Electrochemical process for preparing amines and / or nitriles

Abstract

The present invention relates to an electrochemical method for converting amino acids and / or their salts into amines and / or nitriles. When the reaction medium has a high concentration of amino acids and / or their salts at the beginning of the reaction, the total yield and selectivity of amines and nitriles obtained by the method according to the present invention are higher than those of the prior art.

Description

Technical Field

[0001] The present invention relates to a method for preparing amines and / or nitriles by electrochemical reaction. Background Art

[0002] Amines are of significant importance to the chemical industry. Many amines and their derivatives are used as agrochemicals, pharmaceuticals or food additives. Millions of tons of amines are produced every year. They are widely used in both the bulk and fine chemical industries as base materials, additives, dyes, and agrochemicals.

[0003] Diamines are used as monomers for the preparation of polyamides, polyimides and polyureas. For example, the five-carbon compound 1,5-diaminopentane is gaining more and more attention as a platform chemical, especially as an innovative building block for bio-based polymers. Today, the chemical industry is transitioning from a petrochemical industry to a more bio-based industry. After selective removal of the carboxyl group on the α-carbon atom, amino acids can be interesting starting materials for various nitrogen-containing commodity chemicals. This nitrogen recycling avoids repeated, energy-intensive functionalization of hydrocarbons with ammonia.

[0004] Eur. J. Org. Chem. [European Journal of Organic Chemistry] 2014, 6649-6652 discloses the decarboxylation of a wide range of amino acids with electrically generated hypobromite. The highest total yield of aminovaleronitrile (APN) and diaminopentane (DAP) by decarboxylation of lysine was 93%. However, the concentration of amino acids is quite low. Disadvantageously, low concentrations of reactants require larger reaction vessels and therefore more CAPEX to produce the same amount simultaneously.

[0005] There is still a need to develop an industrially applicable and efficient process for preparing amines under mild conditions with higher selectivity and yield. Summary of the invention

[0006] Therefore, the present invention relates to an electrochemical method for converting an amino acid and / or its salt into an amine and / or nitrile in the presence of a solvent and a compound that generates a reduced mediator in the solvent, wherein the concentration of the amino acid and / or its salt in the solvent is equal to or greater than 0.15 mol / L.

[0007] Without wishing to be bound by any theory, when the reaction medium has a high concentration of amino acid and / or its salt at the beginning of the reaction, the total yield and selectivity of amines and nitrile obtained by the process according to the invention are higher than in the prior art. A higher concentration of reactants reduces the average cost because it increases the yield and is more conducive to large-scale production than small-scale production.

[0008] definition

[0009] Throughout this description, including the claims, unless otherwise indicated, the term "comprising one / an" should be understood to be synonymous with the term "comprising at least one / an", and "between..." should be understood to include the limits.

[0010] As used herein, the term "(C n -C m )" (wherein n and m are each an integer) indicates that the group may contain from n to m carbon atoms per group.

[0011] As used herein, the term "oxidative decarboxylation" reaction is an oxidation reaction that removes a carboxylate group or a carboxylic acid group, forming carbon dioxide.

[0012] As used herein, the term "anode" means an electrode from which electrons migrate to an external circuit and is the electrode where oxidation occurs.

[0013] As used herein, the term "cathode" means an electrode to which electrons migrate from an external circuit and where reduction occurs.

[0014] Use of the articles "a," "an," and "the" means that the grammatical object of the article is one or more than one (ie, at least one).

[0015] The term "and / or" includes the meanings of "and", "or" and also includes all other possible combinations of the elements connected with this term.

[0016] It should be noted that, for the sake of continuity of description, the limiting values ​​are included in the given value ranges unless otherwise indicated.

[0017] Ratios, concentrations, amounts, and other numerical data may be expressed in a range format herein. It should be understood that this range format is used only for convenience and brevity and should be flexibly understood to include not only the values ​​explicitly stated at the limits of the range, but also all individual values ​​or sub-ranges included in the range, just as if each value and sub-range were explicitly stated. DETAILED DESCRIPTION

[0018] The upper limit of the concentration of amino acid and / or its salt is not particularly limited. In certain embodiments, it can be a saturated solution concentration, which depends on the specific amino acid or salt. Preferably, the concentration of amino acid and / or its salt in solution is in the range of 0.15mol / L to 2mol / L and more preferably 0.50mol / L to 1.0mol / L.

[0019] It should be understood that the solvent should have good solubility for both the amino acid or its salt and the compound generating the reduced mediator so that they can have sufficient contact in the solution. Such a solvent can be ethanol, water or a combination thereof. Preferably, the solvent is water.

