Electrochemical process for the production of 1,2,3,4-butane tetracarbonic acid tetraalkyl esters

Description

[0001] The present invention relates to an electrochemical process for the preparation of 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters containing alkyl groups with 1 to 6 carbon atoms. The process comprises the electrohydrodimerization of dialkyl maleates containing alkyl groups with 1 to 6 carbon atoms in a reactant solution containing an alcohol and a conducting salt.

[0002] 1,2,3,4-Butanetetracarboxylic acid tetraalkyl esters are well-known esters in the chemical industry and have the following general structure. where each of the four R groups represents an alkyl group. These esters can be used, for example, as plasticizers.

[0003] 1,2,3,4-Butanetetracarboxylic acid tetraalkyl esters can be produced by both chemical and electrochemical methods. The chemical route involves the synthesis of 1,2,3,4-butanetetracarboxylic acid followed by esterification with an alcohol to yield the corresponding 1,2,3,4-butanetetracarboxylic acid tetraalkyl ester. The electrochemical route involves hydrodimerization of dialkyl maleate, which takes place at the cathode. Some of these processes have already been described in patent literature, for example, in EP 0 816 533 A2, WO 97 / 26389 A1, WO 02 / 42249 A1, and JP H05 156478 A1.

[0004] The known processes have the disadvantage that they are either not economically viable or not sustainable on an industrial scale. Furthermore, an alternative route for the production of the 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters in question should be provided.

[0005] The object of the present invention was therefore to provide an economical and sustainable process for the production of 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters. This object is achieved by the process described in claim 1. Preferred embodiments are specified in the dependent claims.

[0006] The process according to the invention for the production of 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters containing alkyl groups with 1 to 6 carbon atoms, preferably alkyl groups with 2 to 5 carbon atoms, particularly preferably with 5 carbon atoms, is carried out by electrohydrodimerization in at least one reaction zone comprising an anode and a cathode, with a reactant solution comprising dialkyl maleates containing alkyl groups with 1 to 6 carbon atoms, preferably alkyl groups with 2 to 5 carbon atoms, at least one monohydric alcohol with 1 to 6 carbon atoms, preferably with 2 to 5 carbon atoms, and a conducting salt, wherein the dialkyl maleates are electrohydrodimerized at the cathode to form 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters, and wherein boron-doped diamond electrodes are used as the anode and as the cathode.

[0007] The use of boron-doped diamond electrodes as electrode material has the advantage that the cell voltage during the reaction is lower than when using known electrode materials such as graphite or glassy carbon. The electrical energy consumption of an electrolysis is proportional to the cell voltage. Therefore, the process according to the invention can be carried out more energy-efficiently with boron-doped diamond electrodes.

[0008] The dialkyl maleates used in the electrohydrodimerization, which contain alkyl groups with 1 to 6 carbon atoms, preferably alkyl groups with 2 to 5 carbon atoms, and particularly preferably with 5 carbon atoms, are reacted according to a known mechanism. The dialkyl maleates used are available on an industrial scale.

[0009] In a preferred embodiment of the present invention, dialkyl maleates, each having alkyl groups with 5 carbon atoms, i.e., dipentyl maleates, are used. In the process according to the invention, this results in 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters, each having alkyl groups with 5 carbon atoms, i.e., a 1,2,3,4-butanetetracarboxylic acid tetrapentyl ester.

[0010] In this context, the term "pentyl" means that the esters according to the invention can contain the various pentyl isomers n-pentyl (1-, 2-, or 3-pentyl), 2-methylbutyl, 3-methylbutyl, 2-methylbut-2-yl, 3-methylbut-2-yl, 2,2-dimethylpropyl, and in particular 2-methylbutyl and / or 3-methylbutyl and / or n-pentyl. The term "pentyl" thus does not inherently refer to a single specific C5 alkyl group. The 1,2,3,4-butanetetracarboxylic acid tetrapentyl esters preferably prepared according to the invention can therefore contain exclusively 2-methylbutyl groups, exclusively 3-methylbutyl groups, exclusively n-pentyl groups, or a mixture of 2-methylbutyl and / or n-pentyl and / or 3-methylbutyl groups.

