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Green Chemistry
42
NIKOLAI V. IGNATYEV
URS WELZ-BIERMANN
New ionic liquids with
advanced properties
ABSTRACT
The synthesis of two new classes of ionic liquids with
tris(perfluoroalkyl)-trifluorophospate-anion (FAP-anion)
and bis(perfluoroalkyl)phosphinate-anion, (R F ) 2 P(O)O - ,
are described. Ionic liquids with FAP-anion show superior
hydrolytic stabilities, large electrochemical windows and
relatively low viscosities. Convenient, chloride free
technology for the preparation of ionic liquids with triflate
anion has been developed.
RESULTS AND DISCUSSION
Ionic Liquds are new advanced material
with possible application in various fields
of modern chemistry and technology: new
media for chemical reactions, extractions
processes, conducting materials for energy
storage and conversion devices, metal
deposition, etc. 1 .
Recently Merck KGaA (Darmstadt,
Germany) has developed new ionic liquids with
advanced properties, i.e. high thermal and
electrochemical stability, low viscosity and improved
resistance to hydrolysis.
For example, ionic liquids with
tris(perfluoroalkyl)trifluorophospate-anion (FAP-anion)
show superior stability against hydrolysis in comparison
to hydrolytically unstable PF 6 - 2 .
New Hydrophobic Ionic Liquids
Preparation of the ionic liquids with FAP – anion is based
on the use of tris(perfluoroalkyl)trifluorophosphoric acid
of type (II) or its alkali-metal salts 3,4 .
Scheme 1
Phosphorane (I) can be produced by a
well-established industrial method, the
electrochemical fluorination (ECF) of
phosphines in anhydrous hydrofluoric
acid (HF) 5,6 .
The aqueous solution of acid (II) is stable
at room temperature for a long time and
can be used as a convenient starting
material for the preparation of different
salts containing FAP-anion for
application as a new ionic liquids and
conducting salts, for example:
Scheme 2
The synthesis of room temperature ionic liquids with
FAP–anion can be carried out in water.
Scheme 3
1-Hexyl-3-methylimidazolium FAP (III) is a hydrophobic
room temperature ionic liquid with a very low uptake of
water (max. 2030 ppm) that can easily be obtained with
a low content of chloride and residual water (10-15 ppm).
Comparable values of water uptake for 1-hexyl-3methylimidazolium
bis(trifluoromethylsylfonyl)imde and
1-butyll-3-methylimidazolium PF 6 - are 10670 and
22600 ppm, respectively. HMIM FAP (III) possesses high
hydrolytic stability (no detectable HF formation after 5
hours boiling in water), a large electrochemical window
(more than 5.5 V) and a low viscosity (74.3 mm 2 /s at
20°C, 29.8 at 40°C, 14.8 at 60°C and 8.4 at 80°C).
Water-Soluble Ionic Liquids
The synthesis of water soluble ionic liquids containing the
triflate anion is based on direct alkylation of amines,
phospines or heterocyclic compounds with alkyl-triflates,
CF3SO2OR. The practical synthesis of these very strong
alkylating agents was recently7,8 developed by Merck
KGaA.
Scheme 4
chimica oggi • Chemistry Today • September 2004

In these two processes, alkylcarbonates
serve as non-toxic and cheap sources of
alkyl groups in the preparation of the
alkylating agent CF 3 SO 2 OR 7,8 .
By the reaction of the alkyl-triflates with an
organic base, the corresponding salt is
formed quickly and in nearly quantitative yield 8,9 ,
Triflates are not the only type of stable water soluble ionic
liquids. Recently Merck KGaA has developed new ionic
liquids with bis(perfluoroalkyl)phosphinate-anion,
(R F ) 2 P(O)O - 10 .
REFERENCES
1. R.D. Rogers and K.R. Seddon, Eds., “Ionic Liquids. Industrial
Applications to Green Chemistry”, ACS Symposium Series 818,
American Chemical Society, Washington, DC, 2002.
2. R.P. Swatloski, J.D. Holbrey, R.D. Rogers, Green Chemistry, Vol. 5,
Nr. 4 p. 361-363, (2003).
3. M. Schmidt, U. Heider, W.Geissler, N.V.Ignatyev, V. Hilarius, EP 1
162 204 (Merck KGaA, Darmstadt, Germany).
4. N. V. Ignatyev, M. Schmidt, A. Kuehner, V.Hilarius, U. Heider,
A. Kucheryna, WO 03/002579 (Merck KGaA, Darmstadt,
Germany).
5. N. Ignat’ev, P. Sartori, J. of Fluorine Chem., Vol.103, p. 57-61,
(2000).
Scheme 5
6. U. Heider, V. Hilarius, P. Sartori, N. Ignatiev, WO 00/21969 (Merck
KGaA, Darmstadt, Germany).
7. N. Ignatiev, M. Schmidt, U. Heider, P. Sartori, A. Kucheryna,
WO 02/098844 A1 (Merck KGaA, Darmstadt, Germany).
8. M. Schmidt, N. Ignatiev, U. Heider, P. Sartori, A. Kucheryna,
WO 03/053918 (Merck KGaA, Darmstadt, Germany).
9. N. Ignatiev, U. Welz-Biermann, G. Bissky, H. Willner, Patent
Application 2003 (Merck KGaA, Darmstadt, Germany).
10. N. Ignatiev, U. Welz-Biermann, M. Weiden, A. Kucheryna,
H. Willner WO 03/087110 (Merck KGaA, Darmstadt, Germany).
NIKOLAI V. IGNATYEV AND URS WELZ-BIERMANN
Merck KGaA
New Business-Chemicals
Frankfurter Strasse 250, D-64293, Darmstadt,
Germany
Green Chemistry
chimica oggi • Chemistry Today • September 2004 43