Organic Syntheses, CV 4, 473
FERROCENE
[I. METALLIC SODIUM METHOD]
Submitted by G. Wilkinson
1
Checked by N. J. Leonard, Kenneth L. Rinehart, Jr., Donald J. Casey, and Sung Moon.
1. Procedure
In a
250-ml. three-necked flask, fitted with a
mechanical stirrer, a
reflux condenser, and an inlet for admission of
nitrogen, is placed
100 ml. of tetrahydrofuran (Note
1). With stirring,
27.1 g. (0.166 mole) of anhydrous ferric chloride is added in portions, followed by
4.7 g. (0.084 g. atom) of iron powder (Note
2). The mixture is heated with stirring under
nitrogen at the reflux temperature for 4.5 hours, giving a gray powder with a brown supernatant liquid.
During this time, a second system is assembled, consisting of a
500-ml. three-necked flask fitted with a mechanical stirrer, a reflux condenser topped with a
calcium chloride-filled drying tube attached to a
xylene-filled bubbler, and a
pressure-equalizing dropping funnel through which a slow stream of
nitrogen is passed into the flask. In the flask are placed
200 ml. of sodium-dried xylene and
11.5 g. (0.5 g. atom) of sodium. The mixture is heated to boiling, and the
sodium is finely dispersed by rapid stirring (Note
3). Stirring is continued while the mixture is allowed to cool in a
nitrogen atmosphere. The cooled mixture is allowed to settle, and the bulk of the
xylene is siphoned.
Tetrahydrofuran (200 ml.) (Note
1) is added through the
separatory funnel, and to the stirred mixture, cooled in ice, is added
42 ml. (0.5 mole) of cyclopentadiene (Note
4) in portions during 1 hour (Note
5). Stirring is continued for 2–3 hours in the cold, after which only a small amount of
sodium remains unreacted.
The cooled contents of the 250-ml. flask containing
ferrous chloride (Note
6) are added to the cold
sodium cyclopentadienide solution while passing a stream of
nitrogen through both flasks. The combined mixture is stirred for 1.25 hours at a temperature just below reflux. Solvent is removed by distillation, and the
ferrocene is extracted from the residue with several portions of refluxing
petroleum ether (b.p.
40–60°). The product is obtained by evaporation of the
petroleum ether solution.
Ferrocene may be purified by recrystallization from
pentane or
cyclohexane (
hexane,
benzene, and
methanol have also been used) or by sublimation. The yield is
31–34 g. (
67–73%) (Note
7), m.p.
173–174°.
2. Notes
2. The quality of the
iron used in preparing the
ferrous chloride has a marked effect on the yield of
ferrocene. The checkers employed Rascher and Betzold (730 N. Franklin, Chicago, Ill.) 300-mesh
iron powder, reduced by
hydrogen. When 40-mesh
iron filings were used, the yield of
ferrocene was much lower (ca. 33%).
3. The checkers employed a "Mixmaster"-type motor and a
Hershberg stirrer made from
tantalum wire.
4.
Cyclopentadiene, b.p.
40°, is obtained by heating commercial
85% dicyclopentadiene (e.g., from Matheson, Coleman and Bell Company, Norwood, Ohio) under a
short column (
in. diameter × 8–12 in. length) filled with glass helices. The distilled
cyclopentadiene is collected in a
receiver which is maintained at Dry Ice temperature until the
cyclopentadiene is used.
Methylcyclopentadiene and other substituted cyclopentadienes such as
indene may also be employed for the synthesis of the correspondingly substituted ferrocenes. In these cases, the reaction of the hydrocarbon with
sodium is much slower than with
cyclopentadiene, and refluxing for several hours is required to complete the reaction.
7. The submitter reported yields up to
90% by this method.
[II. DIETHYLAMINE METHOD]
Submitted by G. Wilkinson
1
Checked by N. J. Leonard, Kenneth L. Rinehart, Jr., and Peter Woo.
1. Procedure
The conditions given in the preceding preparation are used for obtaining a suspension of
0.25 mole of ferrous chloride in 100 ml. of tetrahydrofuran (Note
1), contained in a 250-ml. flask. The
tetrahydrofuran is then removed under reduced pressure until the residue is almost dry. The flask is cooled in an
ice bath, and to the residue is added a mixture of
42 ml. (0.5 mole) of cyclopentadiene and approximately
100 ml. (about 1 mole) of diethylamine. The mixture is stirred vigorously at room temperature for 6–8 hours or, conveniently, overnight. The excess amine is removed under reduced pressure, and the residue is extracted repeatedly with refluxing
petroleum ether. The extract is filtered hot, and the solvent is evaporated to leave ferrocene. The product is purified by recrystallization from
pentane or
cyclohexane or by sublimation. The yield is
34–39 g. (
73–84%), m.p.
173–174°.
2. Notes
1. All precautions with regard to the purification of
tetrahydrofuran, the quality of the
iron powder, the rapid stirring, the maintenance of a
nitrogen atmosphere, and the handling of
cyclopentadiene, described in the preceding preparation, are followed.
3. Discussion
This preparation is referenced from:
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved