Process for preparation of alkoxylated 2, 5-dihydrofurans

Abstract

The present invention relates to a process for the preparation of an alkoxylated 2, 5-dihydrofuran. The process is carried out in an electrochemical cell reactor with a vertical flow.

Description

[0001] The present invention relates to a novel method for preparing alkoxylated 2,5-dihydrofuran, which is carried out by an electrochemical method.

[0002] Alkoxylated 2,5-dihydrofuran, the compound of formula (I), is a very useful compound.

[0003]

[0004] Wherein R is a linear or branched C1-C6 alkyl group.

[0005] They can be used as intermediates in organic synthesis (eg intermediates for the production of carotenoids).

[0006] Due to the importance of these compounds, there is a constant need for improved methods of synthesizing these compounds.

[0007] WO2006 / 100289 discloses a process for producing 2,5-dihydrofuran derivatives by electrochemical oxidation in the presence of C1- to C6-monoalkyl alcohols.

[0008] Using a cathode and an anode made of graphite, the yield of 2,5-dimethoxy-2,5-dihydrofuran was 46% and the selectivity was 51%.

[0009] The alkoxylated 2,5-dihydrofuran is produced starting from a compound of formula (II), which is preferably in the Z form (as shown below), as shown in the following formula:

[0010]

[0011] Surprisingly, the inventors have found that when the process is carried out under specific conditions, the yield of alkoxylated 2,5-dihydrofuran (compound of formula (I)) is significantly increased.

[0012] Surprisingly, the inventors have found that higher yields (significantly higher than in the prior art) are achieved when using a specific arrangement of electrochemical reactors (cells).

[0013] The inventors have found that higher results can be obtained when using an electrochemical reactor with vertical flow. The term "vertical flow" means flowing from the bottom to the top or from the top to the bottom (preferably from the bottom to the top) of the electrochemical reactor.

[0014] Therefore, the present invention relates to a process (P) for preparing a compound of formula (I),

[0015]

[0016] Wherein R is a linear or branched C1-C6 alkyl group,

[0017] The method comprises electrochemically reacting a compound of formula (II) in Z-form with at least one monohydric alcohol of formula (III),

[0018]

[0019] ROH(III),

[0020] wherein R has the same meaning as R in the compound of formula (I),

[0021] Characterized in that the method is carried out in an electrochemical reactor with vertical flow.

[0022] As can be seen from formula (II), it is in the Z form when used in the process according to the invention.

[0023] However, it is also possible to use small amounts of the compound of formula (II) in the E-form. The E-form may be present in an amount of less than 5 wt-%, based on the total weight of the compound of formula (II) in the process.

[0024] Preferred compounds of formula (I) are those wherein R is -CH3 or -CH2CH3.

[0025] More preferred are compounds of formula (I) wherein R is -CH3.

[0026] Therefore, the present invention relates to a process (P1) which is a process (P) wherein a compound of formula (I) is used wherein R is -CH3 or -CH2CH3.

[0027] The present invention therefore relates to a process (P1') which is a process (P) wherein a compound of formula (I) is used wherein R is -CH3.

[0028] The process of the present invention is usually carried out in a non-aqueous medium.

[0029] In the context of the present invention, the term "non-aqueous" means that water is present in the non-aqueous medium in an amount of less than 50 wt-% (based on the total weight of the non-aqueous medium).

[0030] Typically, the term "non-aqueous" means that water is present in the non-aqueous medium in an amount less than 20 wt-% (based on the total weight of the non-aqueous medium).

[0031] The present invention therefore relates to a process (P2) which is process (P), (P1) or (P1'), wherein the process is carried out in a non-aqueous medium.

[0032] The non-aqueous medium is usually (or includes) at least one linear or branched C1-C 10Alcohol (preferably at least one linear or branched C1-C6 alcohol, more preferably ethanol or methanol, most preferably methanol).

[0033] That is, the monohydric alcohol of formula (III) can also be used as the non-aqueous medium, which can be a mixture of other alcohols and the monohydric alcohol of formula (III).

[0034] Preferably, the monohydric alcohol of formula (III) is also used as the non-aqueous medium.

[0035] The present invention therefore relates to a process (P2') which is process (P2) wherein the non-aqueous medium is at least one linear or branched C1-C 10 alcohol.

