WO2015173307A1

WO2015173307A1 - Preparing an unsaturated carboxylic acid salt from an alkene and carbon dioxide using a heterogeneous alkalinity reservoir

Info

Publication number: WO2015173307A1
Application number: PCT/EP2015/060603
Authority: WO
Inventors: Michael Limbach; Ivana JEVTOVIKJ; Stephan A. Schunk; Michael Lejkowski; Alvaro GORDILLO; Eko PRASETYO
Original assignee: Basf Se
Priority date: 2014-05-16
Filing date: 2015-05-13
Publication date: 2015-11-19

Abstract

Catalytic process for preparing an α, β-ethylenically unsaturated carboxylic acid salt, wherein an alkene and carbon dioxide are reacted in the presence of a carboxylation catalyst and of an organic base that is homogeneously dissolved in a reaction medium, to obtain the α, β-ethylenically unsaturated carboxylic acid salt, wherein the reaction medium is in contact with a heterogeneous alkalinity reservoir, α, β-ethylenically unsaturated carboxylic acid derivatives are efficiently provided from CO₂ and an alkene.

Description

Preparing an unsaturated carboxylic acid salt from an alkene and carbon dioxide using a heterogeneous alkalinity reservoir

Description

The present invention relates to a process for preparing an ^-ethylenically unsaturated carboxylic acid salt by carboxylation of an alkene. More particularly, the invention relates to a process for preparing sodium acrylate by direct carboxylation of ethene with carbon dioxide (CO2). Acrylic acid and derivatives thereof are important industrial chemicals and monomer units for production of water-absorbing resins, called super- absorbents.

The direct addition of CO2 onto ethylene to give acrylic acid is industrially unattractive due to thermodynamic limitations (ΔΘ = 42.7 kJ/mol at 298 K) and the unfavorable equilibrium, which at room temperature is virtually completely to the side of the reac- tants (K298 = 7 x 10^"7). On the other hand, the formation of sodium acrylate and water from CO2, ethylene and sodium hydroxide is thermodynamically favored (ΔΘ = -56.2 kJ/mol at 298 K, K298 = 7.1 ^χ 10⁹). By using a base, it is thus possible to convert the a^-ethylenically unsaturated acid to the salt thereof and thus to shift the equilibrium to the side of the products. The reaction, however, is kinetically inhibited and therefore requires a homogeneous or heterogeneous carboxylation catalyst (Buntine et al., Or- ganometallics 2007, 26, 6784).

The stoichiometric coupling of CO2 and ethene at homogeneous Nickel complexes has been known since more than 30 years (Hoberg et al., J. Organomet. Chem. 1983, C51 ). The formation of nickelalactones as intermediates has been discussed, e.g. by Walther et al. {Chem. Commun. 2006, 23, 2510-2512). These do not spontaneously decompose by ^-hydride elimination, as according to Walther's initial theory. Many nickelalactones are particularly stable and obtained in the form of solids by stoichio- metric coupling of CO2 and ethene (J. Organomet. Chem. 1983, C51 ; J. Organomet. Chem. 1982, 236, C28; Angew. Chem. Int. Ed. Engl. 1987, 26, 771 ). Some nickelalactones may even be isolated at room temperature in the form of stable solids (J. Organomet. Chem. 1982, 236, C28). Nickelalactones are hydrolyzed by mineral acids in a non-catalytic reaction to yield a saturated carboxylic acid rather than an ^-ethylenically unsaturated carboxylic acid. Concurrently, the nickel atom is oxidized. Buntine et al. {Organometallics 2007 , 26, 6784) and Walther et al. {Eur. J. Inorg. Chem. 2007, 2257) suggest that the initially postulated formation of acrylic acid by ^-hydride elimination is energetically unfavored. This also explains for the stability of many nickelalactones. The ^-hydride elimination postulated by Walther et al. and the equilib- rium between nickelalactone and π-complex has never been realized experimentally.

Bases have already been used for cleaving a nickelalactone. Limbach et al.

(WO 2013/098772, Chem. Eur. J. 2012, 18, 14017-14025) disclose a catalytic process for preparing an alkali metal or alkaline earth metal salt of an ^-ethylenically unsatu- rated carboxylic acid, wherein a) a transition metal-alkene complex is reacted with CO2 to give a metallalactone, b) the metallalactone is reacted with a base to give an adduct of the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid with the transition metal complex, the base being selected from alkali metal or alkaline earth metal hydroxides and alkali metal or alkaline earth metal superbases, and c) the adduct is reacted with an alkene to release the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid and regenerate the transition metal-alkene complex. In step c), the transition metal-alkene complex is regenerated and is available again for step a). This completes the catalytic cycle. Sodium acry- late was obtained at an overall yield of 1020 % (2.55 mmol) based on Nickel (0.25 mmol). This yield was obtained in a process wherein the reaction conditions were varied in 18 cycles. Each cycle included increasing and decreasing CO2 partial pressure, increasing and decreasing ethene partial pressure, and adding NaOtBu at decreased gas pressure. Different bases have also been used in subsequent steps of a process for preparing an alkali metal or alkaline earth metal salt of an ^-ethylenically unsaturated carboxylic acid. WO 201 1/107559 discloses a process, wherein a) an alkene, CO2 and a carboxy- lation catalyst are converted to an alkene/C02/carboxylation catalyst adduct, b) the adduct is decomposed to release the carboxylation catalyst with an auxiliary base to give the auxiliary base salt of the ^-ethylenically unsaturated carboxylic acid, c) the auxiliary base salt of the ^-ethylenically unsaturated carboxylic acid is reacted to release the auxiliary base with an alkali metal or alkaline earth metal base to give the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid. The intermediate adduct is cleaved by means of an auxiliary base, for example of a tertiary amine, in order to prepare, in a first step, the ammonium salt of the

a^-ethylenically unsaturated carboxylic acid, which overcomes the fundamental thermodynamic limitation. In a second step, the ammonium cation is exchanged for sodium, for example by treatment with aqueous sodium hydroxide solution. The auxiliary base salt formed in the first step is separated from the reaction medium, e. g. by liquid- liquid phase separation.

Ideally, the base used for deprotonating the metallalactone fulfills the following re- quirements: Its basicity is sufficient for abstracting the -hydrogen atom of the metallalactone. It is accompanied by a cation of sufficient Lewis acidity to coordinate to the carboxylic group formed by cleavage of the metallalactone. Finally, the base should not react with carbon dioxide, allowing for the process to be carried out as a one-pot reaction. The bases proposed hitherto do not equally fulfill all of these requirements.

