WO2015173296A1

WO2015173296A1 - Preparing an unsaturated carboxylic acid salt from an alkene and carbon dioxide using a heterogeneous base

Info

Publication number: WO2015173296A1
Application number: PCT/EP2015/060581
Authority: WO
Inventors: Michael Limbach; Cornelia FUTTER; 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

Process for preparing an α,β-ethylenically unsaturated carboxylic acid salt, comprising, reacting an alkene and carbon dioxide in the presence of a carboxylation catalyst to obtain a catalyst-coordinated carboxylated intermediate, treating the catalyst- coordinated carboxylated intermediate with a heterogeneous base, and releasing the α,β-ethylenically unsaturated carboxylic acid salt, wherein the heterogeneous base comprises an organic basic moiety that is immobilized on a solid support. The process avoids accumulation of the conjugate acid of the base in the reaction medium.

Description

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

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 etal., 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 etal., J. Organomet. Chem. 1983, C51 ). The formation of nickelalactones as intermediates has been discussed, e.g. by Walther etal. {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 to yield a saturated carboxylic acid rather than an ^-ethylenically unsaturated carboxylic acid.

Buntine etal. {Organometallics 2007 ^', 26, 6784) and Walther etal. {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 eta/, and the equilibrium between nickelalactone and π-complex has never been realized experimentally. Bases have already been used for cleaving nickelalactones. Limbach eta/.

(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 unsaturated 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 transi- tion 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. Recycling of the base is not suggested.

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. Preferably, the auxiliary base salt formed in the first step is removed from the reaction medium by liquid-liquid phase separation. In a second step, the ammonium cation is exchanged for sodium, for example by treatment with aqueous sodium hydroxide solution. As enrichment of the bases and their conjugate acids in the respective phases is not expected to be 100%, the quantitative separation of the bases is difficult to achieve by liquid-liquid phase separation.

Releasing the <¾e-ethylenically unsaturated carboxylic acid salt from the al- kene/C02/carboxylation catalyst adduct with a base necessarily produces an equiva- lent of the conjugate acid of the base, e.g. an alcohol if the base employed is an alkaline metal alkoxide. Accumulation of the conjugate acid, e.g. the alcohol, in the reaction medium can have a deleterious effect on further reaction cycles as it alters the polarity and other properties of the reaction medium.

It is an object of the present invention to provide a processes for preparing a^-ethylenically unsaturated carboxylic acid derivatives from CO2 and an alkene such that accumulation of the conjugate acid of the base in the reaction medium is substantially avoided.

The invention provides a process for preparing an ^-ethylenically unsaturated carboxylic acid salt, comprising, reacting an alkene and carbon dioxide in the presence of a carboxylation catalyst to obtain a catalyst-coordinated carboxylated intermediate, treating the catalyst- coordinated carboxylated intermediate with a heterogeneous base, and releasing the a^-ethylenically unsaturated carboxylic acid salt, wherein the heterogeneous base comprises an organic basic moiety that is immobilized on a solid support. The expression "catalyst-coordinated carboxylated intermediate" should be interpreted broadly and may comprise a metallalactone as defined below or related compounds in which a C-C bond between CO2 and the alkene is (pre)formed. The expression shall comprise isolable compounds and (unstable) intermediates. Treating the catalyst-coordinated carboxylated intermediate with the heterogeneous base yields an adduct wherein an ^-ethylenically unsaturated carboxylic acid salt is coordinated to the transition metal of the carboxylation catalyst. Releasing the a^-ethylenically unsaturated carboxylic acid salt can, for example, be accomplished by displacing the ^-ethylenically unsaturated carboxylic acid salt by an alkene. Thus, an adduct of the alkene and the carboxylation catalyst is obtained, that may be reacted with carbon dioxide to enter the next reaction cycle.

The base can be used efficiently as the recycling of the heterogeneous base is possible with little effort. After treating the catalyst-coordinated carboxylated intermediate with the heterogeneous base, the conjugate acid of the base can be readily separated from the reaction medium by solid-liquid phase separation. The conjugate acid of the base can then be converted back into the heterogeneous base, e.g. by treatment with an appropriate alkaline material. The regenerated heterogeneous base can be used again in the process according to the invention. Suitable alkenes are those of the following general formula

wherein

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, when the alkene and carbon dioxide are reacted in the presence of the carboxylation catalyst.

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 industrial 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, when the alkene and carbon dioxide are reacted in the presence of the carboxylation catalyst. The molar ratio of carbon dioxide to alkene in the feed is generally 0.1 to 10 and preferably 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.

The alkene and carbon dioxide are reacted in the presence of the carboxylation catalyst, for example, at pressures between 1 and 300 bar, preferably between 1 and 200 bar, in particular between 1 and 150 bar. The alkene and carbon dioxide are reacted in the presence of the carboxylation catalyst, for example, 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.