[0011] The starting solution comprises, in addition to the dialkyl maleate, at least one monohydric alcohol with 1 to 6 carbon atoms, preferably with 1 to 5 carbon atoms. Preferred alcohols are methanol and pentanol. The pentanol can be a mixture of different isomeric pentanols, for example, a mixture of 2-methylbutanol and / or 3-methylbutanol and / or 1-pentanol. In the electrohydrodimerization according to the invention, the alcohol acts as a solvent because the dialkyl maleate and the conducting salt can be dissolved in the alcohol used. Simultaneously, the alcohol can also serve as a starting material for the anode reaction. In principle, a mixture of two or more monohydric alcohols with different carbon chain lengths can also be used. This can lead to the formation of mixed esters containing different alkyl groups. However, it is preferred that only one alcohol is used.However, this single alcohol can also be a mixture of different isomers with the same number of carbon atoms, as has already been described.

[0012] It is still conceivable in principle that the dialkyl maleate and the alcohol used have different alkyl groups with different numbers of carbon atoms. However, according to the invention, it is preferred that the number of carbon atoms of the alkyl groups of the dialkyl maleate and the number of carbon atoms of the monohydric alcohol are identical. Thus, if a 1,2,3,4-butanetetracarboxylic acid tetrapentyl ester is to be produced from dipentyl maleates, pentanol is used as the solvent.

[0013] One influencing factor in the electrohydrodimerization according to the invention is the concentration of dialkyl maleate relative to the amount of alcohol. A higher concentration of dialkyl maleate can have a positive effect on the yield, selectivity, and current efficiency of the 1,2,3,4-butanetetracarboxylic acid tetraalkyl ester to be formed. In a preferred embodiment of the present invention, the concentration of dialkyl maleate is 0.5 to 4 mol / liter of monohydric alcohol, preferably 1 to 3 mol / liter of monohydric alcohol.

[0014] Furthermore, the reactant solution used in the electrohydrodimerization according to the invention comprises a conducting salt. The conducting salt ensures sufficient conductivity of the solution during the electrochemical reaction. In principle, any conducting salt suitable for the reactant solution and the reaction can be used. Such conducting salts are generally known to those skilled in the art.

[0015] Suitable conducting salts for electrohydrodimerization include, in particular, those containing tetraalkylammonium cations, alkali metal cations, and anions from the group consisting of aromatically substituted sulfonates, alkylsulfonates, acetates, perchlorates, tetrafluoroborates, tetraphenylborates, bromides, iodides, phosphates, phosphonates, sulfates, alkyl sulfates, and hexafluorophosphates. Examples of suitable conducting salts are tetrabutylammonium p-toluenesulfonate and sodium acetate.

[0016] The concentration of the conducting salt can also be an influencing factor in the electrohydrodimerization according to the invention. In particular, low concentrations of the conducting salt would be economically advantageous in themselves, but increase the cell voltage and therefore have a negative effect. Within the scope of the present invention, the concentration of the conducting salt is preferably 0.05 to 0.4 mol / liter of monohydric alcohol, more preferably 0.1 to 0.4 mol / liter of monohydric alcohol.

[0017] The reactant solution must contain at least the dialkyl maleate, the monohydric alcohol, and the conducting salt. In a preferred embodiment of the present invention, the reactant solution for the electrohydrodimerization according to the invention additionally comprises a co-solvent. The use of a co-solvent can lead to a decrease in the cell voltage. Suitable co-solvents do not react at the cathode during the electrohydrodimerization according to the invention. The co-solvent is preferably selected from the group consisting of acetonitrile, dimethyl sulfoxide, tetrahydrofuran, dioxane, propylene carbonate, N,N-dimethylformamide, organic carbonates (e.g., dimethyl carbonate), dichloromethane, chloroform, and acetone.

[0018] The electrohydrodimerization according to the invention takes place in a suitable reaction zone, which may comprise one or more reactors. Since an electrochemical reaction takes place here, a reactor must, as is known, comprise an anode and a cathode. Within the scope of the present invention, the reactors can also be referred to as an electrolysis cell.

