Method for producing aldehydes

Details Method for producing aldehydes Method for producing aldehydes

2001-10-23

2002-10-29

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Oxygen containing

C568S451000

Reexamination Certificate

active

06472565

ABSTRACT:

The present invention relates to a process for preparing aldehydes by reaction of olefins or olefinically unsaturated compounds with hydrogen and carbon monoxide (hydroformylation) in the presence of rhodium or rhodium compounds and a nonaqueous ionic liquid of the formula (Q
+
)
a
A
a−
. In this formula, Q
−
is a singly charged ammonium cation which may be substituted by organic radicals or the equivalent of a multiply charged ammonium cation which may be substituted by organic radicals and A
a−
is the anion of a sulfonated or carboxylated triester of phosphorous acid. a is an integer equal to or greater than 1 and indicates the charge on the anion or the number of cations bearing a charge of +1 in the compounds corresponding to the formula.
Aldehydes are of great economic importance as valuable intermediates in industrial chemistry. They can be used to prepare, for example, alcohols, carboxylic acids and amines which are in turn used as starting materials for producing important end products.
Hydroformylation is among the most widely practiced industrial processes. The reaction is catalyzed by hydridometal carbonyls, preferably of metals of group VIII of the Periodic Table of the Elements. While cobalt was initially used exclusively as catalyst metal in industry, processes using rhodium as catalyst metal are gaining increasing importance.
The preparation of aldehydes by hydroformylation of olefins can be carried out by a single-phase reaction in an organic phase. Here, the catalyst, for example a rhodium/triphenylphosphine complex, is present as a solution in the reaction mixture formed by starting materials and reaction product. An organic solvent, e.g. toluene, xylene or tetrahydrofuran, may additionally be present.
Problems which arise in this process are the separation of the reaction products from the reaction mixture and the recovery of the catalysts which are homogeneously dissolved in the reaction product. This is generally achieved by distilling the reaction product from the reaction mixture. In practice, this route can only be followed in the hydroformylation of lower olefins, e.g. olefins having up to about 5 carbon atoms in the molecule, because of the thermal sensitivity of the aldehydes formed and the resulting formation of by-products with deterioration in the aldehyde yield. In addition, the thermal stressing of the material being distilled can lead to considerable losses of catalyst as a result of decomposition of the catalytically active complexes.
These drawbacks can be avoided if the hydroformylation reaction is carried out in a two-phase system. Such a process is described, for example, in DE-C 26 27 354. This process is characterized by the presence of an organic phase comprising the starting olefins and the reaction product and an aqueous phase in which the catalyst is dissolved. Catalysts used are water-soluble rhodium complexes containing water-soluble phosphines as ligands. The phosphines include, in particular, triarylphosphines, trialkylphosphines and arylated or alkylated disphosphines whose organic radicals are substituted by sulfonic acid groups or carboxyl groups. Their preparation is known from, for example, DE-C 26 27 354.
The two-phase hydroformylation process carried out in the presence of an aqueous catalyst-containing phase is particularly useful in the hydroformylation of lower olefins, particularly in the case of ethylene and propylene. On the other hand, if higher olefins such as hexene, octene or decene are used, the conversion is decreased considerably. The decrease in the conversion may well be attributable to the reduction in the solubility of higher olefins in water, since it is assumed that the reaction between the reactants occurs in the aqueous phase. This hypothesis is supported by the fact that the olefins conversion is significantly increased when a phase transfer reagent (solubilizer) is added to the aqueous catalyst solution. According to EP-B 0 562 451, solubilizers which have been found to be particularly useful are cationic solubilizers of the formula [A-N(R
1
R
2
R
3
)]
+
E
−
, where A is a straight-chain or branched alkyl radical having from 6 to 25 carbon atoms, R
1
, R
2
, R
3
are identical or different and are straight-chain or branched alkyl radicals having from 1 to 4 carbon atoms and E
−
is an anion, in particular sulfate, tetrafluoroborate, acetate, methosulfate, benzenesulfonate, alkylbenzenesulfonate, toluene-sulfonate, lactate or citrate.
Carrying out the hydroformylation process in a two-phase system in the presence of an aqueous catalyst-containing phase requires not only sufficient solubility of the olefin in the aqueous phase but also sufficient stability of the olefin to be reacted toward water. Water-sensitive olefins such as acrylic esters or unsaturated acetals can thus not be used successfully in this process.
To overcome the disadvantage indicated without having to give up the advantage of the two-phase hydroformylation process, the use of nonpolar perfluorinated hydrocarbons, e.g. perfluoromethyl-cyclohexane, as nonaqueous phase immiscible with the organic reaction product has been proposed for the catalytic hydroformylation of olefins. However, specific fluorinated ligands, for example tris(1H, 1H, 2H-perfluorooctyl)phosphine are necessary to dissolve the rhodium complexes in the perfluorinated hydrocarbons (
Science
1994, 266, 72).
Another way of carrying out catalytic reactions in a nonaqueous two-phase system is described in
CHEMTECH,
September 1995, pages 26 to 30. According to this reference, nonaqueous 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]
+
[C1]
−
for short), and aluminum chloride and/or ethylaluminum dichloride are used as solvents for the catalyst. Examples of reactions carried out using such catalyst solutions are olefin dimerization in the presence of nickel complexes, e.g. dimerization of propene to form isomeric hexanes or dimerization of butene to form isooctenes. In these reactions, the reaction product is obtained as an upper phase, while the catalyst-containing nonaqueous ionic liquid forms the lower phase and can be isolated by simple phase separation. The solution of the catalyst in the nonaqueous ionic liquid can be reintroduced into the process.
Am. Chem. So., Div. Pet. Chem.
1992, 37, pages 780 to 785, discloses that a nonaqueous ionic liquid comprising [BMI]
+
[C1]
−
and aluminum chloride is used as a solvent in which, after addition of ethylaluminum dichloride and NiC1
2
(PR
3
)
2
, where R is isopropyl, the dimerization of propene is carried out.
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 99-116. According to this reference, the hydroformylation of olefins, e.g. 1-octene, is carried out using ruthenium carbonyl complexes in the presence of nitrogen- or phosphorus-containing ligands, e.g. 2,2′-bipyridyl or 1,2-bis(diphenylphosphino)ethane, at temperatures of from 120 to 180° C. to give a mixture of n-nonanol and n-nonanal. In this process, a reaction mixture having an n-nonanol content of up to 69% by weight, based on the reaction mixture, is obtained. The isolation of the desired n-nonanal therefore requires a considerable outlay for distillation.
European patent application EP-A-0 776 880 discloses 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
&THgr;
=CR
3
−R
5
−R
3
C=N
&THgr;
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 alkyle

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