Preferably, the carboxylation catalyst is a homogeneous transition metal complex.

The term "transition metal complex" used in the present application comprises, in a generic manner, all transition metal complexes through which the catalytic cycle is supposed to pass, i.e. transition metal-alkene complexes, catalyst-coordinated carbox- ylated intermediates such as 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, palladium, platinum, cobalt, 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. A catalyst-coordinated carboxylated intermediate, in particular 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.

It is assumed that the heterogeneous base deprotonates the catalyst-coordinated car- boxylated intermediate, e.g., metallalactone, at the -carbon atom. The -carbon atom is the carbon atom bound to the carbonyl carbon atom. A counter cation compensates the negative charge. The counter cation can be a cation delivered with the heterogeneous base, a cation from an extraneous source or the conjugate acid of the organic basic moiety, e.g., an ammonium cation formed from a tertiary amine moiety. The cation preferably is alkali metal cation or an alkaline earth metal cation. The catalyst- coordinated carboxylated intermediate is thus preferably treated in the presence of an alkali metal cation or an alkaline earth metal cation with the heterogeneous base.

The formation of the adduct of the ^-ethylenically unsaturated carboxylic acid salt with the transition metal complex probably proceeds, for example, via an intermediate of the general formula

in which M, L, n, R^a, R^b and R^c are each as already defined and M' is an alkali metal or the equivalent of an alkaline earth metal.

The adduct of the ^-ethylenically unsaturated carboxylic acid salt with the transition metal complex can be illustrated by the general formula

in which M, L, n, M', R^a, R^b, and R^c are each as already defined.

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 bidentate. 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 con- nects 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 coordinate 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 resi- dues 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 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 (Ila)

(Ila)

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 phosphorous 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 brid e 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) 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,

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

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 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.

The ligand 1 ,2-bis(dicyclohexylphosphino)ethane is particularly preferred. Suitable monodentate ligands are, for example, monodentate carbene ligands of formula (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 ligands of formula (I Ig)

(iig)

wherein

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

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

R⁶⁷ and R⁶⁸ 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 monocyclic 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)v-PR¹⁶-(C ^{18 19})w-PR¹⁶R¹⁷

(llh) wherein

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

v and w 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 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 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(/>cymene)CI₂]₂, [M(benzene)Cl2]n, [M(COD)₂], [M(CDT)], [M(C₂H₄)3], [MCI₂xH₂0], [MCI₃xH₂0], [M(acetylacetonate)i_-3], [M(DMSO)₄CI₂]).

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 reducing agent which is capable of reducing the deactivated carboxylation catalyst is suitable as the reducing agent. Preferable reducing agents are H₂, Mg, Na and Zn.

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.

It is possible to isolate the catalyst-coordinated carboxylated intermediate, i.e. metalla- lactone, from the reaction medium and to treat the isolated catalyst-coordinated car- boxylated intermediate with the heterogeneous base. The reaction can also be carried out as a one-pot reaction. Thus, the heterogeneous base may be present in the reaction medium while the alkene and carbon dioxide are reacted, or the heterogeneous base may be added afterwards to the reaction medium. Certain heterogeneous bases, in particular heterogeneous bases that comprise a nucleophilic basic moiety, can react with carbon dioxide to form fairly stable adducts and the heterogeneous base is not available for the treatment of the catalyst-coordinated carboxylated intermediate. In these cases, the carbon dioxide pressure should be relieved before the catalyst- coordinated carboxylated intermediate is treated with the heterogeneous base. Heterogeneous base that comprises a non-nucleophilic basic moiety is largely unreactive to- wards carbon dioxide and can be included in the initial reaction medium or added to the reaction medium without prior carbon dioxide pressure relief.

Preferably, the organic basic moiety is an alkyloxide, aryloxide, secondary amide, or tertiary amine moiety.

The organic basic moiety is preferably immobilized covalently on the solid support. It may be immobilized via an optional linking moiety. The heterogeneous base preferably comprises structural units of the general formula (V)

^*-[G]_k-E-D (V) wherein

D is the organic basic moiety,

E is a bond or a linking moiety,

G is an anchoring unit,

k is 0 or 1 , and

^* is the site of attachment to the solid support.

The organic basic moiety D may, for example, be an alkyloxide moiety that correspond to the general formula (Va)

(Va), wherein

R⁸¹ is independently H or an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms. In a preferred alkyloxide moiety of formula (Va), R⁸¹ is independently H, 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, methylcyclopen- tyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, or xylyl.

The organic basic moiety D may, for example, be an aryloxide moietythat correspond to the general formula (Vb)

(Vb), wherein

R is independently F, CI, Br, I, or Ci-C4-alkyl, and

q is 0, 1 , 2, 3, or 4.

A preferred aryloxide moiety of formula (Vb) corresponds to formula (Vb-1 )

(Vb-1 ) wherein

R is independently F, CI, Br, I, or Ci-C4-alkyl, and

q is 0, 1 , or 2.

