1. Process for preparing for preparing ,-unsaturated carboxylic acids or salts thereof, characterized in that it has a process step in which a substance of the formula (I) ELn O O R (I) where E = element of group 4, 6, 7, 8, 9 or 10 of the Periodic Table of the Elements, L = nitrogen- or phosphorus-containing ligand, n = 1 to 4, preferably 1, R = H or an aryl or alkyl radical, is reacted in a solvent in the presence of a halide, wherein the compound of the formula (I) is obtained by reaction of a complex of the formula (II) ELn (II) where E, L and n are as defined above, with an olefin and carbon dioxide, and the process is carried out without isolation of the compound of the formula (I).

2. Process according to Claim 1, characterized in that R in formula (I) is H or an alkyl radical having from 1 to 10 carbon atoms.

3. Process according to Claim 1 or 2, characterized in that R in formula (I) is H or a methyl radical, preferably H.

4. Process according to any of Claims 1 to 3, characterized in that E in formula (I) is nickel.

5. Process according to Claim 1 or 4, characterized in that L is a bidentate ligand.

6. Process according to at least one of Claims 1 to 5, characterized in that L is a bisphosphane or bisphosphonate ligand. 14

7. Process according to at least one of Claims 1 to 6, characterized in that L is a ligand selected from among bis(di-tert-butylphosphino)ethane, bis(dicyclohexylphosphino)ethane or bis(diphenylphosphino)ethane.

8. Process according to at least one of Claims 1 to 7, characterized in that the halide is an iodide.

9. Process according to at least one of Claims 1 to 8, characterized in that the halide is selected from among NaI, LiI and (nBu)4NI.

10. Process according to at least one of Claims 1 to 9, characterized in that the solvent is selected from among cyclic ethers, chlorinated aromatics and aliphatic chlorinated hydrocarbons, particularly preferably chloroform, chlorobenzene and dichloromethane.

11. Process according to Claim 1, characterized in that propene or ethene, preferably ethene, is used as olefin.

12. Use of a composition containing E, an ,-unsaturated carboxylic acid or a salt thereof, and halide ions, with E as defined in one of the preceding claims, for producing superabsorbent materials or as monomer composition for preparing polymers.

13. Use according to Claim 12, characterized in that the ,-unsaturated carboxylic acid or salt thereof is acrylic acid or methacrylic acid or a salt thereof, preferably acrylic acid or a salt thereof.

14. Use according to Claim 12 or 13, characterized in that the proportion of iodide ions is from 20 to 1000 mol%, based on 100 mol% of E.

15. Use according to any of Claims 12 to 14, characterized in that the proportion of the unsaturated carboxylic acid or salt thereof is from 2 to 100% by weight based on the composition minus the amount of halide ions, solvent, E and L, with L defined as in one of the preceding claims.