[0020] As used herein, "mediator" is a redox substance that mediates electron transfer. In the present invention, the substance acts as an electron shuttle between the oxidation electrode and the amino acid and / or its salt. The mediator is not particularly limited as long as it can take the responsibility of transferring electrons between the oxidation electrode and the amino acid and / or its salt.

[0021] Examples of compounds that generate reduced mediators in this solvent are:

[0022] - alkali metal bromides, such as lithium bromide (LiBr), sodium bromide (NaBr) and potassium bromide (KBr);

[0023] - alkali metal chlorides, such as lithium chloride (LiCl), sodium chloride (NaCl) and potassium chloride (KCl);

[0024] - alkali metal iodides, such as lithium iodide (LiI), sodium iodide (NaI) and potassium iodide (KI);

[0025] - ammonium bromide (NH4Br);

[0026] - iron salts, such as iron(II) sulfate (FeSO4), iron(II) bromide (FeBr2), iron(II) chloride (FeCl2), iron(II) iodide (FeI2), iron(II) nitrite (Fe(NO3)2), iron(II) acetate ((C2H3O2)2Fe), potassium(II) ferrocyanide K4[Fe(CN)6] and ferrocene;

[0027] - cerium salts, such as cerium (III) sulfate Ce2(SO4)3;

[0028] - manganese salts, such as manganese(II) sulfate (MnSO4);

[0029] - copper salts, such as copper(II) sulfate (CuSO4), copper(II) bromide (CuBr2), copper(II) chloride (CuCl2), copper(II) iodide (CuI2), copper(II) nitrite (Cu(NO3)2) and copper(II) acetate ((C2H3O2)2Cu);

[0030] - cobalt salts, such as cobalt(II) sulfate (CoSO4), cobalt(II) bromide (CoBr2), cobalt(II) chloride (CoCl2), cobalt(II) iodide (CoI2), cobalt(II) nitrite (Co((NO3)2) and cobalt(II) acetate ((C2H3O2)2Co);

[0031] - Chromium salts, such as chromium (III) sulfate (Cr2(SO4)3), chromium (III) bromide (CrBr3), chromium (III) chloride (CrCl3), chromium (III) iodide (CrI3), chromium (III) nitrite (Cr(NO3)3) and chromium (III) acetate ((C2H3O2)3Cr).

[0032] In some embodiments, sodium bromide (NaBr) or ammonium bromide (NH4Br) may be preferably used.

[0033] In some embodiments, it may be preferred to use environmentally friendly compounds, such as iron salts. Among all iron salts, iron (II) sulfate (FeSO4) is more preferred.

[0034] The concentration of the compound generating a reduced mediator in the solution is in the range of 0.01 mol / L to 1 mol / L and preferably 0.05 mol / L to 0.2 mol / L.

[0035] In the method according to the invention, when the above compounds are dissolved in a solvent, a reduced mediator is obtained. The skilled person will appreciate that when an electric current is passed through the reactor, the reduced mediator is oxidized at the anode to obtain an oxidized mediator. The oxidized mediator then oxidizes the amino acid and / or its salt and simultaneously forms a reduced mediator, which may be the same or different from the reduced mediator obtained when the compound is dissolved.

[0036] Examples of reduced mediators are:

[0037] -Halogen ions, such as Br - , Cl - and I - ;

[0038] -Metal ions, such as Fe 2+ 、Fe(CN)6 4- , Mn 2+ 、MnO4 2- 、Ce 3+ Cr 3+ and Co 2+ .

[0039] Examples of oxidized mediators are:

[0040] -Halogen ions, such as hypobromite (OBr - ), hypochlorite (OCl - ) and hypoiodite (OI - );

[0041] -Metal ions, such as Fe 3+ 、Fe(CN)6 3-、MnO4 2- 、MnO4 - 、Ce 4+ 、HCrO4 - and Co 3+ .

[0042] As used herein, "amino acid" is an organic compound containing amine (-NH2) and carboxyl (-COOH) functional groups and a side chain (R group) that is unique to each amino acid.

[0043] Preferably, the amino acids used in the methods of the present invention are α-amino acids.

[0044] Examples of amino acids used in the method according to the invention are lysine, cysteine, leucine, serine, tyrosine, arginine, histidine, isoleucine. The amino acid may notably have two amino functional groups, such as lysine.

[0045] The salt of the amino acid is not particularly limited. It may notably be a hydrochloride, a hydrobromide or a hydroiodide.

[0046] It should be understood that amino acids and / or their salts are converted into corresponding nitrile or amine by oxidative decarboxylation. For example, an amino acid reactant having the general formula RCH(NH2)COOH, the desired product is a nitrile RCN or in some cases an amine RCH2NH2. The nitrile can then be hydrogenated to an amine with complete conversion by well-known methods.