It is an object of the present invention to provide more efficient catalytic processes for preparing ^-ethylenically unsaturated carboxylic acid derivatives from CO2 and an alkene. The invention provides a catalytic process for preparing an a^-ethylenically unsaturated carboxylic acid salt, wherein an alkene and carbon dioxide are reacted in the presence of a carboxylation catalyst and of an organic base that is homogeneously dissolved in a reaction medium, to ob- tain the ^-ethylenically unsaturated carboxylic acid salt, wherein the reaction medium is in contact with a heterogeneous alkalinity reservoir.

Surprisingly, the specific combination of an organic base and a heterogeneous alkalinity reservoir is particularly effective to yield ^-ethylenically unsaturated carboxylic acid salt.

The term "heterogeneous" means that the alkalinity reservoir is not completely soluble in the reaction medium and thus forms a separate phase. Since the alkalinity reservoir is heterogeneous, the concentration of dissolved alkaline material is limited, thus sup- pressing unwanted side reactions, e.g. the direct reaction of alkaline material with carbon dioxide.

Suitable alkenes are those of the following general formula

wherein

R^a, R^b and R^c are each independently hydrogen, Ci-12-alkyl, C2-i2-alkenyl, or R^a and R^b together with the carbon atoms to which they are bonded are a mono- or dieth- ylenically unsaturated, 5- to 8-membered carbocycle.

Suitable alkenes are, for example, ethene, propene, isobutene, butadiene, piperylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -octene, 1 -nonene, 1 -decene, 2-butene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclooctadiene, or styrene. The alkene to be used in the carboxylation is generally gaseous or liquid under the reaction conditions.

In a preferred embodiment, the alkene is ethene. The process according to the invention makes it possible to obtain an acrylate.

In another embodiment, the alkene is piperylene and a sorbate is obtained.

The alkene partial pressure is for example between 0.5 and 200 bar, preferably between 1 and 100 bar, in particular between 2 and 80 bar.

All pressures indicated herein are absolute pressures.

The CO2 for use in the reaction can be used in gaseous, liquid or supercritical form. It is also possible to use carbon dioxide-comprising gas mixtures available on the indus- trial scale, provided that they are substantially free of carbon monoxide.

CO2 and alkene may also comprise inert gases such as nitrogen or noble gases. Advantageously, however, the content thereof is below 10 mol%, based on the total amount of carbon dioxide and alkene in the reactor.

The carbon dioxide partial pressure is for example between 0.5 and 200 bar, preferably between 2 and 150 bar, in particular between 3 and 100 bar.

The molar ratio of carbon dioxide to alkene in the feed is generally 0.1 to 10 and pref- erably 0.5 to 5.

Preferably, the ratio of carbon dioxide partial pressure to alkene partial pressure is in the range from 0.1 to 10, for example, in the range from 0.5 to 5, in particular in the range from 1 to 4. Preferably, the carboxylation catalyst is a transition metal complex. Preferably, the car- boxylation catalyst is homogeneously soluble in the reaction medium. The term "transition metal complex" used herein comprises, in a generic manner, all transition metal complexes through which the catalytic cycle is supposed to pass, i.e. transition metal-alkene complexes, metallalactones and adducts wherein the a^-ethylenically unsaturated carboxylic acid salt coordinates to the transition metal. In general, the transition metal complex comprises, as the active metal, at least one element of groups 4 (preferably Ti, Zr), 6 (preferably Cr, Mo, W), 7 (preferably Re), 8 (preferably Fe, Ru), 9 (preferably Co, Rh) and 10 (preferably Ni, Pd, Pt) of the Periodic Table of the Elements. Preference is given to nickel, cobalt, iron, rhodium, ruthenium, palladium, platinum, rhenium, tungsten. Particular preference is given to nickel, palladi- urn, platinum, cobalt, iron, rhodium, ruthenium. Most preferably, the transition metal complex is a nickel or a palladium complex, in particular a nickel complex.

The role of the active metal consists in the activation of CO2 and the alkene in order to form a C-C bond between CO2 and the alkene. It is assumed that a metallalactone is formed within the catalytic cycle from the alkene, carbon dioxide and the transition metal complex. The expression "metallalactone" denotes, according to the exchange nomenclature ("a" nomenclature), a lactone (y-lactone) in which a carbon atom has been exchanged for a metal atom. The expression "metallalactone" should be interpreted broadly and may comprise compounds with structures similar to the Hoberg complex, or related compounds of oligomeric or polymeric structure. The expression shall comprise isolable compounds and (unstable) intermediates.

The metallalactone can be illustrated by the following general formula

in which

M is the transition metal,

L is a ligand, n is 1 or 2, and

R^a, R^b and R^c are each as already defined.

An a^-ethylenically unsaturated carboxylic acid salt is released from the metallalac- tone when both, the organic base, and the alkalinity reservoir, are present. The mechanistic details of the formation of the ^-ethylenically unsaturated carboxylic acid salt are not completely understood. The alkalinity reservoir is stoichiometrically consumed during the reaction, whereas no net consumption of the organic base is observed. The overall reaction is illustrated in the following scheme for the specific example wherein the alkalinity reservoir is sodium hydride, the organic base is triethylamin, and the al- kene is ethene:

"Cat" denotes the carboxylation catalyst.

The transition metal complex comprises a ligand. Preferably, the transition metal complex comprises a ligand that coordinates to the transition metal via at least one ligand atom selected from P, N, O, and C.

The ligand preferably comprises at least one phosphorus atom which coordinates to the transition metal. The ligand may be monodentate or polydentate, for example bi- dentate. In general, two monodentate ligands or one bidentate ligand coordinate to the transition metal. Preferred ligands comprise bulky substituents, as for example the tert- butyl groups in 1 ,2-bis(di-tert-butylphosphino)ethane.

The polydentate, e.g. bidentate, ligand may coordinate to the transition metal to form a four-, five-, six-, seven-, or eight-membered ring, i.e. the transition metal, the atoms which coordinate to the transition metal and the atoms of the shortest chain which connects the atoms coordinating to the transition metal together form a four-, five-, six-, seven-, or eight-membered ring. Ligands that coordinate to the transition metal to form a five-, six-, or seven-membered ring are preferred. Alternatively, the atoms which co- ordinate to the transition metal may be directly bound to carbon atoms of two cyclopen- tadienyl ligands bound to a second metal, i.e. iron.

At least one residue is preferably bound via a secondary or tertiary carbon atom to a transition metal coordinating phosphorus atom. More particularly, at least two residues are preferably bound to the phosphorus atom via a secondary or tertiary carbon atom. The term tertiary carbon atom as used herein also includes aromatic carbon atoms. Suitable residues bound to the phosphorus atom via a secondary or tertiary carbon atom are, for example, adamantyl, tert-butyl, sec-butyl, isopropyl, cyclohexyl, cyclopen- tyl, phenyl, tolyl, xylyl, mesityl, naphthyl, fluorenyl, or anthracenyl, especially tert-butyl, isopropyl, cyclohexyl, or cyclopentyl. At least one residue is preferably bound via a primary carbon atom to a transition metal coordinating phosphorous atom. Suitable residues bound to the phosphorus atom via a primary carbon atom are, for example, methyl, 1 -ethyl, 1 -propyl, 1 -butyl.