[0036] The present invention therefore relates to a process (P2") which is process (P2) wherein the non-aqueous medium is a monohydric alcohol of formula (III),

[0037] ROH(III),

[0038] Wherein R is a C1-C6 alkyl group.

[0039] Therefore, the present invention relates to a process (P2") which is process (P2), wherein the non-aqueous medium is at least one alcohol selected from the group consisting of methanol, ethanol, n-propanol and isopropanol.

[0040] Therefore, the present invention relates to a process (P2'") which is process (P2), wherein the non-aqueous medium is methanol and / or ethanol.

[0041] Therefore, the present invention relates to a process (P2"") which is process (P2), wherein the non-aqueous medium is methanol.

[0042] The at least one alcohol of formula (III) is used in an amount of at least 2 molar equivalents of the compound of formula (II). This means that, when not used as non-aqueous medium, the alcohol is always present in at least this amount.

[0043] Of course, the non-aqueous medium may also be an alcohol of at least one compound of the formula (III).

[0044] Therefore, the present invention relates to a process (P3) which is process (P), (P1), (P1'), (P2), (P2'), (P2"), (P2'") or (P2"), wherein the amount of at least one alcohol of formula (III) used is at least 2 molar equivalents of the compound of formula (II).

[0045] An essential feature of the present invention is that the method according to the present invention is carried out in an electrochemical reactor with vertical flow, which can achieve better results. This means that the reaction mixture can flow from the bottom to the top of the electrochemical reactor or from the top to the bottom (preferably from the bottom to the top of the electrochemical reactor). This is usually done by a pump system.

[0046] The size and form / shape (and volume) of the electrochemical reactor may vary.The size and form / shape (and volume) of the electrochemical reactor are not essential features.

[0047] A very common and also preferred form is a three-dimensional rectangular shape (cuboid).

[0048] Therefore, the present invention relates to a method (P4) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2"") or (P3), wherein the method is carried out in an electrochemical reactor of a three-dimensional rectangular shape.

[0049] The flow rates of the starting materials can vary, depending on the size, form and volume of the cuboid electrochemical reactor.

[0050] Typically the (vertical) flow rate is at least 10 mL / min. A typical and preferred range is 10 mL / min to 1000 mL / min.

[0051] Therefore, the present invention relates to a method (P5) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3) or (P4), wherein the (vertical) flow rate is at least 10 mL / min.

[0052] Therefore, the present invention relates to a method (P5') which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3) or (P4), wherein the (vertical) flow rate is from 10 mL / min to 1000 mL / min.

[0053] The electrodes (cathode and electrode) used in the process according to the invention may be made of any customary material alone or of more than one material (such as a metal on a support material or a metal oxide on a support material).

[0054] In this process, the target product is formed at the anode and dihydrogen evolves at the cathode. Therefore, it is advantageous to use metals or alloys instead of graphite as the cathode (graphite is usually used in the prior art) because they are more active in producing dihydrogen. Another advantage of using metals or metal alloys as cathodes is that the cell potential is greatly reduced, which leads to energy savings in the process.

[0055] Examples of cathode materials that may be used are metals (eg iron or noble metals such as platinum), graphite or metal alloys such as steel.

[0056] As described above, in a preferred embodiment of the present invention, the cathode is not made of graphite.

[0057] The anode employs a material that is stable under electrolysis conditions, examples of which are noble metals (such as platinum), oxides (such as ruthenium dioxide on titanium), graphite, highly oriented pyrolytic graphite (HOPG), boron-doped diamond (BDD), dimensionally stable anode (DSA), and glassy carbon.

[0058] Therefore, the present invention relates to a method (P6) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5) or (P5'), wherein the cathode is made of a material selected from the group consisting of metals (e.g. iron or precious metals such as platinum), graphite and metal alloys (such as steel).

[0059] Therefore, the present invention relates to a method (P6') which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5) or (P5'), wherein the cathode is not made of graphite.

[0060] Therefore, the present invention relates to a method (P6") which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5) or (P5'), wherein the cathode is made of a material selected from the group consisting of metals (e.g. iron or precious metals such as platinum) and metal alloys (e.g. steel).

