Synthesis of P-Nitro Acetanilide
Synthesis of p-Nitroacetanilide
(electrophilic aromatic substitution)
In this experiment, we convert acetanilide to p-nitroacetanilide.
[pic]
The mechanism for the nitration is that of electrophilic aromatic substitution. The nitronium ion is directed to the positions ortho and para to the acetamido (-NHCOCH3) group. This occurs because the resonance electron-releasing effect of that group increases the electron density at those positions, helping to stabilize the intermediates that are formed. Substitution para to the acetamido group is favored over substitution ortho to that group, because the great bulk of the acetamido group shields the ortho positions from approach by reagents. This steric hindrance makes ortho substitution much less likely than para substitution, in which the bulk of the acetamido group has no influence. The ortho substitution product is formed in small quantities in this reaction.
SPECIAL INSTRUCTIONS
Concentrated sulfuric and nitric acids, in combination, form a very hazardous and corrosive mixture. These acids should be poured together carefully, and this procedure should be carried out in a hood, since noxious vapors are produced. You will begin with the sample of acetanilide you isolated and purified in the first two experiments. If you do not have the required 1.5 grams of acetanilide, you may obtain more acetanilide from the instructor. As always, avoid contact of all chemicals with skin, eyes, and clothing. Wash all contact areas with large quantities of water.
PROCEDURE
Place 1.5 g of acetanilide in a 125-mL Erlenmeyer flask. Add slowly about 2.5 mL of concentrated sulfuric acid to the acetanilide. Dissolve most of the solid by swirling and stirring the mixture. Do not be concerned if a small amount of undissolved solid remains. It will dissolve in later stages of this procedure. Place the flask in an ice bath. Place 0.9 ml of concentrated nitric acid in another small flask and add about 2.5
(electrophilic aromatic substitution)
In this experiment, we convert acetanilide to p-nitroacetanilide.
[pic]
The mechanism for the nitration is that of electrophilic aromatic substitution. The nitronium ion is directed to the positions ortho and para to the acetamido (-NHCOCH3) group. This occurs because the resonance electron-releasing effect of that group increases the electron density at those positions, helping to stabilize the intermediates that are formed. Substitution para to the acetamido group is favored over substitution ortho to that group, because the great bulk of the acetamido group shields the ortho positions from approach by reagents. This steric hindrance makes ortho substitution much less likely than para substitution, in which the bulk of the acetamido group has no influence. The ortho substitution product is formed in small quantities in this reaction.
SPECIAL INSTRUCTIONS
Concentrated sulfuric and nitric acids, in combination, form a very hazardous and corrosive mixture. These acids should be poured together carefully, and this procedure should be carried out in a hood, since noxious vapors are produced. You will begin with the sample of acetanilide you isolated and purified in the first two experiments. If you do not have the required 1.5 grams of acetanilide, you may obtain more acetanilide from the instructor. As always, avoid contact of all chemicals with skin, eyes, and clothing. Wash all contact areas with large quantities of water.
PROCEDURE
Place 1.5 g of acetanilide in a 125-mL Erlenmeyer flask. Add slowly about 2.5 mL of concentrated sulfuric acid to the acetanilide. Dissolve most of the solid by swirling and stirring the mixture. Do not be concerned if a small amount of undissolved solid remains. It will dissolve in later stages of this procedure. Place the flask in an ice bath. Place 0.9 ml of concentrated nitric acid in another small flask and add about 2.5