Ionic liquids and production and use thereof

Details Ionic liquids and production and use thereof Ionic liquids and production and use thereof

2001-10-16

2004-03-09

McKane, Joseph K. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C568S374000

Reexamination Certificate

active

06703507

ABSTRACT:

The present invention relates to novel ionic liquids which are used as media for carrying out chemical reactions, particularly reactions which proceed in the presence of catalysts. The novel ionic liquids are salts of sulfonated or carboxylated triesters of phosphorous acid as anionic constituent and ammonium ions, which may be substituted by organic radicals, as cationic constituent.
Ionic systems which melt at low temperature and are liquid in a range from about room temperature to a few hundred degrees Celsius can be used as reaction media for a wide range of chemical processes. When used in this way, the ionic liquids frequently fulfil a double task: they serve not only as solvent for the reactants but at the same time as catalysts or catalyst components for the reaction of the reactants to form the desired product. The advantages of such a reaction in a homogeneous phase are known. High reaction rates are frequently achieved and the chemoselectivity, regioselectivity, stereoselectivity and entantioselectivity of the reaction can often be controlled simply and precisely. In some cases, the reaction product is not soluble in the reaction medium. In such a case, the ease of separating product, catalyst and starting material is a further advantage.
In another variant of the chemical reaction procedure, use is made of ionic liquids which serve only as solvent for the catalyst and are immiscible with the reactants and the reaction product. In this case, the reaction between the reactants occurs at the phase interface to the catalyst solution and the reaction product forms a phase separate from the catalyst. This process, which can be described as a reaction in two heterogeneous liquid phases, is advantageous whenever the reaction product has to be removed quickly from the reaction mixture so that it does not undergo further reactions. In addition, catalyst and reaction product can be separated from one another under mild conditions, in particular without thermal treatment methods which can lead to damage to the constituents of the reaction mixture. In the case of catalytic reactions which proceed in heterogeneous systems, too, the ionic liquid can not only act as solvent for the catalyst but can itself be a constituent of the catalyst.
Further advantages of ionic liquids are their chemical and thermal stability which make them suitable for a wide range of applications. Owing to their negligible vapor pressure, they emit no vapors and as a result do not contribute to air pollution and are, compared to conventional solvents used as reaction media, remarkably environmentally friendly. Owing to the many advantages indicated, ionic liquids are attracting increasing interest as reactive components or as reaction auxiliaries in numerous industrial syntheses.
According to CHEMTECH, September 1995, pages 26ff, ionic liquids which are liquid at room temperature, e.g. a mixture of 1,3-dialkylimidazolium chloride, preferably 1-n-butyl-3-methylimidazolium chloride ([BMI]
+
[Cl]
−
for short), and aluminum chloride and/or ethylaluminum chloride, are used as nonaqueous solvents for catalysts. As an example of a reaction in which such catalyst solutions are used, the publication cites the dimerization of olefins in the presence of nickel complexes as catalyst, e.g. the dimerization of propene to form isomeric hexenes and the dimerization of butene to form isooctenes. The reaction mixture forms two phases, of which the reaction product forms the upper phase and the lower phase consists of the catalyst solution. After separation of the phases, the catalyst solution can be returned to the process.
Am.Chem.Soc., Div. Pet. Chem. (1992), 37, pages 370ff, discloses the dimerization of propene in the presence of a solution of NiCl
2
.(PR
3
)
2
, (R=i-C
3
H
7
), in a mixture of [BMI]
+
[Cl]
−
and AlCl
3
as ionic liquid.
The use of low-melting phosphonium salts, e.g. tetrabutylphosphonium bromide, as solvent in hydroformylation reactions is described in Journal of Molecular Catalysis, 47 (1988), pages 99ff. Here, the hydroformylation of 1-octene using ruthenium carbonyl complexes in the presence of nitrogen- and phosphorus-containing ligands, e.g. 2,2′-bipyridyl or 1,2-bis(diphenylphosphino)ethane, at from 120 to 180° C. gives a mixture of n-nonanol and n-nonanal containing up to 69% by weight of the alcohol, based on the reaction mixture. A costly distillation is therefore necessary to isolate the desired n-nonanal.
European patent application EP-A-0 776 880 teaches the hydroformylation of olefins in the presence of quaternary ammonium and/or phosphonium salts as solvents for the catalyst. Preference is given to salts containing [BMI]
+
as cation. Salts of quaternary diamines in which the cation has the formula
R
1
R
2
N
⊕
═CR
3
—R
5
—R
3
C═N
⊕
R
1
R
2
where R
1
, R
2
, R
3
are identical or different and are each hydrogen or a hydrocarbon radical having from 1 to 12 carbon atoms and R
5
is an alkylene radical, e.g. methylene, ethylene or propylene, or a phenylene radical, are used in this publication. Suitable anions are, for example, hexafluorophosphate, hexafluoroantimonate, tetrachloroaluminate or tetrafluoroborate. These quaternary ammonium and/or phosphonium salts are liquid below 90° C., preferably below 85° C. and particularly preferably below 50° C.
The hydroformylation catalyst dissolved in these salts comprises cobalt, rhodium, iridium, ruthenium, palladium or platinum as active metal and a tertiary phosphine or tertiary sulfonated phosphine, a tertiary arsine, tertiary stilbene or a phosphite as ligand. The molar ratio of ligand to metal is 9.5.
The catalytically active metals are used as compounds, for example rhodium in the form of dicarbonylrhodium acetylacetonate or rhodium carbonyl Rh
6
(CO)
16
. The hydroformylation catalyst is formed from them under the reaction conditions. The hydroformylation reaction is particularly preferably carried out at from 30 to 90° C.
According to Angew. Chem. 1995, 107, No. 23/24, pages 2941 ff, too, hydroformylation reactions can be carried out using 1,3-dialkylimidazolium salts which are liquid at room temperature as catalyst-containing solvent which is immiscible with the organic reaction mixture. For this purpose, dicarbonylrhodium acetylacetonate is added as catalyst precursor to a solution of triphenylphosphine in [BMI]
⊕
[PF
6
]
; the molar ratio of phosphorus(III) to rhodium can vary from 3 to 10. The catalyst is preformed by means of synthesis gas (volume ratio of hydrogen to carbon monoxide=1:1). 1-Pentene is subsequently reacted with synthesis gas of the same composition at a temperature of 80° C. In this case too, the organic product phase can be separated in a simple manner from the catalyst-containing, nonaqueous ionic liquid by decantation.
The ionic liquids used for dissolving the catalyst in known hydroformylation processes are salts whose anions display no ligand properties toward the catalytically active metal and are therefore not capable of forming complexes. In favorable cases, they are present as inerts in the reaction mixture and do not participate in the reaction. However, it is not impossible for them to have an adverse effect on the reaction, e.g. for them to reduce the reaction rate or decrease the selectivity.
Furthermore, the prior art (cf. Angew. Chem. 1995, 107, p. 2941 and EP-A-0 776 880) states that the molar ratio of ligand/metal, e.g. phosphorus/rhodium, varies in the range from 3 to 10. Higher molar ratios are obviously regarded as unsuitable, although increasing the proportion of ligand, based on the metal, should improve the stability of the catalytically active complex. It is possible that the solubility of the compounds acting as ligands in the hitherto customary ionic liquids is limited, so that they precipitate from the solution when a maximum concentration is exceeded and thus leave the catalyst phase.
EP-A2-0 353 770 describes carrying out catalytic processes in a

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