Acetylation of Ferrocene

17. October 1996
Experiment #7

In this lab we will be utilizing the Friedel Crafts process of
acetylation of ferrocene. Ferrocene is an atom of iron bounded by two aromatic
rings. We will use some reagents that will cause the ferrocene to add either
one acetyl group to an aromatic ring or add two acetyl groups to each of the
aromatic rings. In order to determine how well this process had worked we
employed: IR spectra analysis, column chromatography, and a little TLC. This
experiment is relevant in today\'s highly industrialized world. By utilizing
many of the techniques we employ in this lab, a company can synthesize new types
of materials or composites that could revolutionize an industry.

When we react the ferrocene with phosphoric acid and acetic anhydride,
we obtain many disparate products. Not only do we get acetylferrocene, but we
also get diacetylferrocene, some unreacted ferrocene reactant, and acetic acid
as well. We will use thin layer chromatography (TLC), column chromatography
(CG), and IR spectra analysis in order to determine the what proportions of
each of these compounds will be present in the final product.
Both TLC and CG are excellent methods of measuring the presence of a
given substance. Both methods turn around a compounds polarity. As one recalls,
polarity is a measure of the electronegativity of a compound determined by their
placement in the periodic chart. Specifically, in this lab we are talking about
the difference in polarity between the atoms of oxygen and carbon. Ferrocene is
relatively low to none in polarity. Acetylferrocene, because of the carbonyl
functional group, is more polar than the ferrocene. Moreover, diacetylferrocene,
because of the 2:1 ratio of the carbonyl groups over the acetylferrocene, is the
most polar of the lot.
As stated above, both TLC and CG take advantage of polarity. Both
methods have an extremely polar stationary phase; specifically, silica or
alumina gel is used. Through this polar stationary phase, a mobile liquid phase
is passed. Now, one can think of a polar stationary phase as a bully that waits
in the high school halls for his hooligan friends. His hooligan friends,
hooley\'s as I like to call them, always stay back to talk him; the rest of the
normal student body simply keep walking and pass him. The idea here is: like-
stays-with- like. Analogously, those compounds which are most similar to the
stationary substrate will stay behind to "hang out". In this case, the more
polar the compound is, then the more it will stay behind as the rest of the
product moves forward in its liquid mobile phase. TLC works by capillary action,
where the mobile phase is drawn up the TLC plate and across a polar TLC plate.
CG, on the other hand, works by having gravity pull the liquid mobile phase
down a polar laden column. The joyous wonder of TLC and CG, then, is that they
are thus able to separate each constituent contained in the product.

Methods & Procedure
The procedure of for this lab may be found in the pre-lab note for this
experiment contained in the appendix. I will only remark on the important
features of the procedure. The amount of start material for this lab was ca. 10
g. The calculation for this may also be found in the pre-lab I first added
acetic anhydride to ferrocene (FC) and then warmed to add in the H3PO4
catalyst. I observed a reddish-violet color to this mix of reactants. I then
did a TLC and noted that the majority of the sample was not the original
ferrocene start material. Please see the pre-lab for reproductions of the TLC
plates used in this lab. Also see table 1.2 for Rf values.
As one can see, this crude\'s Rf is half that of the start material.
This indicates that a reaction has definitely occurred. Next we performed an
extraction on this sample with Methylene Chloride (MeCl) and Sodium Hydroxide
(OH-). Please see the pre-lab for a picture of what the extraction looked like.
Then we transferred the lower organic potion into another vial with a little
sodium sulfate for drying. Then we transferred this to a tarred vial and dried
off the MeCl in a nitrogen stream. MeCl is a great solvent because it
evaporates easily (bp. ca. 48ÝC). Moreover, we used a nitrogen steam so that we
could minimize the amount of moisture in regular air from being reintroduced
into the sample. This was our second crude sample and we did a TLC on it with
FC start material. See Tables 1.1 and 1.2 for amount of crude sample obtained
and the Rf