[0047] Preferred examples of product amines are: 1,5-diaminopentane, 3-methylbutan-1-amine, 1-(4-aminobutyl)guanidine, histamine, 2-methylbutan-1-amine, cysteamine, diaminoethyl disulfide, 2-aminoethanol.

[0048] Preferred examples of product nitriles are: 5-aminovaleronitrile, glutaronitrile, 3-methylbutyronitrile, 1-(3-cyanopropyl)guanidine, 2-(1H-imidazol-4-yl)acetonitrile, 2-methylbutyronitrile, dicyanomethyl disulfide, 2-hydroxyacetonitrile.

[0049] The pH of the solution containing the compound of formula (I) and the compound generating the reduced mediator depends on the mediator and is optionally adjusted by the technician. For example, the pH of the solution containing the compound of formula (I) and the iron salt should be adjusted to less than 4 and preferably less than 3 to prevent the formation of iron (II) / (III) hydroxide. The pH of the solution containing the compound of formula (I) and the alkali metal bromide should be adjusted to an acidic or weakly alkaline solution to prevent the formation of toxic Br2 gas.

[0050] The conversion according to the invention is carried out in such a preferred reactor comprising both an anode and a cathode.

[0051] The anode and / or cathode preferably comprises a catalyst.The catalyst for the anode or cathode may comprise a metal element, which may be in the form of an elemental metal, a metal alloy, a metal oxide or a metal complex.

[0052] The anode catalyst may preferably comprise an element selected from the group consisting of elements of Group IIIA, Group IVA, Group VA of the periodic table and transition metals.

[0053] As used herein, metals of Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB, Group VIIB, and Group VIIIB are generally referred to as transition metals. This group includes elements having atomic numbers of 21 to 30 (Sc to Zn), 39 to 48 (Y to Cd), 72 to 80 (Hf to Hg), and 104 to 112 (Rf to Cn).

[0054] Examples of anode catalysts are notably:

[0055] - an elemental metal comprising an element selected from the group consisting of Pd, Pt, Ru, Au, Rh, Ir, Bi, Sn, B, and any combination thereof.

[0056] -Metal alloys such as Pd-Au, Pd-B and Pt-Ru.

[0057] Preferably, the anode catalyst is Pt.

[0058] The cathode catalyst may preferably comprise an element selected from the group consisting of elements of Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group VIA, Group VIIA of the periodic table, transition metals and lanthanides.

[0059] Examples of cathode catalysts are notably:

[0060] - Elemental metal comprising an element selected from the group consisting of Pt, Ni, Cu, C and any combination thereof.

[0061] Preferably, the cathode catalyst is Ni or Cu and more preferably Cu.

[0062] The above-mentioned catalyst for anode or cathode can be supported on a carrier. The carrier is not particularly limited. Typical examples of the carrier are carbon, alumina and silica.

[0063] In one embodiment, the anode or cathode may include the above-described catalyst and a substrate.

[0064] Preferably, the anode and cathode may be made of a porous substrate structure.

[0065] The anode substrate may include, for example, stainless steel mesh, nickel foam, sintered nickel powder, etched aluminum-nickel mixture, carbon fiber and carbon cloth. Preferably, carbon material and stainless steel are used as the anode substrate.

[0066] Cathode substrates can include stainless steel, nickel foam, sintered nickel powder, etched aluminum-nickel mixture, metal mesh, carbon fiber, and carbon cloth.

[0067] Methods for applying the anode catalyst to the anode substrate and methods for applying the cathode catalyst to the cathode substrate include, for example, spreading, wet spraying, powder deposition, electrodeposition, evaporative deposition, dry spraying, decaling, painting, sputtering, low pressure vapor deposition, electrochemical vapor deposition, tape casting, screen printing, hot pressing and other methods.

[0068] When using a substrate, a preferred range of catalyst loading may include 0.01 mg / cm -2 With 500mg / cm -2 More preferably, the catalyst loading may be between 1 mg / cm -2 With 20mg / cm -2 between.

[0069] In one embodiment, the electrochemical reactor used in the method according to the present invention has two independent compartments. Anode and cathode are respectively located in these two compartments. A membrane can be placed between these two compartments. The membrane can be a neutral membrane or an ion exchange membrane. Preferably, the membrane is a Nafion (fluoropolymer-copolymer based on sulfonated tetrafluoroethylene) cation exchange membrane.

[0070] Advantageously, the distance between the anode and the cathode is in the range of 1 mm to 10 cm and preferably 3 mm to 1 cm.

[0071] Preferably, the reaction temperature may be from 0°C to 100°C, and more preferably from 10°C to 50°C, and most preferably room temperature.

