Sustainable process for manufacture of 1, 1, 4, 4-tetramethoxy-2-butene

Abstract

The present invention relates to a sustainable process for the manufacture of 1, 1, 4, 4-tetramethoxy-2-butene, in particular to a process for the manufacture of 1, 1, 4, 4-tetramethoxy-2-butene from 2, 5-dimethoxy-2, 5-dihydrofuran and methanol in the presence of an acidic ion exchanger as catalyst wherein the molar ratio of 2, 5-dimethoxy-2, 5-dihydrofuran to methanol is > = 1: 45. The invention also relates to a method for separating 1, 1, 4, 4-tetramethoxy-2-butene, methanol and 2, 5-dimethoxy-2, 5-dihydrofuran from one another and from H2O, in which a basic compound, preferably a basic metal salt or a basic ion exchanger, is present. Both methods can be carried out on an industrial scale in a batch or continuous mode and are sustainable due to high selectivity and space time yield and less waste than known methods. A further object of the invention is the use of a basic compound in the distillation of a mixture comprising H2O, 1, 1, 4, 4-tetramethoxy-2-butene and 2, 5-dimethoxy-2, 5-dihydrofuran, and the use of an acidic ion exchanger as a catalyst in the reaction of 2, 5-dimethoxy-2, 5-dihydrofuran with methanol to produce 1, 1, 4, 4-tetramethoxy-2-butene, in which 2, 5-dimethoxy-2, 5-dihydrofuran is reacted with methanol to produce 1, 1, 4, 4-tetramethoxy-2-butene. The molar ratio of the 2, 5-dimethoxy-2, 5-dihydrofuran to the methanol is greater than or equal to 1: 45.

Description

[0001] This application is a divisional application of Chinese patent application 202180016001.3 (PCT / EP2021 / 054979) with an application date of March 1, 2021. Summary of the invention

[0002] The invention relates to a process for producing 1,1,4,4-tetramethoxy-2-butene from 2,5-dimethoxy-2,5-dihydrofuran and methanol in the presence of an acidic ion exchanger as a catalyst, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥ 1:45. The invention also relates to a process for separating 1,1,4,4-tetramethoxy-2-butene, methanol and 2,5-dimethoxy-2,5-dihydrofuran from each other and from H2O, wherein a basic compound, preferably a basic metal salt or a basic ion exchanger, is present.

[0003] Both processes can be carried out on an industrial scale in batch or continuous mode and are sustainable because selectivity and space-time yields are high and less waste is generated compared to known processes.

[0004] A further object of the present invention is the use of a basic compound in the distillation of a mixture comprising H2O, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran, and the use of an acidic ion exchanger as a catalyst in the reaction of 2,5-dimethoxy-2,5-dihydrofuran with methanol to give 1,1,4,4-tetramethoxy-2-butene, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥ 1:45. Background Art

[0005] 1,1,4,4-Tetramethoxy-2-butene (hereinafter referred to as "C4-diacetal") is a synthetic 10 -dialdehyde”), the C 10 - Dialdehydes are required for the chemical synthesis of carotenoids, as has been described, for example, in CN 108752 178A.

[0006] like Figure 1 As shown, C4-diacetal can be prepared by reacting methanol with 2,5-dimethoxy-dihydrofuran (hereinafter referred to as "DMDF") in the presence of a catalyst. Undesirable by-products are PMB (1,1,2,4,4-pentamethoxybutane) or DMB (4,4-dimethoxy-but-2-enal) (see also Figure 1 ).

[0007] Solid catalysts having acid centers are used for this reaction according to the process of EP-A 1 099 676. Disadvantageously, PMB is produced in an amount of at least 1.5%, based on the amount of starting material DMDF (see, for example, Example 5).

[0008] In the processes described in WO 2006 / 108664 and EP 581 097, the acetalizing agent trialkyl orthoformates must be used, which makes these processes more expensive and therefore uneconomical and unsustainable.

[0009] As already stated above, all these known methods have certain disadvantages. It is therefore an object of the present invention to provide a method which does not suffer from such disadvantages.