An aryloxide moiety of formula (Vb-1 ), wherein

R is independently F or CI, preferably F, and

q is 1 , or 2, preferably 1 , is a particularly preferred organic basic moiety.

The alkyloxide moiety is, for example, an alkali metal or alkaline earth metal alkyloxide moiety, preferably a sodium, lithium or potassium alkyloxide moiety, and most preferably a sodium alkyloxide moiety. The organic basic moiety D may, for example, be a secondary amide moiety that respond to the general formula (Vc)

(Vc),

wherein

R⁸⁰ is an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, and

R⁸¹ is independently H or R⁸⁰

In a preferred secondary amide moiety of formula (Vc), R⁸⁰ is 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, or xylyl.

The secondary amide moiety is, for example, a secondary alkali metal or alkaline earth metal amide moiety, preferably a secondary sodium, lithium or potassium amide moiety, and most preferably a secondary sodium amide moiety.

The organic basic moiety D may, for example, be a tertiary amine moiety that correspond to the general formula (Vd)

(Vd), wherein

R⁸⁰ and R⁸² are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, or R⁸⁰ and R⁸², together with the Y and N atoms to which they are attached and the intervening carbon atoms, form a 5- to 8-membered cycle,

R⁸¹ is independently H or an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, b is 0 or 1 , and

Y is N⁺ or C.

In a preferred tertiary amine moiety, R⁸¹ is independently H or R⁸², R⁸² is 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, or xylyl, and b is 0. In another preferred tertiary amine moiety, one R⁸⁰ and one R⁸², together with the Y and N atoms to which they are attached and the intervening carbon atoms, form a 5- to 7-membered cycle, the other R⁸⁰ and the other R⁸², together with the Y and N atoms to which they are attached and the intervening carbon atoms, form a 5- to 7-membered cycle, R⁸¹ is H, and b is 1 .

The heterogeneous base incorporating a tertiary amine moiety is preferably used together with a source of an alkali metal cation or an alkaline earth metal cation, such as alkali metal or alkaline earth metal hydride, i.e. sodium hydride. The alkali metal or alkaline earth metal ion provides a suitable counter ion of the <¾e-ethylenically unsaturat- ed carboxylic acid salt.

Specifc organic basic moieties and metal cations are given in Table 1 .

Table 1 :

Immobilization of the organic basic moiety generally involves the use of a linking moiety. Any linking moiety that is inert under the conditions of the reaction of the alkene and carbon dioxide, to which the organic basic moiety can be covalently bound and to which the solid support can be covalently bound directly or via an anchoring group, is a suitable linking moiety. The linking moiety allows for the covalent linkage of the organic basic moiety and provides accessibility of the immobilized base for the carboxylated intermediate coordinated to the catalyst.

The linking moiety E is preferably selected from (CH2)h-C6H4-(CH2)h-, -(CH₂)r,

-0-(CH₂)_f-, -(CH₂)i-0-(CH₂)i-, -0-(CH₂)i-0-(CH₂)i-, polyalkyleneoxides, polyamides, and polyolefins, wherein each f is independently an integer from 2 to 20, each h is independently an integer from 0 to 16, and each i is independently an integer from 2 to 10. The linking moiety can also be branched. For example, multiple moieties of any of the above formulae (Va), (Vb), (Vc), and (Vd) can be immobilized via the same branched linking moiety.

If the solid support per se does not carry suitable functional groups for covalent attachment, an anchoring group G is preferably used to facilitate attachment. Any anchoring group G that is inert under the conditions of the reaction of the alkene and carbon dioxide, and to which the organic basic moiety can be covalently bound directly or via a linking moiety, and to which the solid support can be bound, i.e. covalently bound, is a suitable linking moiety. Suitable reactants introducing anchoring groups onto inorganic supports such as silica are, e.g., functionalized silanes, such as haloalkyl trial- koxysilanes.

Any solid inorganic or organic material that is inert under the conditions of the reaction of the alkene and carbon dioxide, and to which an organic basic moiety can be attached (optionally via a linking moiety and/or an anchoring group), i.e. covalently attached, is suitable as a solid support.

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 may, for example, be used as solid supports. Alternative solid supports are crosslinked polymers. The crosslinking density of the polymer is such that the polymer is rendered insoluble in the reaction medium. Preferably, the solid support is a silica or a crosslinked polymer. Among the crosslinked polymers, crosslinked polystyrenes are preferred. When the linking moiety is attached to a refractory oxide solid support, a reactant introducing an anchoring group is reacted with the surface of the refractory oxide, i.e. silica, and, optionally, a functional group of the anchoring group is further reacted with a reactant introducing an additional linking moiety. When the linking moiety is attached to a crosslinked polymeric solid support, a reactant introducing the linking moiety is reacted with a functional group of the crosslinked polymer.

