preparation of p-nitroacetanilide- dotsha j. raheem
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Preparation of p-nitroacetanilide which is then hydrolyzed to p-nitroaniline, nitration of acetanilideTRANSCRIPT
Week (1): Nitration of Acetanilide
Preparation of
p-nitroaniline Lecture by: Dotsha J. Raheem
Assistant LecturerDepartment of Chemistry
College of ScienceUniversity of Salahadin
2010
Preparation of Acetanilide
NH2
Aniline
+ CH3
O
H3C
O
O
Acetic anhydride
H3C
O
OH
CH3HN
O
Acetanilide
H3C
O
OH+
Acetic acid
1.
Nitration of Acetanilide2.
CH3HN
O
Acetanilide
HNO3 / H2SO4
CH3HN
OCH3HN
O
+NO2
NO2
o-nitroacetanilide p-nitroacetanilide"Major product"
Hydrolysis of Acetanilide3.
CH3HN
O
NO2
p-nitroacetanilide
1) Hydrolysis
H+, H2O
2) OH
NH2
NO2
p-nitroaniline
Importance of Acetanilide
NH2
Aniline
+ HNO3 / H2SO4
NH3
Anilinium ion
HNO3H2SO4 meta
substitution
Charring and oxidation of aniline
o,p-director
m-director
So, acetylation protects aniline
from protonation, charring and
oxidation
This lab.:
CH3HN
O
Acetanilide
HNO3 / H2SO4
CH3HN
OCH3HN
O
+NO2
NO2
o-nitroacetanilide p-nitroacetanilide"Major product"
Q/ The major product is para, but why not ortho?
This is mainly due to steric effect.
ortho-nitroacetanilidepara-
nitroacetanilide
ortho-nitroacetanilidepara-
nitroacetanilide
Notes on the Experiment
Nitration of acetanilide is an exothermic reaction ; the temperature must be carefully controlled by chilling, stirring, and the slow addition of reagents.
The reaction is conducted below 10˚ C to maintain selectivity by preventing less favorable reactions from occurring [o- and 2,4-dinitro products require higher energy]
Notes on the Experiment
Glacial acetic acid is used because it is a polar solvent capable of dissolving acetanilide, and the acetate ion is a poor nucleophile so no substitution is possible.
A mixture of concentrated nitric and sulfuric acids is used as the nitrating mixture.
Notes on the Experiment
To prevent dinitration of the acetanilide, the nitrating mixture is added in small portions to the acetanilide solution (and not vice versa) so that the concentration of HNO3 is kept at a minimum.
After the addition is complete the beaker is allowed to stand at room temperature for 30 minutes [more than that will lead to the formation of 2,4-dinitroacetanilide].
Notes on the Experiment
o-nitroacetanilide has higher solubility in the aqueous solution than p-nitroacetanilide.