Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02791834 2012-08-31
PRODUCTION OF ETHYLENICALLY UNSATURATED CARBOXYLIC ACID
SALTS BY THE CARBOXYLATION OF ALKENES
DESCRIPTION
The invention relates to a process for preparing an alkali metal or alkaline
earth
metal salt of an a,(3-ethyl enically unsaturated carboxylic acid by direct
carboxylation of
alkenes, especially to a process for preparing an alkali metal or alkaline
earth metal salt of
acrylic acid by direct carboxylation of ethane.
The direct addition of CO2 onto ethylene (scheme 1) is industrially
unattractive
owing to thermodynamic limitations (AG = 34.5 kJ/mol) and the unfavorable
equilibrium,
which is almost completely to the side of the reactants at room temperature
(K293 = 7 X 10-7).
Scheme 1:
Error! Objects cannot I catalyst editing field codes.
Yamamoto et al. (J. Am. Chem. Soc. 1980, 102, 7448) showed 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 forms
the stable
five-membered nickelalactone ring A, known as the "Hoberg complex" (scheme 2).
At
temperatures below 0 C, the same reaction affords an equimolar mixture of the
lactone A
and of the acyclic it complex B. The thermal splitting of A to give free
acrylic acid did
not succeed. Theoretical chemistry studies by Buntine et al. (Organometallics
2007, 26,
6784) show the -40 kcal/mol-1 increase in stability of the intermediate
nickelalactone A
compared to the acrylic acid reaction product.
The same nickelalactone A arises 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 2,2'-bipyridine ligand and an Ni(0) species on other alkenes or
alkynes (e.g.
norbornene) and the nickelacycles derived therefrom. These are isolable as
stable solids
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CA 02791834 2012-08-31
(J. Organomet. Chem. 1982, C28), which demonstrates the exceptional stability
of these
compounds.
Scheme 2:
equim. Ni complex,
PR3, temperature sated from editing field codes.
The treatment of such stable nickelalactones with aqueous mineral acids gives
propionic acid in the case of cycle A, but not acrylic acid. This suggests
that the (3-hydride
elimination needed to equim. Ni complex, ivatives thereof from the complex A
is
hindered. Accordingl, ligand L this reaction has been described as yet.
It was an object of the invention to specify a process suitable for industrial
preparation of a,(3-ethylenically unsaturated carboxylic acid derivatives,
which uses the
reaction of CO2 and an alkene.
It has now been found that additional use of an auxiliary in the form of a
base can
shift the equilibrium of the reaction of CO2 and alkene to the product side.
The formation
of a salt of the a,(3-ethylenically unsaturated carboxylic acid appears to
thermodynamically favor the reaction. Salts of a,(3-ethylenically unsaturated
carboxylic
acids, such as sodium acrylate in particular, are required in large amounts,
for example, for
production of water-absorbing resins (known as superabsorbents).
The invention provides a process for preparing an alkali metal or alkaline
earth
metal salt of an a,(3-ethylenically unsaturated carboxylic acid, wherein
a) an alkene, carbon dioxide and a carboxylation catalyst are converted to an
alkene/carbon dioxide/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 (X,(3-ethylenically
unsaturated
carboxylic acid,
c) the auxiliary base salt of the a,(3-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 a,(3-ethylenically
unsaturated
carboxylic acid.
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Steps a) and b) of the process according to the invention can be performed
successively, but preferably proceed simultaneously as a result of contacting
of alkene,
carbon dioxide and carboxylation catalyst in the presence of the auxiliary
base in a
carboxylation reactor.
The expression "alkene/carbon dioxide/carboxylation catalyst adduct" should be
interpreted in a broad sense and may comprise compounds with structures
similar to the
"Hoberg complex" mentioned at the outset or compounds of unknown structure.
The
expression shall comprise isolable compounds and unstable intermediates.
Suitable alkenes comprise at least 2 carbon atoms, for example 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, in
which case at least one carbon-carbon double bond is terminal and the other
double bond
is anywhere along the carbon skeleton. Suitable alkenes are, for example,
ethene,
propene, isobutene and piperylene. The alkene for use 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, especially sodium acrylate, in high purity and
yield. In
another embodiment, it is possible by the process according to the invention
to obtain, for
example, the potassium salt of sorbic acid from piperylene and KOH.
The carbon dioxide for use in the reaction can be used in gaseous, liquid or
supercritical form. It is also possible to use carbon dioxide-compri sing gas
mixtures
available on the industrial scale, provided that they are substantially free
of carbon
monoxide.
Carbon dioxide and alkene may also comprise inert gases, such as nitrogen or
noble gases. Advantageously, however, the content thereof is less than 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. Suitable
auxiliary bases are anionic bases (generally in the form of salts thereof with
inorganic or
organic ammonium ions or alkali metals or alkaline earth metals) or neutral
bases.
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Inorganic anionic bases include carbonates, phosphates, nitrates or halides;
examples of
organic anionic bases include phenoxides, carboxylates, sulfates of organic
molecular
units, sulfonates, phosphates, phosphonates.
Organic neutral bases include primary, secondary or tertiary amines, and also
ethers, esters, imines, amides, carbonyl compounds, carboxylates or carbon
monoxide.
The auxiliary base is preferably a primary, secondary or tertiary amine. The
auxiliary base is most preferably a tertiary amine. Suitable tertiary amines
have the
general formula (I)
NR'RZR3 (I),
in which the R1 to R3 radicals are the same or different and are each
independently 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, where
individual
carbon atoms may each independently also be replaced by a heteroatom selected
from the
group of -O- and >N-, and two or all three radicals may also be joined to one
another to
form a chain comprising at least four atoms in each case.
Examples of suitable amines include:
- 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.
- Dimethyldecylamine, dimethyldodecylamine, dimethyltetradecylamine, ethyldi(2-
propyl)amine, dioctylmethylamine, dihexylmethylamine.
- Tricyclopentylamine, tricyclohexylamine, tricycloheptylamine,
tricyclooctylamine,
and the derivatives thereof substituted by one or more methyl, ethyl, 1-
propyl, 2-
propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups.
- Dimethylcyclohexylamine, methyldicyclohexylamine, diethylcyclohexylamine,
ethyldicyclohexylamine, dimethylcyclopentylamine, methyldicyclopentylamine.
- Triphenylamine, methyldiphenylamine, ethyldiphenylamine,
propyldiphenylamine,
butyldiphenylamine, 2-ethylhexyldiphenylamine, dimethylphenylamine,
diethylphenylamine, dipropylphenylamine, dibutylphenylamine, bis-(2-
ethylhexyl)phenylamine, tribenzylamine, methyldibenzylamine,
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ethyldibenzylamine and the derivatives thereof substituted by one or more
methyl,
ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups.
- N-C1- to -C12-alkylpiperidines, N,N'-di-C1- to -C12-alkylpiperazines, N-C1-
to -C12-
alkylpyrrolidines, N-C1- to -C12-alkylimidazoles, and the derivatives thereof
substituted by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl
or 2-
methyl-2-propyl groups.
- 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2] octane
(DABCO) N-methyl-8-azabicyclo [3.2.1] octane (tropane), N-methyl-9-
azabicyclo[3.3.1]nonane (granatane), 1-azabicyclo[2.2.2]octane (quinuclidine).
In the process according to the invention, it is of course also possible to
use
mixtures of different bases, especially of different tertiary amines (I).
Preferably, at least one of the R' to R3 radicals bears two hydrogen atoms on
the a-
carbon atom.
The tertiary amine used in the process according to the invention is most
preferably
an amine of the general formula (I) in which the R' to R3 radicals are each
independently
selected from the group of C1- to C12-alkyl, C5- to C8-cycloalkyl, benzyl and
phenyl.
The amount of the auxiliary base for use in the process according to the
invention,
preferably of a tertiary amine, is generally 5 to 95% by weight, preferably 20
to 60% by
weight, based in each case on the overall liquid reaction mixture in the
reactor.
In general, the carboxylation catalyst comprises, as the active metal, at
least one
element from 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. Particular preference is given to nickel,
cobalt, iron,
rhodium, ruthenium.
The role of these active metals is the activation of CO2 and alkene in order
to form
a C-C bond between CO2 and the alkene. This activation can be effected at one
or more
active sites. After formation of this "Hoberg"-like complex, it can be
eliminated in the
presence of the auxiliary base used in accordance with the invention as the
auxiliary base
salt of the a,(3-ethylenically unsaturated carboxylic acid.
In one embodiment, the carboxylation catalyst used is a heterogeneous
catalyst.
Heterogeneous carboxylation catalysts may be present in the form of supported
catalysts
CA 02791834 2012-08-31
or in the form of unsupported catalysts. A supported catalyst consists of a
catalyst support
and one or more active metals, and optionally one or more additives. The
proportion by
weight of active metal, based on the sum of active metal, support material and
additives, is
preferably 0.01 to 40% by weight, more preferably 0.1 to 30% by weight, most
preferably
0.5 to 10% by weight.
The proportion by weight of additives, based on the sum of active metal,
support
material and additives, is preferably 0.001 to 20% by weight, more preferably
0.01 to 10%
by weight, most preferably 0.1 to 5% by weight.
Typical processes for preparing supported catalysts are impregnation
processes, for
example incipient wetness, adsorption processes, for example equilibrium
adsorption,
precipitation processes, mechanical processes, for example the grinding of
active metal
precursor and support material, and further processes known to those skilled
in the art.
Suitable inorganic additives may include: magnesium, calcium, strontium,
barium,
lanthanum, lanthanoids, manganese, copper, silver, zinc, boron, aluminum,
silicon, tin,
lead, phosphorus, antimony, bismuth, sulfur and selenium. Suitable organic
additives may
include: carboxylic acids, salts of carboxylic acids, polymers, for example
PVP
(polyvinylpyrrolidone), PEG (polyethylene glycol) or PVA (polyvinyl alcohol),
amines,
diamines, triamines, imines.
Suitable support materials may include: refractory oxides, for example zinc
oxide,
zirconium oxide, cerium oxide, cerium zirconium oxides, silica, alumina,
silica-alumina,
zeolites, sheet silicates, hydrotalcites, magnesium oxide, titanium dioxide,
tungsten oxide,
calcium oxide, iron oxides, for example magnetite, nickel oxides, cobalt
oxides,
phosphates of the main group and transition group elements, carbides,
nitrides, organic
polymers such as Nafion or functionalized polystyrene, metallic support
materials such as
metal sheets or meshes, MOFs (metal-organic frameworks) or composite materials
of the
aforementioned materials.
Preference is given to refractory oxides, for example zinc oxide, zirconium
oxide,
cerium oxide, cerium zirconium oxides, silica, alumina, silica-alumina,
zeolites, sheet
silicates, hydrotalcites, magnesium oxide, titanium dioxide, tungsten oxide,
calcium oxide,
iron oxides, for example magnetite, nickel oxides or cobalt oxides.
The support materials can be used, for example, in the form of powder,
granules or
tablets, or in another form known to those skilled in the art.
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According to the invention, it is also possible to use unsupported catalysts.
Such
materials can be prepared, for example, by precipitation processes or other
processes
known to those skilled in the art. Such catalysts are preferably present in
metallic and/or
oxidic form.
When a heterogeneous catalyst is used in the process according to the
invention, it
preferably remains in the carboxylation reactor. This is enabled, for example,
by virtue of
it being present in the form of a fixed bed catalyst fixed within the reactor,
or, in the case
of a suspension catalyst, by virtue of it being retained within the reactor by
a suitable sieve
or a suitable filter.
In preferred embodiments, the carboxylation catalyst used is a homogeneous
catalyst. Homogeneous catalysts are generally complexes of the metals. In the
case of a
homogeneous catalyst, the active metals are present homogeneously dissolved in
the
reaction mixture in the form of complex-type compounds.
The homogeneous carboxylation catalyst suitably comprises at least one
phosphine
ligand. The phosphine ligands may be mono-, bi- or polydendate, i.e. the
ligands have
one, two or more than two, e.g. three, tertiary trivalent phosphorus atoms.
The phosphorus
atoms may be unbranched or branched, acyclic or cyclic, aliphatic radicals
having 1 to 18
carbon atoms.
Suitable monodentate phosphine ligands have, for example, the formula (II)
PR4R5R6 (II)
in which R4, R5 and R6 are each independently C1-C12-alkyl, C3-C12-cycloalkyl,
aryl, aryl-
C1-C4-alkyl, where cycloalkyl, aryl and the aryl moiety of aryl-C1-C4-alkyl
are
unsubstituted or may bear 1, 2, 3 or 4 identical or different substituents,
for example Cl,
Br, I, F, C1-C8-alkyl or C1-C4-alkoxy.
Suitable R4, R5 and R6 radicals are, for example, C1-C12-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-undecyl, 1-dodecyl, C3-C10-cycloalkyl which is
unsubstituted or
may bear a C1-C4-alkyl group, for example cyclopentyl, methylcyclopentyl,
cyclohexyl,
methylcyclohexyl, cycloheptyl, cyclooctyl and norbornyl, aryl which is
unsubstituted or
may bear one or two substituents selected from chlorine, C1-C8-alkyl and C1-C8-
alkoxy,
such as phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl.
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Examples of suitable phosphine ligands of the formula (II) comprise
trialkylphosphines such as tri-n-propylphosphine, tri-n-butylphosphine, tri-
tert-
butylphosphine or trioctylphosphine, tricycloalkylphosphines such as
tricyclohexylphosphine or tricyclododecylphosphine, triarylphosphines such as
triphenylphosphine, tritolylphosphine, trianisylphosphine,
trinaphthylphosphine or
di(chlorophenyl)phenylphosphine, and dialkylarylphosphines such as
diethylphenylphosphine or dibutylphenylphosphine. R4, R5 and R6 preferably
have the
same definition.
Suitable bidentate phosphine ligands have, for example, the formula (III)
R7R8P-A-PR9R10 (III)
in which A is C1-C4-alkylene and R7, R8, R9 and R10 are each independently as
defined for
R4, R5 and R6.
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(di-
isopropylphosphino)propane.
The organometallic complex may comprise one or more, for example two, three or
four, of the abovementioned phosphine groups with at least one unbranched or
branched,
acylic or cyclic, aliphatic radical.
In addition, at least one equivalent of the auxiliary base itself may function
as a
ligand on the metal of the homogeneous complex.
Alternatively, the carboxylation catalyst comprises at least one N-
heterocyclic
carbene ligand. Here, N-heterocyclic carbenes of the general formula (IV) or
(V) function
as ligands on the metal:
1-NN--R12
R R1-- N N~R12
R16 _
R13 R 14 R15 R 17) ~ R 18
(IV) (V)
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in which R11 and R12 are each alkyl or aryl, R13, R14, R15 and R16 are each
independently
hydrogen, alkyl or aryl, or two of the R13 to R16 radicals form a saturated
five- to seven-
membered ring, where the two other radicals are each independently hydrogen or
methyl,
R17 and R18 are each independently hydrogen, alkyl or aryl, or R17 and R18,
together with
the carbon atoms to which they are bonded, are a fused ring system with 1 or 2
aromatic
rings.
In addition to the ligands described above, the catalyst may also have at
least one
further ligand which is selected from halides, amines, carboxylates,
acetylacetonate, aryl-
or alkylsulfonates, hydride, CO, olefins, dienes, cycloolefins, nitriles,
aromatics and
heteroaromatics, ethers, PF3, phospholes, phosphabenzenes and mono-, di- and
polydentate phosphinite, phosphonite, phosphoramidite and phosphite ligands.
The homogeneous catalysts can be obtained either directly in their active form
or
preceding from customary standard complexes, for example [M(p-cymene)C12]2,
[M(benzene)C12]", [M(COD)(allyl)], [MC13xH2O], [M(acetylacetonate)3],
[M(DMSO)4C12] where M is an element of group 4, 6, 7, 8, 9 or 10 of the
Periodic Table
with addition of the corresponding ligand(s) only under reaction conditions.
In the case of use of homogeneous catalysts, the amount used of the metal
complexes mentioned in the organometallic complex is generally 0.1 to 5000 ppm
by
weight, preferably 1 to 800 ppm by weight and more preferably 5 to 500 ppm by
weight,
based in each case on the overall liquid reaction mixture in the reactor.
The carboxylation reactors used may in principle be all reactors which are
suitable
for gas/liquid reactions or liquid/liquid reactions at the given temperature
and under 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.b04087, chapter 3.3 "Reactors for gas-liquid
reactions".
Examples include stirred tank reactors, tubular reactors or bubble column
reactors.
The carboxylation can be performed batchwise or continuously. In batchwise
mode, the reactor is filled with the desired liquid or optionally solid
feedstocks and
auxiliaries, and then carbon dioxide and alkene are injected to the desired
pressure and the
desired temperature. After the end of the reaction, the reactor is generally
decompressed.
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In continuous mode, the feedstocks and auxiliaries, including the carbon
dioxide
and alkene, are added continuously. Any heterogeneous carboxylation catalyst
to be used
is preferably present fixed within the reactor. Accordingly, the liquid phase
is removed
continuously from the reactor, such that the liquid level in the reactor
remains the same on
average.
Steps a) and b) are preferably performed in the liquid or supercritical phase
at
pressures between 1 and 150 bar, preferably at pressures between 1 and 100
bar, more
preferably at pressures between 1 and 60 bar. Steps a) and b) of the process
according to
the invention are preferably performed at temperatures between -20 C and 300
C,
preferably at temperatures between 20 C and 250 C, more preferably at
temperatures
between 40 C and 200 C.
In order to achieve good mixing of the reactants and of the medium which
comprises the carboxylation catalyst and the auxiliary base, suitable
apparatus can be
used. Such apparatus may be mechanical stirred apparatus with one or more
stirrers with
or without baffles, packed or non-packed bubble columns, packed or non-packed
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 baffles and delay structures is
explicitly
incorporated into the process according to the invention.
The CO2 and alkene reactants can be fed to the reaction medium either together
or
spatially separately. Such a spatial separation can be accomplished, for
example in a
stirred tank, in a simple manner by means of two or more separate inlets. When
more than
one tank is used, for example, there may be different media charges in
different tanks.
Separation of the addition of the CO2 and alkene reactants in terms of time is
also possible
in the process according to the invention. Such a time separation can be
accomplished, for
example, in a stirred tank by staggering the charging with the reactants. In
the case of use
of flow tubes or apparatus of a similar kind, such charging can be effected,
for example, at
different sites in the flow tube; such a variation of the addition sites is an
elegant way of
adding the reactants as a function of residence time.
In steps a) and b), one or more immiscible or only partly miscible liquid
phases can
be used. The use of supercritical media and ionic liquids and the
establishment of
conditions which promote formation of such states are explicitly incorporated
into the
CA 02791834 2012-08-31
process. The application of phase transfer catalysis and/or the use of
surfactants are
explicitly incorporated into the process according to the invention.
In a preferred embodiment, the auxiliary base salt, formed in step b), of the
a,(3-
ethylenically unsaturated carboxylic acid is removed from the reaction medium.
The
removal of the auxiliary base salt preferably comprises a liquid-liquid phase
separation
into a first liquid phase in which the auxiliary base salt of the a,(3-
ethylenically
unsaturated carboxylic acid is enriched, and a second liquid phase in which
the auxiliary
base is enriched.
In the case of use of a homogeneous carboxylation catalyst, it is preferably
selected
such that it is enriched together with the auxiliary base in the second liquid
phase.
"Enriched" is understood to mean a partition coefficient P of the homogeneous
catalyst of
> 1. The partition coefficient is preferably >I 0 and more preferably >20.
[Concentration of homogeneous
catalyst in the second liquid phase
P=
[Concentration of homogeneous catalyst
in the first liquid phase]
The homogeneous catalyst is generally selected by a simple experiment in which
the partition coefficient of the desired homogeneous catalyst is determined
experimentally
under the planned process conditions.
The liquid-liquid phase separation is promoted by the additional use of a
polar
solvent in which the auxiliary base salt of the a,(3-ethylenically unsaturated
carboxylic
acid has good solubility and which has zero or only limited miscibility with
the second
liquid phase in which the auxiliary base is enriched. The polar solvent should
be selected,
or matched with the auxiliary base, such that the polar solvent is present in
enriched form
in the first liquid phase. "Enriched" is understood to mean a proportion by
weight 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%,
more
preferably > 95% and most preferably > 97%. The polar solvent is generally
selected by
simple tests in which the partition of the polar solvent in the two liquid
phases is
determined experimentally under the process conditions.
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Preferred substance classes which are suitable as polar solvents are diols and
the
carboxylic esters thereof, polyols and the carboxylic esters thereof,
sulfones, sulfoxides,
open-chain or cyclic amides, and mixtures of the substance classes mentioned.
Examples of suitable diols and polyols are 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-hexanediol and glycerol.
Examples of suitable sulfoxides are dialkyl sulfoxides, preferably Ci- to C6-
dialkyl
sulfoxides, especially dimethyl sulfoxide.
Examples of suitable open-chain or cyclic amides are formamide, N-
methylformamide, N,N-dimethylformamide, N-methylpyrrolidone, acetamide and N-
methylcaprolactam.
If desired, it is possible also to use a solvent which is immiscible or has
only
limited miscibility with the polar solvent. Suitable solvents are in principle
those which
(i) are chemically inert with regard to the carboxylation of the alkene, (ii)
in which the
auxiliary base and, in the case of use of a homogeneous catalyst, this too
have good
solubility, (iii) in which the auxiliary base salt of the a,(3-ethylenically
unsaturated
carboxylic acid has good solubility and (iv) which are immiscible or only have
limited
miscibility with the polar solvent. Useful solvents are therefore in principle
chemically
inert, nonpolar solvents, for instance aliphatic, aromatic or araliphatic
hydrocarbons, for
example octane and higher alkanes, toluene, xylene. If the auxiliary base
itself is present
in liquid form in all process stages in the process according to the
invention, the use of a
solvent which is immiscible or has only limited miscibility with the polar
solvent is
unnecessary.
In the case of use of a homogeneous carboxylation catalyst, suitable selection
of
the auxiliary base and optionally of a polar solvent and/or of a solvent which
is immiscible
or has only limited miscibility therewith, for example, achieves the effect
that the
carboxylation catalyst is enriched in the second liquid phase. For instance,
it can be
separated by phase separation from the auxiliary base salt of the a,(3-
unsaturated acid and
be recycled to the reactor with no further workup steps. Owing to the rapid
removal of the
catalyst from the auxiliary base salt formed from the a,(3-unsaturated acid, a
reverse
reaction with decomposition to carbon dioxide and alkene is suppressed. In
addition, the
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CA 02791834 2012-08-31
retention or removal of the catalyst, owing to the formation of two liquid
phases,
minimizes losses of catalyst and hence losses of active metal.
To remove the first liquid phase, the procedure may be to only conduct the
first
liquid phase out of the carboxylation reactor and to leave the second liquid
phase within
the carboxylation reactor. Alternatively, a liquid-liquid mixed-phase stream
can be
conducted out of the carboxylation reactor and the liquid-liquid phase
separation can be
performed in a suitable apparatus outside the carboxylation reactor. The two
liquid phases
are generally separated by gravimetric phase separation. Suitable examples for
this
purpose are standard apparatus and standard methods which can be found, for
example, in
E. Muller et al., "Liquid-Liquid Extraction", in Ullmann's Encyclopedia of
Industrial
Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA,
DOI:10.1002/14356007.b03_06, chapter 3 "Apparatus". In general, the first
liquid phase
enriched with the auxiliary base salt of the (x,(3-ethylenically unsaturated
carboxylic acid is
heavier and forms the lower phase. The second liquid phase can subsequently be
recycled
into the carboxylation reactor.
In step c), the auxiliary base salt of the (x,(3-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 a,(3-
ethylenically
unsaturated carboxylic acid. Suitable alkali metal or alkaline earth metal
bases are
especially alkali metal or alkaline earth metal hydroxides, carbonates,
hydrogencarbonates
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 hydrogencarbonate or
potassium
hydrogencarbonate. Suitable alkali metal and alkaline earth metal oxides are,
for example,
lithium oxide, sodium oxide, calcium oxide and magnesium oxide. Particular
preference
is given to sodium hydroxide.
The alkali metal or alkaline earth metal base is added under conditions which
are
suitable for enabling base exchange between the auxiliary base salt of the
a,(3-
ethylenically unsaturated carboxylic acid and the alkali metal or alkaline
earth metal base.
Step c) of the process according to the invention is preferably performed in
the liquid or
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CA 02791834 2012-08-31
supercritical phase at pressures between 1 and 150 bar, preferably at
pressures between 1
and 100 bar, more preferably at pressures between 1 and 60 bar. Step c) of the
process
according to the invention is preferably performed at temperatures between -20
C and
300 C, preferably at temperatures between 20 C and 250 C, more preferably at
temperatures between 40 C and 200 C. The reaction conditions of step c) may be
the
same as or different than those of steps a) and b).
In step c), one or more immiscible or only partly miscible liquid phases can
be
used. Typically, such immiscible or only partly miscible liquid phases are an
organic
phase and an aqueous phase. The use of supercritical media and ionic liquids,
and the
establishment of conditions which promote the formation of such states, is
explicitly
incorporated into the process.
The alkali metal or alkaline earth metal salt of the (x,(3-ethylenically
unsaturated
carboxylic acid is preferably separated from the auxiliary base released via
the separation
thereof into two different phases. It is thus possible, for example, to remove
the alkali
metal or alkaline earth metal salt of the a,(3-ethylenically unsaturated
carboxylic acid in a
polar aqueous phase, and the auxiliary base in an organic phase. The use of
effects which
facilitate separation, such as the change of phase of ionic liquids or of
supercritical media,
is explicitly incorporated into the process. Pressure or temperature changes
which have a
favorable effect on the separation of the phases are explicitly incorporated
into the
process.
The auxiliary base released is recycled into step b). This recycling is
undertaken
under conditions which are favorable for the process.
The first liquid phase removed is preferably treated with an aqueous solution
of the
alkali metal or alkaline earth metal base to obtain an aqueous solution of the
alkali metal
or alkaline earth metal salt of the a,(3-ethylenically unsaturated carboxylic
acid and an
organic phase which comprises the auxiliary base.
The first liquid phase is generally immiscible or has only limited miscibility
with
the solution of the alkali metal or alkaline earth metal base, such that the
treatment can
appropriately be performed in the form of a liquid-liquid extraction. Liquid-
liquid
extraction can be effected in all apparatus suitable for this purpose, such as
stirred vessels,
extractors or percolators. An aqueous phase is obtained, which comprises an
aqueous
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CA 02791834 2012-08-31
solution of the alkali metal or alkaline earth metal salt of the a,(3-ethyl
enically unsaturated
carboxylic acid, and an organic phase which comprises the auxiliary base.
The auxiliary base released is recycled back into the carboxylation reactor.
As a
result of the simpler process design, the production plant required to perform
the process
according to the invention requires less space and the use of fewer
apparatuses compared
to the prior art. It has a lower capital cost and a lower energy demand.
In another embodiment, in step c), the reaction medium (without preceding
removal of the auxiliary base salt of the a,(3-ethylenically unsaturated
carboxylic acid) can
be extracted with an aqueous solution of the alkali metal or alkaline earth
metal base to
obtain an aqueous solution of the alkali metal or alkaline earth metal salt of
the (x,(3-
ethylenically unsaturated carboxylic acid. The extraction can be effected
directly within
the carboxylation reactor, simultaneously with steps a) and b). For this
purpose, a solution
of the alkali metal or alkaline earth metal base can be introduced into the
carboxylation
reactor, the reaction medium can be extracted in the carboxylation reactor
with the
solution of the alkali metal or alkaline earth metal base, and an aqueous
solution of the
alkali metal or alkaline earth metal salt of the a,(3-ethylenically
unsaturated carboxylic
acid can be removed from the carboxylation reactor.