The present invention relates to a process for preparing ,-unsaturated carboxylic acids (e.g. acrylic or
methacrylic acid) or a salt of the ,unsaturated carboxylic acids, which has a process step in which a
complex is reacted in a solvent in the presence of a halide, a composition comprising ,-unsaturated
carboxylic acids or a salt thereof and also halide ions and the use of these compositions for producing
superabsorbent materials or as monomer composition for preparing polymers, e.g. polymethyl
methacrylate.
To reduce gases which damage the climate, e.g. carbon dioxide, numerous processes in which CO2 is
used as raw material for producing wanted chemical products have been developed recently. One process
is, for example, the preparation of acrylates by reaction of carbon dioxide with olefins in the presence of a
nickel-bisphosphine catalyst and a base, as described by Michael L. Lejkowski et al., "The First Catalytic
Synthesis of an Acrylate from CO2 and an Alkene - A Rational Approach", Chem. Eur. J. 2012; Wiley-VCH
Verlag GmbH&Co. KGaA, Weinheim; Wiley Online Library; DOI: 10.1002/chem.201201757. The catalysis
cycle presented comprises the steps of reaction of an olefin complex with CO2 to form the lactone complex,
conversion of the lactone complex into the acrylate complex and subsequent replacement of the acrylate
ligand with the olefin ligand to give the olefin complex. Strong bases such as sodium butoxide or NaOH are
used in the conversion of the lactone complex into the acrylate complex. A disadvantage of the use of
these strong bases is that in a CO2 atmosphere they tend to react with the carbon dioxide to form
carbonates and are thus no longer available for the catalytic reaction. Relatively complicated engineering
measures in which the catalysis cycle is divided into a CO2-rich part and a low-CO2 part have to be
undertaken in order to avoid this secondary reaction. In the CO2-rich part, the reaction of the olefin complex
with CO2 to form the lactone complex is carried out. In the low-CO2 part, the conversion of the lactone
complex into the acrylate complex and subsequently the replacement of the acrylate ligand with the olefin
ligand are carried out. This sequential approach leads, apart from the high outlay to significant slurry of the
reaction since the catalytic process is achieved only stepwise.
As early as in WO 2011/107559, Limbach et al., who was also involved as author in the abovementioned
publication, described processes for preparing an alkali metal salt or alkaline earth metal salt of an
α,β-ethylenically unsaturated carboxylic acid, in which a) an alkene, carbon dioxide and carboxylation
catalyst are reacted to form an alkene/carbon dioxide/carboxylation catalyst adduct, b) the adduct is
decomposed by means of an auxiliary base with liberation of the carboxylation catalyst to form the auxiliary
base salt of the α,β-ethylenically unsaturated carboxylic acid, c) the auxiliary base salt of the
α,β-ethylenically unsaturated carboxylic acid is reacted with an alkali metal base or alkaline earth metal
2
base to liberate the auxiliary base and form the alkali metal salt or alkaline earth metal salt of the
α,β-ethylenically unsaturated carboxylic acid.
As auxiliary bases, WO 2011/107559 mentioned, for example, anion bases such as salts with inorganic or
organic ammonium ions or alkali metals or alkaline earth metals or neutral bases, where inorganic anion
bases can be, inter alia, carbonates, phosphates, nitrates or halides and organic anion bases can be, inter
alia, phenoxides, carboxylates, sulphates of organic molecular moieties, sulphonates, phosphates,
phosphonates and organic neutral bases can be, inter alia, primary, secondary or tertiary amines, also
ethers, esters, imines, amides, carbonyl compounds, carboxylates or carbon monoxide. Preference is
given to using a primary, secondary or tertiary amine, particularly preferably a tertiary amine, as auxiliary
base.
A disadvantage of the use of amines as auxiliary bases is that the auxiliary bases have to be removed
again in one or more steps. This preferably occurs using alkali metal carbonates, alkali metal hydroxides or
oxides, preferably sodium hydroxide.
A further publication by Bernskoetter et al. "Lewis Acid Induced β-Elimination from a Nickelalactone: Efforts
toward Acrylate Production from CO2 and Ethylene“ (Organometallics, 2013, DOI: 10.1021/om400025h)
describes the synthesis of acrylates using strong (Lewis) acids such as tris(pentafluorophenyl)borane. This
compound was used in the study group in order to achieve additional activation of the nickelalactone. This
enables the ring to be opened and the acrylate finally to be bound to the complex. A disadvantage is the
use of tris(pentafluorophenyl)borane. The route to these compounds is complicated and not ensured on a
