EP2542516A2

EP2542516A2 - Production of ethylenically unsaturated carboxylic acid salts by the carboxylation of alkenes

Info

Publication number: EP2542516A2
Application number: EP11706270A
Authority: EP
Inventors: Michael Limbach; Jeremie Miller; Stephan Schunk
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2010-03-03
Filing date: 2011-03-03
Publication date: 2013-01-09
Also published as: JP2013521261A; CN102884025A; WO2011107559A3; CA2791834A1; WO2011107559A2

Abstract

The invention relates to a method for producing an alkali or earth alkali salt of an α,ß-ethylenically unsaturated carboxylic acid, wherein a) an alkene, carbon dioxide and a carboxylation catalyst is reacted to form an alkene/carbon dioxide/carboxylation catalyst adduct, b) using an auxiliary base, the adduct is decomposed into the auxiliary base salt of the α,ß-ethylenically unsaturated carboxylic acid releasing the carboxylation catalyst, c) using an alkali or earth alkali metal base, the auxiliary base salt of the α,ß-ethylenically unsaturated carboxylic acid is reacted to form the alkali or earth alkali salt of the α,ß-ethylenically unsaturated carboxylic acid releasing the auxiliary base. Salts of α,ß-ethylenically unsaturated carboxylic acids, such as in particular sodium acrylate, are required in large quantities, for example, for producing water-absorbing resins.

Description

Preparation of ethylenically unsaturated carboxylic acid salts by carboxylation of alkenes

description

The invention relates to a process for preparing an alkali metal or alkaline earth metal salt of an α, β-ethylenically unsaturated carboxylic acid by direct carboxylation of alkenes, in particular a process for preparing an alkali or alkaline earth metal salt of acrylic acid by direct carboxylation of ethene.

The direct addition of CO2 to ethylene (Scheme 1) is not industrially due to thermodynamic limitations (ΔΘ = 34.5 kJ / mol) and the unfavorable equilibrium, which is almost completely on the side of the starting materials at room temperature (K293 = 7x10 ^"7 ) attractive.

Scheme 1:

Yamamoto et al. {J. At the. Chem. Soc. 1980, 102, 7448) has shown that the reaction of acrylic acid with a homogeneous Ni (0) species such as bis (1, 5-cyclooctadiene) nickel, in the presence of a tertiary phosphine ligand at temperatures above 0 ° C the stable nickel Five-ring lactone A forms, the so-called "Hoberg complex" (Scheme 2). At temperatures below 0 ° C, the same reaction affords an equimolar mixture of the lactone A and the open-paced π complex B. The thermal cleavage of A into free acrylic acid failed. Theoretical chemical studies by Buntine et al. (Organometallics 2007 ^' , 26, 6784) show the -40 kcal / mol ¹ increased stability of the intermediate nickel-A as compared to the reaction product acrylic acid.

The same nickel alactone A results from the direct coupling of CO2 and ethylene as found by Hoberg (J. Organomet. Chem. 1983, C51). The same reaction is observed with the basic ligand 2,2'-bipyridine and a Ni (0) species on other alkenes or alkynes (eg, norbornene) and the nickelacycles derived therefrom. These can be isolated as stable solids (J. Organomet. Chem., 1982, C28), which proves the particular stability of these compounds. Scheme 2:

<0 ° C: A / B = 1: 1 AB

The treatment of such stable nickelalactones with aqueous mineral acids results in the case of the cycle A propionic acid, but not acrylic acid. This suggests that the β-hydride elimination necessary to form acrylic acid and its derivatives from complex A is difficult. Accordingly, no catalytic variant of this reaction has yet been described. The invention has for its object to provide a process suitable for the industrial production of α, β-ethylenically unsaturated carboxylic acid derivatives, which makes use of the reaction of CO2 and an alkene.

It has now been found that the co-use of an auxiliary in the form of a base, the balance of the reaction of CO2 and alkene can be moved to the product side. The formation of a salt of the α, β-ethylenically unsaturated carboxylic acid seems to favor the reaction thermodynamically. Salts of α, β-ethylenically unsaturated carboxylic acids, in particular sodium acrylate, are in large quantities z. B. for the production of water-absorbing resins (so-called superabsorber) needed.

