 65⁰C.

Mechanism of benzene nitration

Nitronium ion (NO₂⁺) is formed as first step in the mechanism, this formation is facilitated by the presence of concentrated sulfuric acid which behaves as a catalyst. (NO₂⁺) is a electrophile.

The electrophile attacks benzene ring to form an intermediate carbocation.

Bisulfite ion ( HSO₄^-) takes a proton from intermediate carbocation (σ complex) to give nitrobenzene.

Uses of benzene nitration

Major use of nitrobenzene is production of aniline. Also nitrobenzene is used as a solvent in the laboratory.

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Nitration of benzene compounds

Other benzene compounds such as toluene, aniline, phenol and more can be nitrated. But conditions may vary with given compounds.

Example: Nitration of phenol is much easier than nitration of toluene because phenol is a strong activator while toluene is a weak activator.

Nitration with dilute HNO₃

Which benzene substitutes will be nitrated with dilute HNO₃? This means , there are some benzene substituted compounds, which shows nitration without concentrated H₂SO₄ acid as a catalyst.

Nitration of activators

Nitration of activators such as phenol or aniline is easier than benzene and de-activators. Activators can be nitrated with dilute HNO₃ acid. Concentrated H₂SO₄ acid is not required to catalysis the reaction.

Aniline and dilute HNO₃

A product mixture is given as the product. Aniline is an ortho para director. So nitration can be occurred at ortho or para positions with dilute HNO₃ acids.

As ortho product, 2-nitroaniline is given. As para product, 4-nitroaniline is given.

Phenol and dilute HNO₃

A product mixture (ortho and para product) is given as the product. Phenol is an ortho para director. So nitration can be occurred at ortho or para positions with dilute HNO₃ acids.

As ortho product, 2-nitrophenol is given. As para product, 4-nitrophenol is given.

Uses of nitration

1. Benzene nitration is useful to prepare more organic compounds such as aniline, phenol, benzene diazonium salt. So nitrobenzene is used as an intermediate chemical in preparations of those compounds.

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Questions

C₆H₆ + HNO₃ (con H₂SO4

>C₆H₆ and HNO₃ are the raw materials of benzene nitration. con H₂SO₄ is used as a catalyst in this reaction. Also, reactant mixture should be heated to occur the nitration.

What happens when benzene is treated with concentrated H₂SO₄ at 330k?

The sulphonation of benzene can be done when benzene is treated with concentrated H₂SO₄ acid and heat the mixture.

C₆H₆ (benzene) + conc. H₂SO₄ → C₆H₅-SO₃H

Nitration of nitrobenzene

Nitrobenzene is a deactivator. So electron density of benzene ring of nitrobenzene is reduced than benzene. This results, ability of showing electrophilic substitution reactions of benzene decreases. Therefore substituting one more -NO₂ group to nitrebenzene is not easy like nitration of benzene. For the nitration of nitrobenzene, higher temperature than used in the benzene nitration is required.

Reaction of benzene with h2so4 and hno3 to form nitrobenzene, why h2so4 is used?

H₂SO₄ is used as a catalyst to increase the reaction rate by produce nitronium ion (NO₂⁺). When nitronium ion prouction rate increases, reaction rate increases to give the product in a short time.

C₆H₆ (benzene) + H₂SO₄ + HNO₃ , what is this reaction and what are the prouducts?

This reaction is nitration of benzene. A -NO₂ group is substituted to benzene ring instead of hydrogen atom.

H₂SO₄ is used in concentrated state and it behaves as an catalyst in the reaction.

What will happen to anhydrous AlCl₃, after the reaction?

The amount (mol) of anhydrous AlCl₃ is not changed in the reaction because AlCl₃ is a catalysy in this reaction.

In the benzene nitration, is it an oxidation - reduction reaction?

If you want to know whether this is an oxidation - reduction reaction, you have to find oxidation numbers of each element in the right side and left side of the reaction.

Oxidation number of carbon which is joint with nitrogen atom is oxidized. With that, nitrogen atom was in the nitric acid is reduced.

toluene reaction with h2so4 ?

Tolune cannot be oxidized by H₂SO₄ alone. Need a strong oxidizing agent such as potassium permanganate to oxidiz toluene.

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