CHEM 51LC
ELECTROPHILIC AROMATIC SUBSTITUTION: BROMINATION OF AROMATIC COMPOUNDS
In this experiment, you will brominate a variety of activated benzene derivatives. The different
substituents on the benzene ring are all activators and ortho, para- directors, yet some of them are
so strong as activators that they will result in di- or tri-brominated products. The purpose of this
lab is to determine the relative activating effect of the substituents tested based on the products
obtained in each reaction.
H
N
Br3
R
?
CH3COOH
Possible Products
R
R
R
Br
Br
Br
R
R
Br
Br
Br
Br
Br
Br
Four different aromatic compounds will be used in this experiment: aniline, acetanilide, phenol,
and anisole. You will perform a reaction using one of the four substrates, analyze the melting
point of the product you isolate, and then share your data with your class. You should predict the
substitution order (if multiple substitutions occur, which substitution patterns do you expect) and
the reactivity order (which substrates will brominate more than others) before you perform the
experiment. Be sure to justify your predictions. You should include these predictions in your prelab work in your lab notebook and in the Theory section of your written report.
O
NH2
aniline
CHEM 51LC
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HN
CH3
acetanilide
OH
phenol
OCH3
anisole
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Below is a table of all the possible products and their melting points.
Compound
2-bromoaniline
4-bromoaniline
2,4-dibromoaniline
2,6-dibromoaniline
2,4,6tribromoaniline
2-bromoacetanilide
4-bromoacetanilide
2,4dibromoacetanilide
2,6dibromoacetanilide
2,4,6tribromoacetanilide
MP
(°C)
32
66
80
87
122
Compound
2-bromophenol
4-bromophenol
2,4-dibromophenol
2,6-dibromophenol
2,4,6tribromophenol
MP
(°C)
5 66 36 54 96 99
168
145
2-bromoanisole
4-bromoanisole
2,4-dibromoanisole
3 13 60 208
2,6-dibromoanisole
13 232
2,4,6tribromoanisole
87 READING ASSIGNMENT:
! This handout for procedure
! Supplementary information in Janice Gorzynski Smith (4th Ed.) Chapter 18.7-18.10.
PRE-LAB ASSIGNMENT:
! Rewrite the procedure in your lab notebook using your own words.
! Complete the Sapling assignment.
! Don’t forget to include your predictions (discussed below) in your lab notebook!
CAUTION
Pyridinium tribromide is corrosive and dangerous if absorbed through the skin. Can cause eye
damage. Avoid contact with skin and eyes.
Glacial acetic acid is corrosive and has a strong, pungent odor. Use in fume hood. Avoid contact
with skin and eyes.
Aniline, acetanilide, phenol, anisole, and all the brominated derivatives are irritants. Wear
gloves, and avoid all contact with skin, eyes, and clothing.
Ethanol and hexanes are flammable. Inhalation of vapors can be toxic. Work in the fume hood
and keep away from sparks or flames.
CHEM 51LC
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EXPERIMENTAL:
Reaction Set Up:
Add 1 mmol of your assigned aromatic compound to a 10 mL Erlenmeyer flask equipped with a
stir bar. Add 0.75 mL of acetic acid and stir the reaction mixture until the aromatic compound is
completely dissolved. Add 3 mmol of pyridinium tribromide. Stir the reaction mixture at room
temperature for 30 minutes.
Isolation of Product:
Quench the reaction by pouring it in a 25 mL Erlenmeyer containing 5 mL of distilled water and
0.5 mL of saturated sodium bisulfite solution. Stir until the red color disappears. This can take
up to 5 min. Cool the solution in an ice bath for 10-15 min to cause the product to crash out. If
no solid formation occurs, scratch the insides of the flask to induce crystal formation. Filter the
solid using a Hirsch funnel and allow it to dry under vacuum for 10 min.
Purification and Analysis of Product:
Recrystallize the crude solid and obtain a melting range of the pure product. If you started with
aniline or acetanilide, use 95% ethanol for the recrystallization of the product. If you started with
anisole or phenol, use hexanes as the recrystallization solvent.
Collate Data:
Make sure that you have melting point data for the products of the other three reactions from your
peers performed before you leave.
LAB WRITE-UP:
Write a complete lab report as described in the Report Guidelines for Students handout.
Here are some guidelines of how to write your report:
! As the first part of your discussion section, talk about the substitution pattern of your
product and discuss whether it is logical or not based on the amount of bromine added.
! As the second part of the discussion section, report the theoretical yield and percent yield
of your product. At the end of your report attach a sheet showing all your
work/calculations in order to receive full credit – it is not included in the 2 page limit.
! Rationalize the reactivity each starting material possessed. Did some aromatic systems
brominate more than others? Do those results make sense?
As always, draw out the full mechanism of reaction for the aromatic starting material you had.
This is not included in the two-page lab report but should be attached to it.
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