Two-step method for preparing 1, 2, 3, 4-butanetetracarboxylic acid tetraalkyl ester

Abstract

The invention relates to a two-step method for preparing 1, 2, 3, 4-butanetetracarboxylic acid tetraalkyl ester. The subject of the invention is a two-step process for the preparation of 1, 2, 3, 4-butanetetracarboxylic acid tetraalkyl esters containing alkyl groups having 1 to 6 carbon atoms starting from tetrahydrophthalic anhydride (THPA). The invention relates to a process for the preparation of 1, 2, 3, 4-butanetetracarboxylic acid, comprising the oxidation of tetrahydrophthalic anhydride (THPA) followed by the esterification of the resulting 1, 2, 3, 4-butanetetracarboxylic acid with an alcohol having 1 to 6 carbon atoms.

Description

Field of the Invention

[0001] The present invention relates to a two-step process for preparing tetraalkyl 1,2,3,4-butane tetracarboxylates containing alkyl groups having 1 to 6 carbon atoms starting from tetrahydrophthalic anhydride (THPA). The process comprises oxidizing tetrahydrophthalic anhydride (THPA) and subsequently esterifying the resulting 1,2,3,4-butane tetracarboxylic acid with an alcohol having 1 to 6 carbon atoms. Background Art

[0002] Tetraalkyl 1,2,3,4-butane tetracarboxylates are esters known in the chemical industry and have the following general structure

[0003]

[0004] wherein all four groups R each represent an alkyl group. For example, these esters can be used as plasticizers for plastics.

[0005] Tetraalkyl 1,2,3,4-butane tetracarboxylates can in principle be prepared by chemical and electrochemical methods. The chemical route proceeds by synthesizing 1,2,3,4-butane tetracarboxylic acid and subsequently esterifying it with an alcohol to obtain the corresponding tetraalkyl 1,2,3,4-butane tetracarboxylate. The electrochemical route proceeds by the hydrodimerization of dialkyl maleate occurring at the cathode. Some such methods have been described in the patent literature, for example in EP 0816533 A2, WO 97 / 26389 A1 or WO 02 / 42249 A1.

[0006] The disadvantages of the known methods are that they either cannot be operated economically or cannot be operated sustainably on an industrial scale. Alternative routes for preparing the relevant tetraalkyl 1,2,3,4-butane tetracarboxylates are also to be provided. Summary of the Invention

[0007] The process according to the invention is a process for preparing tetraalkyl 1,2,3,4-butane tetracarboxylates containing alkyl groups having 1 to 6 carbon atoms, wherein the process comprises the following steps:

[0008] a) oxidizing tetrahydrophthalic anhydride (THPA) in an aqueous solution using a catalyst with hydrogen peroxide, thereby producing a reaction solution containing at least 1,2,3,4-butane tetracarboxylic acid, unreacted or only partially reacted THPA, and residual hydrogen peroxide,

[0009] b) separating the 1,2,3,4-butane tetracarboxylic acid from the reaction solution obtained in step (a);

[0010] c) esterifying 1,2,3,4-butane tetracarboxylic acid with a C1- to C6-alcohol in the absence or presence of a catalyst;

[0011] d) Separate the water and the excess alcohol formed in the esterification to obtain a tetraalkyl 1,2,3,4-butanetetracarboxylate containing an alkyl group having 1 to 6 carbon atoms.

[0012] The method according to the present invention has the advantage that it uses known and readily available raw materials such as tetrahydrophthalic anhydride (THPA) and hydrogen peroxide. The preparation of tetrahydrophthalic anhydride (THPA) is carried out by the Diels - Alder reaction of maleic anhydride and butadiene. Therefore, the method proposed according to the present invention is also suitable for industrial scale production.