[0061] Therefore, the present invention relates to a method (P7) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6') or (P6"), wherein the anode is made of a material selected from the group consisting of noble metals, oxides, graphite, highly oriented pyrolytic graphite (HOPG), boron-doped diamond (BDD), dimensionally stable anode (DSA) and glassy carbon.

[0062] The electrodes may be in any common form. Such forms may be sheets / plates, wires, rods, cells, meshes, grids, sponges or any other design commonly used.

[0063] Therefore, the present invention relates to a method (P8) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6") or (P7), wherein the electrodes are in the form of sheets / plates, wires, rods, cells, meshes, grids, sponges or any other design commonly used.

[0064] The dimensions of the electrodes used in the process according to the invention may vary and depend on the size, form and construction of the electrochemical reactor (cell).

[0065] The usual size is at least 10cm 2 (per cell). The upper limit of the electrode is not critical.

[0066] The cathode and anode are typically, but not necessarily, the same size.

[0067] Therefore, the present invention relates to a method (P9) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7) or (P8), wherein the size of the electrode is at least 10 cm 2 .

[0068] Therefore, the present invention relates to a method (P10) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8) or (P9), wherein the cathode and the anode have the same size.

[0069] The reaction medium usually and preferably includes at least one electrolyte. The electrolyte can be added to the reaction medium in the form of a salt and / or an acid. In addition to phosphoric acid and / or its salts, any known common electrolyte can be used.

[0070] Suitable supporting electrolytes are, for example, HCl, H2SO4, Na2SO4, NaCl, sodium dodecyl sulfate, methyltributylammonium methyl sulfate, triethylammonium hydrogen sulfate, tetrabutylammonium hydrogen sulfate, tetramethylammonium hydrogen sulfate, tetrabutylammonium acetate (NBu4OAc), tetrabutylammonium sulfate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, methanesulfonic acid, ammonium hydrogen sulfate, tetrabutylphosphonium methanesulfonate, 1-methylimidazolium hydrogen sulfate, tetrabutylammonium perchlorate, and LiClO4.

[0071] Typically, at least one electrolyte is used in a concentration of up to 2M (preferably 0.01-1M, more preferably 0.1-0.5M, 0.2-0.5M).

[0072] In a preferred embodiment, the electrolyte is not phosphoric acid and / or its salts.

[0073] Therefore, the present invention relates to a method (P11) which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9) or (P10), wherein the method is carried out in the presence of at least one electrolyte.

[0074] The present invention therefore relates to a process (P11′) which is a process (P11), wherein at least one electrolyte is not phosphoric acid and / or a salt thereof.

[0075] Therefore, the present invention relates to a process (P11") which is process (P11) or (P11'), wherein at least one electrolyte is selected from the group consisting of HCl, H2SO4, Na2SO4, NaCl, sodium dodecyl sulfate, methyltributylammonium methyl sulfate, triethylammonium hydrogen sulfate, tetrabutylammonium hydrogen sulfate, tetramethylammonium hydrogen sulfate, tetrabutylammonium acetate (NBu4OAc), tetrabutylammonium sulfate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, methanesulfonic acid, ammonium hydrogen sulfate, tetrabutylphosphonium methanesulfonate, 1-methylimidazolium hydrogen sulfate, tetrabutylammonium perchlorate and LiClO4.

[0076] Therefore, the present invention relates to a method (P11'") which is method (P11), (P11') or (P11"), wherein at least one electrolyte is used in a concentration of up to 2M (preferably 0.01-1M, more preferably 0.1-0.5M).

[0077] The pH of the reaction medium in the process according to the invention is preferably in the range from 0 to 7 at the start of the process.

[0078] Therefore, the present invention relates to a process (P12) which is process (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11") or (P11"'), wherein the pH of the reaction medium at the start of the process is from 0 to 7.

[0079] The method according to the present invention is carried out in a temperature range of 0°C to 75°C (preferably 10°C to 60°C, more preferably 15°C to 40°C).

[0080] Therefore, the present invention relates to a method (P13), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"') or (P12, wherein the reaction is carried out at a temperature range of 0 to 75°C.

[0081] Therefore, the present invention relates to a method (P13'), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"') or (P12), wherein the reaction is carried out at a temperature range of 10°C to 60°C.