[0019] At the cathode, the desired conversion of the dialkyl maleate to the target product, 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters, takes place. Naturally, an oxidation process occurs simultaneously at the anode. For example, the monohydric alcohol is oxidized to an aldehyde at the anode. If methanol were used as the monohydric alcohol, formaldehyde would be produced. Using butanol would yield butyraldehyde, and using pentanol as the monohydric alcohol would produce valeraldehyde. Valeraldehyde, in particular, is an important starting material for syntheses in the chemical industry and thus represents a valuable product. Therefore, using pentanol would result in the co-production of two different valuable products: valeraldehyde and 1,2,3,4-butanetetracarboxylic acid tetrapentyl esters. When using dialkyl maleates with different alkyl groups, such as...When di(2-methylbutyl / n-pentyl)maleate is dissolved in pentanol, a small amount of 2-methylbutanol is also released by exchange with pentanol, followed by anodic oxidation to 2-methylbutanal.

[0020] In the present invention, boron-doped diamond electrodes are used as the anode and the cathode. The use of a boron-doped diamond electrode as the cathode for hydrodimerization is disclosed in WO 2009 / 071478 A1.

[0021] When using boron-doped diamond electrodes, the distance between the anode and cathode can preferably be set to at least 1 mm (with a suitable plastic frame as a spacer).

[0022] The arrangement of the anode and cathode relative to each other in the electrolysis cell(s) is not fundamentally limited to specific configurations. It is clear, however, that the arrangement is chosen to achieve the lowest possible cell voltage. In a preferred embodiment of the present invention, the anode and cathode are arranged parallel to each other in the electrolysis cell.

[0023] The electrohydrodimerization process according to the invention can be implemented as a batch process or as a continuous process. In the batch process, the reactant solution is introduced into the reactor(s) or electrolysis cell(s), reacted, and the product mixture is removed. If the electrohydrodimerization is operated continuously, fresh reactant solution must be continuously added to the reactor or electrolysis cell, and the resulting product solution must be removed.

[0024] Whether operating as a batch process or in continuous mode, there is a continuous flow through the reactor or electrolysis cell. This serves, among other things, to transport mass to and from the electrodes. In this context, the flow rate is the volume flowing through the reactor or electrolysis cell per unit of time.

[0025] It can generally be assumed that a higher flow rate improves mass transport to and from the electrode. Within the scope of the present invention, the flow rate is preferably in the range of 50 to 700 l / h per 100 cm² of electrode area for a planar parallel arrangement, and more preferably from 100 to 500 l / h per 100 cm² of electrode area for a planar parallel arrangement.

[0026] A high temperature is advantageous for a low cell voltage; however, this places increased demands on materials, and the vapor pressure of short-chain alcohols rises sharply. The temperature to be set is therefore a compromise between these two requirements. For this reason, within the scope of the present invention, it is preferred that the electrohydrodimerization be carried out at a temperature in the range of 20 to 80 °C, preferably 25 to 65 °C. Furthermore, it is preferred that the electrohydrodimerization be carried out at a pressure of 0.5 to 3 bar, preferably 0.75 to 2 bar.

[0027] Furthermore, the electrochemical parameters are important influencing factors on the electrohydrodimerization according to the present invention. The current density during electrohydrodimerization is preferably between 1 and 25 mA / cm², more preferably between 2 and 15 mA / cm², and particularly preferably between 4 and 10 mA / cm². It is also preferred that only a stoichiometric amount of charge is supplied for the electrochemical reaction. In the present case, this is specified as the amount of electrical charge per mol of dialkyl maleate. Within the scope of the present invention, the amount of electrical charge is preferably in the range of 1 to 1.5 F / mol of dialkyl maleate, more preferably 1 to 1.1 F / mol of dialkyl maleate. Most preferably, only stoichiometric amounts of charge are required for the reaction, i.e., the amount of electrical charge is 1 F / mol of dialkyl maleate.

[0028] To obtain 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters whose alkyl groups have 2 or more carbon atoms, preferably whose alkyl groups have 5 carbon atoms, it would be possible to first produce the respective 1,2,3,4-butanetetracarboxylic acid tetraalkyl ester from dimethyl maleate or diethyl maleate using the process according to the invention and then transesterify this ester with a suitable alcohol.

[0029] The present invention therefore also relates to a process in which 1,2,3,4-butanetetracarboxylic acid tetramethyl ester or 1,2,3,4-butanetetracarboxylic acid tetraethyl ester is produced by electrohydrodimerization and subsequently the 1,2,3,4-butanetetracarboxylic acid tetramethyl ester or the 1,2,3,4-butanetetracarboxylic acid tetraethyl ester is transesterified with at least one monohydric alcohol having 3 to 6 carbon atoms, preferably with 5 carbon atoms, to 1,2,3,4-butanetetracarboxylic acid tetraalkyl esters containing alkyl groups having 3 to 6 carbon atoms, preferably with 5 carbon atoms.