Suitable monodentate ligands have, for example, the formula (lie)

wherein

R^4a, R^4b, and R^4c are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen atoms may independently be replaced by CI, Br, I , or F, and two or all three residues may be covalently bound to one another.

R^4a , R^4b, and R^4c are preferably independently Ci-Ci₂-alkyl, C₃-Ci₂-cycloalkyl, or C₃- Ci4-aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, d-Cs-alkyl and Ci- C4-alkoxy.

R^4a , R^4b, and R^4c are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl) propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2- methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 - decyl, 1 -undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chloro- phenyl or anisyl.

Examples of suitable ligands of formula (lie) are trialkylphosphines, i.e.

tri-n-propylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, trioctylphosphine; tricycloalkylphosphines, i.e. tricyclohexylphosphine, tricyclododecylphosphine; tri- arylphosphines; i.e. triphenylphosphine, tritolylphosphine,

tri(methoxyphenyl)phosphine, trinaphthylphosphine, di-(chlorphenyl)-phenylphosphine; and dialkylarylphosphines, i.e. diethylphenylphosphine, dibutylphenylphosphine.

The ligand is, for example, a bidentate P,P; P,N; P,0; P,carbene; N,N; N,0; N,carbene; 0,0; or 0,carbene, preferably a bidentate Ρ,Ρ; Ρ,Ν; P,0; or P,carbene ligand, in particular a bidentate P,P ligand. In preferred bidentate P,P ligands, the phosphorous atoms are separated by 2 to 4 bridging atoms that may optionally be part of at least one 5- to 7-membered cyclic substructure.

The phosphorous atoms being "separated by 2 to 4 bridging atoms" means that the shortest chain which connects the coordinating phosphorous atoms comprises 2 to 4 atoms.

In preferred bidentate P,P ligands, wherein the bridging atoms are part of at least one 5- to 7-membered cyclic substructure, each bridging atom directly linked to a P atom, together with the P atom to which it is linked, is part of a 5- to 7-membered cyclic substructure; or two neighbouring bridging atoms are part of a 5- to 7-membered cyclic substructure.

Preferred bidentate P,P ligands are ligands of formula (I la)

wherein

R⁶ is independently selected from CHR⁷2, CR⁷3, C3-Cio-cycloalkyl, and optionally alkylated aryl having 6 to 18 carbon atoms,

R⁷ is independently selected from Ci-C4-alkyl, preferably linear Ci-C4-alkyl,

A¹ together with the carbon atoms to which it is bound and the interjacent phospho rous atom forms a 5- to 7-membered cyclic substructure, and R⁸ is independently selected from hydrogen, Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, C3-C12- heterocycloalkyl, C6-Ci4-aryl, C6-Ci4-heteroaryl, Ci-Ci2-alkoxy, C3-C12- cycloalkoxy, C3-Ci2-heterocycloalkoxy, C6-Ci4-aryloxy, and C6-Ci4-heteroaryloxy. A¹ is preferably selected from -(CR⁸ ₂)_r- and -(CR⁹=CR⁹)_S- with both R⁹ being on the same side of the double bond, wherein R⁸ is independently selected from H , C1-C3- alkyl, and -0-Ci-C3-alkyl, R⁹ is selected from H and Ci-C3-alkyl, or at least two R⁹ constitute a bridge of one of the formulae:

r is 2 or 3, and s is 1 or 2.

R⁶ is preferably independently selected from CHR⁷2, CR⁷3, and Cs-Cs-cycloalkyl, most preferably CR⁷3. R⁷ is preferably methyl.

R⁸ is preferably H.

A¹ is preferably selected from ethylene, ethenylene, 1 ,2-phenylene, 1 ,2-naphthylene, 2, -naphthylene, and the following formulae:

Preferred bidentate P,P ligands are ligands of formula (lib)

(lib) wherein

R¹⁰ is independently selected from linear Ci-C4-alkyl,

R¹¹ is independently selected from CHR¹⁰2, CR¹⁰3, C3-Cio-cycloalkyl, and optionally alkylated aryl having 6 to 18 carbon atoms,

X is independently selected from C-H, C-CH3, and N, and

A² together with the moieties X to which it is bound and the interjacent carbon atoms forms a 5- to 7-membered cyclic substructure.

R¹⁰ is preferably independently selected from Ci-C6-alkyl and C3-C7-cycloalkyl and R¹¹

R¹⁰ may, for example, be independently selected from linear Ci-C4-alkyl, in particular from linear Ci-C2-alkyl.

R¹¹ is preferably independently selected from CHR¹⁰2, CR¹⁰3, and Cs-Cs-cycloalkyl A² is preferably a -CH=CH- bridge. X is preferably CH.

Preferred bidentate P,P ligands are ligands of formula (lie)

(lie) wherein

R¹³ and R¹⁴ are independently selected from C3-Cio-cycloalkyl, and

_R15 is H, O-d-Ce-alkyl, or both R¹⁵ together constitute a -CH=CH- bridge.

R¹⁵ is preferably H or OCH3 and most preferably H.

Preferred bidentate P,P ligands are ligands of formula (lid) _R16_R17_P_(_{C R}18_R19)_e_p_R16_R17

(lid)

wherein

R¹⁶ and R¹⁷ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen atoms may independently be replaced by CI, Br, I , or F, and any two residues bound to the same phosphorous atom may be covalently bound to one another,

e is 1 , 2, 3, 4, or 5, preferably 2, 3, or 4,

R¹⁸ is independently selected from H, d-Cs-alkyl, Ci-Cs-alkoxy, C3-C10- cycloalkyl, C3-Cio-cycloalkoxy, C6-Cio-aryl, and C6-Cio-aryloxy, and R¹⁹ is independently selected from H, C-i-Cs-alkyl, C3-Cio-cycloalkyl, and C6-

Preferably, (CR¹⁸R¹⁹)_e is -CH2-CH2-, -CH₂-CH₂-CH₂-, or -CH2-CH2-CH2-CH2-.

R¹⁶ and R¹⁷ are preferably independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-Ci4-aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, C-i-Cs-alkyl and Ci-C4-alkoxy.

R¹⁶ and R¹⁷ are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcy- clohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl.

In a particularly preferred process of the invention, the ligand is selected from 1 ,2- bis(di-tert-butylphosphino)ethane, 1 ,2-bis(diisopropylphosphino)ethane, 1 ,3- bis(diisopropylphosphino)propane, 1 ,4-bis(diisopropylphosphino)butane, 1 ,2-bis(tert- butylmethylphosphino)ethane, 1 ,2-bis(dicyclopentylphosphino)ethane, 1 ,3- bis(dicyclopentylphosphino)propane, 1 ,4-bis(dicyclopentylphosphino)butane, 1 ,2- bis(dicyclohexylphosphino)ethane, 1 ,3-bis(dicyclohexylphosphino)propane, 1 ,4- bis(dicyclohexylphosphino)butane,

Cy is cyclohexyl.