The invention provides a process for preparing an alkali metal or alkaline earth metal salt of an α, β-ethylenically unsaturated carboxylic acid, comprising: a) reacting an alkene, carbon dioxide and a carboxylation catalyst to form an alkene / carbon dioxide / carboxylation catalyst adduct

b) the adduct is decomposed with the release of the carboxylation catalyst with an auxiliary base to the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid, c) the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid with the release of the auxiliary base with an alkali or Alkaline earth metal base to alkali or

Alkaline salt of the α, β-ethylenically unsaturated carboxylic acid. The steps a) and b) of the process according to the invention can be carried out successively, but are preferably carried out simultaneously by contacting alkene, carbon dioxide and carboxylation catalyst in the presence of the auxiliary base in a carboxylation reactor.

The term "alkene / carbon dioxide / carboxylation catalyst adduct" is to be construed broadly and may include compounds having structures similar to the aforementioned "Hoberg complex" or compounds of unknown structure. The term is intended to include isolatable compounds and unstable intermediates.

Suitable alkenes include at least 2 carbon atoms, e.g. 2 to 8 carbon atoms or 2 to 6 carbon atoms, and at least one ethylenically unsaturated double bond. The double bond is preferably in the terminal position. The alkene may also be a diene, wherein at least one carbon-carbon double bond is terminal and the other double bond is located at any position along the carbon skeleton. Suitable alkenes are for. Ethene, propene, isobutene and piperylene. The alkene to be used in the carboxylation is generally gaseous or liquid under the carboxylation conditions.

In a preferred embodiment, the alkene is ethene. The process according to the invention makes it possible to obtain concentrated aqueous solutions of alkali metal or alkaline earth metal acrylates, in particular sodium acrylate, in high purity and yield. In another embodiment, according to the inventive method of piperylene and KOH z. B. the potassium salt of sorbic acid accessible.

The carbon dioxide to be used in the reaction can be used in gaseous, liquid or supercritical form. It is also possible to use gas mixtures containing large quantities of carbon dioxide, provided they are substantially free of carbon monoxide.

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

The molar ratio of carbon dioxide to alkene in the feed of the reactor is generally 0.1 to 10 and preferably 0.5 to 3. The auxiliary base may be an organic or inorganic auxiliary base. Anionic bases (usually in the form of their salts with inorganic or organic ammonium ions or alkali or alkaline earth metals) or neutral bases are suitable. Inorganic anion bases include carbonates, phosphates, nitrates or halides; Examples of organic anion bases include phenolates, carboxylates, sulfates of organic molecular units, sulfonates, phosphates, phosphonates.

Organic neutral bases are, inter alia, primary, secondary or tertiary amines, furthermore ethers, esters, imines, amides, carbonyl compounds, carboxylates or carbon monoxide.

The auxiliary base is preferably a primary, secondary or tertiary amine. Most preferably, the auxiliary base is a tertiary amine. Suitable tertiary amines have the general formula (I)

NR R ² R ³ (I) in which the radicals R ¹ to R ^{3 are} identical or different and independently of one another an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, wherein individual carbon atoms can also be selected independently of one another by a heteroatom selected from the group -O- and> N-substituted and two or all three radicals can also be connected together to form a chain comprising at least four atoms ,

Examples of suitable amines are: tri-n-propylamine, tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, Tri-n-decylamine, tri-n-undecylamine, tri-n-dodecylamine, tri-n-tridecylamine, tri-n-tetradecylamine, tri-n-pentadecylamine, tri-n-hexadecylamine, tri (2-ethylhexyl) amine ,

- Dimethyl-decylamine, dimethyl-dodecylamine, dimethyl-tetradecylamine, ethyl-di- (2-propyl) amine, dioctyl-methylamine, dihexyl-methylamine.

Tricyclopentylamine, tricyclohexylamine, tricycloheptylamine, tricyclooctylamine and their substituted by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups derivatives. Dimethylcyclohexylamine, methyldicyclohexylamine, diethylcyclohexylamine, ethyldicyclohexylamine, dimethylcyclopentylamine, methyldicyclopentylamine.

