Expt 2 -
Friedel Crafts Acylation of Anisole
Relevant textbook reading - Klein,
Chapter 18.1-18.10, especially 18.6
Reference for Procedure - Miles, W. H.; Nutaitis,
C. F.; Anderton, C. A. J. Chem. Ed., 1996,
73, 272.
Overview - You will react anisole with propionyl
chloride in the presence of iron(III) chloride as a
catalyst. The overall procedure is described in the
experimental part of the above Journal of Chemical
Education reference.
Procedure Notes
- Run the reaction in the apparatus as described in the
paper and diagrammed in Fig 7.4a (p 63) in Mohrig. Set
the apparatus toward the back of the fume hood and it
will not be necessary to use an inverted funnel as a gas
trap.
- Evaporation of the solvent will be carried out using
the rotary evaporator.
- Obtain the 1H NMR and IR spectra of
the final product. One group will also be asked to
obtain a C-13 NMR.
Assigned Questions
- Why is iron(III) chloride attractive as an alternative
to the traditional AlCl3 as a catalyst for
Friedel Crafts reactions? Do the results of this
experiment bear this out?
- The methoxy group is generally considered an o,p-director
in electrophilic aromatic substitution reactions.
Discuss the theory behind this, writing the mechanism,
and discussing factors that stabilize the intermediates
of ortho and para attack of the
electrophile.
- o,p-Directing substituents often give mixtures
of both ortho and para products, with
the ortho isomer being statistically favored
but sterically hindered. Thus, bulkier substituents tend
to give lower yields of ortho product. (a) Did
the reaction carried out here give detectable amounts of
ortho product? (Look carefully at the proton NMR for
impurity peaks that could be due to the ortho isomer.)
(b) The methoxy group is not, by any stretch, a "bulky
substituent", so why is so little ortho product
formed? (c) Does the "accepted mechanism" given in Klein
adequately explain these results? If warranted, propose
an alternative mechanism that better explains the very
large role that steric hindrance plays in this reaction.
|