[0082] Therefore, the present invention relates to a method (P13") which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"') or (P12), wherein the reaction is carried out at a temperature in the range of 15°C to 40°C.

[0083] The process according to the invention is generally carried out at ambient pressure.

[0084] Therefore, the present invention relates to a method (P14), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13') or (P13"), wherein the reaction is carried out at ambient pressure.

[0085] Depending on the battery, the method according to the present invention can be carried out batchwise or continuously. A continuous method is preferred.

[0086] Therefore, the present invention relates to a method (P15'), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"), (P12), (P13), (P13'), (P13") or (P14), wherein the reaction is carried out batchwise or continuously.

[0087] Therefore, the present invention relates to a method (P15'), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"), (P12), (P13), (P13'), (P13") or (P14), wherein the reaction is carried out continuously.

[0088] The current density used in the method according to the present invention is preferably in the range of 1-1000 mA / cm 2 Preferably 10-1000mA / cm 2 , more preferably 20-1000mA / cm 2 .

[0089] Therefore, the present invention relates to a method (P16), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15) or (P15'), wherein the reaction is carried out at 1-1000 mA / cm 2 carried out at a current density of .

[0090] Therefore, the present invention relates to a method (P16'), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"), (P2"), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11")'), (P12), (P13), (P13'), (P13"), (P14), (P15) or (P15'), wherein the reaction is carried out at 10-1000 mA / cm 2 carried out at a current density of .

[0091] Therefore, the present invention relates to a method (P16"), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15) or (P15'), wherein the reaction is carried out at 20-1000 mA / cm 2 carried out at a current density of .

[0092] The potential between the anode and cathode may be 12 V or less. A suitable range is 0.5-12 V, preferably 0.5-10 V; more preferably 0.5-8 V; most preferably 1-8 V.

[0093] Therefore, the present invention relates to a method (P17), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15), (P15'), (P16), (P16') or (P16"), wherein the potential between the anode and the cathode is 12 V or less.

[0094] Therefore, the present invention relates to a method (P17'), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15), (P15'), (P16), (P16') or (P16"), wherein the potential between the anode and the cathode is 0.5-12V.

[0095] Therefore, the present invention relates to a method (P17"), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15), (P15'), (P16), (P16') or (P16"), wherein the potential between the anode and the cathode is 0.5-10 V.

[0096] Therefore, the present invention relates to a method (P17"'), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15), (P15'), (P16), (P16') or (P16"), wherein the potential between the anode and the cathode is 0.5-8V.

[0097] Therefore, the present invention relates to a method (P17""), which is a method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11"'), (P12), (P13), (P13'), (P13"), (P14), (P15), (P15'), (P16), (P16'), (P16"), wherein the potential between the anode and the cathode is 1-8V.

[0098] The method according to the invention can be performed in galvanostatic mode or in potentiostatic mode.

[0099] Therefore, the present invention relates to a method (P18), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11""), (P12), (P13), (P13"), (P13"), (P14), (P15), (P15'), (P16), (P16'), (P16"), (P16"'), (P17), (P17'), (P17"), (P17"') or (P17""), wherein the method is carried out in constant current mode.

[0100] Therefore, the present invention relates to a method (P19), which is method (P), (P1), (P1'), (P2), (P2'), (P2"), (P2"'), (P2""), (P3), (P4), (P5), (P5'), (P6), (P6'), (P6"), (P7), (P8), (P9), (P10), (P11), (P11'), (P11"), (P11""), (P12), (P13), (P13"), (P13"), (P14), (P15), (P15'), (P16), (P16'), (P16"), (P16"'), (P17), (P17'), (P17"), (P17"'), (P17"") or (P18, wherein the method is carried out in a potentiostatic mode.

[0101] The reaction product (compound of formula (I)) can be isolated from the reaction medium by conventional methods.

[0102] The following examples are used to illustrate the present invention. Unless otherwise specified, all parts are expressed by weight and temperatures are expressed in ° C. Example

[0103] Example 1

[0104] Electrochemical oxidation of 1 M Z-2-butene-1,4-diol (compound of formula (Ia)) to 2,5-dihydro-2,5-dimethoxyfuran was carried out in methanol in an undivided flow-cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), 5.6wt% methyltributylammonium sulfate methyl ester was used as electrolyte. 2 ) electrode was used as the anode, and a stainless steel (100 cm 2 ) was used as the cathode. The electrolysis was carried out by applying 100 mA cm at 20 °C. -2 The reaction was carried out galvanostatically with a current of 5.9 V (the cell potential was measured at 5.9 V). The reaction mixture was pumped vertically through the flow cell from bottom to top at a flow rate of 400 mL / min. After 90 minutes, the conversion of Z-2-butene-1,4-diol reached 96% and methanol was distilled out. The evaporated reaction mixture was distilled to give DMDF in the distillate with an overall yield of 70% and a Faradaic efficiency of 62%. Quantitative MTBS was obtained in the residue with a purity of 73%.

[0105] Example 2

[0106] Electrochemical oxidation of 2M Z-2-butene-1,4-diol (compound of formula (Ia)) to 2,5-dihydro-2,5-dimethoxyfuran was carried out in methanol in an undivided flow cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), 5.1wt% methyltributylammonium sulfate methyl ester was used as electrolyte. 2 ) electrode was used as the anode, and a stainless steel (100 cm 2 ) was used as the cathode. The electrolysis was carried out by applying 100 mA cm at 20 °C. -2 The reaction was carried out galvanostatically with a current of 1.5 V (the cell potential was measured at 6.5 V). The reaction mixture was pumped vertically through the flow cell from the bottom to the top at a flow rate of 400 mL / min. After 190 minutes, the conversion of Z-2-butene-1,4-diol reached 97%. The DMDF content in the reaction mixture was 63% and the Faradaic efficiency was 52%.

[0107] Example 3

[0108] Electrochemical oxidation of 1 M Z-2-butene-1,4-diol (compound of formula (Ia)) to 2,5-dihydro-2,5-dimethoxyfuran was carried out in methanol in an undivided flow cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), using 8.2wt% triethylammonium hydrogen sulfate as the electrolyte. Graphite (100cm 2 ) electrode was used as the anode, and graphite (100 cm 2 ) was used as the cathode. The electrolysis was carried out by applying 100 mA cm at 20 °C. -2 The reaction was carried out galvanostatically with a current of 1.5 V (the cell potential measured was 6.2 V). The reaction mixture was pumped vertically through the flow cell from the bottom to the top at a flow rate of 400 mL / min. After 90 minutes, the conversion of Z-2-butene-1,4-diol reached 97%. The DMDF content in the reaction mixture was 66% and the Faradaic efficiency was 58%.

[0109] Example 4

[0110] Electrochemical oxidation of 1 M Z-2-butene-1,4-diol (compound of formula (Ia)) to 2,5-dihydro-2,5-dimethoxyfuran was carried out in methanol in an undivided flow cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), using 8.2wt% triethylammonium hydrogen sulfate as the electrolyte. Graphite (100cm 2 ) electrode was used as the anode, and a graphite (100 cm 2) was used as the cathode. The electrolysis was performed by applying 150 mA cm at 20 °C. -2 The reaction was carried out galvanostatically with a current of 1.5 V (the cell potential measured was 7.3 V). The reaction mixture was pumped vertically through the flow cell from the bottom to the top at a flow rate of 400 mL / min. After 60 minutes, the conversion of Z-2-butene-1,4-diol reached 98%. The DMDF content in the reaction mixture was 68% and the Faradaic efficiency was 60%.

[0111] Example 5

[0112] Electrochemical oxidation of 1 M Z-2-butene-1,4-diol (compound of formula (Ia)) to 2,5-dihydro-2,5-dimethoxyfuran was carried out in methanol in an undivided flow cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), using 8.2wt% triethylammonium hydrogen sulfate as the electrolyte. Graphite (100cm 2 ) electrode was used as the anode, and a stainless steel (100 cm 2 ) was used as the cathode. The electrolysis was performed by applying 150 mA cm at 20 °C. -2 The reaction was carried out galvanostatically with a current of 1.5 V (the cell potential measured was 6.0 V). The reaction mixture was pumped vertically through the flow cell from the bottom to the top at a flow rate of 400 mL / min. After 60 minutes, the conversion of Z-2-butene-1,4-diol reached 98%. The DMDF content in the reaction mixture was 65% and the Faradaic efficiency was 57%.