Triphenylamine, methyldiphenylamine, ethyldiphenylamine, propyldiphenylamine, butyldiphenylamine, 2-ethylhexyldiphenylamine, dimethylphenylamine, diethylphenylamine, dipropylphenylamine, dibutylphenylamine, bis (2-ethylbenzylamine), hexyl) - phenylamine, tribenzylamine, methyl-dibenzylamine, ethyl-dibenzylamine and their by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl 2-propyl groups substituted derivatives.

A / C 1 -C 12 -alkyl-piperidines, Λ /, Λ / '- di-C 1 -C 12 -alkyl-piperazines, A / C 1 -C 12 -alkylpyrrolidines, / S / -C1- bis-Ci2-alkyl-imidazoles and their by one or more

Methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups substituted derivatives.

- 1, 8-diazabicyclo [5.4.0] undec-7-ene (DBU), 1, 4-diazabicyclo [2.2.2] octane (DABCO) A / methyl-8-azabicyclo [3.2.1] octane (Tropan ), A / -methyl-9-azabicyclo [3.3.1] nonane (garnetane), 1-azabicyclo [2.2.2] octane (quinuclidine).

Of course, mixtures of different bases, in particular different tertiary amines (I) can also be used in the process according to the invention. At least one of the radicals R ¹ to R ³ preferably carries two hydrogen atoms on the α-carbon atom.

Very particular preference is given in the process according to the invention as a tertiary amine, an amine of general formula (I) in which the radicals R ¹ to R ^{3 are} independently selected from the group C to Ci2-alkyl, C5- to Cs-cycloalkyl , Benzyl and phenyl.

The amount of auxiliary base to be used in the process according to the invention, preferably a tertiary amine, is generally from 5 to 95% by weight, preferably from 20 to 60% by weight, based in each case on the entire liquid reaction mixture in the reactor.

In general, the carboxylation catalyst comprises as 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) of the Periodic Table of the Elements. Preference is given to nickel, cobalt, iron, rhodium, ruthenium, palladium, rhenium, tungsten. Particularly preferred are nickel, cobalt, iron, rhodium, ruthenium. The role of these active metals is the activation of CO2 and alkene to establish a C-C bond between CO2 and the alkene. This activation can take place at one or more so-called active centers. After formation of this "Hoberg" -like complex, it can be cleaved off in the presence of the auxiliary base used according to the invention as an auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid.

In one embodiment, a heterogeneous catalyst is used as the carboxylation catalyst. Heterogeneous carboxylation catalysts can be present as a so-called supported catalyst or as a so-called full catalyst. A supported catalyst consists of a catalyst support and one or more active metals, and optionally one or more additives. Preferably, the weight fraction of active metal, based on the sum of active metal, support material and additives, 0.01 to 40 wt.%, Particularly preferably 0.1 to 30 wt .-%, very particularly preferably 0.5 to 10 wt .-%.

The weight fraction of additives, based on the sum of active metal, support material and additives, is preferably from 0.001 to 20% by weight, particularly preferably from 0.01 to 10% by weight, very particularly preferably from 0.1 to 5% by weight.

Typical preparation processes for supported catalysts are impregnation processes, such as, for example, incipient wetness, adsorption processes, such as, for example, equilibrium adsorption, precipitation processes, mechanical processes, such as milling of active metal precursor and support material, and other processes known to the person skilled in the art.

Suitable inorganic additives may include, but are not limited to, magnesium, calcium, strontium, barium, lanthanum, lanthanides, manganese, copper, silver, zinc, boron, aluminum, silicon, tin, lead, phosphorus, antimony, bismuth, sulfur and selenium. Suitable organic additives may include, but are not limited to, carboxylic acids, salts of

Carboxylic acids, polymers such as PVP (polyvinylpyrrolidone), PEG (polyethylene glycol) or PVA (polyvinyl alcohol), amines, diamines, triamines, imines.

Suitable support materials may include: refractory oxides such as zinc oxide, zirconium oxide, cerium oxide, cerium zirconium oxides, silica, alumina, silica alumina, zeolites, phyllosilicates, hydrotalcites, magnesia, titania, tungsten oxide, calcium oxide, iron oxides such as magnetite, nickel oxides, Cobalt oxides, phosphates of the main and subgroup elements, carbides, nitrides, organic polymers such as Nafion or functionalized.es polystyrene, metallic support materials such as Sheets or nets, MOFs (Metal Organic Frameworks) or composite materials of the aforementioned materials.