large industrial scale. In addition, the reaction was carried out stepwise and the nickelalactone complex
required for the reaction was synthesized separately beforehand. The complete catalysis cycle was thus
not carried out.
It was an object of the present invention to provide a process for preparing ,-unsaturated carboxylic
acids such as (meth)acrylates from olefins and CO2, which process avoids one or more disadvantages of
the existing processes of the prior art.
It has surprisingly been found that the addition of salts from the group of alkali metal halides to the reaction
mixture likewise enables the above-described reaction to be catalysed. It was found here that simple
halides, in particular iodides such as lithium iodide, sodium iodide or also potassium iodide, can function as
Lewis acid in order to destabilize or cleave the nickelalactone formed.
3
An advantage over the method of Limbach et al. is, in particular, that all iodides used have only a low
basicity and no binding of CO2 to form carbonates, as is the case for strong bases (e.g. sodium butoxide or
lithium hexamethyldisilazane (LiHMDS)), thus occurs. Compared to the above-described Lewis acid
tris(pentafluorophenyl)borane, the halides used are more readily available and simpler to handle even
when large amounts are used. Since the compounds are also stable over a relatively wide temperature
range, the salts can be separated off and reused more easily.
In addition, simple ammonium iodides such as tetrabutylammonium iodide are also suitable for the
reaction. Last but not least, the use of sodium iodide as salt and Lewis acid can lead directly to formation of
sodium acrylate, and intermediate for the synthesis of superabsorbents.
The process of the invention has, in particular, the advantage that the synthesis of ,-unsaturated
carboxylic acids or salts thereof can be carried out directly from the starting materials olefin and CO2
without isolation of specific intermediates.
The process of the invention, the composition of the invention and the use thereof are described by way of
example below without the invention being intended to be restricted to these illustrated embodiments.
Where ranges, general formulae or classes of compounds are indicated below, these are intended to
encompass not only the corresponding ranges or groups of compounds which are explicitly mentioned but
also all subranges and subgroups of compounds which can be obtained by leaving out individual values
(ranges) or compounds. Where documents are cited in the present description, the contents thereof, in
particular with regard to the subjects referred to, are fully incorporated by reference into the disclosure
content of the present invention. Where percentages are indicated in the following, these are, unless
indicated otherwise, % by weight. Where averages are indicated below, these are, unless indicated
otherwise, the number average. Where material properties such as viscosities or the like are indicated
below, these are, unless indicated otherwise, the material properties at 25°C. Where chemical (empirical)
formulae are used in the context of the present invention, the indices indicated can be both absolute
numbers and averages. In the case of polymeric compounds, the indices are preferably averages. If the
term “(meth)acrylic acid" or (meth)acrylate is used in the present patent application, this encompasses both
methacrylic acid and acrylic acid or both methacrylate and acrylate.
The process of the invention for preparing ,-unsaturated carboxylic acids or a salt of the ,-unsaturated
carboxylic acids, preferably (meth)acrylic acid or a salt of (meth)acrylic acid, preferably acrylic acid or a salt
of acrylic acid, is characterized in that it has a process step in which a substance of the formula (I)
4
(I)
where
E = element of group 4, 6, 7, 8, 9 or 10 of the Periodic Table of the Elements, preferably nickel,
L = nitrogen or phosphorus-containing, preferably bidentate phosphorus ligand,
n = 1 to 4, preferably 1,
R = H or an aryl or alkyl radical, preferably H or a branched or unbranched alkyl radical having from 1 to 10
carbon atoms, particularly preferably H or a methyl group and very particularly preferably H,
is, preferably as an intermediate (or temporarily), reacted in a solvent in the presence of a halide, preferably
selected from the group consisting of alkali metal halides, alkaline earth metal halides and ammonium
halides. Preference is given to using NaI, LiCl, LiI and (nBu)4NI as halides. Particular preference is given to
using iodides, in particular NaI and/or LiI, as halides.
L in the process of the invention is preferably a ligand selected from among phosphanes and
phosphonates, preferably bisphosphanes and bisphosphonates, preferably selected from among
trialkylbisphosphane, dialkylarylbisphosphane, alkyldiarylbisphosphane and triarylbisphosphane ligands. L