Suitable monodentate ligands are, for example, monodentate carbene ligands of for- mula (llf)

(I If) wherein

R⁶¹ and R⁶² are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and where individual hydrogen atoms may independently be replaced by CI, Br, I, or F,

R⁶³ and R⁶⁴, are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen atoms may independently be replaced by CI, Br, I , or F, and both residues may be covalently bound to one another, and

_R65 _{a n d R}66 together are a chemical bond, or as defined for R⁶³ and R⁶⁴.

R⁶¹ and R⁶² are preferably independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-Ci4-aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, d-Cs-alkyl and Ci-C4-alkoxy.

R⁶¹ and R⁶² are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcy- clohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl.

Preferably R⁶³, R⁶⁴, R⁶⁵ and R⁶⁶ are independently hydrogen, Ci-Ci₂-alkyl, or C1-C14- aryl; or R⁶³ and R⁶⁴ are independently hydrogen, Ci-Ci2-alkyl, or Ci-Ci4-aryl, and R⁶⁵ and R⁶⁶ together are a chemical bond; or R⁶³ and R⁶⁴ are independently hydrogen, or methyl, and R⁶⁵ and R⁶⁶ together are a C3-Cio-alkane-1 ,3-diyl, C3-Cio-alkane-1 ,4-diyl, or C3-Cio-alkane-1 ,3-diyl bridge; or R⁶⁵ and R⁶⁶ together are a chemical bond, and R⁶³, and R⁶⁴, together with the carbon atoms to which they are bound, are part of a monocyclic or bicyclic aromatic ring system.

Suitable ligands are, for example, bidentate and multidentate ligands that comprise one or two coordinating phosphorous atoms and an additional carbon atom or hetero atom that is bound to the transition metal. Preferably, a 5-membered ring is formed, when the additional carbon atom or hetero atom binds to the transition metal, as for example with (Diphenylphosphino)acetate known from the SHOP-Process or with 2- (Dimethylphosphino)-N,N-dimethylethanamine. Specific bidentate ligands are of formula (llg)

(iig)

wherein

W is phosphorous (P) or phosphite (P=0),

R⁶², R⁶³, R⁶⁴, R⁶⁵ and R⁶⁶ are each as already defined,

_R67 _{a n d R}68 are as defined for R⁶³ and R⁶⁴, and

R⁶⁹ and R⁷⁰ are as defined for R⁶³ and R⁶⁴.

Preferably R⁶³, R⁶⁴, R⁶⁵ and R⁶⁶ are independently hydrogen, Ci-Ci₂-alkyl, or C1-C14- aryl; or R⁶³ and R⁶⁴ are independently hydrogen, Ci-Ci2-alkyl, or Ci-Ci4-aryl, and R⁶⁵ and R⁶⁶ together are a chemical bond; or R⁶³ and R⁶⁴ are independently hydrogen, or methyl, and R⁶⁵ and R⁶⁶ together are a C3-Cio-alkane-1 ,3-diyl, C3-Cio-alkane-1 ,4-diyl, or C3-Cio-alkane-1 ,3-diyl bridge; or R⁶⁵ and R⁶⁶ together are a chemical bond, and R⁶³, and R⁶⁴, together with the carbon atoms to which they are bound, are part of a mono- cyclic or bicyclic aromatic ring system.

R⁶², R⁶⁷ and R⁶⁸ are preferably independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-C14- aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, Ci-Cs-alkyl and C1-C4- alkoxy.

R⁶², R⁶⁷ and R⁶⁸ are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 - butyl, 2-butyl, tert-butyl, 1 -(2-methyl) propyl, 2-(2-methyl)propyl, 1 -pentyl, 1 -(2- methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 - decyl, 1 -undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chloro- phenyl or anisyl. The ligand may also be a bidentate or multidentate ligand that comprises one or two coordinating nitrogen atoms and an additional carbon atom that is bound to the transition metal. Preferably, a 5-membered ring is formed, when the additional carbon atom binds to the transition metal, as for example with 2-phenylpyridine or 6-phenyl-2,2'- bipyridine.

Suitable tridentate ligands are, for example, ligands of formula (llh) R ⁶R ⁷P-(CR¹⁸R¹⁹)rPR¹⁶-(CR¹⁸R¹⁹)g-PR¹⁶R¹⁷

(llh) wherein

R¹⁶, R¹⁷, R¹⁸, and R¹⁹ are each as already defined, and

f and g are independently 1 , 2, 3, 4, or 5, preferably 2, 3, or 4.

Exemplary tridentate ligands are ((methylphosphinediyl)bis-

(methylene))bis(dimethylphosphine), ((ethylphosphindiyl)bis(methylene))bis(diethyl- phosphine), and ((methylphosphinediyl)bis(methylene))bis(diphenylphosphine).

In addition, at least one equivalent of the organic base may itself coordinate to the metal of the transition metal complex.

In addition to the above-described ligands, the transition metal complex may also have at least one further ligand selected from halides, amines, amides, oxides, phosphides, carboxylates, acetylacetonate, aryl- or alkylsulfonates, hydride, CO, olefins, dienes, cycloolefins, nitriles, aromatics and heteroaromatics, ethers, PF3, phospholes, and mono-, di- and polydentate phosphinite, phosphonite, phosphoramidite and phosphite ligands.

Any optional organic base and/or further ligand can be displaced when the alkene and carbon dioxide are reacted.

The transition metal complex may for example be obtained from the ligand and the transition metal or from the ligand and a transition metal source comprising the transition metal at oxidation state 0. Alternatively, the transition metal complex may for example be obtained by reducing a salt of the transition metal with a reducing agent, e.g. H2, Mg, Na or Zn. Useful transition metal sources and salts are commercially available and include, for example MX2, MX3, where X is selected from halide, pseudohalide, carboxylate, alkox- ide, carbonate, sulfate, nitrate, hydroxide, acetylacetonate, cyclopentadiene, and the corresponding adducts with solvents such as ethers, DMSO, or water, and M is the active metal of the transition metal complex (e.g. [M(p-cymene)Cl2]2, [M(benzene)Cl2]n, [M(COD)₂], [M(CDT)], [M(C₂H₄)3], [MCI₂xH₂0], [MCI₃xH₂0], [M(acetylacetonate)i_-3], [M(DMSO)₄CI₂]).

The reaction medium preferably comprises 0.1 to 20000 ppm by weight, preferably 1 to 1000 ppm by weight, in particular 5 to 500 ppm by weight of transition metal, based on the total weight of the reaction medium.