[0013] The first step a) of the method according to the present invention is the oxidation of tetrahydrophthalic anhydride (THPA) with hydrogen peroxide. This oxidation is carried out in an aqueous solution using a catalyst, and a reaction solution containing at least butanetetracarboxylic acid, unreacted or only partially reacted THPA, and residual hydrogen peroxide is formed. The reaction scheme for the oxidation of the above THPA (1) to 1,2,3,4-butanetetracarboxylic acid (7) is shown below. A plurality of intermediate steps are carried out in the oxidation, in which at least the following intermediate products are formed:

[0014] 1,2,3,6 - tetrahydrophthalic acid (2), 4,5 - epoxycyclohexane - 1,2 - dicarboxylic acid (3), 4,5 - dihydroxycyclohexane - 1,2 - dicarboxylic acid (4), 1,5 - dipentanal - 2,3 - dicarboxylic acid (6), and 5 - oxopentane - 1,2,3 - tricarboxylic acid (6).

[0015]

[0016] The tetrahydrophthalic anhydride (THPA) used for the oxidation according to step a) is commercially available with a purity of at least 99.5%. Hydrogen peroxide is preferably used as an aqueous solution for the oxidation in step a), and particularly preferably added to the oxidation in step a) in the form of a hydrogen peroxide solution with at least 35% by weight of hydrogen peroxide.

[0017] In principle, the hydrogen peroxide can be used in any required amount for the oxidation in step a), as long as the reaction can proceed as required. However, according to the present invention, it is preferred that the hydrogen peroxide, especially the hydrogen peroxide solution, is added in an amount in excess of 5% to 50%, preferably 15% to 40%, and particularly preferably 20% to 30%.

[0018] The oxidation in step a) should preferably be carried out at an elevated temperature to allow the reaction to proceed within an acceptable time. Preferably, the reaction temperature in the oxidation of step a) is 50°C to 100°C, preferably 70°C to 98°C, and particularly preferably 80°C to 95°C. The pressure present in the oxidation of step a) is less critical. Preferably, the oxidation in step a) is carried out at a pressure of 0.5 to 5 bar, preferably at ambient pressure.

[0019] The oxidation in step a) is still carried out in the presence of a suitable catalyst. Catalysts that promote the oxidation reaction are known to those skilled in the art. In the context of the present invention, tungsten-containing catalysts are preferred. Suitable examples of tungsten-containing catalysts include phosphotungstic acid and sodium tungstate, and sodium tungstate is particularly preferably used. It should be understood that the catalyst should be used in a catalytically active amount. Higher amounts of the catalyst can also be used, even if this does not seem reasonable for cost reasons. In a preferred embodiment of the present invention, in the oxidation of step a), the catalyst is used in an amount of 0.01 to 0.1 mol / 3 mol THPA.

[0020] The oxidation in step a) can be carried out either continuously or in batch mode. Those skilled in the art can choose the mode according to the respective circumstances. This also applies to equipment technology. The oxidation in step a) can be carried out in a single reactor, but can also be carried out in multiple reactors in parallel or in series. Suitable reactors are known to those skilled in the art in principle. An example of a suitable reactor for the oxidation in step a) is a continuous stirred tank reactor.

[0021] In terms of process technology, attention can be paid to how to add each component in the oxidation. Therefore, according to the present invention, it is preferred that first tetrahydrophthalic anhydride (THPA), the catalyst and water are pre-loaded in the reactor, then the mixture is heated and stirred, and only then hydrogen peroxide is added to start the reaction.

[0022] In another preferred embodiment of the present invention, during the oxidation in step a) of the method, an inert gas is supplied to the one or more reactors. Thereby, the oxygen concentration that can be formed by the decomposition of hydrogen peroxide can be kept low to avoid problems that may occur due to the presence of oxygen. The inert gas used can be various gases that are inert in the oxidation of step a). The inert gas is preferably nitrogen, argon or helium. Nitrogen is particularly preferred. If an inert gas is used, the reaction solution formed in the oxidation is fed into a flash unit to degas the reactor output. This can especially remove the inert gas.

[0023] A reaction solution containing at least 1,2,3,4-butanetetracarboxylic acid, unreacted or only partially reacted THPA and residual hydrogen peroxide is obtained by the oxidation in step a). Then, in the following step b), the obtained butanetetracarboxylic acid is separated from the reaction solution, preferably by crystallization and subsequent filtration. The term "only partially reacted THPA" refers to all the intermediate products formed in the reaction. This especially includes the intermediate products (2) to (6) described in the above reaction scheme.