[0010] Furthermore, there is a growing need to improve the efficiency and sustainability of industrial chemical processes in order to minimize negative environmental impacts regarding waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The reaction of methanol with 2,5-dimethoxy-dihydrofuran to prepare C4-diacetal is shown. DETAILED DESCRIPTION

[0012] These needs are met by the present invention, which relates to a process for the preparation of 1,1,4,4-tetramethoxy-2-butene (=C4-diacetal) (" Method 1 ”), the method comprising the following steps:

[0013] a) providing 2,5-dimethoxy-2,5-dihydrofuran, which optionally contains 1,1,4,4-tetramethoxy-2-butene;

[0014] b) reacting the 2,5-dimethoxy-2,5-dihydrofuran provided in step a), optionally in the presence of 1,1,4,4-tetramethoxy-2-butene, with methanol in the presence of an acidic ion exchanger as catalyst, optionally in the presence of water, to form a mixture comprising H2O and 1,1,4,4-tetramethoxy-2-butene, until up to 79% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted to 1,1,4,4-tetramethoxy-2-butene, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥ 1:45;

[0015] c) optionally adding a basic compound to a mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran;

[0016] d) distilling the mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene, and 2,5-dimethoxy-2,5-dihydrofuran in the presence of the basic compound to separate these compounds from each other, thereby obtaining 1,1,4,4-tetramethoxy-2-butene, methanol, and unreacted 2,5-dimethoxy-2,5-dihydrofuran;

[0017] Therein, a basic compound is added to the mixture in step c), or a basic compound is present during the distillation in step d).

[0018] In a preferred embodiment of process 1, the unreacted 2,5-dimethoxy-2,5-dihydrofuran obtained in step d) is recycled back to step a) or b), respectively, thereby increasing the sustainability of the process.

[0019] The individual steps are disclosed in more detail below.

[0020] Step a)

[0021] The amount of C4-diacetal relative to the amount of DMDF is preferably <1 mol %, more preferably <0.5 mol %, most preferably <0.1 mol %.

[0022] Step b)

[0023] Preferably, the reaction is carried out in a continuous mode in a reactor, as known to the person skilled in the art. Particular preference is given to fixed bed or tubular reactors or tube bundle reactors.

[0024] The reaction is preferably performed at a temperature in the range of 0°C to 50°C, more preferably in the range of 10°C to 30°C, most preferably in the range of 15°C to 25°C, and / or preferably under atmospheric pressure.

[0025] catalyst

[0026] In a preferred embodiment, the catalyst used in step b) is an acidic ion exchanger having an acid site concentration of at least 2.5 equivalents / kg, preferably at least 3.0 equivalents / kg, more preferably at least 4.0 equivalents / kg, and most preferably 5.0 equivalents / kg. If an acidic ion exchanger with an acid site concentration of less than 2.5 equivalents / kg is used, selectivity and conversion are still high, but the reaction time is longer (see Example 1F compared with Examples 1A to 1E).

[0027] In a more preferred embodiment, the catalyst is an acidic ion exchanger containing sulfonic acid groups and having an acid site concentration of at least 2.5 equivalents / kg, preferably at least 3.0 equivalents / kg, more preferably at least 4.0 equivalents / kg, most preferably 5.0 equivalents / kg.

[0028] Surprisingly, it has been found that the use of acidic ion exchangers having a certain particle size distribution and a certain water-retention capacity with the preferences given above leads to even higher selectivities for the product, namely the C4-diacetal.

[0029] This preferred catalyst yes an acidic ion exchanger having a particle size distribution of ≥400 μm and a water retention capacity of <60%, preferably a water retention capacity in the range of 40% to 60%, more preferably a water retention capacity in the range of 50% to 60%, or It is an acidic ion exchanger with a particle size distribution of <400 μm and a water retention capacity of >60%, preferably a water retention capacity in the range of 60% to 80%, more preferably a water retention capacity in the range of 60% to 75%.

[0030] Acidic ion exchangers exhibit high activity over long periods of time. However, if their activity decreases, they can be reactivated by washing with polar organic solvents, preferably by washing with methanol, or by washing with protic organic solvents, or by washing with protic inorganic solvents (e.g. acids).

