Chapter 29
Friedel-Crafts Alkylation of Benzene
Purpose
• In this experiment a mixture of benzene and alkyl
chloride is treated with AlCl3 (Lewis acid). The dialkyl
product is isolated by adding water and extracting.
• The organic phase is then washed, dried and
evaporated to give an oily product which should
solidify upon cooling. You may also use filtering paper
to absorb any oil from the solid product.
Reaction Mechanism
• The Friedel-Crafts alkylation is a typical electrophilic
substitution reaction. The electrophile is t-butyl cation
generated by the reaction of alkyl halide and Lewis
acid. The dialkyl product is formed stepwise.
“Mystery” Modification
• Shown product can be obtained in case of using excess
of t-Butyl Chloride (at least 5 mmols per 1 mmol of
benzene) under the same reaction conditions. You
should provide a reasonable reaction mechanism in
your lab report.
Comments
• Follow pp. 438-440 (microscale).
• Follow the lab handout for all experimental
procedures.
• AlCl3 is highly hydroscopic and looses catalytic
activity after absorbtion moisture from the air.
Keep it AWAY from prolong contact with air!
• Perform GC/MS and optionally IR analysis of the
products from both reactions.
• Prepare samples of the products in CDCl3 for
NMR.
• Calculate yields. Moderate yields should be
achieved.
(Moles Product / Moles Starting Material) x 100 = %
Safety
• Benzene is highly flammable, irritating to eyes and
skin and may cause lung damage if swallowed. Also,
as shown on animal models, may cause cancer and
inheritable genetic damages by prolonged exposure.
Do not swallow, do not inhale and avoid contact with
eyes and skin. Wear gloves and handle with extreme
caution.
• Aluminum chloride is corrosive, wear gloves and
handle with care.
• Again: wearing rubber gloves is absolutely necessary
during this lab! You will work with toxic, carcinogenic
and corrosive compounds.