WO2013014160A1

WO2013014160A1 - Method for producing formamides and formic acid esters

Info

Publication number: WO2013014160A1
Application number: PCT/EP2012/064508
Authority: WO
Inventors: Thomas Schaub; Rocco Paciello; Marek Pazicky; Giuseppe Fachinetti; Debora Preti
Original assignee: Basf Se
Priority date: 2011-07-27
Filing date: 2012-07-24
Publication date: 2013-01-31
Also published as: EP2736872A1; JP2014523448A; CN103702968A; BR112014001571A2; ZA201401358B; KR20140044871A; RU2014107102A; CA2837793A1

Abstract

The invention relates to a method for producing carboxylic acid derivatives of general formula (1a): H-(C=0)-R (la), in which R is selected from the group comprising OR¹ and NR²R³, wherein R¹ is unsubstituted or at least monosubstituted C₁-C₁₅ alkyl, C₅-C₁₀ cycloalkyl, C₅-C₁₀ heterocyclyl, C₅-C₁₀ aryl, or C₅-C₁₀ heteroaryl, wherein the substituents are selected from the group comprising C₁-C₁₅ alkyl, C₁-C₆ alkoxy, C₅-C₁₀ cycloalkyl, and C₅-C₁₀ aryl; R² and R³, independently of one another, are hydrogen or unsubstituted or at least monosubstituted C₁-C₁₅ alkyl, C₅-C₁₀ cycloalkyl, C₅-C₁₀ heterocyclyl, C₅-C₁₀ aryl, or C₅-C₁₀ heteroaryl, wherein the substituents are selected from the group comprising C₁-C₁₅ alkyl, C₅-C₁₀ cycloalkyl, and C₅-C₁₀ aryl, or R² and R³ form a five- or six-membered ring together with the nitrogen atom, which ring optionally additionally contains one or more heteroatoms selected from O, S, and N, which heteroatom bears the substituent R⁴, wherein R⁴ is hydrogen or C₁-C₆ alkyl; by reacting a reaction mixture (Rg) containing carbon dioxide, hydrogen, and an alcohol of general formula (Ib): R¹-OH (Ib), in which R¹ has the aforementioned meanings, or an amine of general formula (Ic): NHR²R³ (Ic), in which R² and R³, independently of each other, have the aforementioned meanings, in a hydrogenation reactor in the presence of a catalyst containing gold at a pressure in the range of 0.2 to 30 MPa and a temperature in the range of 20 to 200 °C.

Description

The present invention relates to a process for the preparation of formamides and formic acid esters, ie of formamide and its / V-substituted derivatives, as well as esters of formic acid and alcohols starting from carbon dioxide and hydrogen. Formamide and its N-substituted derivatives are important selective solvents and extractants because of their polarity. They are z. B. for the extraction of butadiene from C ₄ cuts, acetylene from C ₂ cracker fractions and aromatics used from aliphatic.

Formic acid esters such as methyl formate or ethyl formate are used as foaming agents or fragrances.

All large-scale production processes for the production of formamide and its alkyl derivatives as well as formic acid esters use carbon monoxide as C building block.

Formamide, / V-alkylformamide and / V, / V-dialkylformamide are prepared by reacting methyl formate, which is accessible by the reaction of carbon monoxide with methanol, with ammonia, / V-alkylamines or / V, / V-dialkylamines. The liberated methanol can be recycled to the Methylformiatsynthese from carbon monoxide and methanol. Other formic acid esters are obtained by the reaction of formic acid with the corresponding alcohol with dehydration.

In another, also technically used synthesis, ammonia or the abovementioned amines are reacted at 20 to 100 ° C. and 2 to 10 MPa directly with carbon monoxide instead of methyl formate. Work is carried out in methanol as a solvent with alkoxides as catalysts (Hans-Jürgen Arpe, Industrial Organic Chemistry, 6th edition, 2007, pages 48 to 49). Carbon monoxide is a comparatively expensive Cr building block. A disadvantage of carbon monoxide is beyond its toxicity, which makes working under high safety precautions necessary. Furthermore, the relatively high pressures in the production of formamides from carbon monoxide are costly.

Many attempts have therefore been made to carbon monoxide by the cheap, non-toxic and abundant CrBaustein carbon dioxide (eg, Applied Homogeneous Catalysis with Organometallic Compounds, Volume 2, pages 1058 to 1072, 1996, VCH Verlagsgesellschaft and W. Leitner, Angew Chem. Int. Ed., Engl., 1995, 34, pages 2207 to 2221). In most of these works, however, homogeneously dissolved catalysts are used whose separation from the product and recycling to the hydrogenation is difficult.

It has been attempted to immobilize the homogeneous catalysts on support materials in order to be able to separate them more easily. This method is described for dimethylformamide in Y. Kayaki, Y. Shimokawatoko, T. Ikariya, Adv. Synth. Catal. 2003, 345, 175-179. But for this concept, special, expensive to produce carrier materials such as diphosphine-modified polystyrenes or silica gels are needed. Another disadvantage is that the catalyst activity decreases significantly at each recycling step. This is due, among other things, to the fact that the homogeneous catalyst does not remain completely immobilized. The preparation of the economically attractive formamide is not described in this work.

