Mr Cole Chemistry

Nitration of Benzene Questions

Reactions of Benzene

Aromatic Chemistry Worksheet

Nitration of Benzene

Benzene can be used to make nitrobenzene.
a) State the name of the mechanism for the reaction.
Answer

Electrophilic substitution

b) Name and draw the structure of the species that attacks the Benzene in this reaction.
Answer

Nitronium ion (NO2+)

Nitronium Ion Structure

(Charge can be displayed on the nitrogen or one of the oxygens)

c) Write an equation for the formation of the attacking species, and state the conditions required for the reaction.
Answer

HNO3 + 2H2SO4 → NO2+ + 2HSO4– + H3O+

Conditions: Conc. H2SO4 and Conc. HNO3 at 50°C.

d) Outline the mechanism for the reaction between Benzene and the attacking species and describe each step of the reaction.
Answer Mechanism of Nitration of Benzene
  • The benzene ring π-bond electrons attract the NO2+ electrophile. Two electrons move from the delocalised ring to form a bond between one of the carbons and the nitrogen. This forms a break in the ring and a positive charge (Wheland intermediate).
  • The C-H bond breaks and the electron pair moves to reform the ring of delocalised electrons. This is aided by a hydrogensulfate ion (HSO4–) taking the hydrogen atom, resulting in the regeneration of sulfuric acid.
e) State the role of sulfuric acid in this process and explain how your answers to questions 1c and 1d demonstrate this.
Answer

Sulfuric acid is a catalyst.

It is consumed in the first step (1c) to generate the electrophile and then regenerated in the final step of the mechanism (1d).

Reactions of Methylbenzene

Methylbenzene undergoes a similar reaction to the one above.
a) Draw the most likely product from the reaction between methylbenzene and limited amount of nitric acid in the presence of sulfuric acid, and at a low temperature.
Answer

2-nitromethylbenzene (or 4-nitromethylbenzene)

2-nitromethylbenzene Structure

The methyl group is 2,4-directing. Monosubstitution occurs.

b) Draw the most likely product from the reaction between methylbenzene and excess nitric acid in the presence of sulfuric acid, and at a high temperature.
Answer

2,4,6-trinitromethylbenzene (TNT)

Trinitrotoluene Structure

Excess acid and high temperature causes multiple substitutions at the 2, 4, and 6 positions.

Reduction of Nitrobenzene

Nitrobenzene can be reduced to form another product.
a) Write the equation and the ½ equation for the reaction where nitrobenzene is reduced.
Answer

C6H5NO2 + 6[H] → C6H5NH2 + 2H2O

Half Equation:

C6H5NO2 + 6H+ + 6e– → C6H5NH2 + 2H2O

b) State the reagents and conditions for the reaction.
Answer

Sn and HCl (or Fe and HCl), high temperature.

or H2 using a Ni catalyst.

c) State one use for the product of this reaction.
Answer

Used to make azodyes.

d) The product of the reaction in question 3a will react with hydrochloric acid. Write an equation for this reaction and state the name of this type of reaction.
Answer

C6H5NH2 + HCl → C6H5NH3Cl

Type: Neutralisation (Acid-Base reaction).

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