Expt #3. Friedel Crafts Acylation;
Preparation of 4-Methoxypropiophenone
Relevant textbook reading -Smith
, Chapter 18.1-18.10
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 using the procedure
outlined 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 diagramed in
Fig 7.4a (p 63) in Mohrig. Set the apparatus toward
the back of the fume hood and it will not be necessary
- 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 support the idea that it is
an effective alternative?
- 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 product being statistically favored but
sterically hindered. Thus, bulkier substituents tend
to give less of the 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
Smith adequately explain these results? If warranted,
propose an alternative mechanism that better explains
the very large role that steric hindrance plays in
this reaction.
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