is very particularly preferable selected from among bis(dicyclohexylphosphino)ethane (dcpe), bis(di-tertbutylphosphino)
ethane and bis(diphenylphosphino)ethane.
As solvent, it is possible to use all known solvents, the solvent is preferably selected from among
halogenated hydrocarbons, halogenated aromatics and cyclic ethers, preferably chlorobenzene or
dichloromethane or tetrahydrofuran. Particular preference is given to using chloroform, dichloromethane or
chlorobenzene, preferably chlorobenzene, as solvent.
In the process of the invention, the process step is very particularly preferably carried out by reacting a
substance of the formula (I) in which E = nickel (Ni0), n = 1, L = bis(diphenylphosphino)ethane or
bis(dicyclohexylphosphino)ethane in a solvent, preferably chlorobenzene, dichloromethane or
tetrahydrofuran, preferably chlorobenzene, in the presence of an iodide selected from among NaI, LiI and
(nBu)4NI.
The reaction can be carried out at atmospheric pressure or superatmospheric pressure. The reaction of
the compound of the formula (I) (the nickelalactone) is preferably carried out at partial pressures of from 1
to 50 bar of CO2 and from 1 to 50 bar of the respective olefins.
5
The reaction can be carried out at any desired temperature. The reaction is preferably carried out at a
temperature of from 0 to 150°C, preferably from 15 to 100°C and particularly preferably at a temperature of
from 25 to 60°C.
The molar ratio of halide ions to element E is preferably from 0.1 : 1 to 50 : 1, more preferably from 1 : 1 to
20 : 1.
It can be advantageous for the substance of the formula (I) to be obtained by reaction of a complex of the
formula (II)
ELn (II)
where E, L and n are as defined above, with an olefin and carbon dioxide. As olefins, preference is given to
using hydrocarbons which have at least one unsaturated carbon-carbon bond. Hydrocarbons which have
from 1 to 10 carbon atoms are preferably used as olefins. Particular preference is given to using ethene or
propene as olefins, with very particular preference being given to ethene.
This reaction can, for example, be carried out as described in Michael L. Lejkowski et al., "The First
Catalytic Synthesis of an Acrylate from CO2 and an Alkene - A Rational Approach", Chem. Eur. J. 2012;
Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim; Wiley Online Library; DOI: 10.1002/chem.201201757. In
addition, a simple method of preparing the compound of the formula (I) may be found in an article by Heinz
Hoberg und Dietmar Schäfer "Nickel(0)-induzierte C-C-Verknüpfung zwischen Kohlendioxid und Ethylen
sowie Mono- oder Di-substituierte Alkenen" J. Organomet. Chem. 1983, 251, C51-C53 (Elsevier Sequoia).
For the preparation of the compound of the formula (I), preference is given to using
(1,5-cyclooctadiene)2nickel (Ni(cod)2) and dissolving this together with ligand L, preferably
1,2-bis(dicyclohexylphosphino)ethane, bis(di-tert-butylphosphino)ethane or bis(diphenylphosphino)ethane,
in tetrahydrofuran. Olefin, preferably ethene or propene, more preferably ethene, and CO2 are
subsequently added. The molar ratio of the compounds relative to one another is complex of the formula
(II) : CO2 : olefin, preferably ethene, = 1 : 1 : 5. After removal of tetrahydrofuran, the compound of the
formula (I) can be obtained as yellow-green compound in a yield of 50%.
The substance of the formula (I) is preferably prepared by direct reaction of a catalyst precursor of the
element E with a preferably bidentate phosphane or phosphonate ligand in a halogenated solvent or cyclic
ether in a CO2/olefin atmosphere, preferably a CO2/ethene or CO2/propene atmosphere, more preferably
in a CO2/ethene atmosphere.
6
Particular preference is given to reacting a complex of the formula (II) in which E = nickel (Ni0), n = 2 and
L = bis(diphenylphosphino)ethane or bis(dicyclohexylphosphino)ethane, preferably bis(dicyclohexylphosphino)
ethane, with an olefin, preferably ethene or propene, more preferably ethene, and carbon dioxide in
a molar ratio of 10/40 at from 1 to 75 bar, preferably from 30 to 60 bar, more preferably about 50 bar, in
chlorobenzene, dichloromethane or tetrahydrofuran, preferably chlorobenzene, at from 30 to 60°C.
The process of the invention makes it possible to obtain the compositions of the invention, which comprise
halide ions and ,-unsaturated carboxylic acid, preferably (meth)acrylic acid, particularly preferably acrylic
acid or salts thereof (with alkali metal ions, alkaline earth metal ions or ammonium ions), in particular the
compositions according to the invention described below.
The compositions of the invention containing the ,-unsaturated carboxylic acid or a salt thereof are
characterized in that they comprise halide ions, preferably iodide ions. The proportion of halide ions,
preferably iodide ions, is preferably from 20 to 1000 mol%, more preferably from 50 to 500 mol%, based