Preference is given to refractory oxides such as zinc oxide, zirconium oxide, cerium oxide, cerium-zirconium oxides, silica, alumina, silica-alumina, zeolites, phyllosilicates, hydrotalcites, magnesium oxide, titanium dioxide, tungsten oxide, calcium oxide, iron oxides such as magnetite, nickel oxides or cobalt oxides.

The support materials can be used, for example, as powders, granules or tablets or in another form known to the person skilled in the art.

Full catalysts can also be used according to the invention. Such materials may be prepared, for example, by precipitation methods or other methods known to those skilled in the art. Such catalysts are preferably present in metallic and / or oxidic form.

If a heterogeneous catalyst is used in the process according to the invention, this preferably remains in the carboxylation reactor. This is made possible, for example, by the fact that this is in the form of a fixed-bed catalyst firmly fixed in the reactor or, in the case of a suspension catalyst, retained by a suitable sieve or a suitable filter in the reactor.

In preferred embodiments, a homogeneous catalyst is used as the carboxylation catalyst. Homogeneous catalysts are usually complex compounds of the metals. In the case of a homogeneous catalyst, the active metals are homogeneously dissolved in the form of complex-like compounds in the reaction mixture.

Suitably, the homogeneous carboxylation catalyst comprises at least one phosphine ligand. The phosphine ligands may be mono-, bi- or polydentate, i. H. the ligands have one, two or more than two, e.g. B. three tertiary trivalent phosphorus atoms. The phosphorus atoms may carry unbranched or branched, acyclic or cyclic, aliphatic radicals having 1 to 18 carbon atoms.

Suitable monodentate phosphine ligands have, for example, the formula (II)

PR ⁴ R ⁵ R ⁶ (II) in which R ⁴ , R ⁵ and R ⁶ independently of one another are C 1 -C 12 -alkyl, C 3 -C 12 -cycloalkyl, aryl, aryl-C 1 -C 4 -alkyl, where cycloalkyl, aryl and the aryl part of aryl-C 1 -C 4 -alkyl unsubstituted tuiert or 1, 2, 3 or 4 may carry the same or different substituents such. As Cl, Br, I, F, Ci-C ₈ -alkyl or Ci-C ₄ -alkoxy.

Suitable radicals R ⁴ , R ⁵ and R ⁶ are, for example, C 1 -C 12 -alkyl, such as methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-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 -nedecyl, 1 -dodecyl, C3-Cio-cycloalkyl which is unsubstituted or may carry a Ci-C ₄ alkyl groups, such as cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl and norbornyl, aryl which is unsubstituted or may carry one or two substituents selected from chlorine, C 1 -C 8 -alkyl and C 1 -C -alkoxy, such as phenyl, naphthyl, tolyl, xylyl, chlorophenyl or anisyl.

Examples of suitable phosphine ligands of the formula (II) include trialkylphosphines, such as tri-n-propylphosphine, tri-n-butyl-phosphine, tri-ferric-butylphosphine or tri-tocylphosphine, tricycloalkylphosphines such as tricyclohexylphosphine or tricyclododecylphosphine, triarylphosphines such as triphenylphosphine, Tritolylphosphine, trianisylphosphine, trinaphthylphosphine or di (chlorophenyl) phenylphosphine and dialkylarylphosphines such as diethylphenylphosphine or dibutylphenylphosphine. Preferably, R ⁴ , R ⁵ and R ^{6 have} the same meaning.

Suitable bidentate phosphine ligands have, for example, the formula (III)

R ⁷ R ⁸ PA-PR ⁹ R ¹⁰ (III) where A is C 1 -C ₄ -alkylene and R ⁷ , R ⁸ , R ⁹ and R ¹⁰ independently of one another have the meanings given for R ⁴ , R ⁵ and R ⁶ ,

Examples of bidentate phosphines are 1, 2-bis (dicyclohexylphosphino) ethane, 1, 2-bis (dicyclohexylphosphino) methane, 1, 2-bis (dimethylphosphino) ethane, 1, 2-bis (dimethylphosphino) methane, 1, 2-bis (di-tert-butylphosphino) methane or 1,2-bis (diisopropylphosphino) propane.

