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 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 prove that it should be
- 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
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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