on the substance of the formula (I).
In the case of compositions according to the invention which have been obtained by a process according
to the invention in which the substance of the formula (I) is not isolated, the compositions of the invention
also comprise ,-unsaturated carboxylic acid or a salt thereof and a halide ion, preferably iodide ions. The
proportion of halide ions, preferably iodide ions, is preferably from 50 to 5000 mol%, more preferably from
100 mol% to 500 mol%, based on E. In this process, preference is given to using ligands L which are
selected from the group consisting of bis(dicyclohexylphosphino)ethane and bis(di-tertbutylphosphino)
ethane (dtBupe). The content of E can be determined by known suitable analytical
methods. When E is, for example, nickel, the nickel content can, for example, be determined by means of
atomic absorption spectrometry (AAS) at 232.0 nm, e.g. as described in Welz, B.; Sperling, M.,
Atomabsorptionsspektrometrie, Wiley-VHC: Weinheim, (1997); p. 565. The halide determination can be
carried out by known suitable analytical methods. The determination of chloride, iodide and bromide is
preferably carried out by the "Volhard titration" method, as is described in known chemistry textbooks.
The compositions of the invention, in particular those containing acrylic acid or salts thereof, can, for
example, be used for producing superabsorbent materials or as monomer compositions for preparing
polymers. The preparation of such polymers or superabsorbent materials is described, for example, in the
book "Modern Superabsorbent Polymer Technology", John Wiley & Sons; edition: 1st edition
(11 December 1997), ISBN-13: 978-0471194118.
7
The compositions of the invention, in particular those containing methacrylic acid or salts thereof, can be
used, for example, for preparing polymethyl methacrylates and semifinished parts or plates produced
therefrom.
The present invention is described by way of example in the following examples without the invention,
whose scope is indicated by the total description and the claims, being restricted to the embodiments
mentioned in the examples.
8
Examples:
Measurement methods:
1H-, 13C- and 31P-NMR spectra were recorded at room temperature by means of an NMR spectrometer
(Avance III, 400 MHz, from Bruker). All spectra were referenced by means of TMS or by means of the
solvent peak of the deuterated solvent. Infrared measurements were recorded using an IR spectrometer
(2000 FT-IR, from Perkin-Elmer). Acrylic acid was detected by means of GC using a gas chromatograph
Shimadzu GC-2010 (from Shimadzu) and a CP-Wax (ffap) cb column (from Agilent).
Example 1: Preparation of a substance of the formula (I) for decomposition experiments
In a glass flask, 300 mg (1.21 mmol) of tetramethylethylenediaminenickelalactone were dissolved in 15 ml
of tetrahydrofuran and admixed with 488.8 mg (1.23 mmol) of diphenyldiphosphinoethane under an inert
gas atmosphere. The yellow suspension was subsequently stirred at 22°C for 16 hours. The solvent was
subsequently removed under reduced pressure and the remaining yellow solid was washed 5 times
with10 ml of tetrahydrofuran. The product was subsequently dried under reduced pressure.
Example 2: In situ generation of a substance having the formula (I) for catalytic experiments with
simultaneous conversion into acrylic acid
In a 4 ml reaction vessel provided with a magnetic stirrer, 13.5 mg (0.049 mmol) of (1,5-
cyclooctadiene)2nickel (Ni(cod)2), 0.049 mmol of the respective ligand (1 equivalent) and
0.25 mmol (5 equivalents) of halide salt were admixed with 2 ml of solvent and the mixture was
subsequently placed in an autoclave. The pressure in the autoclave was set to 10 bar of
ethylene. After one hour, the pressure was set to 50 bar of CO2 and the system was heated to
50°C. After 96 hours, the pressure was released and the mixture of substances was analysed.
For this purpose, the reaction was stopped by addition of 0.02 ml of trifluoroacetic acid and
unreacted nickelalactone was converted into free propionic acid. The reaction mixture was
dissolved in 1.0 ml of tetrahydrofuran and admixed with 1 mg of acetic acid in 0.5 ml of
tetrahydrofuran (internal standard). The mixture was subsequently filtered through silica gel and
analysed by means of GC and NMR.
Example 3: Reaction of a substance of the formula (I) in a solvent in the presence of a
halide
In a reaction vessel having a total volume of 2 ml, 5.3 mg (0.125 mmol) of lithium chloride were added to a
solution consisting of 1 ml of dichloromethane (DCM) and 13.3 mg (0.025 mmol) of
(diphenylphosphinoethane)Ni(C3H4O2) (I) under an inert gas atmosphere. The mixture was subsequently
9
stirred at 22°C for 20 hours. The mixture of substances was subsequently worked up and analysed as per
Example 2.
Further studies on the decomposition reaction were carried out in a manner analogous to