A suitable crosslinked polymer may be functionalized with any functional group that facilitates the formation of a bond from the support to the linking moiety. The functional group bound to the linking moiety attaching to the solid support may, for example, be a leaving group, i.e. halogen, that is displaced by a nucleophilic group bound to the solid support. The functional group bound to the linking moiety attaching to the solid support may, for example, be a nucleophilic group that displaces a leaving group, i.e. halogen, bound to the solid support. The functional group bound to the linking moiety attaching to the solid support may, for example, be transformed into another functional group by reaction with the solid support, e.g., an isocyanate may become a urea or carbamate, an ester may become an amide, and a thiol may become a disulfide. Alternatively, the functional group bound to the linking moiety attaching to the solid support will remain of the same type, e.g., a phosphate, phosphonate, or organosilane may remain a phosphate, phosphonate, or organosilane, albeit with different substituents.

Suitable polystyrene precursors to which organic basic moieties or linking moiety can be readily attached, are commercially available, i.e. Merrifield Resin or Wang Resin. Merrifield Resin is a polystyrene resin based on a copolymer of styrene and chlorome- thylstyrene, crosslinked with divinylbenzene.

The functional group bound to the linking moiety may, for example, be organosilane, ester, amino, hydroxyl, isocyanate, halogen, sulfate, sulfonic acid, phosphate, phos- phonate, phosphonic acid or carboxy or a salt thereof.

In place of the organic basic moiety, a precursor of the organic basic moiety, i.e. the conjugate acid of the organic basic moiety, can be attached to the solid support. The immobilized precursor may then be reacted into the organic basic moiety.

When the solid support is selected from refractory oxides, and in particular, when it is silica, the heterogeneous base preferably comprises structural units of the general formula (Ve)

(Ve) wherein

m is 0, 1 , or 2,

R⁴⁰ is H or a branched or unbranched, linear or cyclic Ci-Ci6-alkyl,

E is a linking moiety,

D is the organic basic moiety, i.e. an alkyloxide, an aryloxide, a secondary amide, or a tertiary amine moiety, and

* is the site of attachment to the solid support.

In formula (Ve), the linking moiety is anchored via a siloxy anchoring group to the silica support. Tetravalency of the silicon atom results from the oxygen bridges to the solid support and any unreacted residues -OR⁴⁰.

In formula (Ve), the linking moiety E is preferably selected from -(CH2)h-C6H4-(CH2)h-, -(CH₂)_f-, -0-(CH₂)r, -(CH₂)i-0-(CH₂)i-, -0-(CH₂)i-0-(CH₂)i-, polyalkyleneoxides, polyam- ides, and polyolefinsin particular from -(CH₂)h-C6H4-, -(CH₂)r, -(CH₂)i-0-(CH₂)r, and polyolefins, wherein each f is independently an integer from 2 to 20, each h is inde- pendently an integer from 0 to 16, and each i is independently an integer from 2 to 10.

When the solid support is a crosslinked polystyrene, the heterogeneous base preferably comprises structural units of the general formula (Vf)

(Vf) wherein

E is a bond or a linking moiety, and D is as defined in formula (Ve).

In formula (Vf), the linking moiety E is preferably selected from -(CH2)h-C6H4-(CH2)h-, -(CH₂)_f-, -0-(CH₂)_f-, -(CH₂)i-0-(CH₂)i-, -0-(CH₂)i-0-(CH₂)i-, polyalkyleneoxides, polyam- ides, and polyolefins, in particular from -(CH₂)h-C6H4-, -(CH₂)r, -(CH₂)i-0-(CH₂)r, poly- olefins, and phenylene, wherein each f is independently an integer from 2 to 20, each h is independently an integer from 0 to 16, and each i is independently an integer from 2 to 10. In a particularly preferred process according to the invention, the heterogeneous base comprises an organic basic moiety that is immobilized when the solid support is synthesized, e.g. by a polymerization reaction. A monomer comprising the organic basic moiety can, for example, be polymerized, preferably with at least one other monomer, to obtain a polymer comprising the organic basic moiety. In place of the monomer comprising the organic basic moiety, a monomer comprising a precursor of the organic basic moiety, i.e. the conjugate acid of the organic basic moiety, can be incorporated. The incorporated precursor may then be reacted into the organic basic moiety.

The monomer comprising the organic basic moiety or a precursor thereof may, for ex- ample, correspond to the general formula (Vg)

(Vg), wherein

E is a bond or a linking moiety, in particular a bond, and

D¹ is an organic basic moiety, i.e. D, as specified above or a precursor thereof, or a protonated precursor moiety of D, e.g. an alkylhydroxide, arylhydroxide, or secondary amine.