[0031] One skilled in the art will select the amount of catalyst according to the amount of reaction mixture, ie the bed volume.

[0032] Any acidic ion exchanger having one or more of the preferred characteristics given above can be successfully employed in the process of the invention.

[0033] The most preferred acidic ion exchangers have all the preferred features as given above.

[0034] Amount of methanol

[0035] The molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol in step b) is preferably in the range of 1:45 to 1:100, more preferably in the range of 1:50 to 1:90, even more preferably in the range of 1:60 to 1:80, most preferably in the range of 1:70 to 1:80.

[0036] Conversion rate

[0037] Preferably, the reaction is carried out until at most 75% of DMDF has reacted to C4-diacetal, more preferably until 20% to 72% of DMDF has reacted to C4-diacetal, even more preferably until 35% to 70% of DMDF / 40% to 65% of DMDF / 45% to 60% of DMDF, respectively, have reacted to C4-diacetal, most preferably until 50% to 60% of DMDF has reacted to C4-diacetal.

[0038] No acetalizing agents other than methanol are present

[0039] In a preferred embodiment of the process of the invention, no acetalizing agent other than methanol is present. The use of trialkyl orthoformates, as used in the processes of EP 581 097 and WO 2006 / 108664, is particularly excluded, since the use of trialkyl orthoformates leads to the formation of methyl formate, which increases the waste generated in the process. Since no acetalizing agent other than methanol is present in the process of the invention, the amount of waste is minimized.

[0040] Since H2O is formed during the reaction, which facilitates the reaction back to the starting material, as well as reacting to the by-product DMB, the amount of H2O is preferably below a certain level to still ensure sufficient conversion. It has been found that when the reaction of step b) is stopped, the amount of water is preferably in the range of 0 mol% to 100 mol%, more preferably in the range of 20 mol% to 80 mol%, and most preferably in the range of 30 mol% to 65 mol% relative to the amount of 2,5-dimethoxy-2,5-dihydrofuran.

[0041] The combination of steps c) and d) is also an invention. The present invention therefore also relates to a process for separating 1,1,4,4-tetramethoxy-2-butene (=C4-diacetal), methanol and 2,5-dimethoxy-2,5-dihydrofuran (=DMDF) from a mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran ("DMDF"). Method 2 ”), the method comprising the following steps:

[0042] i) providing a mixture comprising H2O, methanol, C4-diacetal, DMDF and optionally a basic compound;

[0043] ii) optionally adding a basic compound to the mixture;

[0044] iii) distilling the mixture comprising H2O, methanol, C4-diacetal and DMDF in the presence of the basic compound to separate methanol, C4-diacetal and DMDF from each other;

[0045] The basic compound is already present in the mixture provided in step i), or the basic compound is added in step ii).

[0046] Steps c and d) / steps i) and ii) respectively

[0047] Based on the total amount of C4-diacetal and DMDF, the starting mixture contains preferably <70 mol% DMDF, more preferably an amount in the range of 20 mol% to 70 mol% DMDF, even more preferably an amount in the range of 30 mol% to 60 mol% DMDF, most preferably an amount in the range of 40 mol% to 50 mol% DMDF.

[0048] Based on the total amount of C4-diacetal and DMDF, the amount of C4-diacetal in the starting mixture is preferably >30 mol%, more preferably it is in the range of 30 to 80 mol%, even more preferably it is in the range of 40 to 70 mol%, most preferably it is in the range of 50 to 60 mol%.

[0049] Based on the total amount of C4-diacetal, H2O and DMDF, the amount of water in the starting mixture is preferably >30 mol%, more preferably in the range of 30 mol% to 80 mol%, even more preferably in the range of 40 mol% to 70 mol%, most preferably in the range of 50 mol% to 60 mol%.

[0050] Preferably, the basic compound is a heterogeneous basic compound, more preferably it is an alkali metal salt or a basic ion exchanger or a mixture thereof, most preferably the basic compound is a basic ion exchanger. Advantageously, the basic compound can be recycled.