In one embodiment, the carboxylation catalyst used is a heterogeneous catalyst.

Heterogeneous carboxylation catalysts may be present in the form of supported catalysts or in the form of unsupported catalysts. A supported catalyst consists of a catalyst support and one or more active metals, and optionally one or more additives. The proportion by weight of active metal, based on the sum of active metal, support material and additives, is preferably 0.01 to 40% by weight, more preferably 0.1 to 30% by weight, most preferably 0.5 to 10% by weight.

The proportion by weight of additives, based on the sum of active metal, support material and additives, is preferably 0.001 to 20% by weight, more preferably 0.01 to 10% by weight, most preferably 0.1 to 5% by weight. Typical processes for preparing supported catalysts are impregnation processes, for example incipient wetness, adsorption processes, for example equilibrium adsorption, precipitation processes, mechanical processes, for example the grinding of active metal precursor and support material, and further processes known to those skilled in the art.

Suitable inorganic additives may include: magnesium, calcium, strontium, barium, lanthanum, lanthanoids, manganese, copper, silver, zinc, boron, aluminum, silicon, tin, lead, phosphorus, antimony, bismuth, sulfur and selenium. Suitable organic additives may include: carboxylic acids, salts of carboxylic acids, polymers, for example PVP (polyvinylpyrrolidone), PEG (polyethylene glycol) or PVA (polyvinyl alcohol), amines, diamines, triamines, imines.

Suitable support materials may include: refractory oxides, for example zinc oxide, zirconium oxide, cerium oxide, cerium zirconium oxides, silica, alumina, silica-alumina, zeolites, sheet silicates, hydrotalcites, magnesium oxide, titanium dioxide, tungsten oxide, calcium oxide, iron oxides, for example magnetite, nickel oxides, cobalt oxides, phosphates of the main group and transition group elements, carbides, nitrides, organic polymers such as Nafion or functionalized polystyrene, metallic support materials such as metal sheets or meshes, MOFs (metal-organic frameworks) or composite materials of the aforementioned materials.

Preference is given to refractory oxides, for example zinc oxide, zirconium oxide, cerium oxide, cerium zirconium oxides, silica, alumina, silica-alumina, zeolites, sheet silicates, hydrotalcites, magnesium oxide, titanium dioxide, tungsten oxide, calcium oxide, iron oxides, for example magnetite, nickel oxides or cobalt oxides.

The support materials can be used, for example, in the form of powder, granules or tablets, or in another form known to those skilled in the art.

According to the invention, it is also possible to use unsupported catalysts. Such materials can be prepared, for example, by precipitation processes or other processes known to those skilled in the art. Such catalysts are preferably present in metallic and/or oxidic form.

When a heterogeneous catalyst is used in the process according to the invention, it preferably remains in the carboxylation reactor. This is enabled, for example, by virtue of it being present in the form of a fixed bed catalyst fixed within the reactor, or, in the case of a suspension catalyst, by virtue of it being retained within the reactor by a suitable sieve or a suitable filter.

In one embodiment of the process according to the invention, a transition metal complex, through which the catalytic cycle is supposed to pass, is preformed and used as the carboxylation catalyst or added to the reaction medium in addition to another car- boxylation catalyst. The preformed transition metal complex is, for example, a transition metal-alkene complex, a metallalactone, or an adduct wherein an ^-ethylenically unsaturated carboxylic acid salt coordinates to the transition metal. Preferably, the preformed transition metal complex is a metallalactone of formula (III c)

(lllc) wherein

M is the transition metal, preferably nickel, palladium, platinum, cobalt, iron, rhodium, or ruthenium, most preferably nickel,

L is a ligand, preferably a ligand of any of formulae (lla), (lib), (lie), (lid), (lie), (llf), (llg), and (llh),

h is 1 or 2, and

R^a', R^b' and R^c' are each independently hydrogen, Ci-12-alkyl, C2-i2-alkenyl, or R^a' and

R^b' together with the carbon atoms to which they are bonded are a mono- or diethyleni- cally unsaturated, 5- to 8-membered carbocycle. Preferably, the organic base is aprotic. Aprotic means that the organic base is not capable of acting as a proton donor under the conditions of the reaction of the alkene with carbon dioxide. In particular, the organic base does not comprise hydrogen atoms bound to heteroatoms such as N, O, S, or P. The PKA (at 25 °C in acetonitrile) of conjugate acids of preferred organic bases is between 5 and 50. The PKA (at 25 °C in acetonitrile) of conjugate acids of particularly preferred organic bases is between 5.1 and 42.7.

The organic base is preferably selected from tertiary amines, phosphazene bases, and tertiary phosphines.

Preferred tertiary amines correspond to the general formula (Ilia)

NR²⁶R²⁷R²⁸ (Ilia) in which R²⁶ to R²⁸ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and two or all three radicals may be covalently bound to one another.

Preferably, R²⁶ to R²⁸ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where two or all three radicals may be covalently bound to one another.

Preferred phosphazene bases correspond to the general formula (1Mb),

(1 M b) wherein

R²⁹ is an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, D¹ is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

D² is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

D³ is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

R³⁰ is independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and any two radicals R³⁰ may be covalently bound to one anoth- er, and

R³¹ is independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may each independently be replaced by a hetero group selected from the group of -O- and >N-, and any two radicals R³¹ that are part of the same D¹, D², or D³, may be covalently bound to one another.

R²⁹ is preferably an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, for example an unbranched or branched aliphatic radical having 1 to 16 carbon atoms. R³⁰ is preferably independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 5 carbon atoms, where any two radicals R³⁰ may be covalently bound to one another. R³⁰ is, for example, methyl, ethyl, or propyl, or two radicals R³⁰ form a 1 ,4-butylene, or 1 ,5-pentylene bridge.

R³¹ is preferably independently an unbranched aliphatic radical having 1 to 5 carbon atoms.

In preferred embodiments, the organic base is selected from triethylamine, trioctyla mine, N,N-dimethylanilin, Ν,Ν-diethylanilin, 1 ,8-diazabicyclo[5.4.0]undec-7-ene,

and

The molar ratio of transition metal comprised by the carboxylation catalyst to organic base is, for example, between 1 :1 and 1 :1000, preferably between 1 :1 and 1 :500, and most preferably between 1 :1 and 1 :200.

The organic base can be added in solid form or as a solution. In one embodiment of the process, the organic base is selected from organic bases that are gaseous under standard conditions (273.15 K, 1 bar) and brought into a supercritical state under the conditions of the reaction of the alkene and carbon dioxide. The reaction medium preferably comprises 1 to 100000 ppm by weight, preferably 5 to 25000 ppm by weight, in particular 25 to 10000 ppm by weight of the organic base, based on the total weight of the reaction medium.

