BACKGROUND
Principle:
Insertion of benzoyl moiety instead of an active hydrogen atom present in hydroxyl (OH) primary amino (NH2) or secondary amino group (NH) is usually termed as benzoylation reaction.1
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This particular reaction essentially bears a close resemblance to the phenomenon of acetylation except that in this specific instance the reagent is (benzoyl chloride) which reacts in the presence pyridine or 10% NaOH and not benzoic anhydride.
The amines are more soluble in acid chloride than in NaOH, the reaction occurs preferably between benzoyl chloride and amine. In the preparation of benzanilide, NaOH neutralizes the liberated HCl and also catalyze the reaction.2
Aim: To prepare benzanilide from aniline.
Reaction:
Mechanism:
Benzoylation of compounds those are containing active hydrogen such as phenol, aniline, alcohol etc. form benzoyl chloride in the presence of aqueous NaOH (Schotten Baumann reaction).
Use:
It is used as fungicide and acaricide (pesticide that kill ticks and mites).
REQUIREMENTS
Chemicals: Aniline – 2 ml, 10% NaOH -30 ml, Benzoyl chloride – 3 ml, Cold water, Hot alcohol
Apparatus: Conical flask – 250 ml, Buchner funnel, Measuring cylinder, Filter paper,
PROCEDURE
Place 2 ml (2.08 g) of aniline 30 ml of 10% NaOH solution in 250 ml conical flask, then add 3 ml (3.4 g) of benzoyl chloride slowly with vigorous shaking. Cork the flask and shake for further 15-20 min or till the odour of benzoyl chloride can no longer be detected.
Dilute the reaction mixture with cold water, filter the crude benzanilide with suction on a Buchner funnel, wash with cold water and crystallize from hot alcohol. Dry the product and calculate the percentage yield.3
Calculation:
Here limiting reagent is aniline; hence yield should be calculated from its amount taken.
C6H7N = Molecular formula of aniline
C13H11ON = Molecular formula of benzanilide
Molecular weight of aniline = 93 g/mole
Molecular weight of benzanilide = 197 g/mole
Theoretical yield:
93 g aniline forms 197 g benzanilide
Therefore, 2.08 g (2 ml) aniline will form ………? (X) g benzanilide
X =( 197 × 2.08)/93 = 4.4 gs
Theoretical yield = 4.4 gs
Practical yield = ————- gs
% Yield = (Practical Yield)/(Theoretical Yield) × 100
CONCLUSION
Benzanilide was synthesized and the percentage yield was found to be………..%. (Benzanilide is colourless crystals, m.p. 163°: yield 3.2 g)
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REFERENCES
- Laboratory Manual of Organic Chemistry by Raj K. Bansal, Page No.111.
- Practical Organic Chemistry by Frederick George Mann and Bernard Charles Saunders Published by Longan Inc., Fourth Edition; Page No. 245.
- College Practical Chemistry by V K Ahluwalia, Sunita Dhingra; Published by Universities Press (India) Private Limited 2005; Page No- 235.
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