[0051] In general, any alkaline salt soluble in methanol is suitable. Such salts are, for example, alkali metal salts, alkaline earth metal salts and ammonium salts soluble in methanol. Preferred examples of such salts are potassium carbonate, sodium carbonate and diammonium hydrogen phosphate, of which potassium carbonate and sodium carbonate are preferred. Mixtures of these salts may also be used, especially mixtures of these preferred salts.

[0052] Basic ion exchangers encompass strong anion exchange resins containing hydroxyl groups or corresponding salts.

[0053] The amount of the basic compound is preferably in the range of 0.01 wt % to 1 wt %, more preferably in the range of 0.02 wt % to 0.75 wt %, even more preferably in the range of 0.03 wt % to 0.5 wt %, most preferably in the range of 0.03 wt % to 0.3 wt %, based on the total weight of the reaction mixture comprising methanol, H2O, C4-diacetal and DMDF.

[0054] Higher amounts of alkaline compounds can be used, but will result in more waste, making the process less sustainable.

[0055] The presence of the basic compound prevents the loss of the desired product (=C4-diacetal) and unreacted starting material (=DMDF) during the distillation of the mixture. Due to the presence of the basic compound, the loss of these two compounds, C4-diacetal and DMDF, can be reduced to an amount less than 7 mol%, preferably reduced to an amount less than 5 mol%.

[0056] Step iii

[0057] Step iii) is preferably performed at a temperature in the range of 20°C to 180°C, more preferably in the range of 30°C to 150°C, most preferably in the range of 40°C to 110°C, and / or preferably at a pressure in the range of 0.1 mbar to 1013 mbar, more preferably in the range of 0.5 mbar to 500 mbar, most preferably in the range of 1 mbar to 100 mbar.

[0058] The present invention covers any combination of one or more preferred embodiments of methods 1 and 2 as described above.

[0059] A further embodiment of the present invention is the use of a basic compound as defined above in the distillation of a mixture comprising H2O, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran, and the use of an acidic ion exchanger as a catalyst in the reaction of 2,5-dimethoxy-2,5-dihydrofuran with methanol to give 1,1,4,4-tetramethoxy-2-butene, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥ 1:45.

[0060] The invention will now be further illustrated in the following non-limiting examples.

[0061] Example

[0062] The following acidic ion exchangers were tested:

[0063] Acidic ion exchanger

[0064] Amberlyst 15WET (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): macropores; particle size distribution: 400-1200 μm; water retention capacity: 52-57%; concentration of acid sites: 5 equivalents / kg ion exchanger;

[0065] Amberlyst 46 (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): macropores; particle size distribution: 400-1200 μm; water retention capacity: 26-36%; concentration of acid sites: 1 equivalent / kg of ion exchanger;

[0066] Dowex 88H (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): macropores; particle size distribution: 300-1200 μm; water retention capacity: 42-48%; concentration of acid sites: 5 equivalents / kg ion exchanger;

[0067] Dowex 50WX4 50-100 mesh (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): gel; particle size distribution: 200-400 μm; water retention capacity: 64-72%; concentration of acid sites: 5 equivalents / kg ion exchanger;

[0068] Dowex 50WX4 16-25 mesh (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): gel; particle size distribution: 400-1200 μm; water retention capacity: 64-72%; concentration of acid sites: 5 equivalents / kg ion exchanger;

[0069] Dowex 50WX4 200-400 mesh (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): gel; particle size distribution: 37-74 μm; water retention capacity: 64-72%; concentration of acid sites: 5 equivalents / kg ion exchanger;

[0070] Basic ion exchangers

[0071] Amberlyst A26 (commercially available from Dupont Water Solutions—DDP Specialty Products Germany GmbH & Co. KG, Neu-Isenburg, Germany): particle size distribution: 560-700 μm; water retention capacity: 66-75%; surface area: 30 m 2 / g (nitrogen BET); pore diameter:

[0072] Examples 1A to 1H: Acid-catalyzed conversion of DMDF to C4-diacetals

[0073] The reactor was filled with 50 mm glass wool and then the acidic ion exchanger (= catalyst) according to Table 1 to Table 3 was added. Methanol was then pumped through the catalyst bed until the solvent was colorless. A solution of DMDF (408 mmol) in methanol (1250 ml, 31.2 mol) was prepared and pumped through the catalyst bed at different temperatures (11-21 ° C) and flow rates (1-24 mL / min). Under constant conditions, samples were taken after flowing through three times the bed volume. The starting solution and samples were analyzed by gas chromatography.