Any material that is capable of converting the conjugate acid of the organic base into the organic base and thereby releases alkali metal cations or alkaline earth metal cations, preferably sodium, lithium or potassium cations, in particular sodium cations, may serve as alkalinity reservoir. This does not mean that the conversion of conjugate acid of the organic base into the organic base does necessarily occur in the process according to the invention.

When the alkalinity reservoir is selected from alkali metal or alkaline earth metal anion bases, converting the conjugate acid of the organic base into the organic base involves the transfer of a proton from the conjugate acid of the organic base to the anion of the alkali metal or alkaline earth metal anion base. When the proton is transferred to the anion of the anion base, the alkali metal or alkaline earth metal anion is released.

When the alkalinity reservoir is selected from elemental alkali metals, converting the conjugate acid of the organic base into the organic base goes in hand with the reduction of the proton from the conjugate acid to hb, the oxidation of the elemental alkali metal to the alkali metal cation, and release of the alkali metal cation.

The alkalinity reservoir may be solid or liquid under the conditions of the reaction of the alkene and carbon dioxide. The alkalinity reservoir is preferably solid under the conditions of the reaction of the alkene and carbon dioxide. The alkalinity reservoir is prefer- ably dispersed in the reaction medium. It may, for example, be present in the form of a discontinuos liquid or solid phase that is dispersed in the reaction medium.

Preferably, the alkalinity reservoir is selected from elemental alkali metals, alkali metal or alkaline earth metal anion bases, and their mixtures.

The elemental alkali metal may, for example, be sodium, lithium or potassium. Sodium is preferred. A suitable anion base is, for example, selected from alkali metal hydrides, alkaline earth metal hydrides, alkali metal amides, alkaline earth metal amides, alkali metal phosphides, alkaline earth metal phosphides, and their mixtures. Alkali metal hydrides, alkaline earth metal hydrides, alkali metal phosphides, alkaline earth metal phosphides, and their mixtures are preferred. Alkali metal hydrides are particularly preferred. Sodium hydride is particularly preferred.

The cation of the anion base may, for example, be selected from sodium, lithium, potassium, magnesium, and calcium. Sodium, lithium, and potassium are preferred. So- dium is particularly preferred.

Particularly preferred anion bases are sodium hydride, potassium hydride and lithium hydride. The most prefered alkalinity reservoir is sodium hydride.

It is possible to use the organic base in substoichiometric amounts based on the carboxylation catalyst. In another embodiment, the organic base is used as a solvent. The maximum content of heterogeneous alkalinity reservoir in the reaction mixture is then such that the reaction mixture can still be stirred. The person of ordinary skill in the art can find the maximum content heterogeneous alkalinity reservoir for a specific reaction medium by means of routine experimentation.

In one embodiment of the process, a precursor of the organic base is added to the reaction medium, and the organic base is released from the precursor under the conditions of the reaction of the alkene and carbon dioxide. The molar ratio of organic base to alkali metal or alkaline earth metal of the heterogeneous alkalinity reservoir is, for example, between 1 :1 and 1 :1000, preferably between 1 :1 and 1 :500, and most preferably between 1 :1 and 1 :100.

It may happen that part of the carboxylation catalyst is deactivated by oxidation of the active metal. The deactivation reduces the overall efficiency of the process. Preferably a reducing agent is added. Apparently, the reducing agent reactivates the deactivated carboxylation catalyst by reduction of the oxidized active metal. Thus, the alkene and carbon dioxide are preferably reacted in the presence of a reducing agent. Any reduc- ing agent which is capable of reducing the deactivated carboxylation catalyst is suitable as the reducing agent. Preferable reducing agents are hb, Mg, Na or Zn.

Suitably, the reaction medium comprises an aprotic organic solvent. Suitable aprotic organic solvents are in principle those which (i) are chemically inert with regard to the carboxylation of the alkene, (ii) in which the organic base and the carboxylation catalyst (the transition metal complex) have good solubility, and (iii) which are immiscible or only have limited miscibility with the polar solvent. Useful aprotic organic solvents are therefore in principle chemically inert, nonpolar solvents, for instance aliphatic, aro- matic or araliphatic hydrocarbons, for example octane and higher alkanes, benzene, toluene, xylene, and chlorobenzene. The reaction medium may for example comprise an aprotic organic solvent selected from aromatic hydrocarbons, halogenated aromatic hydrocarbons, alkylated aromatic hydrocarbons, alkanes, ethers, and mixtures thereof. Examples of suitable ethers are dimethylether, diethylether, di-tert-butylether, di-n- butylether, tetrahydrofuran, and 2-methyl-tetrahydrofuran.

In a specific embodiment, the reaction medium consists of more than one liquid phase and the transition metal complex is enriched in one of the liquid phases. The reactors used may in principle be all reactors which are suitable in principle for gas/liquid reactions or liquid/liquid reactions at the given temperature and the given pressure. Suitable standard reactors for liquid-liquid reaction systems are specified, for example, in K. D. Henkel, "Reactor Types and Their Industrial Application", in

Ullmann^'s Encyclopedia of Industrial Chemistry 2005, Wiley VCH Verlag GmbH & Co KGaA, DOI: 10.1002/14356007.b04_087, chapter 3.3 "Reactors for gas-liquid reactions". Examples include stirred tank reactors, tubular reactors or bubble columns.

The process may be performed as a continuous process or as a discontinuous process. In the discontinuous process, the ligand, the transition metal which may for ex- ample be in the form of the transition metal source, the base, carbon dioxide and the alkene are given into the reactor. Preferably, gaseous carbon dioxide and gaseous alkene are passed into the reactor at the desired pressure. After the reaction has slowed down, the pressure may be reduced. The process may for example be performed at pressures between 1 and 300 bar, preferably between 1 and 200 bar, in particular between 1 and 150 bar. The process may for example be performed at temperatures between -20 and 300 °C, preferably between 20 and 250 °C, in particular between 40 and 200 °C or between 50 and 180°C, most preferably between 60 and 170 °C. CO2, the alkene, the organic base, and the heterogeneous alkalinity reservoir can be fed to the reaction medium either together or spatially separately. Such a spatial separation can be accomplished, for example in a stirred tank, in a simple manner by means of two or more separate inlets. When more than one tank is used, for example, there may be different media charges in different tanks. Separation of the addition of the CO2 and alkene reactants in terms of time is also possible in the process according to the invention. Such a time separation can be accomplished, for example, in a stirred tank by staggering the charging with the reactants. In the case of use of flow tubes or apparatus of a similar kind, such charging can be effected, for example, at different sites in the flow tube; such a variation of the addition sites is an elegant way of adding the reactants as a function of residence time. In the process of the present invention, there is no need of separately feeding the CO2, the alkene, the organic base and the heterogeneous alkalinity reservoir to the reaction medium.