The organometallic complex may contain one or more, for example two, three or four, of the abovementioned phosphine groups, having at least one unbranched or branched, acyclic or cyclic, aliphatic radical.

Furthermore, at least one equivalent of the auxiliary base itself may act as a ligand on the metal of the homogeneous complex. Alternatively, the carboxylation catalyst comprises at least one A / heterocyclic carbene ligand. Here, so-called / V-heterocyclic carbenes of the general formula (IV) or (V) function as ligands on the metal

(IV)

(V) wherein R ¹¹ and R ^{12 is} alkyl or aryl, R ¹³ , R ¹⁴ , R ¹⁵ and R ^{16 are} independently hydrogen, alkyl or aryl, or two of R ¹³ to R ^{16 is} a saturated five to form a seven-membered ring, wherein the other two radicals independently of one another represent hydrogen or methyl, R ¹⁷ and R ¹⁸ independently of one another represent hydrogen, alkyl or aryl or R ¹⁷ and R ¹⁸ , together with the carbon atoms to which they are attached , for a fused ring system, with 1 or 2 aromatic rings. In addition to the ligands described above, the catalyst may also contain at least one other ligand selected from halides, amines, carboxylates, acetylacetonate, aryl or alkylsulfonates, hydride, CO, olefins, dienes, cyclo-olefins, nitriles, aromatics and Heteroaromatics, ethers, PF3, phospholes,

Phosphabenzenes and mono-, bi- and polydentate phosphinite, phosphonite, phosphoramidite and phosphite have.

The homogeneous catalysts can be prepared both directly in their active form and from standard complexes such as [M (p-cymene) Cl2] 2, [M (benzene) Cl ₂ ] n, [M (COD) (allyl)], [ MCI ₃ xH ₂ 0], [M (acetylacetonate) ₃ ], [M (DMSO) ₄ Cl ₂ ] with M is the same element of the 4th, 6th, 7th, 8th, 9th and 10th group of the periodic table Addition of the respective ligands or are generated only under reaction conditions.

When using homogeneous catalysts, the amount of said metal component in the organometallic complex used is generally from 0.1 to 5000 ppm by weight, preferably from 1 to 800 ppm by weight, and more preferably from 5 to 500 ppm by weight, in each case based on to the entire liquid reaction mixture in the reactor. In principle, all reactors which are fundamentally suitable for gas / liquid reactions or liquid / liquid reactions under the given temperature and given pressure can be used as carboxylation reactors. Suitable standard reactors for liquid-liquid reaction systems are described, for example, in KD Henkel, Reactor Types and Their Industrial Application, in Ullmann ^'s Encyclopedia of Industrial Chemistry 2005, Wiley VCH Verlag GmbH & Co KGaA, DOI:

10.1002 / 14,356,007th b04_087, chapter 3.3 "Reactors for gas-liquid reactions". Examples which may be mentioned stirred tank reactors, tubular reactors or bubble column columns.

The carboxylation can be carried out batchwise or continuously. In the batchwise procedure, the reactor is filled with the desired liquid or optionally solid feedstocks and auxiliaries, and then carbon dioxide and alkene are pressed to the desired pressure and the desired temperature. After the end of the reaction, the reactor is usually depressurized.

In a continuous mode of operation, the feedstocks and auxiliaries, including the carbon dioxide and alkenes, are continuously added. An optionally used heterogeneous carboxylation catalyst is preferably already fixed in the reactor. Accordingly, the liquid phase is continuously removed from the reactor, so that the liquid level in the reactor remains the same on average.