[0113] Example 6

[0114] Electrochemical oxidation of 0.5 M BED (Z-2-butene-1,4-diol) to DMDF (2,5-dihydro-2,5-dimethoxyfuran) was carried out in methanol in an undivided flow cell (V = 10 mL, surface area 100 cm 2 , electrode spacing 1mm), using 3.1wt% sodium dodecyl sulfate as the electrolyte. 2 ) electrode was used as the anode, and a stainless steel (100 cm 2 ) was used as the cathode. The electrolysis was performed by applying 50 mA cm at 20 °C. -2 The reaction mixture was pumped vertically through the flow cell from the bottom to the top at a flow rate of 400 mL / min. After 360 minutes, the conversion of BED reached 98%, the total yield of DMDF was 70%, and the Faradaic efficiency was 61%.

[0115] Embodiment 7-15

[0116] In methanol, various electrolytes were used in an undivided flow cell (V = 1 mL, surface area 10 cm 2 Electrochemical oxidation of 0.5 M BED (Z-2-butene-1,4-diol) to DMDF (2,5-dihydro-2,5-dimethoxyfuran) was carried out on graphite (10 cm 2 ) electrode was used as the anode, and different electrode materials (10 cm 2 ) was used as the cathode. Electrolysis was performed by applying 17-50 mA cm at 20 °C (changing the cell potential). -2 The reaction mixture was pumped vertically through the flow cell from bottom to top at a flow rate of 50 mL / min.

[0117]

Claims

1. A method for preparing a compound of formula (I) Wherein R is a linear or branched C1-C6 alkyl group, The method comprises electrochemically reacting a compound of formula (II) in Z-form with at least one monohydric alcohol of formula (III), wherein R has the same meaning as R in the compound of formula (I), It is characterized in that The process is carried out in an electrochemical reactor with vertical flow.

2. The method according to claim 1, wherein R is -CH3 or -CH2CH3.

3. The method according to claim 1, wherein R is -CH3.

4. A process according to any one of the preceding claims, wherein the process is carried out in a non-aqueous medium.

5. The process according to claim 4, wherein the at least one alcohol of formula (III) is used in an amount of at least 2 molar equivalents of the compound of formula (II).

6. The method according to claim 4, wherein the non-aqueous medium is (or includes) at least one linear or branched C1-C 10 alcohol.

7. The method according to claim 4, wherein the non-aqueous medium is a monohydric alcohol of formula (III), ROH(III), Wherein R is a linear or branched C1-C6 alkyl group.

8. The method according to any one of the preceding claims, wherein the method is carried out in a cuboid electrochemical reactor.

9. A method according to any preceding claim, wherein the cathode is not made of graphite.

10. A method according to any one of the preceding claims, wherein the cathode is made of a material selected from the group consisting of metals and metal alloys.

11. The method according to any one of the preceding claims, wherein the anode is made of a material selected from the group consisting of noble metals, oxides, graphite, highly oriented pyrolytic graphite (HOPG), boron doped diamond (BDD), dimensionally stable anode (DSA) and glassy carbon.

12. The method according to any one of the preceding claims, wherein the current density applied in the method is in the range of 1-1000 mA / cm 2 between.

13. The method according to any one of the preceding claims, wherein the method is carried out in the presence of at least one supporting electrolyte.

14. The method according to claim 13, wherein the at least one electrolyte is not phosphoric acid and / or a salt thereof.

15. The method of claim 13, wherein the at least one electrolyte is selected from the group consisting of HCl, H2SO4, Na2SO4, NaCl, sodium dodecyl sulfate, methyltributylammonium methyl sulfate, triethylammonium hydrogen sulfate, tetrabutylammonium hydrogen sulfate, tetramethylammonium hydrogen sulfate, tetrabutylammonium acetate (NBu4OAc), tetrabutylammonium sulfate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, methanesulfonic acid, ammonium hydrogen sulfate, tetrabutylphosphonium methanesulfonate, 1-methylimidazolium hydrogen sulfate, tetrabutylammonium perchlorate, and LiClO4.

16. A process according to any one of the preceding claims, wherein the reaction is carried out batchwise or continuously.

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