Example 3 with variation of salt and solvent at 50°C, as per Table 1. The results for the
decomposition reaction of the substance of the formula (I) in which E = nickel (Ni0), n = 1,
L = bis(diphenylphosphino)ethane when using different salts and solvents are shown in Table 1.
Table 1: Variation of the solvent and of the salts at 50°C as per Example 3.
Complex Salt Solvent T
(°C)
Acrylate
(%)a
(I) LiCl THF 50 17
DMF 50 13
(I) LiBr THF 50 4
(I) LiI THF 50 16
MeOH 50 7
DMF 50 32
CHCl3 50 74
Propylene carbonate 50 4
Toluene 50 47
(I) LiOTf DMF 50 18
(I) NaI THF 50 19
DMF 50 30
(I) NaCl THF 50 5
(I) NaBr THF 50 6
(I) KCl THF 50 5
(I) KBr THF 50 5
(I) KI THF 50 16
DMF 50 31
(I) NaOTf THF 50 12
DMF 50 39
(I)
KOTf THF 50 9
DMF 50 32
(I) LiB(C6F5)4 50
a Relative GC peaks were determined by correlation between acrylate and propionate using
acetic acid as internal standard.
10
Further studies on the decomposition reaction were carried out in a manner analogous to
Example 3 with variation of salt and solvent at 22°C, as per Table 2. The results for the
decomposition reaction of the substance of the formula (I) in which E = nickel (Ni0), n = 1,
L = bis(diphenylphosphino)ethane when using various salts and solvents are shown in Table 2.
Table 2: Variation of the solvent and of the salts at 22°C as per Example 3.
Complex Salt Solvent T
(°C)
Acrylate
(%)a
(I) LiCl THF 22 4
DMF 22 4
(I) LiBr CHCl3 22 40
Toluene 22 3
(I) LiI THF 22 7
MeOH 22 4
DMF 22 27
MeCN 22 5
Toluene 25 12
Chlorobenzene 22 3
Acetone 22 3
Et2O 22 4
CHCl3 22 68
Propylene carbonate 22 2
(I) LiOTf DMF 22 24
THF 22 3
(I)
(I) LiPF6 DMF 22 26
(I) NaI THF 22 7
CHCl3 22 2
(I) TBAI DMF 22 29
a Relative GC peaks were determined by correlation between acrylate and propionate using
acetic acid as internal standard.
Further studies on the decomposition reaction were carried out in a manner analogous to
Example 3 with variation of salt and solvent at 100°C, as per Table 3. The results for the
11
decomposition reaction of the substance of the formula (I) in which E = nickel (Ni0), n = 1,
L = bis(diphenylphosphino)ethane when using different salts and solvents are shown in Table 3.
Table 3: Variation of the solvent and of the salts at 100°C as per Example 3.
Complex Salt Solvent T
(°C)
Acrylate
(%)a
(I) LiI Toluene 100 56
(I) LiBr Toluene 100 35
(I) NaI Toluene 100 5
a Relative GC peaks were determined by correlation between acrylate and propionate using
acetic acid as internal standard.
In the experiments at elevated temperature, it was found that the best results can be achieved using
halide-containing salts, in particular iodides, while only low yields of acrylates were obtained using the
triflates (OTf) used for comparison. Here, only halide-free solvents such as alcohols or ethers such as
tetrahydrofuran were used.
Further studies on the decomposition reaction were carried out in a manner analogous to Example 3 with
variation of the salt at 22°C, as per Table 4. The results for the decomposition reaction of the substance of
the formula (I) in which E = nickel (Ni0), n = 1, L = bis(diphenylphosphino)ethane when using various salts
and dichloromethane (DCM) are shown below.
Table 4: Variation of the salts in dichloromethane at 22°C as per Example 3.
Starting
material
Salt Solvent T
(°C)
Acrylate
(%)a
(I) LiCl DCM 22 3
(I) LiI DCM 22 65
(I) NaI DCM 22 4
(I) NaOTf DCM 22 4
(I) TBAI DCM 22 68
(I) LiOTf DCM 22 2
(I) Li2CO3 DCM 22 6
(I) LiB(C6F5)4 DCM 22 2
a Relative GC peaks were determined by correlation between acrylate and propionate using
acetic acid as internal standard.
12
In the experiments, the particular suitability of halides, in particular iodides, becomes clear. Thus, high
acrylate yields could be achieved even at room temperature by the use of lithium iodide or
tetrabutylammonium iodide (TBAI). In addition, halogenated solvents are preferred for the reaction.
Owing to the poor suitability of dichloromethane as solvent in large-scale industrial applications,
experiments using chlorobenzene as solvent were carried out in situ.
Experiments on the in situ formation of acrylic acid from the starting materials were carried out in a manner
analogous to Example 2, as per Table 5. The corresponding intermediate (I) was in this case not isolated
but converted directly into the acrylate by addition of the halide.
Table 5: Variation of the salts in chlorobenzene at 50°C for the in situ experiments as per
Example 2.
Catalyst Ligand Salt Acrylate
(%)a
Ni(cod)2 dtBupe LiCl 2
Ni(cod)2 dtBupe LiI 6
Ni(cod)2 dcpe LiI 80
a Relative GC peaks were determined by correlation between acrylate and propionate using
acetic acid as internal standard.
It can be seen from the results in Table 5 that direct reaction of ethylene and CO2 via the intermediate (I)
formed in situ is possible in the presence of lithium chloride and lithium iodide in halogenated solvents.