[0024] The separation of butanetetracarboxylic acid in step b) is preferably carried out by crystallization. A possible crystallization method is cooling crystallization, in which the reaction solution from step a) is transferred to a suitable crystallization device, and then at least part of the 1,2,3,4-butanetetracarboxylic acid crystallizes at a temperature of 2 °C to 25 °C, preferably 3 °C to 22 °C. Ambient pressure is preferably present during cooling crystallization. By crystallization, at least part of the formed 1,2,3,4-butanetetracarboxylic acid precipitates as a solid.

[0025] Another possible way is evaporation crystallization, in which the reaction solution from step a) is transferred to a suitable crystallization device, and then at least part of the 1,2,3,4-butanetetracarboxylic acid crystallizes at a temperature of 50 °C to 70 °C, preferably 55 °C to 65 °C. The reaction is preferably carried out under vacuum, i.e., at a pressure below ambient pressure. By crystallization, at least part of the formed 1,2,3,4-butanetetracarboxylic acid precipitates as a solid.

[0026] During evaporation crystallization, at least part of the water present in the reaction solution is evaporated. In a particularly preferred embodiment of the present invention, the condensation energy of the evaporated water can be utilized. The evaporated water is condensed in a heat exchanger, and the energy is used for evaporation in the crystallization device. In a preferred embodiment of the present invention, the water vapor formed during evaporation crystallization is used for heat integration in such a way that the water vapor is initially compressed to a higher pressure level, and then the energy from the compressed water vapor is transferred in one or more heat exchangers during the process, for example, used for heating the crystallization solution in crystallization, for heating an inert gas, or for heating in drying. Thereby, less external energy needs to be supplied.

[0027] Regardless of which crystallization method is adopted, 1,2,3,4-butanetetracarboxylic acid exists as a solid in the reaction solution or in a part of the reaction solution. To separate it from the solution, filtration is preferably carried out. Filtration methods, possibly by using centrifugation, are familiar to those skilled in the art. After filtration, 1,2,3,4-butanetetracarboxylic acid is retained as a filter cake. The remaining reaction solution is obtained as a liquid phase or so-called mother liquor. The liquid phase or mother liquor obtained after filtration, which contains at least unreacted or only partially reacted THPA, catalyst, and residual hydrogen peroxide, is optionally returned to the oxidation in step a) after a further crystallization step. The mother liquor may also contain oxidation intermediate products according to the above reaction scheme. If these intermediate products are recycled to the oxidation, they can undergo further reactions to obtain 1,2,3,4-butanetetracarboxylic acid. By recycling, the overall conversion rate can also be increased.

[0028] The solid 1,2,3,4-butanetetracarboxylic acid obtained as a filter cake can be subjected to a washing step before the esterification in step c) to reduce or completely remove the amount of residual catalyst or other impurities. To wash the solid 1,2,3,4-butanetetracarboxylic acid, various suitable liquids can be used, such as water or ethanol. Washing with water is particularly preferred, for example, even the water that evaporates and then condenses during evaporation crystallization.

[0029] Regardless of whether the obtained solid 1,2,3,4-butanetetracarboxylic acid has been washed, drying can be carried out before the esterification in step c). However, drying is not mandatory. Therefore, embodiments of the method according to the invention can be envisaged, in which the 1,2,3,4-butanetetracarboxylic acid is not dried after the separation in step b) and is then used for the esterification in step c).

[0030] However, embodiments of the method according to the invention can also be envisaged, in which the 1,2,3,4-butanetetracarboxylic acid is dried after the separation in step b) and is then used for the esterification in step c). The drying can be carried out either at an elevated temperature or by freeze-drying.

[0031] However, a certain drying can also be carried out before the esterification in step c) in such a way that the esterification catalyst is added to the esterification in step c) only when the water content of the 1,2,3,4-butanetetracarboxylic acid has been reduced, preferably by heating to a temperature of greater than or equal to 70 °C, preferably greater than or equal to 100 °C.