[0030] Transesterification is a process known per se to those skilled in the art, in which, according to the present teaching, a longer-chain alcohol displaces methanol (when using dimethyl maleate) or ethanol (when using diethyl maleate) from the ester. The transesterification with the monohydric alcohol having 2 to 6 carbon atoms, preferably 5 carbon atoms, is preferably carried out in the presence of one or more catalysts, for example, using Brønsted or Lewis acids or bases as catalysts. Sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, metals, or their compounds have proven to be particularly suitable catalysts. Examples of particularly preferred metal catalysts are tin powder, tin(II) oxide, tin(II) oxalate, titanium esters such as tetraisopropyl orthotitanate or tetrabutyl orthotitanate, and zirconium esters such as tetrabutyl zirconate, as well as sodium methoxide and potassium methoxide.

[0031] The transesterification can be carried out in typical reactors known to those skilled in the art under standard operating conditions. Preferably, the process takes place at temperatures at or above the boiling point of the alcohol formed in the reaction, so that it can be distilled off from the reaction mixture. The transesterification is preferably carried out at a temperature of 100 to 300°C, more preferably at 120 to 270°C, and particularly at 140 to 250°C. The internal pressure is preferably between 0.1 and 20 or 15 bar, particularly between 0.1 and 10 bar.

[0032] The present invention is explained below by means of examples. The specific exemplary embodiments shown are intended to clarify, but not to limit, the subject matter of the invention. Examples Experimental apparatus:

[0033] For electrohydrodimerization, an electrolysis cell with a plane-parallel arrangement of anode and cathode plates, each with an area of ​​100 cm², was used. The anode and cathode materials were either glassy carbon / glassy carbon, graphite / graphite, or boron-doped diamond / boron-doped diamond. When using glassy carbon and boron-doped diamond, a 1 mm thick PTFE spacer frame was employed; when using graphite, a 2 mm thick PTFE spacer frame was used (a 1 mm spacer resulted in short-circuiting and prevented electrosynthesis). The electrodes were connected to a power supply and an additional voltmeter.

[0034] The outlet at the top of the cell was directed into a glass intermediate chamber with a temperature-controlled outer jacket, which in turn was connected to a thermostat. The outlet of the intermediate chamber was connected to the suction side of a peripheral pump. The pump delivered the water to the inlet at the bottom of the cell from the pressure side. Example 1 (not according to the invention):

[0035] In this experiment, glassy carbon was used as the electrode material. 74 g of di(2-methylbutyl / n-pentyl) maleate (289 mmol) and 24 g (58 mmol) of tetrabutylammonium p-toluenesulfonate were dissolved in 150 ml of pentanol and, after taking a sample, placed in the intermediate reservoir of the experimental apparatus. After starting the pump circulation at 280 l / h and setting the temperature jacket to 50 °C, a current of 600 mA (current density 6 mA / cm²) was applied. The experiment lasted 13 hours. During this time, an electrical charge of 0.29 F (corresponding to 1.01 F / mol of di(2-methylbutyl / n-pentyl) maleate) was applied. The cell voltage was 7.2 V at the beginning of the experiment and rose to 7.5 V by the end. After the experiment ended, 212 g of product electrolyte solution were obtained, which was analyzed by gas chromatography.This contained 38.4 g of Tetra(2-methylbutyl / n-pentyl)-1,2,3,4-butanetetracarboxylate (yield 52%, current yield 51%), 13.3 g of Di(2-methylbutyl / n-pentyl)succinate (yield 18%), and 20.7 g of Di(2-methylbutyl / n-pentyl)maleate (corresponding to a conversion of 72%). Example 2 (not according to the invention):