[0074] Table 1: Various acidic ion exchangers tested under similar conditions

[0075]

[0076]

[0077] Table 2: Amberlyst 15WET tested at various catalyst bed retention times

[0078]

[0079] Table 3: Amberlyst 15WET tested at various reaction temperatures

[0080]

[0081] Examples 2A to 2E: Acid-catalyzed conversion of DMDF to C4-diacetal

[0082] The reactor was filled with 50 mm glass wool and the acidic ion exchanger Amberlyst 15 WET (= catalyst) was added. Methanol was then pumped through the catalyst bed until the solvent was colorless. A solution of DMDF (408 mmol) in methanol (1250 ml, 31.2 mol) was prepared and pumped through the catalyst bed at a flow rate of 4 mL / min at 21° C. Samples were taken after a certain period of time. The starting solution and samples were analyzed by gas chromatography. As shown in Table 4 below, the catalyst still showed a constant high selectivity even after more than 70 hours.

[0083] Table 4: Amberlyst 15WET: Long-term stability under constant reaction conditions

[0084]

[0085]

[0086] Examples 3A to 3E: Acid-catalyzed conversion of a mixture of DMDF and C4-diacetal to C4-diacetal

[0087] The reactor was filled with 50 mm glass wool and the acidic ion exchanger Amberlyst 15 WET (= catalyst) was added. Methanol was then pumped through the catalyst bed until the solvent was colorless. Solutions of DMDF (408 mmol) and various amounts of C4-diacetal (0-142.8 mmol) in methanol (1250 ml, 31.2 mol) were prepared and pumped through a catalyst bed of Amberlyst 15 WET at different flow rates (2-14 mL / min) at 20 ° C. Samples were taken after a certain period of time. The starting solution and samples were analyzed by gas chromatography. The results are shown in Table 5.

[0088] Table 5: Amberlyst 15WET catalytic conversion of a mixture of DMDF and C4-diacetal to C4-diacetal

[0089]

[0090] In the presence of C4-diacetal, the selectivity remains high.

[0091] Examples 4A to 4B: Acid-catalyzed conversion of a mixture of DMDF, C4-diacetal and H2O to C4-diacetal

[0092] The reactor was filled with 50 mm glass wool and the acidic ion exchanger Amberlyst 15 WET (= catalyst) was added. Methanol was then pumped through the catalyst bed until the solvent was colorless. A solution of DMDF (408 mmol), C4-diacetal (142.8 mmol) and H2O (0 or 1224 mmol) in methanol (1250 ml, 31.2 mol) was prepared and pumped through the catalyst bed of Amberlyst 15 WET at 22° C. for a residence time of 18 minutes. Samples were taken after a certain period of time. The starting solution and the samples were analyzed by gas chromatography. The results are shown in Table 6.

[0093] Table 6

[0094]

[0095] If water is present in an amount 3 times the amount of DMDF, the conversion of DMDF to C4-diacetal decreases.

[0096] Examples 5A to 5D: Stability testing of DMDF and C4-diacetal in the presence of water during distillation

[0097] Into a 2000mL round-bottom flask, DMDF (245mmol), C4-diacetal (245mmol) and H2O (0 or 1000mmol) dissolved in methanol (1000ml, 25mol) were charged, and additional basic compounds were added according to Table 7. The reaction mixture was evaporated to a certain amount at 70°C / 700 mbar. The evaporated solution and the starting solution were analyzed by gas chromatography. The results are shown in Table 7.

[0098] Table 7

[0099]

[0100]

[0101] 5A to 5D are starting solutions.

[0102] "ev" means that the corresponding sample has evaporated until the amount given in Table 7 remains.

[0103] Sample 5A (887 g) for example initially contained 249 mmol of C4-diacetal and 245 mmol of DMDF; the remainder was methanol. When the solvent had evaporated (=sample "5A (ev)"), 245 mmol of C4-diacetal (98.4% of the original amount) and 242 mmol of DMDF (98.8% of the original amount) were obtained.