In order to achieve good mixing of the reactants and of the medium comprising the carboxylation catalyst and the base, suitable apparatuses can be used. Such apparatuses may be mechanical stirrer apparatuses with one or more stirrers, with or without baffles, packed or nonpacked bubble columns, packed or nonpacked flow tubes with or without static mixers, or other useful apparatuses known to those skilled in the art for these process steps. The use of baffles and delay structures is explicitly included in the process according to the invention.

In order to extract the ^-ethylenically unsaturated carboxylic acid salt formed in the reaction medium, water can be added such that a mixture comprising two phases is obtained. Preferably, the aqueous phase is separated from the organic phase. The aqueous phase comprising the main part of the ^-ethylenically unsaturated carboxylic acid salt (i.e. sodium acrylate) can be concentrated in order to obtain sodium acrylate. The organic phase that contains the organic base and the transition metal complex, can be recycled into the carboxylation reactor. The use of lipophilic organic bases is preferred in order to minimize losses of organic base into the aqueous phase. If a significant part of the organic base is transferred into the aqueous phase, other separation techniques (e.g. fractional distillation) can be applied in order to recover the organic base from the aqueous phase.

Traces of water comprised by the organic phase can be removed by contacting the organic phase with a drying agent. Preferably, the organic phase comprising the transition metal complex and the organic base is recirculated to the carboxylation reactor via a column that is filled with drying agent. Heterogeneous alkalinity reservoir is added into the reactor and the reaction of the alkene and carbon dioxide continued with the recycled catalyst and the organic base.

The liquid-liquid phase separation may, for example, be promoted by the additional use of a polar solvent in which the ^-ethylenically unsaturated carboxylic acid salt has good solubility and which has zero or only limited miscibility with the organic phase in which the carboxylation catalyst and the base are enriched. The polar solvent should be selected such that the polar solvent is present in enriched form in the aqueous phase. "Enriched" is understood to mean a proportion by weight of > 50% of the polar solvent in the aqueous phase based on the total amount of polar solvent in both liquid phases. The proportion by weight is preferably > 90%, more preferably > 95% and most preferably > 97%. The polar solvent is generally selected by simple tests in which the partition of the polar solvent in the two liquid phases is determined experimentally under the process conditions.

Preferred substance classes which are suitable as polar solvents are alcohols, diols and the carboxylic esters thereof, polyols and the carboxylic esters thereof, sulfones, sulfoxides, open-chain or cyclic amides, and mixtures of the substance classes mentioned.

Examples of suitable alcohols are methanol, ethanol, 1 -propanol, isopropanol, tert- butanol and butanol. Examples of suitable diols and polyols are ethylene glycol, diethy- lene glycol, triethylene glycol, polyethylene glycol, 1 ,3-propanediol, 2-methyl-1 ,3- propanediol, 1 ,4-butanediol, dipropylene glycol, 1 ,5-pentanediol, 1 ,6-hexanediol and glycerol.

In a preferred embodiment, the polar solvent is an alcohol. In a particularly preferred embodiment, the polar solvent is methanol, isopropanol or tert-butanol. The two liquid phases are generally separated by gravimetric phase separation.

Suitable examples for this purpose are standard apparatus and standard methods which can be found, for example, in E. Muller et al., "Liquid-Liquid Extraction", in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI:10.1002/14356007.b03_06, chapter 3 "Apparatus". In general, the liquid phase enriched with the ^-ethylenically unsaturated carboxylic acid salt is heavier and forms the lower phase. The second liquid phase can subsequently be recycled into the carboxylation reactor. Suitable selection of the organic base and optionally of the polar solvent and/or of the aprotic organic solvent which is immiscible or has only limited miscibility therewith, for example, achieves the effect that the transition metal complex and the organic base are enriched in the organic phase. The transition metal complex and the organic base can be separated by phase separation from the ^-ethylenically unsaturated carboxylic acid salt and be recycled to the reactor as described above. Owing to the rapid separation of the ^-ethylenically unsaturated carboxylic acid salt from the catalyst, a reverse reaction with decomposition to carbon dioxide and alkene is suppressed. In addition, losses of active metal and base are minimized, as the catalyst, base and its conjugate acid are retained in the organic phase.

The invention is illustrated in detail by the examples which follow.

The following abbreviations are used:

DEA N,N-diethylaniline

DMA N,N-dimethylaniline

DMF dimethylformamide

Ex. example

NaBARF sodium tetrakis(3,5-trifluoromethyl)phenylborate

NaHMDS sodium bis(trimethylsilyl)amide

Ni(COD)₂ bis(cyclooctadiene)nickel(0)

rpm rotations per minute

TEA triethylamine

THF tetrahydrofuran

TOA trioctylamine

TON turnover number with respect to transition metal

Phosphazene base abbreviations:

P1 P2

P4 BEMP

Different organic bases and heterogeneous alkalinity reservoir were tested as combinations of bases in the process for preparing an ^-ethylenically unsaturated carboxylic acid salt.

General procedure

An autoclave (inner volume = 160 mL) was made inert overnight (100 °C, vacuum), and then flushed with ethylene until the inner volume of the autoclave had been quantitatively exchanged. 1 ,2-Bis(dicyclohexylphosphino)ethane (0.22 mmol, 92.9 mg), Ni(COD)2 (0.2 mmol, 55 mg), and the organic base were dissolved in THF (45 mL) and a heterogeneous alkalinity reservoir added to the solution. The resulting mixture was transferred into the autoclave under inert conditions immediately after the heterogene- ous alkalinity reservoir had been added. The autoclave was pressurized with ethene and CO2. The temperature in the autoclave was adjusted and the reaction mixture stirred at 2000 rpm. After the indicated reaction time, the autoclave was cooled to room temperature. The excess pressure was released within 10 minutes. A mixture of D2O (15 mL) and THF (10 mL) was added dropwise to the reaction mixture. The resulting mixture was diluted with D2O (15 mL) and then extracted twice (2 x 20 mL Et.20). Upon addition of NMe4l (0.125 mmol, 25.1 mg) or 2,2,3,3-tY4-3-(trimethylsilyl)propionic acid (0.167 mmol, 28.7 mg) to the aqueous phase as internal standard, the amount of acry- late dissolved therein was determined by ¹H-NMR spectroscopy and the TON calculat- ed from the amount of acrylate.