[0032] The method also includes the following embodiment of the method, in which the reaction solution is subjected to cooling crystallization followed by filtration, in which a crystalline product (solid 1,2,3,4-butanetetracarboxylic acid) and a liquid mother liquor are formed after filtration, and the liquid mother liquor is recycled to one or more reactors in step a). The crystalline product is preferably washed with water and then dried.

[0033] In step c) of the method according to the invention, the 1,2,3,4-butanetetracarboxylic acid prepared in step a) and separated in step b) is esterified with a C1- to C6-alcohol. In this way, the desired product, i.e., 1,2,3,4-butanetetracarboxylic acid tetraalkyl ester containing an alkyl group having 1 to 6 carbon atoms, is formed.

[0034] In the esterification reaction in step c), the C1- to C6-alcohol is preferably used in excess. In a preferred embodiment of the invention, the C1- to C6-alcohol is used in an amount of 115% to 200% of the stoichiometric amount required for complete esterification, particularly preferably 120% to 150% of the amount.

[0035] The alcohol used in the esterification of step c) is a C1- to C6-alcohol, in particular a C1- to C6-monohydric alcohol, i.e., an alcohol having only a single alcohol group. In a preferred embodiment of the present invention, a C4- to C6-alcohol is used in the esterification of step c), thereby forming a tetraalkyl 1,2,3,4-butanetetracarboxylate comprising an alkyl group having 4 to 6 carbon atoms.

[0036] Available C4- to C6-alcohols include 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-3-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, 3,3-dimethyl-1-butanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-2-butanol, 3-ethyl-1-butanol or a mixture of two or more thereof. The C4- to C6-alcohol used is preferably 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol or a mixture thereof. The C4- to C6-alcohol used is particularly preferably a mixture of at least two of 1-pentanol, 2-methyl-1-butanol and 3-methyl-1-butanol.

[0037] The esterification of step c) can be carried out in the absence or presence of a catalyst. The esterification of step c) is preferably carried out in the presence of a catalyst. In principle, known catalyst systems suitable for esterification can be used for this purpose. Suitable catalysts for the esterification to prepare the C1- to C6-alkyl 1,2,3,4-butanetetracarboxylate according to the present invention are titanate catalysts such as tetra-n-butyl titanate, zirconates or sulfonic acids.

[0038] The esterification of step c) for preparing the ester according to the present invention is preferably carried out at a temperature of 120 °C to 250 °C, more preferably at a temperature of 140 °C to 230 °C, particularly preferably at a temperature of 160 °C to 215 °C. The pressure during the esterification process should preferably not be too high, as this would increase the boiling temperature and thus also the esterification temperature. Therefore, the pressure during the esterification process is 0.5 to 7 bar absolute pressure, preferably 3 bar absolute pressure or lower, particularly preferably not less than 0.5 bar absolute pressure. The esterification of step c) is very particularly preferably carried out at ambient pressure.

[0039] During the esterification process of step c), water is formed due to the reaction of the acid groups with C1- to C6-alcohols. This water is also referred to as reaction water. In a preferred embodiment of the present invention, at least a portion of the formed reaction water is separated during the ongoing reaction. This can especially shift the equilibrium of the reaction in the correct direction.

[0040] The progress of the esterification reaction can be monitored by observing parameters. For example, the acid value or the water content can be monitored. Monitoring can also be carried out by gas chromatography, where the ratio of reactants and / or products can be determined. The reaction can also be traced by on-line analysis.

[0041] Once the reaction has proceeded to a sufficient extent, the reaction can be terminated in different ways. The catalyst can first be destroyed by adding an alkali solution. At the same time, the acids still present are saponified. Then the reaction solution can be post-treated by known methods. For this purpose, in step d), the water and the excess alcohol formed during the esterification are separated to obtain a tetraalkyl butanetetracarboxylate containing alkyl groups having 1 to 6 carbon atoms. This separation is preferably carried out by thermal separation.

