Advanced Organic Chemistry. 447 chem (Lab).
1
Exp.06: preparation of p-bromo acetanilide
Objectives:
- Preparation of p-bromo acetanilide (Bromination reaction).
Discussion:
This mechanism is a classic example of electrophilic aromatic substitution. An amine
may lead to di- and tri- substituted products. If an amide is used in place of the amine,
monosubstitution usually predominates (the electron-withdrawing carbonyl group
makes the benzene ring less nucleophilic). This ortho-, para- directing group will tend
to only add groups para- to itself because of the steric bulk of the amide group.
Experimental Procedure:(all manipulations should be done in the chemical fume hood).
- Place 3 g (0.022 mol) of acetanilide into a 100 mL conical vial. Add 10 mL of
glacial acetic acid.Stirring with a glass rod may be necessary to help dissolve
the acetanilide (r.t).
- Now, in the hood,prepare the bromine solution by adding 1.5 mL of bromine
into 10 mL of acetic acid (first but 10 mL of the acid then 1.5 mL of
bromine using dropper “Fast”)
- in the hood,add bromine-acetic acid solution to acetanilide solution with
stirring then leave the mixture 15 min.
(Wear gloves and, of course, goggles. Use extreme caution. Bromine burns can
be quite severe).
- Transfer the mixture into beaker contain 100 mL of water with stirring.
- Collect the product by vacuum filtration using Büchner funnel.
- Purify the product by crystallization method using ethanol.
- Collect the white crystals by vacuum filtration, dried and weigh and calculate
the percent yield.
- Obtain melting point and compare with literature data. Obtain the 1H NMR
spectra and compare to what is given.
HN
O
HN
O
Br
Br2
Bromoacetanilide
Acetanilide