[0104] However, when water is already present in the starting solution and no basic compound is present (see Examples 5B and 5B(ev) respectively), only 150 mmol of C4-diacetal (60.3% of the original amount) and 215 mmol of DMDF (87.8% of the original amount) are obtained; this results in a significant loss of the desired product (=C4-diacetal) and unreacted starting material (=DMDF).

[0105] The presence of a basic compound can prevent this loss - see Examples 5C / 5C(ev) and 5D / 5D(ev), respectively:

[0106] In the presence of 0.5 g of K2CO3 in the starting solution 5C, 244 mmol of C4-diacetal (99.2% of the original amount) and 245 mmol of DMDF (100.4%* of the original amount) were obtained after evaporation.

[0107] In the presence of 2.0 g of the basic ion exchanger Amberlyst A26 in the starting solution 5D, 237 mmol of C4-diacetal (96.7% of the original amount) and 244 mmol of DMDF (100% of the original amount) were obtained after evaporation.

[0108] * In the presence of a basic compound, the by-product DMB reacts with DMDF so that more DMDF is obtained than was initially present.

Claims

1. A method for producing 1,1,4,4-tetramethoxy-2-butene, the method comprising the following steps: a) providing 2,5-dimethoxy-2,5-dihydrofuran, which optionally contains 1,1,4,4-tetramethoxy-2-butene; b) reacting the 2,5-dimethoxy-2,5-dihydrofuran provided in step a), optionally in the presence of 1,1,4,4-tetramethoxy-2-butene, with methanol in the presence of an acidic ion exchanger in which water is optionally present as a catalyst, to form a mixture comprising H2O and 1,1,4,4-tetramethoxy-2-butene, until up to 79% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted to 1,1,4,4-tetramethoxy-2-butene, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥ 1:45; c) optionally adding a basic compound to a mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran; d) distilling the mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene, 2,5-dimethoxy-2,5-dihydrofuran in the presence of the basic compound to separate these compounds from each other, thereby obtaining 1,1,4,4-tetramethoxy-2-butene, methanol and unreacted 2,5-dimethoxy-2,5-dihydrofuran, Therein a basic compound is added to the mixture in step c) or a basic compound is present during the distillation in step d).

2. The process according to claim 1, wherein the unreacted 2,5-dimethoxy-2,5-dihydrofuran obtained in step d) is recycled back to step a) or b), respectively.

3. The process according to claim 1 and / or 2, wherein the catalyst used in step b) is an acidic ion exchanger having an acid site concentration of at least 2.5 equivalents / kg, preferably at least 3.0 equivalents / kg, more preferably at least 4.0 equivalents / kg, most preferably 5.0 equivalents / kg, and / or wherein the catalyst used in step b) is an acidic ion exchanger containing sulfonic acid groups and having an acid site concentration of at least 2.5 equivalents / kg, preferably at least 3.0 equivalents / kg, more preferably at least 4.0 equivalents / kg, most preferably 5.0 equivalents / kg.

4. The method according to any one or more of claims 1 to 3, wherein the acidic ion exchanger has a particle size distribution of ≥400 μm and a water retention capacity of <60%, preferably a water retention capacity in the range of 40% to 60%, more preferably a water retention capacity in the range of 50% to 60%.

5. The method according to any one or more of claims 1 to 3, wherein the acidic ion exchanger has a particle size distribution of <400 μm and a water retention capacity of >60%, preferably a water retention capacity in the range of 60% to 80%, more preferably a water retention capacity in the range of 60% to 75%.

6. The method according to any one or more of claims 1 to 5, wherein the reaction in step b) is carried out at a temperature in the range of 0°C to 50°C, preferably in the range of 10°C to 30°C, more preferably in the range of 15°C to 25°C, and / or under atmospheric pressure.