[0042] Another possible way to terminate the reaction is to first separate, in step d), the water and the excess alcohol formed during the esterification to obtain a tetraalkyl butanetetracarboxylate containing alkyl groups having 1 to 6 carbon atoms. This separation is preferably carried out by thermal separation. Then the catalyst is destroyed by adding an alkali solution.

[0043] The C1- to C5-alkyl esters of 1,2,3,4-butanetetracarboxylic acid obtained according to the present invention, preferably C4- to C6-alkyl esters, particularly preferably C5-alkyl esters, have advantageous properties when used as plasticizers for polymers. Therefore, another subject of the present invention is the use of C1- to C5-alkyl esters of 1,2,3,4-butanetetracarboxylic acid, preferably C4- to C6-alkyl esters, particularly preferably C5-alkyl esters, as plasticizers for polymers. Suitable polymers are listed below, but PVC or copolymers containing vinyl chloride are preferred.

[0044] The subject of the present invention is also a plasticizer composition which contains not only C1- to C5-alkyl esters of 1,2,3,4-butanetetracarboxylic acid, preferably C4- to C6-alkyl esters, particularly preferably C5-alkyl esters, but also other plasticizers. Depending on the intended application, the plasticizer composition can contain one or more additional plasticizers, especially different from the tetraisoamyl butanetetracarboxylate mixture according to the present invention, in order to specifically adjust the properties of the resulting plasticizer mixture. However, according to a particularly preferred embodiment, the plasticizer composition contains less than 5% by weight, more preferably less than 0.5% by weight, particularly preferably less than 0.1% by weight of phthalates.

[0045] The additional plasticizers in the plasticizer composition according to the invention can be selected from: adipates, benzoates such as monobenzoates or ethylene glycol dibenzoates, chlorinated hydrocarbons (so-called chlorinated paraffins), citrates, cyclohexanedicarboxylates, epoxidized fatty acid esters, epoxidized vegetable oils, epoxidized acylated glycerol esters, furandicarboxylates, phosphates, succinates, sulfonamides, sulfonates, terephthalates, isophthalates, trimellitates and oligomeric or polymeric esters based on adipic acid, succinic acid or sebacic acid. In a preferred embodiment of the invention, the plasticizer composition comprises further plasticizers selected from the group consisting of alkyl benzoates, alkyl sulfonates of phenol, dialkyl adipates, glycerol esters, C4- to C6-acids of polyols, trialkyl citrates, acetylated trialkyl citrates, ethylene glycol dibenzoates, trialkyl trimellitates, dialkyl terephthalates, dialkyl phthalates, dialkyl isophthalates, furandicarboxylates, dialkanoyl esters of dianhydrohexitols (such as isosorbide), alkyl epoxidized fatty acid esters, polymeric plasticizers (such as polyadipates), and dialkyl esters of 1,2-, 1,3- or 1,4-cyclohexanedicarboxylic acid.

[0046] In a further preferred embodiment, the further plasticizers comprised in the plasticizer composition are selected from C8- to C13-alkyl benzoates, C4- to C10-dialkyl adipates, pentaerythritol tetrapentanoates, acetylated trialkyl citrates having C4- to C9-alkyl groups, C4- to C10-trialkyl trimellitates, C4- to C9-dialkyl terephthalates, C4- to C13-dialkyl phthalates, especially C9- to C13-dialkyl phthalates and C4- to C10-dialkyl esters of 1,2-, 1,3- or 1,4-cyclohexanedicarboxylic acid.

[0047] Accordingly, the subject of the invention is also a plastic composition which contains C1- to C5-alkyl esters, preferably C4- to C6-alkyl esters, particularly preferably C5-alkyl esters of 1,2,3,4-butanetetracarboxylic acid according to the invention or the plasticizer composition and one or more polymers.