Through the use of heterogeneous hydrogenation catalysts, a simple catalyst separation and reuse of the catalyst can be made possible. No. 4,269,998 describes the use of copper chromite catalysts in combination with group VIII compounds for the preparation of dialkylformamides. The disadvantage is that only dialkylformamides are accessible by this method. The preparation of formamide or formic esters is not described. In addition, the group VIII compounds are sensitive to carbon monoxide. However, carbon monoxide is often present as an impurity in the hydrogen or carbon dioxide used. So that in this process, high-purity hydrogen and high-purity carbon dioxide must be used.

Liu, G. Guo, Z. Zhang, T. Jiang, H. Liu, J. Song, H. Fan, B. Han, Chem. Commun. 2010, 46, 5770-5772 describe copper / zinc oxide catalysts without a group VIII compounds for the preparation of dimethylformamide. A disadvantage of this method is that also only dimethylformamide is accessible. The preparation of formamide or formic acid esters will not be described. The object of the present invention is to provide a process for the preparation of carboxylic acid derivatives, in particular formamide and N-substituted formamide derivatives and formic acid esters, based on the starting materials carbon dioxide, hydrogen and an amine or an alcohol. The process should preferably be able to be operated continuously. The preparation of the carboxylic acid derivatives, in particular of formamide and N- substituted formamide derivatives and formic acid esters, should preferably take place in one reaction step (integrated process). The target products, ie formamide, the N-substituted formamide derivatives or the formic esters are to be made accessible with high yields and selectivities. The work-up of the reaction product from the hydrogenation reactor and the catalyst separation should be technically simple, require little energy, and preferably exclusively with substances already present in the process, without additional auxiliaries.

This object is achieved by a process for the preparation of carboxylic acid derivatives of the general formula (Ia)

H- (C = O) -R (Ia),

in the

R is selected from the group consisting of OR ¹ and NR ² R ^3, wherein unsubstituted or at least monosubstituted CRCI ₅ alkyl, C5-C ₁ 0-cycloalkyl, C ₅ -C ₁₀ heterocyclyl, C ₅ -C ₁₀ aryl, or C ₅ -C ₁₀ heteroaryl, wherein the substituents are selected from the group consisting of C 1 -C ₅ -alkyl, C -C ₆ -alkoxy, C ₅ -C ₁₀ -cycloalkyl and C ₅ -C ₁₀ -aryl;

R ² and R ³ are independently hydrogen, unsubstituted or at least mono-substituted Ci-C ₅ alkyl, C ₅ -C ₁₀ cycloalkyl, C ₅ -C ₁₀ - heterocyclyl, C ₅ -C ₁₀ aryl or C ₅ -C ₁₀ - Heteroaryl are, wherein the substituents are selected from the group consisting of CrCi ₅ alkyl, C ₅ -C ₁₀ cycloalkyl and C ₅ -C ₁₀ aryl or

R ² and R ³ together with the nitrogen atom form a five- or six-membered ring, which optionally additionally contains one or more heteroatoms selected from O, S and N, which carries the substituent R ⁴ , wherein

R ^{4 is} hydrogen or CC ₆ alkyl; by reaction of a reaction mixture (Rg) comprising carbon dioxide, hydrogen and an alcohol of the general formula (Ib) R ¹ -OH (Ib)

in which R ^{1 has} the above meanings or an amine of the general formula (Ic)

NHR ² R ³ (Ic) wherein R ² and R ³ are each independently as defined above, in a hydrogenation reactor in the presence of a catalyst containing gold at a pressure in the range of 0.2 to 30 MPa and a temperature in the range of 20 to 200 ° C.

The inventive method allows the use of inexpensive carbon dioxide instead of the relatively expensive carbon monoxide as a Ci building block. In addition, the inventive method allows easy separation of the catalyst, good product yield and simple workup of the product mixture.

In the process according to the invention, a reaction mixture (Rg) is reacted which contains carbon dioxide, hydrogen, an alcohol (Ib) or an amine (Ic). In the event that a reaction mixture (Rg) containing an alcohol (Ia) is used, forms as the carboxylic acid derivative (Ia) formic acid ester (Ia1) according to the general reaction equation (II), wherein for the formic acid ester (Ia1) the abovementioned definitions apply to R ¹ accordingly. This means that one mole of carbon dioxide, one mole of hydrogen and one mole of alcohol (Ib) form one mole of formic acid ester (Ia1) and one mole of water of reaction.

In the event that a reaction mixture (Rg) containing an amine (Ia) is used, forms as carboxylic acid derivative (Ia) a formamide compound (Ia2) according to the general reaction equation (I II), wherein for the formamide compound (Ia2), the above Definitions for R ² and R ³ apply accordingly. This means that one mole of carbon dioxide, one mole of hydrogen and one mole of amine (Ic) form one mole of formamide compound (Ia2) and one mole of water of reaction. O

C0 ₂ + H ₂ + R ¹ -OH HC OR ¹ + H ₂ 0 (II)

(Ib) (Ia1)

O

C0 ₂ + H ₂ + NHR ² R ³ HC NR ² R ³ + H ₂ O (III)

(lc) (Ia2)

For the preparation of formic acid esters (Ia1), in a preferred embodiment, alcohols R OH (Ib) are used in which

R ^{1 is} unsubstituted or at least monosubstituted C ¹ -C ₈ -alkyl, wherein the substituents are selected from the group consisting of CC ₆ alkyl and CC ₆ alkoxy.

In this case, the corresponding formic esters of the general formula (Ia1)

H (C = O) -OR ¹ (Ia1) obtained in the

R ^{1 is} unsubstituted or at least monosubstituted C ¹ -C ₈ -alkyl, the substituents being selected from the group consisting of CC ₆ -alkyl and CC ₆ -alkoxy.

In the context of the present invention, branched, unbranched, saturated and unsaturated groups are understood by C 1 -C ₁₅ -alkyl. Preferred are saturated alkyl groups having 1 to 6 carbon atoms (C 1 -C ₆ -alkyl). More preferred are saturated alkyl groups having 1 to 4 carbon atoms (C ₁ -C ₄ alkyl).

Examples of saturated alkyl groups are methyl, ethyl, n-propyl, isopropyl, isobutyl, sec-butyl, tert-butyl, amyl and hexyl. Examples of unsaturated alkyl groups (alkenyl, alkynyl) are vinyl, allyl, butenyl, ethynyl and propynyl.

The C -C alkyl group may be unsubstituted or substituted with one or more substituents selected from the group Ci-C ₅ alkyl, d-Ce-alkoxy, C ₅ -C ₁₀ - cycloalkyl, C ₅ -C ₁₀ aryl.

C ₅ -C ₁₀ -cycloalkyl is understood here to mean saturated, unsaturated monocyclic and polycyclic groups. Examples of C ₅ -C ₀ cycloalkyl are cyclopentyl, cyclohexyl or cycloheptyl. The cycloalkyl groups may be unsubstituted or substituted with one or more substituents as above to the group C- | -C ₁₅ alkyl has been defined.

In the context of the present invention, C ₅ -C ₁₀ -aryl means an aromatic ring system having 5 to 10 carbons. The aromatic ring system may be monocyclic or bicyclic. Examples of aryl groups are phenyl, naphthyl, such as 1-naphthyl and 2-naphthyl. The aryl group may be unsubstituted or substituted with one or more substituents as defined above for C 1 -C ₁₅ alkyl. In the context of the present invention, C ₅ -C ₁₀ heteroaryl is understood as meaning a heteroaromatic system which contains at least one heteroatom selected from the group consisting of N, O and S. The heteroaryl groups may be monocyclic or bicyclic. In the case where nitrogen is a ring atom, the present invention also includes N-oxides of the nitrogen-containing heteroaryls. Examples of heteroaryls are thienyl, benzothienyl, 1-naphthothienyl, thianthrenyl, furyl, benzofuryl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolyl, isoindolyl, indazolyl, purinyl, isoquinolinyl, quinolinyl, acridinyl, naphthyridinyl, quinoxalinyl, Quinazolinyl, cinnolinyl, piperidinyl, carbolinyl, thiazolyl, oxazolyl, isothiazolyl, isoxazolyl. The heteroaryl groups may be unsubstituted or substituted with one or more substituents defined above under C 1 -C ₁₅ alkyl.

In the context of the present invention, C ₅ -C ₁₀ -heterocyclyl is understood as meaning five- to ten-membered ring systems which contain at least one heteroatom from the group consisting of N, O and S. The ring systems can be monocyclic or bicyclic. Examples of suitable heterocyclic ring systems are piperidinyl, pyrrolidinyl, pyrrolinyl, pyrazolinyl, pyrazolidinyl, morpholinyl, thiomorpholinyl, pyranyl, thiopyranyl, piperazinyl, indolinyl, dihydrofuranyl, tetrahydrofuranyl, dihydrothiophenyl, tetrahydrothiophenyl, dihydropyranyl and tetrahydropyranyl. For the purposes of the present invention, C 1 -C ₆ -alkoxy (C 1 -C ₆ -alkyl-O-) radicals are understood. Examples of the alkyl moiety of the alkoxy group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, amyl and hexyl. Particularly preferred as alcohol (Ib) is an alcohol selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 1 - Pentanol, 1 -hexanol, 1-heptanol and 1 - used octanol. As a result, the corresponding formic acid esters (Ia1) are selected from the group consisting of methyl formate, ethyl formate, 2-methoxyethyl formate, 1-propyl formate, 2-propyl formate, 1-butyl formate, 2-butyl formate, 2-methyl-1-propyl formate, 1-pentyl formate, 1-Hexylformiat, 1-Heptylformiat, 1-Octylformiat accessible.

In a further preferred embodiment, methanol is used as the alcohol (Ib) and methyl formate is obtained as the formic acid ester (Ia1).

In the context of the present invention, "formamide compound (Ia2)" is understood as meaning both formamide (H- (C =O) -NH ₂ ) itself and N-substituted formamide derivatives For the preparation of formamide compounds (Ia 2), in a preferred embodiment as amine (Ic) an amine selected from the group consisting of ammonia, methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, di-n-propylamine, isopropylamine, diisopropylamine, n-butylamine, di-n-butylamine, isobutylamine, diisobutylamine As a result, the corresponding formamide compounds (Ia2) are selected from the group consisting of formamide, methylformamide, dimethylformamide, ethylformamide, diethylformamide, n-propylformamide, di-n-propylformamide, isopropylformamide, diisopropylformamide, n-butylformamide, Di-n-butylformamide, isobutylformamide, diisobutylformamide, N-formylmorpholine, N-formylpiperidine and N-formylpiperazine accessible.

In a further preferred embodiment, an amine selected from the group consisting of ammonia, methylamine and dimethylamine is used as the amine (Ic). As a result, the corresponding formamide compounds (Ia2) selected from the group consisting of formamide, methylformamide, dimethylformamide accessible.

In a particularly preferred embodiment, ammonia is used as the amine (Ic) and formamide is obtained as the formamide compound (Ia2).

In a further particularly preferred preferred embodiment, morpholine is used as amine (Ic) and formylmorpholine is obtained as formamide compound (Ia2). As hydrogenation reactors, it is possible in principle to use all reactors which are fundamentally suitable for heterogeneously catalyzed gas / liquid reactions under the given temperature and given pressure. Suitable standard reactors for gas-liquid reaction systems are described, for example, in KD Henkel, "Reactor Types and Their Industrial Applications" and in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.b04_087. Examples which may be mentioned stirred tank reactors, tubular reactors, tube bundle reactors or fixed bed reactors.

The amines (Ic) or alcohols (Ib) used in the process according to the invention are fed to the hydrogenation reactor in liquid or gaseous form. The molar ratio of the alcohol (Ib) or amine (Ic) used in the process according to the invention to the carbon dioxide used is generally from 0.01 to 30 and preferably from 0.2 to 5.

The carbon dioxide used in the reaction of carbon dioxide with hydrogen in the hydrogenation reactor can be used solid, liquid or gaseous. It is also possible to use commercially available carbon dioxide-containing gas mixtures. The hydrogen and carbon dioxide may also contain other inert gases such as nitrogen or noble gases. It has surprisingly been found that the gold catalysts used in the process according to the invention are also tolerant of carbon monoxide, which often leads to poisoning of hydrogenation catalysts. The hydrogen used in the reaction in the hydrogenation reactor and the carbon dioxide may therefore also contain carbon monoxide as an impurity. Advantageously, the carbon monoxide content in the gas streams fed to the hydrogenation reactor is below 20 mol% based on the total amount of carbon dioxide and hydrogen in the hydrogenation reactor. While larger amounts may also be tolerable, they generally require the use of a higher pressure in the reactor, requiring further compression energy.

The hydrogenation of carbon dioxide takes place in the liquid phase preferably at a temperature of 20 to 200 ° C and a total pressure of 0.2 to 30 MPa abs., The total pressure preferably at least 1 MPa abs. and more preferably at least 5 MPa abs and preferably at most 15 MPa abs. is. Preferably, the temperature is at least 30 ° C and more preferably at least 100 ° C and preferably at most 180 ° C, more preferably at most 170 ° C and most preferably at most 160 ° C. The partial pressure of the carbon dioxide is generally at least 0.5 MPa and preferably at least 2 MPa and generally at most 8 MPa. The partial pressure of hydrogen is generally at least 0.5 MPa and preferably at least 1 MPa and generally at most 25 MPa and preferably at most 15 MPa.

The molar ratio of hydrogen to carbon dioxide in the feed of the hydrogenation reactor is preferably 0.1 to 10 and more preferably 1 to 3.

The molar ratio of carbon dioxide to the amine (Ic) or alcohol (Ib) in the feed of the hydrogenation reactor is generally from 0.01 to 30 and preferably from 0.2 to 5.

The catalyst used in the process according to the invention contains a catalytically active metal component which contains gold. Preferably, a heterogeneous catalyst is used. Preferably, gold is present in metallic form, ie oxidation state (0). The metal component of the catalyst may contain, in addition to gold, one or more other metals, such as noble metals selected from the group consisting of Pd, Pt, Ag and Cu in the form of alloys. The metal component may also contain metal promoters. Preference is given to using pure metal as the metal component, ie a metal component which contains at least 50% by weight, preferably at least 70% by weight and in particular 90% by weight of gold, based in each case on the total weight of the metal component. The metal component of the catalyst is preferably used in the form of nanoparticles. The average particle diameter (D ⁵⁰ ) is usually in the range of 0.1 to 50 nm.

The metal component of the catalyst can be used as such. In this case, the metal component itself forms the actual catalyst, i. the metal component of the catalyst is used in unsupported form.

As a heterogeneous catalyst, for example, gold itself is suitable, d. H. in pure form, or gold, on a support material (supported gold). In the case of gold itself, it is preferred to use "gold black", i.e., colloidally precipitated elemental gold.

It is also possible to use a catalyst containing the metal component and a support material (supported catalyst). The metal component is then fixed on the surface of the carrier material. Supported gold nanoparticles can also be used. It is also possible to use as catalysts gold alloys such as Au-M on supports, wherein M may be a noble metal such as Pd or Pt as well as other metals such as Ag or Cu. Different metal promoters can also be located in one and the same catalyst.

Preferably supported gold catalysts are used in the process according to the invention. As carriers, a wide variety of materials may be used, such as inorganic oxides, graphite, polymers or metal. In the case of inorganic oxides, silica, magnesia, zirconia and / or titania are preferred. Particular preference is given to magnesium oxide, aluminum oxide, silicon oxide, gallium oxide, zirconium oxide, cerium oxide and / or titanium oxide as support material. Furthermore, it is also possible to use mixtures of different inorganic oxides. The heterogeneous catalyst can be used in a wide variety of geometric shapes and sizes, such as pellets, cylinders, hollow cylinders, spheres, rods or extrudates. The average particle diameter is usually between 1 and 10 mm. In the case of metals or polymers as carriers, nets, woven mesh wires or knits are also applicable.

In the case of a supported catalyst, the heterogeneous catalyst generally contains between 0.01 and 50% by weight, preferably between 0.1 and 20% by weight and more preferably 0.1 to 5% by weight of gold based on the total mass of the catalyst used supported catalyst. In the case of an unsupported catalyst, the gold content is generally between 0.01 and 100 wt.% With respect to the total amount of catalyst used.

Suitable gold catalysts are commercially available or can be obtained by treating a support material with the solution of a gold compound or by coprecipitation followed by drying, heat treatment and / or calcination by known methods.

Regardless of whether the gold-containing catalyst is supported or not and regardless of whether more metals are included (eg in the form of gold alloys), the gold catalyst generally contains gold particles with a diameter of 0.1 to 50 nm, measured by means of X-ray diffraction. In addition, particles with a diameter of less than 0.1 nm or even particles larger than 50 nm may be included. Furthermore and irrespective of whether the gold-containing catalyst is supported or not and regardless of whether even more metals are contained (eg in the form of gold alloys), the heterogeneous catalyst has a BET surface area in the range of 1 m ² / g to 1000 m ² / g (determination of the BET surface according to DIN ISO 9277). Preferably, the BET surface area of the heterogeneous catalyst is in the range of 10 m ² / g to 500 m ² / g.

The volume of the heterogeneous catalyst in the hydrogenation reactor is generally between 0.1 and 95% of the reaction volume of the hydrogenation reactor, the catalyst volume being calculated from the catalyst mass divided by the bulk density of the catalyst.

In the process according to the invention, the reaction mixture (Rg) may additionally contain a polar solvent. This is particularly advantageous when an amine (Ic) is reacted with carbon dioxide and hydrogen to formamide compound (Ia2) according to the general reaction equation (III). Amines (Ic), such as ammonia, can form salts with carbon dioxide. By using a polar solvent, the solubility of these salts in the reaction mixture (Rg) can be improved.

In the process of the invention, the reaction mixture (Rg) may contain a polar solvent or mixtures of two or more polar solvents. Suitable classes of substances which are suitable as polar solvents are preferably alcohols and diols and also their formic acid esters, formamides such as formamide, methylformamide or dimethylformamide, or water.

Examples of suitable alcohols are methanol, ethanol, 2-methoxyethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol and 2-methyl-1-propanol. Suitable classes of compounds which are suitable as polar solvents are preferably diols and also their formic acid esters, polyols and also their formic acid 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-hexanediol and glycerol.

A suitable sulfone is tetramethylene sulfone (sulfolane). Suitable sulfoxides are, for example, dialkyl sulfoxides, preferably C to C ₆ - dialkyl sulfoxides, in particular dimethyl sulfoxide.

Examples of suitable open-chain or cyclic amides are formamide, methylformamide, dimethylformamide, / V-methylpyrrolidone, acetamide and / V-methylcaprolactam.

The molar ratio of the polar solvent or solvent mixture to be used in the process according to the invention to the amine (Ic) used is generally 0.5 to 30 and preferably 1 to 20.