The steps a) and b) are preferably carried out in the liquid or supercritical phase at pressures of from 1 to 150 bar, preferably at pressures of from 1 to 100 bar, more preferably at pressures of from 1 to 60 bar. The steps a) and b) of the process of the invention are preferably carried out at temperatures between -20 ° C to 300 ° C, preferably at temperatures between 20 ° C to 250 ° C, more preferably at temperatures between 40 ° C to 200 ° C. In order to achieve a thorough mixing of the reactants and the medium containing the carboxylation catalyst and the auxiliary base, suitable apparatuses can be used. Such apparatus may be mechanical agitators with one or more agitators with or without baffles, packed or unpacked bubble columns, packed or unpacked flow tubes with or without static mixers, or other useful apparatus known to those skilled in the art for these process steps. The use of Stromstorern and Verweiler structures is explicitly included in the inventive method. The reactants CO2 and alkene can be fed to the reaction medium either together or spatially separated. Such a spatial separation can be done, for example, in a stirred tank simply by two or more separate discharges. If several boilers are used, different media loads can be carried out, for example, in different boilers. A temporal separation of the addition of the reactants CO2 and alkene is possible in the context of the method according to the invention. Such a temporal separation can be carried out, for example, in a stirred tank by temporally staggering the application of the reactant. When using flow tubes or similar types of apparatus, such an application can be carried out, for example, at different locations in the flow tube, by such a variation of the addition sites can elegantly be done depending on the residence time, the addition of the reactants.

In step a) and b) one or more immiscible or only partially miscible liquid phases can be used. The use of supercritical media and ionic liquids and the adjustment of conditions that favor formation of such conditions are explicitly included in the process. The use of a phase-transfer catalysis and / or the use of surface-active agents are explicitly included in the process according to the invention.

In a preferred embodiment, the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid formed in step b) is separated off from the reaction medium. Preferably, the separation of the auxiliary base salt comprises a liquid-liquid phase separation in a first liquid phase, in which the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid is enriched, and a second liquid phase, in which the auxiliary base is enriched.

When using a homogeneous carboxylation catalyst, this is preferably selected so that it accumulates together with the auxiliary base in the second liquid phase. By "enriched" is meant a distribution coefficient P of the homogeneous catalyst of> 1. Preferably, the distribution coefficient is> 10, and more preferably at -20.

[Concentration homogeneous catalyst

in the second liquid phase]

P =

[Concentration homogeneous catalyst

in the first liquid phase] The selection of the homogeneous catalyst is generally made by a simple experiment in which the partition coefficient of the desired homogeneous catalyst is experimentally determined under the intended process conditions. The liquid-liquid phase separation is assisted by the concomitant use of a polar solvent in which the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid dissolves well and that with the second liquid phase in which the auxiliary base accumulates, or only limited is miscible. The polar solvent is to be selected or matched with the auxiliary base such that the polar solvent is enriched in the first liquid phase. By "enriched" is meant a weight fraction of> 50% of the polar solvent in the first liquid phase, based on the total amount of polar solvent in both liquid phases. The proportion by weight is preferably> 90%, particularly preferably> 95% and very particularly preferably> 97%. The choice of polar solvent is generally made by simple experiments in which the distribution of the polar solvent in both liquid phases under the process conditions is determined experimentally.

Suitable classes of substances which are suitable as polar solvents are preferably diols and their carboxylic esters, polyols and their carboxylic esters, sulfones, sulfoxides, open-chain or cyclic amides and mixtures of the mentioned classes of substances.

Suitable diols and polyols are, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, dipropylene glycol, 1,5-pentanediol, 1,6 Called hexanediol and glycerin.

Examples of suitable sulfoxides are dialkyl sulfoxides, preferably C.sub.1- to C.sub.6-dialkyl sulfoxides, in particular dimethyl sulfoxide.

Examples of suitable open-chain or cyclic amides are formamide, N-methylformamide, A /, A / dimethylformamide, A / methylpyrrolidone, acetamide and N-methylcaprolactam. If desired, it is also possible to use a solvent which is immiscible with the polar solvent or has only limited miscibility. Suitable solvents are, in principle, those which are (i) chemically inert with respect to the carboxylation of the alkene, (ii) in which the auxiliary base and, in the case of the use of a homogeneous catalyst, these also dissolve well, (iii) in which the auxiliary base Salt of the α, β-ethylenically unsaturated saturated carboxylic acid dissolves well and (iv) which are not or only partially miscible with the polar solvent. In principle, therefore, come chemically inert, non-polar solvents such as aliphatic, aromatic or araliphatic hydrocarbons, such as octane and higher alkanes, toluene, xylenes. If the auxiliary base itself is liquid in all process stages in the process according to the invention, the use of a solvent which is immiscible or only slightly miscible with the polar solvent is dispensable.

