Preparation of Acetanilide

Acetanilide is an important organic compound which is vastly used in the pharmaceutical industry. It is an odorless, white, solid or flaky compound. Its preparation method is used to introduce students with synthesis of organic compounds in chemistry labs. It is prepared by acetylation of aniline. 

Aim – To prepare acetanilide from aniline, glacial acetic acid (acetic anhydride) and zinc dust. 

Theory – On heating, aniline reacts with acetic anhydride in presence of zinc dust and glacial acetic acid and yields acetanilide. Thus, formed acetanilide is recrystallized to get pure crystals. Purpose of using zinc dust is to prevent oxidation of aniline during the reaction. The chemical reaction involved in preparation of acetanilide is given below –

 

Acetanilide is also known as N-phenylacetamide, N-phenylethanamide and methanol.

Requirements – Round bottom flask of 100 ml, wire gauze, tripod stand, burner, clamp, reflux condenser, stirrer, filter paper, beaker, pipette, electronic balance, iron stand, measuring cylinder, aniline (20 ml), acetic anhydride and glacial acetic acid mixture (40 ml), zinc dust. 

Procedure –

  1. Wash all the apparatus with distilled water carefully before starting the experiment. 

  2. Add 20 ml aniline and 40 ml mixture of acetic anhydride and glacial acetic acid in a round bottom flask of 100 ml.

  3. Keep stirring the reaction mixture. 

  4. Now add zinc dust in the flask. 

  5. Fix a water reflux condenser to the round bottom flask containing the reaction mixture using clamps and iron stand. 

  6. Now fix the round bottom flask on the burner for heating the reaction mixture using a tripod stand, wire gauze and sand bath. Keep heating the mixture for 30-40 min.

  7. Keep stirring the mixture. 

  8. Now pour the reaction mixture from the round bottom flask into a beaker containing ice cold water. 

  9. Keep stirring the mixture. 

  10. Once all acetanilide is precipitated, filter the reaction mixture. 

  11. Thus, obtained acetanilide crystals are crude or not pure so a recrystallization process should be carried out. 

  12.  For Recrystallization - 

  • Dissolve crude acetanilide in 50 ml distilled water using a beaker and stirrer.

  • Add a bit of ethanol as well.

  • Now heat this solution until it gets clear and keep stirring it as well. After this you will get solution almost like this – image will be added soon.

  • Now cool down the solution and filter it. 

  • Let the crystals dry. You will get the crystals almost looking like this – image will be added soon.

  • If you want to get more pure crystals of acetanilide then you can perform the recrystallization process twice. 

  • Determine the melting point of the crystals obtained.

Observation Table – 

Color of the crystals 

White 

Odor of crystals 

Odorless 

Appearance 

Flaky 

Melting point 

115℃

 

Result -  Weight of the acetanilide crystals obtained = _____g. Its Melting point is 115℃.

Precautions –

  • Aniline is a carcinogenic compound so it must be handled very carefully. 

  • Don’t inhale the fumes of acetic anhydride. 

  • Always dry the crystals before taking their weight and melting point to avoid error due to moisture. 

  • Keep stirring the reaction mixture during the experiment. Vigorous heating is must when mixture is added in ice cold water. 

This was the experiment to prepare acetanilide from aniline, if you want to know procedures, theories of other experiments such as titrations etc. as well then register yourself on Vedantu or download Vedantu learning app for class 6-10, IIT JEE and NEET.