Table 1

Heterogeneous

Reaction

Ex. Organic base alkalinity reservoir T p(C₂H₄) p(C0₂) TON time

or other reagent

[mmol] [mmol] [°c] [h] [bar] [bar]

1* PI 2.5 - - 80 18 5 10 0

2* - - NaH 10 80 18 5 10 0

3*† PI 2.5 NaH 10 80 18 5 10 0

4 PI 2.5 NaH 10 80 75 5 10 3.3

5 PI 2.5 NaH 10 80 18 5 10 1.4

6 PI 2.5 NaH 10 90 18 5 10 1.6

7 PI 2.5 NaH 10 100 18 5 10 2.1

8 PI 2.5 NaH 10 100 72 5 10 3.9

9 PI 2.5 NaH 100 80 18 5 10 1.1

10 PI 0.2 NaH 10 80 120 5 10 2.6

11 PI 5 NaH 10 80 120 5 10 3.4

12 PI 2.5 NaH 10 80 120 5 10 3.1

NaBARF 0.2

13 PI 2.5 80 92 5 10 1.2

+NaH +10

14 PI 2.5 LiH 10 80 72 5 10 1.1

15 PI 2.5 KH 10 80 72 5 10 1.5

16* PI 2.5 LiCI 10 80 18 5 10 0

17 P2 2.5 NaH 10 80 75 5 10 2.1

18 P2 2.5 NaH 10 80 18 5 10 1.2

19 P2 2.5 LiH 10 80 72 5 10 1.1

20 BEMP 2.5 NaH 10 80 72 5 10 2.4

21 P4 1 NaH 10 80 72 5 10 1.6

22 DBU 2.5 NaH 10 80 18 5 10 1.3

23 DBU 2.5 NaH 10 80 72 5 10 3.0

24 TEA 100 NaH 100 100 72 5 10 6.0

25 TEA 2.5 NaH 10 80 72 5 10 2.0

26 TEA 2.5 NaH 10 100 18 5 10 3.6

27 TEA 10 NaH 10 100 18 5 10 5.4 28 TEA 10 NaH 10 100 72 5 10 4.1

29 TEA 10 NaH 10 100 72 5 10 3.3

30 TEA 10 NaH 10 100 72 5 10 3.5

31 TEA 10 NaH 10 100 72 10 20 5.3

32 TEA 10 KH 10 100 72 10 20 1.1

33 TOA 10 NaH 10 100 20 10 20 4.5

34 TOA 10 NaH 10 100 72 10 20 11.9

35 DMA 2.5 NaH 10 80 72 5 10 3.9

36 DEA 2.5 NaH 10 80 72 5 10 2.7

37 PI 10 NaH 10 100 72 10 20 15.1

38 PI 10 NaH 10 100 72 10 20 12.9

39 TEA 10 NaH 10 100 72 10 20 18.8

40 TEA 10 NaH 10 100 20 10 20 5.5

41 TEA 0.1 NaH 10 100 20 10 20 4.7

42 TEA 0.5 NaH 5 100 20 10 20 5.4

43 TEA 20 NaH 20 100 20 10 20 6.0

44 TEA 5 KH 5 100 20 10 20 2.2

45 TOA 10 NaH 10 100 20 10 20 8.3

46 TOA 10 NaH 10 100 20 10 20 16.9

Examples 1 and 2 were conducted with either pure amine or pure hydride. Both did not provide an acrylate. This shows that only a mixture of both, organic base and heterogeneous alkalinity reservoir, is active in the reaction.

*: reference example

†: Example was carried out without Ni(COD)2

In examples 37 to 46, 0.1 mmol of the following nickelalactone:

(Cy = cyclohexyl) were used in place of 1 ,2-bis(dicyclohexylphosphino)ethane and Ni(COD)2.

Claims

1 . A catalytic process for preparing an ^-ethylenically unsaturated carboxylic acid salt, wherein an alkene and carbon dioxide are reacted in the presence of a carboxylation catalyst and of an organic base that is homogeneously dissolved in a reaction medium, to obtain the ^-ethylenically unsaturated carboxylic acid salt, wherein the reaction medium is in contact with a heterogeneous alkalinity reservoir.

The catalytic process according to claim 1 , wherein the alkalinity reservoir is selected from elemental alkali metals, alkali metal or alkaline earth metal anion bases, and their mixtures.

The catalytic process according to claim 2, wherein the anion base is selected from alkali metal hydrides, alkaline earth metal hydrides, alkali metal amides, alkaline earth metal amides, alkali metal phosphides, alkaline earth metal phosphides, and their mixtures.

The catalytic process according to according to any of the preceding claims, wherein the organic base is selected from tertiary amines, phosphazene bases, and tertiary phosphines.

The catalytic process according to any of the preceding claims, wherein the organic base is selected from tertiary amines that correspond to the general formula (Ilia)

NR²⁶R²⁷R²⁸ (Ilia) in which R²⁶ to R²⁸ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and two or all three radicals may be cova- lently bound to one another, and phosphazene bases that correspond to the general formula (1Mb), D '

2 I 29

D- P=NR

D

(1Mb) wherein

R²⁹ is an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-,

D¹ is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

D² is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

D³ is selected from NR³⁰ ₂, and N=P(NR³¹ ₂)₃,

R³⁰ is independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and any two radicals R³⁰ may be covalently bound to one another, and

6. The catalytic process according to any of the preceding claims, wherein the organic base is selected from triethylamine, Ν,Ν-dimethylanilin, N,N-diethylanilin, 1 ,8-diazabicyclo[5.4.0]undec-7-ene,

and ^{ύ ύ}

7. The catalytic process according to any of the preceding claims, wherein the carboxylation catalyst is a transition metal complex.

8. The catalytic process according to claim 7, wherein the transition metal complex comprises a ligand that coordinates to the transition metal via at least one ligand atom selected from P, N, O, and C.

9. The catalytic process according to claim 8, wherein the ligand is selected from bidentate P,P; P,N; P,0; P,carbene; N,N; N,0; N,carbene; 0,0; and 0,carbene ligands.

10. The catalytic process according to claim 8 or 9, wherein the ligand is a bidentate P,P ligand. 1 1 . The catalytic process according to any of claims 8 to 10, wherein the transition metal complex is a nickel or a palladium complex.

12. The catalytic process according to any of claim 1 to 7, wherein the carboxylation catalyst is a heterogeneous catalyst. The catalytic process according to any of the preceding claims, wherein the al kene is ethene and the ^-ethylenically unsaturated carboxylic acid is acrylic id.

The catalytic process according to any of the preceding claims, wherein the reaction medium comprises an aprotic organic solvent.

The catalytic process according to claim 14, wherein the aprotic organic solvent is selected from aromatic hydrocarbons, halogenated aromatic hydrocarbons, alkylated aromatic hydrocarbons, alkanes, ethers, and mixtures thereof.

The catalytic process according to any of the preceding claims, wherein a preformed metallalactone of formula III c)

(lllc)

wherein

M is the transition metal,

L is a ligand,

h is 1 or 2, and

R^a', R^b' and R^c' are each independently hydrogen, Ci-12-alkyl, C2-i2-alkenyl, or R^a and R^b' together with the carbon atoms to which they are bonded are a mono- or diethylenically unsaturated, 5- to 8-membered carbocycle, is used as the carboxylation catalyst or added to the reaction medium in addition to another carboxylation catalyst.