In the case of the use of a homogeneous Carboxylierungskatalysators is achieved, for example, by suitable choice of the auxiliary base and optionally a polar solvent and / or a thus immiscible or only limited miscible solvent, that the carboxylation enriched in the second liquid phase. Thus, this can be separated by phase separation from the auxiliary base salt of the α, β-unsaturated acid and recycled without further workup steps to the reactor. Due to the rapid separation of the catalyst from the formed auxiliary base salt of the α, β-unsaturated acid, a reverse reaction with decomposition to carbon dioxide and alkene is suppressed. In addition, the retention or separation of the catalyst due to the formation of two liquid phases losses of catalyst and thus losses of active metal are minimized.

To separate off the first liquid phase, it is possible to proceed in such a way that only the first liquid phase is led out of the carboxylation reactor and the second liquid phase remains in the carboxylation reactor. Alternatively, a liquid-liquid mixed-phase stream may be withdrawn from the carboxylation reactor and the liquid-liquid phase separation carried out in a suitable apparatus outside the carbonylation reactor. The separation of the two liquid phases is generally carried out by gravimetric phase separation. Suitable for this purpose are, for example, standard apparatuses and standard methods, which are described, for example, in E. Müller et al., "Liquid-Liquid Extraction", in Ullmann's Encylcopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.b03_06, Chapter 3 "Apparatus". In general, the first liquid phase enriched in the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid is heavier and forms the lower phase. The second liquid phase can then be returned to the carboxylation reactor.

In step c), the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid is reacted with the release of the auxiliary base with an alkali metal or alkaline earth metal base to form the alkali or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid. Suitable alkali or alkaline earth metal bases are, in particular, alkali metal or alkali metal hydroxides, carbonates, bicarbonates or oxides. Suitable alkali metal and alkaline earth metal hydroxides are, for example, sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide. Suitable alkali metal and alkaline earth metal carbonates are, for example, lithium carbonate, sodium carbonate, potassium carbonate and calcium carbonate. Suitable alkali metal hydrogencarbonates are, for example, sodium bicarbonate or potassium bicarbonate. Suitable alkali metal and alkaline earth metal oxides are, for example, lithium oxide, sodium oxide, calcium oxide and magnesium oxide. Particularly preferred is sodium hydroxide. The alkali or alkaline earth metal base is added under conditions suitable for facilitating base exchange between the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid and the alkali or alkaline earth metal base. Step c) of the process according to the invention is preferably carried out in the liquid or supercritical phase at pressures of from 1 to 150 bar, preferably at pressures of from 1 to 100 bar, particularly preferably at pressures of from 1 to 60 bar. The step c) of the method according to the invention is preferably carried out at temperatures between -20 ° C to 300 ° C, preferably at temperatures between 20 ° C to 250 ° C, more preferably at temperatures between 40 ° C to 200 ° C. The reaction conditions of step c) may be the same or different from those of step a) and b).

In step c) one or more immiscible or only partially miscible liquid phases can be used. Typically, such immiscible or only partially miscible liquid phases are an organic and an aqueous phase. The use of supercritical media and so-called ionic liquids and the setting of conditions that favor formation of such conditions is explicitly included in the process.

A separation of the alkali metal or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid from the liberated auxiliary base preferably takes place via its separation into two different phases. Thus, for example, the alkali metal or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid in a polar aqueous phase and the auxiliary base in an organic phase can be separated off. The use of effects that facilitate separation, such as ionic liquid phase change or supercritical media, is explicitly included in the process. Pressure or temperature changes, which have a favorable effect on the separation of the phases, are explicitly included in the process. The liberated auxiliary base is returned to step b). This recycling is carried out under conditions favorable to the process.

The separated first liquid phase is preferably treated with an aqueous solution of the alkali or alkaline earth metal base to obtain an aqueous solution of the alkali or alkaline earth salt of the α, β-ethylenically unsaturated carboxylic acid and an organic phase comprising the auxiliary base.

