Synthesis of P-Nitroacetanilide from Acetanilide

Synthesis of p-Nitroacetanilide from Acetanilide

Theory:

Para-Nitroacetanilide is also known as 4-nitro acetanilide. This is a chemical compound that is a Nitroacetanilide derivative prepared from acetanilide and nitrating mixture along with a trace amount of ortho product is also formed. This organic compound is prepared from acetanilide. For this purpose acetanilide is treated with a nitrating mixture that is a mixture of nitric acid (HNO3) and sulphuric acid, para-nitro acetanilide is formed. Ortho product is also formed as a minor product. Ortho product is readily soluble in alcohol. So it is very easy to isolate the Para product through crystallization. (Synthesis of P-Nitroacetanilide from Acetanilide)

Substitution reaction:

The formation of para-nitro acetanilide is an electrophilic substitution reaction. In this reaction, the electrophile is nitro group NO2 which attaches to the para position. The reason for it is that NHCOCH3 is an electron-rich species. Similarly, nitro aniline can be prepared by this reaction as the nitration of aniline is not possible because the amino group gets oxides with a nitrating mixture. In order to protect the amino group from this oxidation, acetanilide is first nitrated to get the para-nitro acetanilide, and then through hydrolysis, it gives p-nitroaniline which is very difficult to get by direct reaction i.e. nitration. This reaction is an electrophilic substitution reaction by nature from which the nitronium ion is formed which is directed towards the para and ortho position. Para product is more feasible because of a steric hindrance at the ortho position. As ortho product is more soluble in ethanol so it can remain in the mother liquor therefore only para product is separated out easily.

Uses or application:

  • Para-nitroacetanilide is used in pharmaceuticals in the preparation of phenacetin and paracetamol
  • It can also be used in pesticides and rubber
  • It is also being used in the formation of intermediate dyes

Structure:

Synthesis of P-Nitroacetanilide from Acetanilide

Procedure:

  • 3 g of acetanilide is taken in finely powdered form in a clean beaker. It dissolves it by the addition of glacial acetic acid with stirring the content carefully at room temperature
  • Now gently warm the mixture to dissolve acetanilide completely
  • Cool the solution and add concentrated sulphuric acid slowly with continuously shaking or stirring
  • The solution will become warm, so must be kept in the ice-bath to obtain a clear solution
  • Fuming nitric acid is added to dropwise to cool the solution by using a dropping funnel with constant shaking or stirring
  • The temperature should be maintained at 20oC during the whole reaction procedure
  • The beaker is removed from the freezing mixture ice bath when the addition of nitric acid is completed, then allow it to stand for a while at room temperature
  • Pour the mixture into 100 gm of crushed ice beaker and stir well to cool it
  • Large crystals of p-Nitroacetanilide are obtained which are then filtered by filtration
  • These separated crystals are washed by cold water to remove excess acid

Precautions:

  • The temperature should not exceed 20oC
  • Add the nitric acid into the reaction mixture when it is dipped in the ice-bath
  • Fuming acid should add drop by drop and avoid inhaling the fumes of nitric acid

Reaction:

Synthesis of P-Nitroacetanilide from Acetanilide

Mechanism:

Synthesis of P-Nitroacetanilide from Acetanilide

Other examples:

  • Bromination of acetanilide with Br2 in the presence of FeBr3 to give a mixture of ortho and para product as

Synthesis of P-Nitroacetanilide from Acetanilide

  • Sulphonation of acetanilide with concentrated sulphuric acid to give para product is also a good example of electrophilic aromatic substitution reaction

Synthesis of P-Nitroacetanilide from Acetanilide

Synthesis of p-Nitroacetanilide from Acetanilide

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