"Preparation of p-Bromo acetanilide from Acetanilide"

 

"Preparation of p-Bromo acetanilide from Acetanilide"

Theory:

p-Bromo acetanilide is prepared by the bromination of acetanilide. Acetanilide is an amide compound that reacts with bromine to substitute one of the hydrogen atoms on the aromatic ring with a bromine atom. This reaction occurs under acidic conditions.

Chemicals required:

1. Acetanilide (C₈H₉NO)
2. Bromine (Br₂)
3. Glacial Acetic acid (CH₃COOH)
4. Ice

Material required:

1. Round-bottom flask
2. Filter funnel
3. Ice bath
4. Glass rod
5. Distilled water

Chemical reaction:

Mechanism:

The reaction mechanism involves the bromination of acetanilide in the presence of acetic acid as a solvent and sulfuric acid as a catalyst. The bromine molecule attacks the benzene ring, and one of the hydrogen atoms on the ring is replaced by a bromine atom.

Procedure:

1. I dissolved 4.5 grams of acetanilide in 15 mL of glacial acetic acid in a round-bottom flask.
2. Then, I placed the flask on ice bath.
3. On the other hand, I dissolved 3.5 ml of bromine in 15 mL of glacial acetic acid in another flask.
4. I poured the bromine solution into the round bottom flask containing solution of acetanilide with continuous stirring set in ice bath.  
5. Now, the reaction mixture was stand for about 10 minutes to maintain the temperature of reaction for about 20-25^oC.
6. After that, the mixture was poured over the beaker containing crushed ice.
7. The white shiny crystals of p-bromo acetanilide was obtained.
8. The filter funnel was used to separate the crystals from water. Then, I dried them.
9. I weighed the dried product to determine the yield.
10. I measured the melting point of the p-bromoacetanilide to confirm its purity.
    
    
    

Calculations:

Molecular weight of acetanilide (C₈H₉NO) = 135.17 g/mol

Molecular weight of p-bromoacetanilide (C₈H₈BrNO) = 214.08 g/mol

Now, let's calculate the theoretical yield and percentage yield;

Theoretical yield:

The molar ratio between acetanilide and p-bromoacetanilide is 1:1, which means

1 mole of acetanilide = 1 mole of p-bromoacetanilide.

Moles of acetanilide used = mass of acetanilide / molecular weight of acetanilide = 4.5 g / 135.17 g/mol = 0.0333 mol

Therefore, the theoretical yield of p-bromoacetanilide is also 0.0333 mol.

Mass of p-bromoacetanilide = moles of p-bromoacetanilide x molecular weight of p-bromoacetanilide = 0.0333 mol x 214.08 g/mol = 7.13 g

Actual yield:

The mass of the obtained p-bromoacetanilide crystals.

Assuming you obtained 6.5 g of p-bromoacetanilide crystals as the actual yield.

Percentage yield = (Actual yield / Theoretical yield) x 100 = (6.5 g / 7.13 g) x 100 = 91.2%

The percentage yield in this case is 91.2%.

Melting Point:

The melting point of p-bromoacetanilide is approximately 164-166°C.