1
Experiment 14: The Friedel-Crafts Acylation of Ferrocene
A Friedel-Crafts acylation is an electrophilic aromatic substitution reaction that
introduces an acyl group onto an aromatic ring. The electrophile is an acyl cation that is often
coupled to a Lewis acid catalyst, such as aluminum chloride. In order for the reaction to take
place, the aromatic ring system must be very electron rich and thus cannot contain any electron
withdrawing groups.
Ferrocene was discovered by accident in 1951 and is an example of the now well-known
metallocene or “sandwich” compounds. The highly electron rich cyclopentadienyl rings in
ferrocene are aromatic and undergo many of the same reactions as benzene. In fact, most
metallocenes are more reactive toward electrophilic reagents than is benzene, which indicates
that the electrons are more readily available. Thus, while the Friedel-Crafts acylation of benzene
requires aluminum chloride as a catalyst, ferrocene can be acylated by acetic anhydride under
milder conditions using phosphoric acid as the catalyst.
In addition, the second ring may also be acetylated to give 1,1'-diacetylferrocene,
Fe(C5H4COCH3)2. The highly colored acyl derivatives are easily separated by thin layer
chromatography (TLC). You will use TLC not only to analyze the product(s) but also to follow
the course of the reaction. Review Chapter 18, pp 255-269, in LTOC.
Outline the steps of the following procedure:
The glassware used for the reaction must be very dry. Clean a 10x100 mm reaction tube
from the microscale kit, then dry it in an oven briefly before beginning the experiment. Insert a
short length of Teflon tubing (1-2 inches) into a rubber septum that fits on a 10x100 mm reaction
tube.
Begin heating a beaker of water on a hot plate.
+
R
C
X
O
AlCl3
Δ
C
R
O
+ HX
C
O
CH3
C
+ CH3COOH
CH3
O
C
CH3
O
+
O
Ferrocene
M.W. 186.04 g/mol
m.p. 174-176°
Acetylferrocene
M.W. 228.07 g/mol
m.p. 81-83°
Acetic anhydride
M.W. 102.09 g/mol
density 1.082 g/mL
b.p. 138-140°
Fe
Fe H3PO4
