(325g) High-Pressure Phase Behavior of Ternary Systems Containing Ionic Liquids + Carbon Dioxide + Organometallic Compounds

It is expected that future
chemical engineering processes will use more environmentally benign solvents as
reaction and separation media. For instance, a new method has been recently
developed based on miscibility switch phenomena, in which reactions and
separations are carried out efficiently in one step in presence of alternative
solvents i.e., ionic liquids (ILs) and supercritical carbon dioxide (scCO₂)[1].
In this process, the reaction
can be performed in a homogenous phase, which location depends on pressure,
temperature and CO₂ concentration. After the completion of the
reaction, changing the conditions results in a multi-phase system in which one
of the phases is substantially free of IL from which the product can be
recovered.

      It is our aim to apply the above-mentioned
process set-up on the production of acetylferrocene (AcF), which can be synthesized
from ferrocene (Fc) by the Friedel-Crafts reaction [2]. This reaction has been identified as playing a significant role
in many applications of organometallic chemistry and materials science, and in asymmetric and electro-catalysis [3,4].
Conventionally, this reaction is carried out in toxic and volatile organic compounds
such as dichloromethane or carbon disulfide, resulting in environmental
and human health risks [5]. Moreover, corrosion issues and
considerable quantities of harmful waste can be confronted depending on the
Lewis acid used as catalyst. Recently,
comprehensive investigation of the acetylation of Fc to AcF was conducted in
the presence of ILs as solvent instead of the conventional organic solvents [6].
The promising results showed that up to 100% conversion and up to a 100% yield could
be reached using imidazolium-based ILs as solvents with scandium
triflate as the catalyst. Here, we intend to add scCO₂ to carry out
the reaction at a higher rate in a homogeneous phase, and use the scCO₂
subsequently as separation medium.

In order
to determine the operational conditions for applying the new process, accurate
phase behaviour data are essential. Currently, phase behavior data for systems consisting of Fc or AcF in presence
of ILs and/or scCO₂are not available in the literature. The aim of this work is to measure the binary and ternary solubility data
of the above-mentioned metal compounds in scCO₂
and ILs.

The phase behavior of the binary system consisting of Fc/AcF + scCO₂
was measured by using an analytical method with a quasi-flow apparatus at (308, 318, 328,
338 and 348) K and pressures between (8 and 24). High-performance liquid
chromatography (HPLC) was applied through an online sampling to determine the solubility
of Fc/AcF in the scCO₂ [7].

Ternary phase behavior data of systems
containing Fc/AcF + [bmim][Tf₂N] + CO₂
were determined experimentally by a synthetic method using the Cailletet
apparatus. This equipment allows measurements of phase equilibria within a
pressure range of (0.1 to 15 MPa) and temperatures from (255 to 470 K)
depending on the heat transferring fluid used. Using a Cailletet apparatus, it
is possible to keep temperature (or pressure) at desired values, and the
pressure (or the temperature) is varied until a phase change is visually
observed for a sample with a constant overall composition [8].

The solubility of Fc and AcF at 308
K is investigated. The experimental molar solubility of the product AcF in scCO₂
ranged from 2.5 to 44.5 · 10^-4 at 308 K, which is sufficiently high
for separation using the new process set-up. Moreover, it can be noticed that
the solubility of the product AcF in scCO₂ is higher than the
solubility of the reactant Fc in scCO₂, indicating that it is suitable
solvent for separation. Results at other temperatures and the existence of a
crossover area will be presented.

Phase behavior measurements of binary and ternary systems
consisting of the organometallic compounds AcF and Fc in combination with ILs
and CO₂ have been carried out. The solubility of AcF and Fc in CO₂
ranges from 2.5 to 44.5 · 10^-4, and from 8.9 to 15.6 · 10^-4,
at 308 K, respectively. The results of the ternary Fc + [bmim][Tf₂N]
+ CO₂ system shows  crystallizing
the Fc in lower temperatures. The results are used to find the optimal
operating conditions for the reaction of Fc into AcF in IL + CO₂
systems and for the subsequent separation. References

[1] M. C. Kroon, et. al., International
Patent WO 2006/088348 A1, (2006)

[2] R. Ojani, J. B. Raoof,B.  Norouzi, Electroanalysis, 20 (12), 1378-1382,
(2008)

[3] R. Gomez, et. al., Angew. Chem. Int. Ed., 45, 7674-7715, (2006)

[4] Z. Gao, et. al., Appl. Organomet. Chem., 19, 1149-1154,
(2005)

[5] R. J. Hu, et. al.,  Tetrahedron Letters., 49, 387-389,
(2008)

[6] S. Berardi, et. al., J.  Org. Chem., 693,
3015?3020, (2008)

[7] H. Perrotin-Brunel, et. al., J. Supercrit. Fluids, 52, 6-10 (2010)

[8] S. Raeissi and Cor J. Peters, J. of Supercritical Fluids, 35, 10?17
(2005)