The hydrogenation of carbon dioxide can be carried out batchwise or continuously in the process according to the invention. In the batchwise procedure, the reactor is equipped with the desired liquid and optionally solid feedstocks and auxiliaries, and then carbon dioxide and hydrogen are pressed to the desired pressure at the desired temperature. After completion of the reaction, the reactor is usually depressurized and the liquid reaction mixture is separated from the heterogeneous catalyst. In the continuous mode, the feeds and auxiliaries, including the carbon dioxide and hydrogen, are continuously fed to the hydrogenation reactor. The catalyst can be used as a fixed bed (fixed bed reactor). In the case of a fixed bed reactor, the heterogeneous catalyst is fixed in the hydrogenation reactor. It is also possible to suspend the catalyst in the reaction mixture (Rg). In the case of a suspended heterogeneous catalyst, this may already be in the hydrogenation reactor before the beginning of the reaction. In continuous operation, however, it is preferable to supply the heterogeneous catalyst in the same amount to the hydrogenation reactor in which it is continuously withdrawn from the reactor.

In a continuous procedure, a liquid phase is continuously removed from the hydrogenation reactor, so that the liquid level in the reactor remains the same on average. Preference is given to the continuous hydrogenation of carbon dioxide. The average residence time of the reaction mixture (Rg) in the hydrogenation reactor is generally 10 minutes to 5 hours.

Regardless of the type of heterogeneous catalyst and regardless of whether the hydrogenation is carried out continuously or batchwise, in the reaction of the reaction mixture (Rg) in the hydrogenation reactor, a hydrogenation mixture (H) obtained, which contains the carboxylic acid derivative (Ia), water of reaction and optionally unreacted alcohol (Ib) or unreacted amine (Ic). The hydrogenation mixture (H) may additionally contain the polar solvent or solvent mixture. In the event that a suspended heterogeneous catalyst is used, this is also contained in the hydrogenation mixture (H).

In the case of a fixed bed catalyst, the catalyst usually remains by its fixation in the hydrogenation reactor and the hydrogenation mixture contains no catalyst, i. less than 5 ppm of the gold catalyst based on the total weight of the reaction mixture (Rg). In the case of unfixed, suspended heterogeneous catalysts, these are usually retained by known measures, such as fabric or filter, in the reactor outlet in the hydrogenation reactor. However, the catalyst can also be separated off after the reaction by simple measures such as filtration, decantation or centrifugation in a subsequent step of the hydrogenation mixture (H) and recycled to the hydrogenation reactor. After separation of the catalyst, the hydrogenation mixture (H) is virtually free of gold (hydrogenated hydrogenation mixture (Ha)), i. the gold content of the worked-up hydrogenation mixture (Ha) is below 5 ppm by weight, based on the worked-up hydrogenation mixture (Ha). After separation of the catalyst, the reclaimed hydrogenation mixture (Ha) is worked up by distillation to give first stream containing the carboxylic acid derivative (Ia), a second stream containing unreacted alcohol (Ib) or unreacted amine (Ic), and a third stream containing the water of reaction.

In the event that the reaction is carried out in the presence of a polar solvent, this can be separated via a fourth stream. However, it is also possible to separate off the polar solvent together with the unreacted alcohol (Ib) or unreacted amine (Ic) (second stream). In addition, it is possible to separate the polar solvent together with the water of reaction (third stream).

The work-up by distillation can be one, two or more stages depending on the separation problem. In the preparation of formamide compounds (Ia2) in the presence of a polar solvent, the distillation can be carried out on removal of low-boiling polar solvents such as the monohydric alcohols methanol, ethanol, propanols and butanols under atmospheric pressure or in vacuo. In a preferred embodiment, the polar solvents are recycled to the hydrogenation reactor. Even if low-boiling carboxylic acid derivatives (Ia), such as methyl formate, ethyl formate or propyl formate, are prepared, these are preferably separated off from the water of reaction and unreacted alcohol (Ib) under normal pressure or slight overpressure (up to 0.2 MPa). Unreacted alcohol R ¹ -OH is recycled in a preferred embodiment to the hydrogenation reactor and the water of reaction is discarded.

In contrast, when using diols as polar solvents and to obtain higher-boiling carboxylic acid derivatives (Ia) such as formamides, the distillative workup at reduced pressure, preferably in the range of 0.1 to 500 mbar abs. prefers. Unreacted amine (Ic) is separated in a preferred embodiment in the distillation and recycled to the hydrogenation reactor. Likewise, we recycled an optional polar solvent in a preferred embodiment after distillation to the hydrogenation reactor. The separated reaction water is discarded.

Depending on the separation problem, different apparatus can be used as distillation units for the work-up by distillation of the worked-up hydrogenation mixture (Ha). At widely spaced boiling points of the substances involved, carboxylic acid derivative (la), unreacted alcohol (Ib) or unreacted amine (Ic) and optionally polar solvent, z. B. evaporators such as falling film evaporator can be used. However, the distillation unit to be used generally comprises a distillation column containing packing, packing and / or trays.

When using an additional polar solvent, the distillation unit consists of at least one, preferably two to three, distillation columns. These columns contain, depending on the separation problems z. B. packing, packages and / or floors.