The loading of the solid support is, for example, from 0.001 to 10 mmol/g, preferably from 0.002 to 9 mmol/g, in particular from 0.005 to 8 mmol/g, most preferably from 0.02 to 6 mmol/g. The unit "mmol/g" specifies the molar amount of immobilized organic basic moiety per gram of heterogeneous base. When the carboxylated intermediate is treated with the heterogeneous base, the organic basic moiety comprised by the heterogeneous base is consumed stoichiometrically, i.e. it is protonated such that its conjugate acid is obtained. The heterogeneous base can be regenerated by reacting it with an alkaline material which is capable of deproto- nating the conjugate acid of the organic basic moiety. Accordingly, the process of the invention preferably comprises regenerating the heterogeneous base by treating the spent heterogeneous base with an alkaline material. Every alkaline material that is capable of deprotonating the conjugate acid of the base is suitable for regenerating the heterogeneous base.

Preferred alkaline materials are alkali metals, alkali and alkaline earth metal hydrides, alkali and alkaline earth metal hydrogen carbonates, alkali and alkaline earth metal carbonates, alkali and alkaline earth metal hydroxides. Na, NaH, LiH, NaHC03, Na2C03, NaOH are preferred alkaline materials.

When the heterogeneous base is regenerated, the heterogeneous base and an alkaline material, i.e. NaH or LiH, may, for example, be suspended in a suitable solvent and reacted until no more hydrogen gas is released from the regeneration reaction.

The regeneration of the heterogeneous base may further include washing the heterogeneous base with a solvent. Any solvent that is capable of removing any impurities deposited on the base is suitable for washing the heterogeneous base. Preferably, the reaction of the alkene and carbon dioxide in the presence of the car- boxylation catalyst to obtain the carboxylated intermediate is carried out in a carboxyla- tion reactor. 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 reaction of the alkene and carbon dioxide is preferably carried out in 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, and (ii) in which the car- boxylation catalyst (the transition metal complex) has good solubility. Useful aprotic organic solvents are therefore in principle chemically inert, nonpolar solvents, for instance aliphatic, aromatic 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 one embodiment, the heterogeneous base is, for example, fixed, i.e. stationary ar- ranged, in a treating zone and reaction medium leaving the carboxylation reactor is passed through the treating zone. Conveniently, the treating zone is a column filled with the particulate heterogeneous base or with a mixture of heterogeneous base and inert material. The process can be carried out as a continuous process wherein a continuous stream of reaction medium leaving the carboxylation reactor is continuously passed through the treating zone.

The base-treated reaction medium leaving the treating zone may be passed to a releasing zone. In the releasing zone, the base-treated reaction medium containing an adduct of the <¾e-ethylenically unsaturated carboxylic acid salt with the transition metal complex, is exposed to an alkene, e.g. ethene. The partial pressure of the alkene in the releasing zone is preferably 1 to 150 bar, most preferably 1 to 100 bar, in particular 1 to 60 bar. The temperature in the releasing zone is, for example, 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. The alkene displaces the <¾e-ethylenically unsaturated carboxylic acid salt in the adduct and an <¾e-ethylenically unsaturated carboxylic acid salt is released.

The solubility of the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acry- late, in the reaction medium is limited. At least part of the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, is thus obtained in the form of a solid. After exposure of the base-treated reaction medium to the alkene, the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate is therefore preferably recovered from the base-treated, alkene-exposed reaction medium by solid-liquid phase separation, e.g. filtration. The organic liquid phase comprising the catalyst may be recycled into the carboxylation reactor.

In a second embodiment, the process is a discontinuous process. In a preferred discontinuous process, the carbon dioxide pressure is first relieved in the carboxylation reactor and then the reaction medium is brought into contact with the heterogeneous base. The base may, for example either be added into the carboxylation reactor, or the reaction medium is transferred from the carboxylation reactor into another reactor comprising the heterogeneous base. The reaction medium may, for example, be brought into contact with the heterogeneous base at high alkene partial pressure, such that a base-treated, alkene-exposed reaction medium is obtained. The partial pressure of the alkene is preferably 1 to 150 bar, most preferably 1 to 100 bar, in particular 1 to 60 bar. The reaction medium may, for example, be brought into contact with the heterogeneous base at a temperature 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. The <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, and spent heterogeneous base, are preferably recovered from the base-treated, alkene-exposed reaction medium by solid-liquid phase separation, e.g. filtration. The liquid, e.g. filtrate, obtained from the solid-liquid phase separation, e.g. filtration, comprises the catalyst and can be recycled into the carboxylation reactor. The recovered <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, and spent heterogeneous base are then exposed to water in order to dissolve the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate. Another solid-liquid phase separation, e.g. filtra- tion, is then applied in order to separate the spent heterogeneous base from the

<¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, dissolved in the water. Alternatively, the base-treated, alkene-exposed reaction medium may, for example, be brought into contact with water such that a three phase solid/liquid/liquid mixture is obtained. The <¾e-ethylenically unsaturated carboxylic acid salt is enriched in the aqueous phase. The solid phase that essentially consists of spent heterogeneous base conjugate acid, may then be separated by solid-liquid phase separation, e.g. filtration. The liquid organic and aqueous phases are separated by liquid-liquid phase separation. The organic phase comprising the catalyst may be recycled into the carboxylation reactor.

