Principle: p-bromoacetanilide is prepared by bromination process. Mono substituted products of primary amine can not prepared easily by direct action of a reagent. Bromination of acetanilide gives para brominated acetanilide, mainly because amino group of acetanilide is protected by acetyl group.1
Aim: To prepare p-bromoacetanilide from acetanilide by Bromination reaction.
Mechanism: Bromination is an electrophilic substitution reaction on an aromatic ring.
Use: Used as analgesic and antipyretic agent.
Chemicals: Acetanilide (10 g)
Glacial acetic acid (70 ml)
Bromine (4.2 ml)
Sodium bisulphite (sufficient quantity)
Apparatus: Conical flask
Burette/separating funnel etc.
10 g of acetanilide is dissolved in 45 ml glacial acetic acid in a 250 ml conical flask and cooled to below 5 degrees. Then 4.2 ml of bromine is added drop wise in to 25 ml cold acetic acid with constant stirring and the bromine solution is transferred to a burette/separating funnel supported over the flask. The bromine solution is added slowly with constant stirring to acetanilide solution and the flask is placed in cold water as the reaction is exothermic. When addition of all the bromine is complete the solution turns orange due to the presence of slight excess of bromine, then allowed to stay at room temperature for 30 min. Contents of the flask are poured directly into a beaker having 200 ml ice cold water. The conical flask is further rinsed with 50 ml cold water and transferred into the beaker with stirring. Here para bromo acetanilide separates as a white solid. If the colour of the solution is persistently yellow, about 4-5 g of sodium bisulphite is added with constant stirring to bleach coloration. The crude product is filtered with suction, the residue washed with cold water, recrystallized from rectified spirit, dried in an oven at 100 oC and the percentage yield is calculated. The p-bromo acetanilide is obtained as colourless crystals, m.p. 167°. Yield, 10 g.
Molecular formula of acetanilide = C8H9NO
Molecular formula of p–bromo acetanilide = C8H8NOBr
Weight of acetanilide = 135 g/mole
Weight of p-bromo acetanilide = 214 g/mole
135 g of acetanilide gives 214 g of p-bromo acetanilide
Therefore, 10 g of acetanilide would give…………………. ? (X) g of p-bromo acetanilide
The yield of synthesized p-bromo acetanilide was found to be 63.09 %
Practical Organic Chemistry by Frederick George Mann and Bernard Charles Saunders Published by Longman Inc., Fourth Edition; Page No. 166.
Vogel’s Textbook of Practical Organic Chemistry by Brian S. Furniss, Antony J. Hannaford, Peter WG Smith & Austin R. Tatchell; Fifth Edition; Page No. 918.
Advanced Practical Organic Chemistry by O.P. Agarwal, Page No. 6.