We Claim:
1. Process for preparing for preparing ,-unsaturated carboxylic acids or salts thereof, characterized
in that it has a process step in which a substance of the formula (I)
ELn O O
R
(I)
where
E = element of group 4, 6, 7, 8, 9 or 10 of the Periodic Table of the Elements,
L = nitrogen- or phosphorus-containing ligand,
n = 1 to 4, preferably 1,
R = H or an aryl or alkyl radical,
is reacted in a solvent in the presence of a halide, wherein the compound of the formula (I) is
obtained by reaction of a complex of the formula (II)
ELn (II)
where E, L and n are as defined above,
with an olefin and carbon dioxide, and the process is carried out without isolation of the compound of
the formula (I).
2. Process according to Claim 1, characterized in that R in formula (I) is H or an alkyl radical having
from 1 to 10 carbon atoms.
3. Process according to Claim 1 or 2, characterized in that R in formula (I) is H or a methyl radical,
preferably H.
4. Process according to any of Claims 1 to 3, characterized in that E in formula (I) is nickel.
5. Process according to Claim 1 or 4, characterized in that L is a bidentate ligand.
6. Process according to at least one of Claims 1 to 5, characterized in that L is a bisphosphane or
bisphosphonate ligand.
14
7. Process according to at least one of Claims 1 to 6, characterized in that L is a ligand selected from
among bis(di-tert-butylphosphino)ethane, bis(dicyclohexylphosphino)ethane or
bis(diphenylphosphino)ethane.
8. Process according to at least one of Claims 1 to 7, characterized in that the halide is an iodide.
9. Process according to at least one of Claims 1 to 8, characterized in that the halide is selected from
among NaI, LiI and (nBu)4NI.
10. Process according to at least one of Claims 1 to 9, characterized in that the solvent is selected from
among cyclic ethers, chlorinated aromatics and aliphatic chlorinated hydrocarbons, particularly
preferably chloroform, chlorobenzene and dichloromethane.
11. Process according to Claim 1, characterized in that propene or ethene, preferably ethene, is used as
olefin.
12. Use of a composition containing E, an ,-unsaturated carboxylic acid or a salt thereof, and halide
ions, with E as defined in one of the preceding claims, for producing superabsorbent materials or as
monomer composition for preparing polymers.
13. Use according to Claim 12, characterized in that the ,-unsaturated carboxylic acid or salt thereof is
acrylic acid or methacrylic acid or a salt thereof, preferably acrylic acid or a salt thereof.
14. Use according to Claim 12 or 13, characterized in that the proportion of iodide ions is from 20 to
1000 mol%, based on 100 mol% of E.
15. Use according to any of Claims 12 to 14, characterized in that the proportion of the unsaturated
carboxylic acid or salt thereof is from 2 to 100% by weight based on the composition minus the
amount of halide ions, solvent, E and L, with L defined as in one of the preceding claims.