Alternatively, the reaction medium may, for example, be brought into contact with the heterogeneous base in an inert gas atmosphere, e.g. in an argon or nitrogen atmosphere. Increased alkene partial pressure of preferably 1 to 150 bar, most preferably 1 to 100 bar, in particular 1 to 60 bar, may then, for example, be applied after the reac- tion medium has been separated from the heterogeneous base by solid-liquid phase separation, e.g. filtration. The temperature may, for example be 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, when the increased alkene partial pressure is applied. After exposure of the base-treated reaction medium to the alkene, the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate is preferably recovered from the base-treated, alkene-exposed reaction medium by solid- liquid phase separation, e.g. filtration. The organic liquid phase comprising the catalyst may be recycled into the carboxylation reactor.

In a third embodiment, the reaction of the alkene and carbon dioxide is carried out in the presence of the heterogeneous base. A heterogeneous base that comprises a non- nucleophilic organic basic moiety has to be used. Preferably a heterogeneous base comprising an aryloxide moiety, e.g. of formula (Vb) or (Vb-1 ) is used. A base-treated, alkene-exposed reaction medium is obtained. The <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, and spent heterogeneous base, are preferably recovered from the base-treated, alkene-exposed reaction medium by solid-liquid phase separation, e.g. filtration. The liquid, e.g. filtrate, obtained from the solid-liquid phase separation, e.g. filtration, comprises the catalyst and can be recycled into the carboxylation reactor. The recovered <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate, and spent heterogeneous base are then exposed to water in order to dissolve the <¾e-ethylenically unsaturated carboxylic acid salt, e.g. sodium acrylate. Another solid-liquid phase separation, e.g. filtration, is then applied in order to separate the spent heterogeneous base from the <¾e-ethylenically unsaturated carbox- ylic acid salt, e.g. sodium acrylate, dissolved in the water. Alternatively, the base- treated, alkene-exposed reaction medium may, for example, be brought into contact with water such that a three phase solid/liquid/liquid mixture is obtained. The σ, 2-ethylenically unsaturated carboxylic acid salt is enriched in the aqueous phase. The solid phase that essentially consists of spent heterogeneous base conjugate acid, may then be separated by solid-liquid phase separation, e.g. filtration. The liquid organic and aqueous phases are separated by liquid-liquid phase separation. The organic phase comprising the catalyst may be recycled into the carboxylation reactor.

When the organic phase that comprises the catalyst comprises traces of water, the traces of water can be removed by contacting the organic phase with a drying agent. Preferably, the organic phase is passed through a column that is filled with the drying agent.

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

The following abbreviations are used: dcpe 1 ,2-bis(dicyclohexylphosphino)ethane

dppf 1 ,1 '-Bis(diphenylphosphino)ferrocene Ex. example

LiPCy₂ lithium dicyclohexylphosphide

Ni(COD)₂ bis(cyclooctadiene)nickel(0)

THF tetrahydrofuran

TON turnover number with respect to transition metal

Various heterogeneous bases have been tested in a process according to the invention. The heterogeneous bases have been generated just before their use in the car- boxylation of ethene by reacting the heterogeneous polymer B1 , B2, B3, B4, B5, B6, BR7, BR8, or BR9 with sodium hydride as described below. The heterogeneous polymers B1 , B2, B3, B4, B5, and B6 are listed in Table 2.

Table 2:

"PS" indicates that the respective acid or base moiety is covalently immobilized on a polystyrene support. The heterogeneous polymers B1 to B4 have been purchased from commercial suppliers. B1 : AlfaAesar, product code L19594. B2: SigmaAldrich, product code 38343. B3: SigmaAldrich, product code 578282. B4: SigmaAldrich, product code 547514. B5 and B6 were synthesized as described below. Preparation of the heterogeneous polymer B5:

2-Fluoro-4-bromophenol (5.73 g, 0.03 mol) and imidazole (4.22 g, 0.062 mol) were dissolved in DMF (20 ml.) and stirred at 0 °C. tert-Butyldimethylsilyl chloride (5.1 g, 0.034 mol) was added slowly. The reaction mixture was slowly warmed to 25 °C and stirred for further 18 hours. The protected phenol was extracted with n-hexane/water (30 mL / 30 mL). The organic phase was then washed with brine (30 mL) and dried over MgSC . After drying in vacuo, 7.823 g of tert-butyldimethylsilyl-2-fluoro-4- bromophenolate was isolated (85.4 % yield).

