Questions of the Day:
The following Friedel-Crafts reactions do not work, i.e.
no reaction. Why? (Think of mechanism…)
a) Toluene reacting with chlorobenzene in the
presence of aluminum chloride catalyst
b) Benzaldehyde reacting with chloromethane in the
presence of aluminum chloride catalyst
Today:
• Conclusion of Friedel-Crafts/GC
• Introduction to NBS-Bromination (Exp. 3)
• MiniQuiz
Friedel-Crafts Alkylations (Exp.II)
Reaction equation for the reaction of p-xylene with 1bromopropane in the presence of aluminum trichloride (our lab
experiment):
Mechanism… :
Which carbocation intermediates are formed?
Gas Chromatography
1. Which is the moving phase, which is the stationary
phase in our GC?
2. What peaks do you expect to get in your GC of
Exp.II? What determines their approximate
sequence?
Calculations for Friedel-Crafts Experiment
II.
Weight of product mixture
What is in product mixture?
3. Percent
by
weight
of
mono
n-propyl
product
in
product
mixture
Weight fraction… Remember: Different molecular weights…
Theoretical yield in grams of mono n-propyl product
1.
Balanced equation (assuming that only mono n-propyl product is
formed), mols, mol ratios …
4. Percent yield mono n-propyl product*
[Actual yield / theor. yield]
2.
x %
Ratio of n-propyl to isopropyl product*
GC! Area ratio =mol ratio
Synthesis of Bromoethylbenzene; H-NMR (Manual Exp.III)
Br
Br
CH 2 CH 3
NBS
CCl 4
CHCH 3
NBS
CCl 4
CCH 3
Br
What is the structure of N-Bromosuccinimide (NBS)?
What type of a reaction is this?
1. What is a “radical” in chemistry?
2. What is the geometry of a carbon radical?
3. What reaction conditions generally tend to lead to
radical intermediates?
4. What are the major steps found in every radical
reaction?
Synthesis of Bromoethylbenzene; H-NMR (Manual Exp.III)
Br
Br
CH 2 CH 3
NBS
CHCH 3
CCl 4
NBS
CCl 4
CCH 3
Br
1. Why does bromination in our reaction occur at the αposition only?
2. What is the function of NBS?
3. What is the function of dibenzoyl peroxide?
Propagation
How can you explain that the reaction mixture
goes through a series of color changes?
Synthesis of Bromoethylbenzene (Manual Exp.III)
1. Properties of CCl4?
2. Why is CCl4 a good solvent for our reaction
mixture?
3. What are criteria for a "good solvent" in general?
4. What is the purpose of adding cyclododecane?
Next time:
•NMR (Concl. of Exp.3)
•Introduction to Diels-Alder (Exp.4)
•MiniQuiz on this lecture
MiniQuiz 2 Question:
Write the structures of two(2) carbocation
intermediates that are formed during our
Friedel-Crafts reaction (Exp.2)