1766
KURBANOV
1H NMR study of a mixture of pyridine with cyclo-
pentadiene dimer (22–24%) and trimer (11–13%), and
the remaining cyclopentadiene is converted into a
polymer. In the case of monomethylaniline the
ferrocene yield reaches 37–43%, and the reaction mix-
ture contains only 10–15% of the cyclopentadiene
dimer. When the intermediate complex was prepared
with pyridine, the yield of ferrocene was over 70%.
pentadiene showed the presence of two signals only,
belonging to the protons of the pyridine–cyclo-
pentadiene complex. One signal is shifted upfield to
the position with chemical shift δ = 0.75 ppm, while
the proton signal of cyclopentadienyl anion is shifted
downfield to δ = 16.57 ppm.
We found that at equimolar ratio of cyclopenta-
diene, amine, and FeCl2 in 2-propanol at 20°C, 2 h
after mixing a mixture is formed, which in the case of
dimethylaniline consists of ferrocene (22–26%), cyclo-
Thus, using the data on the complexing ability of
cyclopentadiene with the tested amines we found the
following series of decrease in activity depending on
the nature of the organic groups:
H
CH3
+
+
+
_
_
_
NH ...
NH ...
NH...
>
>
CH3
CH3
The higher activating ability of pyridine compared
to other aromatic amines is due apparently to its
structural features: the nitrogen atom in the aromatic
ring exhibits a sufficiently basicity and forms with
cyclopentadiene a stronger complex than other amines.
Of particular interest here is the neutralization of
the pyridine hydrochloride, its treatment and re-use of
pyridine as an activator in the reaction (1) with
cyclopentadiene. To this end, it was necessary to find
an appropriate neutralizing agent to carry out this
reaction effectively. As the neutralizing agent might be
used NaOH, the most common and cost-effective
reagent. However, NaOH is unacceptable for the
C5H5N·HCl decomposition since it reacts simultane-
ously with the admixtures of i-C3H7OH, (C5H5)2Fe,
and others complicating further purification of C5H5N.
Therefore, for the neutralization we used i-C3H7ONa
[reaction (2)]. This allowed the return of the
neutralizing agent into the reaction (2) as 2-propanol,
and excluded decomposition of the present ferrocene
and other compounds. The by-product in the reac-
tion (2) is only NaCl.
On the other hand, the above experimental data
support the hypothesis that, in the exothermic reac-
tion (1) the less stable imide complexes easily decom-
pose into the initial compounds, and the formed cyclo-
pentadiene immediately transforms in dimer, trimer
and polymer, impeding the isolation of ferrocene from
the reaction mixture. Therefore, pyridine is a more
effective activator of cyclopentadiene.
The intermediate imido complex of cyclopenta-
diene and pyridine thus obtained was subsequently
used for the synthesis of ferrocene in the reaction with
anhydrous iron dichloride solvated by anhydrous 2-
propanol, at 30–40°C. After processing the reaction
mixture, the pure ferrocene yield was over 70%.
C5H5N·HCl + 2i-C3H7ONа
H2O
(2)
2C5H5N + 2i-C3H7OH + 2NаCl.
FeCl2·(i-C3H7OH)2 + 2[C5H5NHC5H5–]
i-C3H7OH
(1)
(C5H5)2Fe + 2[C5H5N·HCl].
Thus, we investigated the reaction between the
anhydrous iron dichloride in the form of solvated salt
FeCl2·(i-C3H7OH)2, and cyclopentadiene activated
with pyridine, in anhydrous 2-propanol, as well as a
possibility of obtaining ferrocene in a high yield. We
found that the ferrocene formed in this reaction can be
easily separated from the pyridine hydrochloride, and
the latter after neutralization with sodium isopropoxide
can be returned as an activator to the reaction with
cyclopentadiene, providing effective and waste-free
method of producing ferrocene.
Ferrocene was isolated from the reaction mixture
by extraction with a light fraction of petroleum ether
(bp 40–70°C).
We found that after extraction of the product
obtained in reaction (1) the residue consisted mainly of
pyridine hydrochloride C5H5N·HCl, a small amount of
ferrocene, isopropyl alcohol, 1.2% of pyridine, and
some other compounds which were not unidentified
[5].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011