7. The process according to claim 1 , wherein the reaction is carried out until at most 75% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted to 1,1,4,4-tetramethoxy-2-butene (step b)), preferably until 20% to 72% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted to 1,1,4,4-tetramethoxy-2-butene, more preferably until 35% to 70% % of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted into 1,1,4,4-tetramethoxy-2-butene, even more preferably until 40% to 65% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted into 1,1,4,4-tetramethoxy-2-butene, most preferably until 45% to 60% of the 2,5-dimethoxy-2,5-dihydrofuran has been reacted into 1,1,4,4-tetramethoxy-2-butene.

8. The process according to any one or more of claims 1 to 7, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol in step b) is in the range of 1:45 to 1:100, preferably wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol in step b) is in the range of 1:50 to 1:90, more preferably wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol in step b) is in the range of 1:60 to 1:80, most preferably wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol in step b) is in the range of 1:70 to 1:

80.

9. The process according to any one or more of claims 1 to 8, wherein no acetalizing agent other than methanol is present, preferably wherein no trialkyl orthoformates are present.

10. The process according to any one or more of claims 1 to 9, wherein when the reaction of step b) is stopped, the amount of water is in the range of 0 mol% to 100 mol% relative to the amount of 2,5-dimethoxy-2,5-dihydrofuran, preferably in the range of 20 mol% to 80 mol% relative to the amount of 2,5-dimethoxy-2,5-dihydrofuran, more preferably in the range of 30 mol% to 65 mol% relative to the amount of 2,5-dimethoxy-2,5-dihydrofuran.

11. A method for separating 1,1,4,4-tetramethoxy-2-butene, methanol and 2,5-dimethoxy-2,5-dihydrofuran from a mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran, the method comprising the steps of: i) providing a mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene, 2,5-dimethoxy-2,5-dihydrofuran and optionally a basic compound; ii) optionally adding a basic compound to the mixture; iii) distilling the mixture comprising H2O, methanol, 1,1,4,4-tetramethoxy-2-butene, and 2,5-dimethoxy-2,5-dihydrofuran in the presence of the basic compound to separate methanol, 1,1,4,4-tetramethoxy-2-butene, and 2,5-dimethoxy-2,5-dihydrofuran from each other; The basic compound is already present in the mixture provided in step i), or the basic compound is added in step ii).

12. The method according to claim 11, wherein the amount of the basic compound is preferably in the range of 0.01 wt% to 1 wt%, more preferably in the range of 0.02 wt% to 0.75 wt%, even more preferably in the range of 0.03 wt% to 0.5 wt%, and most preferably in the range of 0.03 wt% to 0.3 wt%, based on the total weight of the reaction mixture comprising methanol, H2O, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran.

13. The process according to claim 11 and / or 12, wherein the basic compound can be recycled and / or is a heterogeneous basic compound, more preferably, wherein the basic compound is a basic metal salt or a basic ion exchanger or a mixture thereof.

14. The process according to claim 13, wherein the alkaline metal salt is an alkali metal, alkaline earth metal and / or ammonium salt soluble in methanol, preferably wherein the alkaline metal salt is potassium carbonate, sodium carbonate or diammonium hydrogen phosphate or any mixture thereof.

15. The method according to claim 13, wherein the basic ion exchanger is a strong anion exchange resin containing a hydroxyl group or a corresponding salt.

16. The method according to any one or more of claims 11 to 15, wherein step iii) is performed at a temperature in the range of 20°C to 180°C, preferably in the range of 30°C to 150°C, more preferably in the range of 40°C to 110°C, and / or at a pressure in the range of 0.1 mbar to 1013 mbar, preferably in the range of 0.5 mbar to 500 mbar, more preferably in the range of 1 mbar to 100 mbar.

17. The process according to any one or more of claims 1 to 16, wherein the process is carried out continuously.

18. Use of a basic compound in the distillation of a mixture comprising H2O, 1,1,4,4-tetramethoxy-2-butene and 2,5-dimethoxy-2,5-dihydrofuran.

19. Use of an acidic ion exchanger as a catalyst in the reaction of 2,5-dimethoxy-2,5-dihydrofuran and methanol to produce 1,1,4,4-tetramethoxy-2-butene, wherein the molar ratio of 2,5-dimethoxy-2,5-dihydrofuran to methanol is ≥1:45.

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