Magnesium (87.6 mg, 3.6 mmol) was suspended in THF (5 mL). A small amount of iodine was added and the suspension was stirred at 0 °C for 10 min. tert- Butyldimethylsilyl-2-fluoro-4-bromphenolate (1.00 g, 3.276 mmol) was dissolved in THF (5 mL) and added to the suspension. The reaction mixture was stirred at 50 °C for 1 hour and then cooled to 0 °C. Bromo-functionalized polystyrene (2.34 g, 2.8 mmol Br/g, 4-bromomethyl polystyrene from Carbosynth, Productcode: FB29922) was added and it was stirred at 0 °C for 20 hours. The product was filtered, washed with THF (3 x 20 mL) and dried in vacuo (Elemental analysis: content of tert-butyldimethylsilyl-2- fluorophenyl moieties: 0.37 mmol/g).

1 g (Loading: 0.37 mmol/g) of the tert-butyldimethylsilyl-2-fluorophenyl-functionalized polystyrene was suspended in a tetrabutylammonium fluoride solution (1 mmol, 1 M in THF) and stirred at 0 °C for 30 min. The reaction mixture was diluted with ethyl acetate (10 mL), acidified with HCI (10 mL, 1 M), filtered, washed with ethyl acetate (4 x 10 mL) and dried. Synthesis of heterogeneous polymer B6:

2-Fluoro-4-bromophenol (3.82 g, 20 mmol) and PdC dppf (146.2 mg, 0.2 mmol) were dissolved in THF (20 mL). The reaction mixture was stirred at -78 °C for 10 min, vinyl magnesium bromide solution (2 equiv, 0.7 M in THF) was slowly added at -78 °C and it was stirred for another 10 min. The reaction mixture was slowly heated and stirred un- der reflux for 2 hours. After cooling, the reaction mixture was quenched with HCI (1 M, 40 mmol, 40 mL) and stirred for another 30 min. The product was extracted with diethyl ether(2x 20 mL). The diethyl ether phase was dried with MgSC and the solvent was removed in vacuo. 2-Fluoro-4-vinylphenol was recrystallized from ether/hexane (1.86 g, 67% yield).

To a solution of 2-fluoro-4-vinylphenol (414.4 mg, 3 mmol), styrene (729.0 mg, 7 mmol) and 1 ,4-divinylbenzene (2.6 mg, 0.02 mmol) in chlorobenzene (1 mL) was added AIBN (0.05 mmol, 0.2 mL, 0.2 M solution in toluene), and the reaction mixture was stirred under argon at 60 °C for 12 hours. The product was precipitated with methanol (20 mL). The polymer was dissolved in THF (20 mL) and precipitated again with methanol (20 mL). The purification step was carried out twice. The polymer was then dried in vacuo. Yield: 295 mg (Elemental analysis: 85.7 wt% C, 7.2 wt% H, 3.2 wt% F, loading: 1 .6844 mmol/g)

Recycling of used B1 to obtain BR7, BR8, and BR9: Used B1 (phenol polystyrene, load 3.5 mmol/g, 1 .5 g, as obtained from example 10) was washed with ethanol (3 x 20 mL), suspended in an excess of HCI solution (1 M, 20 mL) at 25 °C and stirred for 30 min. The polymer was filtered and washed with ethanol (3 x 50 mL). The regeneration (suspending in HCI, stirring, filtering, and washing) was performed three times to remove all reactants. BR8 was obtained accordingly from used BR7 (phenol polystyrene, load 3.5 mmol/g, 1.5 g, as obtained from example 1 1 ). BR9 was obtained accordingly from used BR8 (phenol polystyrene, loading: 3.5 mmol/g, 1 .5 g, as obtained from example 12). Mixing of polymer and alkaline material:

The heterogeneous polymer (Loading: 3.5 mmol/g, 1 .5 g) was suspended in THF (20 mL) and NaH (240 mg) was added slowly. The mixture was stirred for 15 minutes and used directly in the carboxylation reaction. Carboxylation reaction:

An autoclave (inner volume = 160 mL) was completely dried under vaccum at 100 °C (14 h) and then purged with ethylene until the inner atmosphere was fully replaced. 1 ,2- bis(dicyclohexylphosphino)ethane (0.22 mmol, 92.9 mg), Ni(COD)2 (0.2 mmol, 55 mg) and the mixture obtained from "mixing of polymer and alkaline material" were suspend- ed in THF (25 mL) and transferred at room temperature under inert conditions in the autoclave. The autoclave was pressurized as indicated with ethylene and CO2 at room temperature. The autoclave was brought to the specified temperature and stirred at 2000 rpm. After the reaction time specified, the autoclave was cooled to room temperature and the excess pressure was released within 10 minutes. A mixture of THF and D2O (15 mL/10 mL) was added dropwise to the reaction mixture. The resulting mixture was diluted with D2O (15 mL). The biphasic liquid was extracted with Et.20 (2 x 20 mL), the aqueous phase was mixed with 2,2,3,3-d4-3-(trimethylsilyl)propionic acid (0.167 mmol, 28.7 mg) and analyzed by ¹H-NMR spectroscopy (Table 3).