[0048] Suitable polymers are preferably selected from: PVC, homopolymers or copolymers of ethylene, propylene, butadiene, vinyl acetate, glycidyl acrylate, glycidyl methacrylate, ethyl acrylate, butyl acrylate or methacrylates of alkoxys of branched or unbranched alcohols having 1 to 10 carbon atoms, acrylonitrile or cycloolefins, polyvinylidene chloride (PVDC), polyacrylates, especially polymethyl methacrylate (PMMA), polyalkyl methacrylates (PAMA), polyureas, silanized polymers, fluorine-containing polymers, especially polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyvinyl acetals, especially polyvinyl butyral (PVB), polystyrene polymers, especially polystyrene (PS), expandable polystyrene (EPS), acrylonitrile-styrene-acrylate (ASA), styrene-acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), styrene-maleic anhydride copolymer (SMA), styrene-methacrylic acid copolymer, polyolefins, especially polyethylene (PE) or polypropylene (PP), thermoplastic polyolefins (TPO), polyethylene-vinyl acetate (EVA), polycarbonate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyamides (PA), polyethylene glycol (PEG), polyurethanes (PU), thermoplastic polyurethanes (TPU), polysulfides (PSu), biopolymers, especially polylactic acid (PLA), polyhydroxybutyral, polyhydroxybutyrate (PHB), polyhydroxyvaleric acid (PHV), polyesters, starch, cellulose and cellulose derivatives, especially nitrocellulose (NC), ethyl cellulose (EC), cellulose acetate (CA), cellulose acetate / butyrate (CAB), rubbers or silicones.

[0049] In a preferred embodiment, at least one polymer or preferably at least 90 wt% of the various polymers in the plasticizer composition are selected from polyvinyl chloride (PVC), polyalkyl methacrylates (PAMA), polyvinyl butyral (PVB), polyurethanes, polysulfides, polylactic acid (PLA), polyhydroxybutyral, polyhydroxybutyrate (PHB), nitrocellulose and copolymers of vinyl chloride with vinyl acetate or butyl acrylate. Among them, PVC is particularly preferred.

[0050] The amount of the inventive mixture of tetra - isopentyl 1,2,3,4 - butanetetracarboxylate in the plastic composition or of the plasticizer composition is preferably from 5 to 150 parts by mass, preferably 10 to 120 parts by mass, particularly preferably 15 to 110 parts by mass, very particularly preferably 20 to 100 parts by mass, per 100 parts by mass of polymer. However, it is also conceivable to have compositions containing one or more polymers which contain less than 20 parts by mass, preferably C4 - to C6 - alkyl esters, particularly preferably C5 - alkyl esters, of 1,2,3,4 - butanetetracarboxylic acid per 100 parts by mass of polymer.

[0051] Another preferred subject of the invention is a plastic composition which contains C1 - to C5 - alkyl esters, preferably C4 - to C6 - alkyl esters, particularly preferably C5 - alkyl esters, of 1,2,3,4 - butanetetracarboxylic acid, and a fast - gelling plasticizer selected from dibutyl terephthalate, di(iso)pentyl terephthalate, isodecyl benzoate, isononyl benzoate, tributyl acetylcitrate, tributyl citrate, dipropylene glycol dibenzoate, diethylene glycol dibenzoate, triethylene glycol dibenzoate and mixtures of two or more thereof, and at least one polymer, preferably PVC.

[0052] The plastic composition according to the invention is preferably an ingredient of the following articles: adhesives, sealants, coatings, paints, lacquers, plastisols, dry blends, foams, synthetic leathers, floor coverings, especially their surface layer or foam layer, roof sheets, bottom protection layers, fabric coatings, cables, wire insulations, hoses, extruded articles, films, articles in the field of automotive interiors, wallpapers, inks, toys, contact membranes, food packaging or medical articles, especially tubes or blood bags.

[0053] Accordingly, another subject of the invention is the use of the plastic composition in the following articles: adhesives, sealants, coatings, paints, lacquers, plastisols, foams, synthetic leathers, floor coverings, especially the surface layer or foam layer, roof sheets, bottom protection layers, fabric coatings, cables, wire insulations, hoses, extruded articles, films, the field of automotive interiors, wallpapers, inks, toys, contact membranes, food packaging or medical articles, especially tubes or blood bags. Detailed Description

[0054] The invention is illustrated below with reference to examples. These examples relate to preferred embodiments but should not be construed as limiting the invention.