The carboxylic acid derivatives (Ia) (target products) are discharged from the process and, if necessary, fed to a preferably distillative fine purification.

The invention will be explained with reference to the following figures, without limiting them thereto.

The figures show in detail: 1 shows a block diagram of a plant for a preferred embodiment of the process according to the invention for the preparation of formamide compounds (Ia2) starting from carbon dioxide, hydrogen and an amine (Ic)

2 shows a block diagram of a plant for a preferred embodiment of the process according to the invention for the preparation of formic acid esters (Ia1) starting from carbon dioxide, hydrogen and an alcohol (Ib). FIG. 3 shows a block diagram of a plant for a preferred embodiment of the process according to the invention for the preparation of formamide compounds (Ia2) starting from carbon dioxide, hydrogen and an amine (Ic) with the addition of a polar solvent

In Figures 1, 2 and 3, the reference numerals have the following meanings:

Figure 1 1-1 hydrogenation reactor

11-1 distillation unit

1 stream containing carbon dioxide

2 stream containing hydrogen

3 stream containing amine (Ic)

4 stream containing formamide compound (Ia2), water of reaction, not

reacted amine (Ic); worked up hydrogenation mixture (Ha)

5 stream containing formamide compound (Ia2); Target product; first stream 6 stream containing reaction water; third stream

7 Stream containing unreacted amine (Ic), second stream

Figure 2 I-2 hydrogenation reactor

II-2 distillation unit

1 1 stream containing carbon dioxide

12 stream containing hydrogen 13 stream containing alcohol (Ib)

14 stream containing formic acid ester (Ia1), water of reaction, not

converted alcohol (Ib); worked up hydrogenation mixture (Ha)

15 stream containing formic acid ester (Ia2); Target product; first stream 16 stream containing reaction water; third stream

17 stream containing unreacted amine (Ic), second stream

hydrogenation reactor

distillation unit

21 stream containing carbon dioxide

22 Electricity containing hydrogen

23 stream containing amine (Ic)

24 stream containing formamide compound (Ia2), water of reaction, polar

Solvent, unreacted amine (Ic); unregenerate

Hydrogenation mixture (Ha)

25 stream containing formamide compound (Ia2); Target product; first stream

26 stream containing reaction water; third stream

27 Stream containing unreacted amine (Ic), second stream

28 stream containing polar solvent

In the embodiment according to FIG. 1, carbon dioxide, stream 1, hydrogen, stream 2, and the amine (Ic), stream 3, are fed into the hydrogenation reactor 1-1. In this they are reacted in the presence of the heterogeneous gold catalyst to the formamide compound (Ia2) and water of reaction. From the liquid hydrogenation mixture (H) containing the formamide compound (Ia2), water of reaction, the heterogeneous catalyst and unreacted amine (Ic), the heterogeneous catalyst is separated. The reclaimed hydrogenation mixture (Ha) thus obtained is supplied as stream 4 to the distillation unit 11-1. In this, the worked-up hydrogenation mixture (Ha) is separated by distillation to give the formamide compound (Ia2), stream 5, reaction water effluent, stream 6, and unreacted amine (Ic), stream 7, which is recycled to the hydrogenation reactor 11-1.

In the embodiment of Figure 2, carbon dioxide, stream 1 1, hydrogen, stream 12, and the alcohol (Ib), stream 13 are fed into the hydrogenation reactor I-2. In this they are in the presence of the heterogeneous gold catalyst for Formic acid ester (Ia1) and reacted water. From the liquid hydrogenation mixture (H) containing the formic acid ester (Ia1), water of reaction, the heterogeneous catalyst and unreacted alcohol (Ib), the heterogeneous catalyst is separated off. The reclaimed hydrogenation mixture (Ha) thus obtained is fed as stream 14 to the distillation unit II-2. In this, the worked-up hydrogenation mixture (Ha) is separated by distillation to give the formic acid ester (Ia1), stream 15, elution of water of reaction, stream 6, and unreacted alcohol (Ib), stream 17, which is recycled to the hydrogenation reactor II-2. In the embodiment of Figure 3, carbon dioxide, stream 21, hydrogen, stream 22, and the amine (Ic) stream 23 are fed to the hydrogenation reactor I-3, which also contains a polar solvent. In this they are reacted in the presence of the heterogeneous gold catalyst to a formamide compound (Ia2) and water of reaction. From the liquid hydrogenation mixture (H) containing the formamide compound (Ia2), water of reaction, polar solvent, the heterogeneous catalyst and unreacted amine (Ic), the heterogeneous catalyst is separated. The reclaimed hydrogenation mixture (Ha) thus obtained is supplied as stream 44 to the distillation unit 11-3. In this, the reclaimed hydrogenation mixture (Ha) is separated by distillation to give the formamide compound (Ia2), stream 25, elution of water of reaction, stream 26, and unreacted amine (Ic), stream 27, which is recycled to the hydrogenation 11-3 and of the polar solvent, which as stream 28 is also recycled to the hydrogenation reactor 11-3.