[0036] Graphite was used as the electrode material in this experiment. 74 g of di(2-methylbutyl / n-pentyl) maleate (289 mmol) and 24 g (58 mmol) of tetrabutylammonium p-toluenesulfonate were dissolved in 150 ml of pentanol and, after taking a sample, placed in the intermediate reservoir of the experimental apparatus. After starting the pump circulation at 280 l / h and setting the temperature jacket to 50 °C, a current of 600 mA (current density 6 mA / cm²) was applied. The experiment lasted 13 hours. During this time, an electrical charge of 0.29 F (corresponding to 1.01 F / mol of di(2-methylbutyl / n-pentyl) maleate) was applied. The cell voltage was 9.6 V at the start of the experiment and dropped to 9.2 V by the end of the experiment. After the experiment, 211 g of product electrolyte solution were obtained, which was analyzed by gas chromatography.This solution contained 27.5 g of tetra(2-methylbutyl / n-pentyl)-1,2,3,4-butanetetracarboxylate (yield 37%, current yield 37%), 14.3 g of di(2-methylbutyl / n-pentyl)succinate (yield 19%), and 31.9 g of di(2-methylbutyl / n-pentyl)maleate (corresponding to a conversion of 57%). The solution also contained n-pentanal (valeraldehyde) and 2-methylbutanal, which, unlike the aforementioned cathode products, are anode products. Example 3 (not according to the invention):

[0037] Graphite was used as the electrode material in this experiment. 74 g of di(2-methylbutyl / n-pentyl) maleate (289 mmol) and 24 g (58 mmol) of tetrabutylammonium p-toluenesulfonate were dissolved in 150 ml of pentanol and 27 ml of acetonitrile. After taking a sample, the solution was transferred to the intermediate reservoir of the experimental apparatus. After starting the pump circulation at 280 l / h and setting the temperature jacket to 50 °C, a current of 600 mA (current density 6 mA / cm²) was applied. The experiment lasted 13 hours. During this time, an electrical charge of 0.29 F (corresponding to 1.01 F / mol of di(2-methylbutyl / n-pentyl) maleate) was applied. The cell voltage was 5.8 V at the start of the experiment and rose to 6.6 V by the end of the experiment. After the experiment, 224 g of product electrolyte solution were obtained, which was analyzed by gas chromatography.This contained 34.1 g of Tetra(2-methylbutyl / n-pentyl)-1,2,3,4-butanetetracarboxylate (yield 46%, current yield 46%), 12.6 g of Di(2-methylbutyl / n-pentyl)succinate (yield 17%), and 17.3 g of Di(2-methylbutyl / n-pentyl)maleate (corresponding to a conversion of 77%). Example 4 (according to the invention):

[0038] In this experiment, boron-doped diamond was used as the electrode material. 74 g of di(2-methylbutyl / n-pentyl) maleate (289 mmol) and 24 g (58 mmol) of tetrabutylammonium p-toluenesulfonate were dissolved in 150 ml of pentanol and, after taking a sample, placed in the intermediate reservoir of the experimental apparatus. After starting the pump circulation at 280 l / h and setting the temperature jacket to 50 °C, a current of 600 mA (current density 6 mA / cm²) was applied. The experiment lasted 13 hours. During this time, an electrical charge of 0.29 F (corresponding to 1.01 F / mol of di(2-methylbutyl / n-pentyl) maleate) was applied. The cell voltage was 5.7 V at the beginning of the experiment and rose to 6.2 V by the end. After the experiment ended, 210 g of product electrolyte solution were obtained, which was analyzed by gas chromatography.This contained 35.6 g of Tetra(2-methylbutyl / n-pentyl)-1,2,3,4-butanetetracarboxylate (yield 48%, current yield 48%), 14.9 g of Di(2-methylbutyl / n-pentyl)succinate (yield 20%), and 20.7 g of Di(2-methylbutyl / n-pentyl)maleate (corresponding to a conversion of 72%).

[0039] The results of embodiments 1 to 4 are compared with each other in the following Table 1. Table 1: Overview of the results of examples 1 to 4 Example 1 2 3 4** Anode / cathode material Glassy carbon / vitreous carbon Graphite / Graphite Graphite / Graphite Boron-doped diamond Anode area / cm² < 100 100 100 100 Cathode area ( / cm²< 100 100 100 100 Electrode gap / mm 1 2 2 1 Current density / mA / cm² < 6,0 6,0 6,0 6,0 Temperature / °C 50 50 50 50 Add acetonitrile / ml - - 27 - Power output * / [%] 51 37 46 48 Average cell voltage over the entire test duration / V 7,35 9,4 6,2 5,95 Electrical energy consumption / kWh / t * 1495 2646 1404 1291 * = Tetra(2-methylbutyl / n-pentyl)-1,2,3,4-butanetetracarboxylate ** = according to the invention

[0040] The overview in Table 1 shows that the lowest average cell voltage was achieved when using boron-doped diamond electrodes. As a result, the electrical energy consumption for electrohydrodimerization was the lowest compared to all other experiments.