[0055] Examples

[0056] Preparation of 1,2,3,4 - butanetetracarboxylic acid

[0057] The preparation of 1,2,3,4-butanetetracarboxylic acid is carried out in a glass stirred reactor equipped with a heating jacket and an internal cooling coil. For this purpose, first, tetrahydrophthalic anhydride (456 g or 3 mol) and sodium tungstate dihydrate (16.5 g or 0.05 mol) are pre-loaded in the reactor in water (1 L), heated to 65 °C and stirred for about 45 minutes. Subsequently, a 35% hydrogen peroxide solution (1457 g, 25% in excess) is added within 40 minutes and the reaction starts. During the reaction, the temperature is limited to a maximum of 90 °C by reverse cooling (water cooling through the internal cooling coil) and maintained until the desired conversion (about 6 hours).

[0058] Crystallization of 1,2,3,4-butanetetracarboxylic acid from the reaction solution has occurred during the cooling process after termination. Then the reaction solution is concentrated by evaporating water at 60 °C in a rotary evaporator. The crystallized 1,2,3,4-butanetetracarboxylic acid is separated by filtration to obtain a white solid.

[0059] Preparation of tetraisoamyl 1,2,3,4-butanetetracarboxylate

[0060] In the apparatus (three-necked flask, stirrer and cooler with a water separator), the above-prepared 1,2,3,4-butanetetracarboxylic acid and a 50:50 mixture of 2-methylbutanol and n-pentanol (25% excess alcohol) (2-methylbutanol: Sigma-Aldrich, purity ≥ 99%; n-pentanol: Honeywell, purity ≥ 99%) are charged. Tetrabutyl titanate is added as a catalyst (molar ratio of 1,2,3,4-butanetetracarboxylic acid:catalyst = 500:1) and the reaction is started. The reaction is carried out under a nitrogen sweep. The reactants are slowly heated to the reaction temperature of 200 °C. Once the reaction temperature is reached, additional alcohol is metered in. During the metering-in process, ensure that the reaction temperature does not drop below 200 °C.

[0061] Water is continuously formed during the esterification process and forms an azeotrope with the alcohol. The azeotrope is condensed and then the water is removed by the water separator and the alcohol is re-added to the reaction. The progress of the reaction is monitored at regular intervals by SZ (acid value) until the SZ reaches <0.5 mg KOH per g of sample. Then the excess alcohol is distilled off under vacuum at 160 °C. After further cooling to 80 °C, the remaining acid is neutralized by adding an alkali solution and the catalyst is destroyed. In the final step, the solid is separated from the product by filtration at 80 °C.

Claims

1. A process for preparing tetraalkyl 1,2,3,4 - butanetetracarboxylate having an alkyl group with 1 to 6 carbon atoms, wherein the process comprises the following steps: a) oxidizing tetrahydrophthalic anhydride (THPA) in an aqueous solution with hydrogen peroxide using a catalyst, thereby producing a reaction solution containing at least 1,2,3,4 - butanetetracarboxylic acid, unreacted or only partially reacted THPA, and residual hydrogen peroxide; b) separating said 1,2,3,4 - butanetetracarboxylic acid from the reaction solution obtained in step (a); c) esterifying 1,2,3,4 - butanetetracarboxylic acid with a C1 - to C6 - alcohol in the presence or absence of a catalyst; d) separating the water and the excess alcohol formed in the esterification to obtain tetraalkyl 1,2,3,4 - butanetetracarboxylate having an alkyl group with 1 to 6 carbon atoms.

2. The process according to claim 1, wherein a C4 - to C6 - alcohol is used in the esterification, thereby forming tetraalkyl 1,2,3,4 - butanetetracarboxylate having an alkyl group with 4 to 6 carbon atoms.