Table 3:

Ex. Poly- n(immboilized n(NaH) T Reaction time p(C₂H₄) p(C0₂) TON ly- Base)

mer

[mmol] [mmol] [°C] [h] [bar] [bar]

1 - - 10 80 20 5 10 0

2 B1 3.3 6.6 70 18 5 10 0.5

3 B1 3.3 6.6 70 18 5 10 0.5

4 B2 2.5 10 80 18 5 10 0.7

5 B3 2.5 10 80 18 5 10 0.6

6 B4 2.5 10 80 18 5 10 0.8

7 B1 5 10 80 72 5 10 1.6

8 B5 0.368 10 80 68 5 10 0.3

9 B6 0.18 10 100 20 10 20 31

10 B1 5 10 100 20 10 20 1.6

11 BR7 5 10 100 20 10 20 1.2

12 BR8 5 10 100 20 10 20 1.3

13 BR9 5 10 100 20 10 20 1.2

Claims

A process for preparing an o^-ethylenically unsaturated carboxylic acid salt, comprising, reacting an alkene and carbon dioxide in the presence of a carboxylation catalyst to obtain a catalyst-coordinated carboxylated intermediate, treating the catalyst- coordinated carboxylated intermediate with a heterogeneous base, and releasing the <¾e-ethylenically unsaturated carboxylic acid salt, wherein the heterogeneous base comprises an organic basic moiety that is immobilized on a solid support.

The process according to claim 1 , wherein the organic basic moiety is an alkylox- ide, aryloxide, secondary amide, or tertiary amine moiety.

The process according to claim 1 or 2, wherein the heterogeneous base comprises structural units of the general formula (V)

wherein

D is the organic basic moiety,

E is a bond or a linking moiety,

G is an anchoring unit,

k is 0 or 1 , and

^* is the site of attachment to the solid support.

The process according to any of the preceding claims, wherein the organic basic moiety is an alkyloxide moiety that corresponds to the general formula (Va)

81

R

C— O^" (Va), wherein

R⁸¹ is independently H or an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms; an aryloxide moiety that corresponds to the general formula (Vb)

(Vb), wherein

R is independently F, CI, Br, I, or Ci-C4-alkyl, and

q is 0, 1 , 2, 3, or 4; a secondary amide moiety that corresponds to the general formula (Vc)

(Vc),

wherein

R⁸¹ is independently H or R⁸⁰; or a tertiary amine moiety that corresponds to the general formula (Vd)

(Vd), wherein

R⁸⁰ and R⁸² are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, or

R⁸⁰ and R⁸², together with the Y and N atoms to which they are attached and the intervening carbon atoms, form a 5- to 8-membered cycle,

R⁸¹ is independently H or an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms,

b is 0 or 1 , and

Y is N⁺ or C.

The process according to any of the preceding claims, wherein the solid support is a silica or a crosslinked polymer.

The process according to claim 5, wherein the crosslinked polymer is a cross- linked polystyrene.

7. The process according to any of the preceding claims, wherein the heterogeneous base comprises structural units of the general formula (Ve)

(Ve) wherein

m is 0, 1 , or 2, _R40 is H or a branched, unbranched, or cyclic Ci-Ci6-alkyl,

E is a linking moiety,

D is the organic basic moiety, and

* is the site of attachment to the solid support, or wherein the solid support is a crosslinked polystyrene and the heterogeneous base comprises structural units of the general formula (Vf)

wherein

E is a bond or a linking moiety, and

D is as defined in formula (Ve).

8. The process according to any of the preceding claims, wherein the heterogeneous base is fixed in a treating zone and reaction medium leaving the carboxylation reactor is passed through the treating zone.

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

The process according to any of the preceding claims, wherein the transition metal complex comprises a ligand selected from bidentate Ρ,Ρ; Ρ,Ν; P,0; and P,carbene ligands.

1 1 . The process according to any of the preceding claims, wherein the transition metal is nickel or palladium.

The process according to any of the preceding claims, wherein the alkene is eth- ene and the <¾e-ethylenically unsaturated carboxylic acid is acrylic acid.

The process according to any of the preceding claims, wherein the process is a continuous process.

The process according to any of claims 1 to 7 or 9 to 12, wherein the organic basic moiety is an aryloxide or tertiary amine moiety and the heterogeneous base is present in the reaction medium while the alkene and carbon dioxide are reacted.

The process according to any of claims 1 to 13, wherein the carbon dioxide pressure is relieved before the catalyst-coordinated carboxylated intermediate is treated with the heterogeneous base.

16. The process according to any of the preceding claims, comprising regenerating the heterogeneous base by treating the spent heterogeneous base with an alkaline material.