Claims

1. Process for producing tetraalkyl 1,2,3,4-butanetetracarboxylates containing alkyl groups having 1 to 6 carbon atoms by electrohydrodimerization in at least one reaction zone comprising an anode and a cathode with a reactant solution comprising dialkyl maleates containing alkyl groups having 1 to 6 carbon atoms, at least one monohydric alcohol having 1 to 6 carbon atoms and a conducting salt, wherein the dialkyl maleates are electrohydrodimerized to afford tetraalkyl 1,2,3,4-butanetetracarboxylates at the cathode, and the anode and the cathode employed are boron-doped diamond electrodes.

2. Process according to Claim 1, wherein the number of carbon atoms of the alkyl groups of the dialkyl maleate and the number of carbon atoms of the monohydric alcohol are identical.

3. Process according to Claim 1 or 2, wherein conducting salts having tetraalkylammonium cations, alkali metal cations and having anions from the group consisting of aromatic-substituted sulfonates, alkylsulfonates, acetates, perchlorates, tetrafluoroborates, tetraphenylborates, bromides, iodides, phosphates, phosphonates, sulfates, alkylsulfates, hexafluorophosphates are employed.

4. Process according to any of the preceding claims, wherein the tetraalkyl 1,2,3,4-butanetetracarboxylates and the dialkyl maleates each have alkyl groups having 5 carbon atoms, preferably each alkyl groups selected from the group consisting of 2-methylbutyl, 3-methylbutyl and n-pentyl.

5. Process according to any of the preceding claims, wherein the monohydric alcohol employed is methanol, butanol or a pentanol, preferably 1-pentanol.

6. Process according to any of the preceding claims, wherein the electrohydrodimerization additionally employs a cosolvent selected from the group consisting of acetonitrile, dimethyl sulfoxide, tetrahydrofuran, dioxane, propylene carbonate, N,N-dimethylformamide, organic carbonates, dichloromethane, chloroform and acetone.

7. Process according to any of the preceding claims, wherein the electrohydrodimerization is performed at a temperature in the range from 20°C to 80°C, preferably 25°C to 65°C.

8. Process according to any of the preceding claims, wherein the electrohydrodimerization is performed at a pressure of 0.5 to 3 bar, preferably 0.75 to 2 bar.

9. Process according to any of the preceding claims, wherein the electrohydrodimerization is carried out in an electrolysis cell and the flow rate in the electrolysis cell is in the range between 50 and 700 l / h per 100 cm2 of electrode surface area, preferably between 100 and 500 l / h per 100 cm2 of electrode surface area.

10. Process according to any of the preceding claims, wherein the monohydric alcohol having 1 to 6 carbon atoms is reacted to afford an aldehyde at the anode during the process.

11. Process according to Claim 10, wherein, when using pentanol as the monohydric alcohol, valeraldehyde and also 2-methylbutanal are formed.

12. Process according to any of the preceding claims, wherein the electrohydrodimerization produces the tetramethyl 1,2,3,4-butanetetracarboxylate and subsequently the tetramethyl 1,2,3,4-butanetetracarboxylate is transesterified with at least one monohydric alcohol having 2 to 6 carbon atoms to afford tetraalkyl 1,2,3,4-butanetetracarboxylates containing alkyl groups having 2 to 6 carbon atoms.

13. Process according to any of Claims 1 to 12, wherein the electrohydrodimerization produces the tetraethyl 1,2,3,4-butanetetracarboxylate and subsequently the tetraethyl 1,2,3,4-butanetetracarboxylate is transesterified with at least one monohydric alcohol having 3 to 6 carbon atoms to afford tetraalkyl 1,2,3,4-butanetetracarboxylates containing alkyl groups having 3 to 6 carbon atoms.

14. Process according to Claim 12 or 13, wherein the transesterification is performed at a temperature of 100°C to 300°C, preferably at 120°C to 270°C.