As a rule, the first liquid phase can not or only to a limited extent be mixed with the solution of the alkali metal or alkaline earth metal base, so that the treatment can expediently be carried out in the form of a liquid-liquid extraction. The liquid-liquid extraction can be carried out in all suitable equipment, such as stirred tanks, extractors or percolators. An aqueous phase is obtained which comprises an aqueous solution of the alkali metal or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid and an organic phase which comprises the auxiliary base.

The released auxiliary base is returned to the carboxylation reactor. As a result of the simpler process concept required for carrying out the method according to the invention production requires compared to the prior art, a smaller footprint and the use of fewer apparatus. It has a lower capital expenditure and a lower energy requirement.

In another embodiment, in step c), the reaction medium (without prior separation of the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid) with an aqueous solution of alkali or alkaline earth metal base extract, wherein an aqueous solution of the alkali or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid. The extraction can take place directly in the carboxylation reactor, simultaneously with the steps a) and b). For this purpose, a solution of the alkali metal or alkaline earth metal base can be introduced into the carboxylase reactor, the reaction medium in the carboxylation reactor can be extracted with the solution of the alkali metal or alkaline earth metal base, and an aqueous solution of the alkali or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid from the carboxylation reactor remove.

Claims

claims

A process for the preparation of an alkali metal or alkaline earth metal salt of an α, β-ethylenically unsaturated carboxylic acid, which comprises: a) reacting an alkene, carbon dioxide and a carboxylation catalyst to form an alkene / carbon dioxide / carboxylation catalyst adduct, b) reacting the adduct to release the carboxylation catalyst an auxiliary base to the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid decomposes,

c) reacting the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid with release of the auxiliary base with an alkali or alkaline earth metal base to the alkali metal or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid.

Process according to claim 1, wherein the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid formed in step b) is separated off from the reaction medium.

The method of claim 2, wherein the separating comprises a liquid-liquid phase separation into a first liquid phase in which the auxiliary base salt of the α, β-ethylenically unsaturated carboxylic acid is enriched, and a second liquid phase in which the auxiliary base is enriched.

Process according to claim 3, wherein in step c) the separated first liquid phase is treated with an aqueous solution of the alkali or alkaline earth metal base to obtain an aqueous solution of the alkali or alkaline earth salt of the α, β-ethylenically unsaturated carboxylic acid and an organic phase, which includes the auxiliary base.

Process according to claim 1, wherein in step c) the reaction medium is extracted with an aqueous solution of the alkali metal or alkaline earth metal base and an aqueous solution of the alkali or alkaline earth metal salt of the α, β-ethylenically unsaturated carboxylic acid is obtained.

6. The method according to any one of the preceding claims, wherein the auxiliary base is a tertiary amine.

7. The method according to claim 6, wherein the tertiary amine has the general formula (I) NR R ² R ³ (I), in which the radicals R ¹ to R ^{3 are} identical or different and independently of one another represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to 16 carbon atoms, where individual carbon atoms can also be substituted independently of one another by a hetero group selected from the group consisting of -O- and> N-, and two or all three radicals can also be linked together to form a chain comprising at least four atoms each.

8. The method according to any one of the preceding claims, wherein the carboxylation tion catalyst comprises at least one element of groups 4, 6, 7, 8, 9 or 10 of the Periodic Table of the Elements.

The process of claim 8, wherein the carboxylation catalyst comprises a complex of Ni °.

10. The method according to any one of the preceding claims, wherein lierungskatalysator used as a heterogeneous catalyst as the carboxy.

1 1. Method according to one of claims 1 to 9, wherein the carboxylation catalyst used is a homogeneous catalyst.

12. The method according to any one of claims 3 to 9, wherein the carboxylation catalyst used is a homogeneous catalyst and the carboxylation catalyst enriches in the second liquid phase.

13. A process according to any one of the preceding claims, wherein the carboxylation catalyst comprises at least one phosphine ligand.

14. A process according to any one of claims 1 to 12, wherein the carboxylation catalyst comprises at least one N-heterocyclic carbene ligand.

15. The method according to any one of the preceding claims, wherein the alkene is ethene and the α, β-ethylenically unsaturated carboxylic acid is acrylic acid.