The invention will be explained in more detail below with reference to embodiments, without limiting it thereto.

embodiments

A 250 mL Hastelloy C autoclave equipped with a magnetic stirrer bar was placed under inert conditions with the educts (alcohol (Ib) or amine (Ic)) indicated in Table 1 below and the heterogeneous gold catalyst which was located in a catalyst basket. filled. In the synthesis of formic acid esters of the corresponding alcohol or when using liquid amines this was filled. Subsequently, the autoclave was closed and at room temperature carbon dioxide (C0 ₂ ), hydrogen (H ₂ ) and optionally the ammonia or dimethylamine pressed and the reactor with stirring (700 U / min) heated. After the appropriate reaction time, the autoclave was cooled and the reaction mixture was depressurized. The catalyst remains in the catalyst basket. The composition of the reaction solution (worked up hydrogenation mixture (Ha)) was determined by gas chromatography, the gold content was determined by Atomic absorption spectroscopy (AAS) determined. The parameters and results of the individual experiments are given in Table 1.

Examples A-1 to A-1 show that formamides and formic acid esters are easily obtained by using the gold catalysts by CO ₂ hydrogenation. In the reaction solution (worked up hydrogenation mixture (Ha)) can be found within the detection limit no gold, which allows a very simple catalyst separation and recycling.

Comparative tests:

Comparative Examples A12 and A13 show that with the use of standard hydrogenation catalysts such as Raney nickel or palladium on carbon under otherwise identical conditions as in the gold catalysts no formamide (Raney nickel) or only in much poorer yields (factor 15 lower at Pd). This shows the advantage of using the catalysts of the invention for this reaction.

Claims

claims

Process for the preparation of carboxylic acid derivatives of the general formula (Ia)

H- (C = O) -R (Ia),

in the

R is selected from the group consisting of OR ¹ and NR ² R ³ , where

R ¹ is unsubstituted or at least mono-substituted Ci-C ₅ alkyl, C ₅ -C ₁₀ - cycloalkyl, C ₅ -C ₁₀ heterocyclyl, C ₅ -C ₁₀ aryl or C ₅ -C ₁₀ -heteroaryl, where the substituents selected are selected from the group consisting of C 1 -C ₅ -alkyl, C -C ₆ -alkoxy, C ₅ -C ₁₀ -cycloalkyl and C ₅ -C ₁₀ -aryl;

R ^{4 is} hydrogen or CC ₆ alkyl; by reaction of a reaction mixture (Rg) comprising carbon dioxide, hydrogen and an alcohol of the general formula (Ib)

R ¹ -OH (Ib) in which R ^{1 has} the above meanings or an amine of the general formula (Ic)

2. The method according to claim 1, wherein the catalyst is a heterogeneous catalyst.

3. The method according to claim 1 or 2, wherein the catalyst is at least one

Containing carrier material.

4. The method of claim 3, wherein the support material is selected from the group consisting of silica, alumina, zirconia, magnesia and titania.

5. The method according to claim 3 or 4, wherein the heterogeneous catalyst contains 0.1 to 20 wt.% Gold with respect to the total mass of the supported catalyst used.

6. The method according to any one of claims 1 to 5, wherein an alcohol of the general formula (Ib) is used, in the

R ^{1 is} unsubstituted or at least monosubstituted C ¹ -C ₈ -alkyl, where the substituents are selected from the group consisting of d-Ce-alkyl and CC ₆ -alkoxy.

7. The method according to claim 6, wherein as alcohol (Ib) an alcohol selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1 propanol, 1-pentanol, 1-hexanol, 1 -

Heptanol and 1-octanol is used.

8. The method according to claim 6 or 7, wherein as the alcohol (Ib) methanol is used and as the carboxylic acid derivative (la) is obtained methyl formate.

9. The method according to any one of claims 1 to 5, wherein as amine (Ic) an amine selected from the group consisting of ammonia, methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, di-n-propylamine, isopropylamine, diisopropylamine, n Butylamine, di-n-butylamine, isobutylamine, diisobutylamine, morpholine, piperidine and piperazine is used.

10. The method according to claim 9, wherein as amine (Ic) an amine selected from the group consisting of ammonia, methylamine and dimethylamine is used.

1 1. A process according to claim 9 or 10, wherein it is used as the amine (Ic) ammonia and is obtained as the carboxylic acid derivative (Ia) formamide.

12. The method according to any one of claims 1 to 1 1, wherein the residence time of the reaction mixture (Rg) in the hydrogenation reactor is 10 minutes to 5 hours.

A process according to claim 12, wherein the mixture obtained in the reaction is worked up in a distillation apparatus to obtain a first stream containing the carboxylic acid derivative (Ia), a second stream, the unreacted alcohol (Ib) or unreacted amine ( Ic), and a third stream containing the reaction water formed in the reaction.

14. A process according to claim 12 or 13, wherein the second stream is recycled to the hydrogenation reactor.