3. The process according to claim 1 or 2, wherein the C4 - to C6 - alcohol used is 1 - butanol, 2 - butanol, 2 - methyl - 1 - propanol, 2 - methyl - 2 - propanol, 1 - pentanol, 2 - pentanol, 3 - pentanol, 2 - methyl - 1 - butanol, 2 - methyl - 2 - butanol, 3 - methyl - 1 - butanol, 3 - methyl - 2 - butanol, 2,2 - dimethyl - 1 - propanol, 1 - hexanol, 2 - hexanol, 3 - hexanol, 2 - methyl - 1 - pentanol, 3 - methyl - 1 - pentanol, 4 - methyl - 1 - pentanol, 2 - methyl - 2 - pentanol, 3 - methyl - 2 - pentanol, 4 - methyl - 2 - pentanol, 2 - methyl - 3 - pentanol, 3 - methyl - 3 - pentanol, 2,2 - dimethyl - 1 - butanol, 2,3 - dimethyl - 1 - butanol, 3,3 - dimethyl - 1 - butanol, 2,3 - dimethyl - 2 - butanol, 3,3 - dimethyl - 2 - butanol, 3 - ethyl - 1 - butanol or a mixture of two or more thereof, preferably 1 - pentanol, 2 - pentanol, 3 - pentanol, 2 - methyl - 1 - butanol, 2 - methyl - 2 - butanol, 3 - methyl - 1 - butanol, 3 - methyl - 2 - butanol, 2,2 - dimethyl - 1 - propanol or a mixture thereof, and particularly preferably a mixture of at least two of 1 - pentanol, 2 - methyl - 1 - butanol and 3 - methyl - 1 - butanol.

4. The process according to any one of the preceding claims, wherein hydrogen peroxide is added in an amount in excess by 5% to 50%, preferably 15% to 40%, particularly preferably 20% to 30%.

5. The process according to any one of the preceding claims, wherein the catalyst used in the oxidation of step a) is a tungsten - containing catalyst, preferably phosphotungstic acid or sodium tungstate, and particularly preferably sodium tungstate.

6. The process according to any one of the preceding claims, wherein the separation of 1,2,3,4 - butanetetracarboxylic acid in step b) is carried out by crystallization and subsequent filtration.

7. The process according to claim 6, wherein 1,2,3,4 - butanetetracarboxylic acid is retained as a filter cake.

8. The method according to claim 6 or 7, wherein the crystallization of 1,2,3,4-butanetetracarboxylic acid is carried out by cooling crystallization or evaporation crystallization.

9. The method according to claim 8, wherein the cooling crystallization of 1,2,3,4-butanetetracarboxylic acid is carried out at a temperature of 2 °C to 25 °C, preferably 3 °C to 22 °C.

10. The method according to claim 8, wherein the evaporation crystallization of 1,2,3,4-butanetetracarboxylic acid is carried out at a temperature of 50 °C to 70 °C, preferably 55 °C to 65 °C, and optionally under vacuum.

11. The method according to any one of claims 8 to 10, wherein the degassed reactor output is subjected to cooling crystallization or evaporation crystallization, followed by filtration, wherein a crystalline product and a liquid mother liquor are formed after filtration, and wherein the liquid mother liquor is recycled to one or more reactors.

12. The method according to any one of claims 8 to 11, wherein the water vapor formed in the evaporation crystallization is used for heat integration in such a way that the water vapor is initially compressed to a higher pressure level, and then the energy from the compressed water vapor is transferred in one or more heat exchangers in the process, for example, for heating the crystallization solution in crystallization, for heating an inert gas, or for heating in drying.

13. The method according to any one of the preceding claims, wherein an inert gas is supplied in the esterification of step c).

14. The method according to any one of the preceding claims, wherein the 1,2,3,4-butanetetracarboxylic acid is dried after the separation in step b) and then used in the esterification of step c).

15. The method according to any one of the preceding claims, wherein the esterification catalyst is added to the esterification in step c) only when the water content of 1,2,3,4-butanetetracarboxylic acid has been reduced, preferably by heating to a temperature greater than or equal to 100 °C.

Images