[0072] According to the present invention, room temperature is between 15°C and 25°C.

[0073] Preferably, the reaction can be in the range of 0.1 mA / cm 2 Up to 150mA / cm 2 And preferably from 10mA / cm 2 Up to 20mA / cm 2 carried out at a current density of .

[0074] Preferably, the reaction may be carried out at a potential ranging from 0.0001V to 10V and more preferably from 1.5V to 4V.

[0075] The skilled person will use an appropriate reaction time based on the above reaction parameters. The reaction time may be from 10 h to 100 h, and preferably 10 h to 80 h.

[0076] The following examples are included to illustrate embodiments of the invention. It goes without saying that the invention is not limited to the examples described.

[0077] Experimental Section

[0078] Material

[0079] -Sodium bromide: CAS No. 7647-15-6, from Sigma-Aldrich

[0080] -Iron(II) sulfate heptahydrate: CAS No. 7782-63-0, from Sigma-Aldrich

[0081] -L-Lysine monohydrochloride: CAS No. 657-27-2, from Sigma-Aldrich

[0082] - Sulfuric acid: CAS No. 7664-93-9, from China National Pharmaceutical Group Co., Ltd. (Sinopharm)

[0083] Example 1 (Comparative Example)

[0084] As a batch reactor, a 10 ml glass container (2.5 cm in diameter) was used. A Pt coil (coil = 0.5 cm high, 1 cm in diameter, circumference = 3.1 cm, surface area = 1.6 cm 2 ) was used as anode. As cathode, Ni foam was bent into a cylinder (dimensions = 5.5 cm x 5.5 cm - long enough to extend out of the reactor). It was bent into a cylinder and wrapped around a cylindrical foam (diameter = 2 cm). Cathode surface area = 5.5 cm x 0.5 cm (Pt coil height) = 2.75 cm 2 The Pt wire above the coil is insulated by a PTFE tube to prevent the wire from electrochemically reacting and is pierced through the spacer to hold the Pt electrode in place. The Ni cathode is notched so that the Pt coil can be seen. The distance between the two electrodes is 3mm

[0085] No reference electrode or stirring is used.

[0086] The reactor was filled with 6 ml of a solution of lysine monohydrochloride (0.14 M) and NaBr (0.19 M). The pH was measured to be about 6.

[0087] Reaction parameters: Total experimental time: 7h, current = 41mA (equivalent to 15mA / cm at the anode 2 of current density).

[0088] During the reaction, samples were taken and analyzed by NMR. The results are summarized in Table 1.

[0089] Example 2 (Bromide mediator, 0.28 M lysine monohydrochloride, Ni cathode)

[0090] As a batch reactor, a 10 ml glass container (2.5 cm in diameter) was used. A Pt coil (coil = 0.5 cm high, 1 cm in diameter, circumference = 3.1 cm, surface area = 1.6 cm 2 ) was used as anode. As cathode, Ni foam was bent into a cylinder (dimensions = 5.5 cm x 5.5 cm - long enough to extend out of the reactor). It was bent into a cylinder and wrapped around a cylindrical foam (diameter = 2 cm). Cathode surface area = 5.5 cm x 0.5 cm (Pt coil height) = 2.75 cm 2 The Pt wire above the coil is insulated by a PTFE tube to prevent the wire from electrochemically reacting and is pierced through the spacer to hold the Pt electrode in place. The Ni cathode is notched so that the Pt coil can be seen. The distance between the two electrodes is 3mm

[0091] No reference electrode or stirring is used.

[0092] • Reactor was filled with 5 ml of lysine monohydrochloride (0.28 M) and NaBr (0.14 M). The pH was measured to be about 6.

[0093] Reaction parameters: Total experimental time: 14 h, current = 41 mA (equivalent to 15 mA / cm at the anode 2 of current density).

[0094] During the reaction, samples were taken and analyzed by NMR. The results are summarized in Table 1.

[0095] Example 3 (Bromide mediator, 1M lysine monohydrochloride, Ni cathode)

[0096] As a batch reactor, a 10 ml glass container (2.5 cm in diameter) was used. A Pt coil (coil = 0.5 cm high, 1 cm in diameter, circumference = 3.1 cm, surface area = 1.6 cm 2 ) was used as anode. As cathode, Ni foam was bent into a cylinder (dimensions = 5.5 cm x 5.5 cm - long enough to extend out of the reactor). It was bent into a cylinder and wrapped around a cylindrical foam (diameter = 2 cm). Cathode surface area = 5.5 cm x 0.5 cm (Pt coil height) = 2.75 cm 2The Pt wire above the coil is insulated by a PTFE tube to prevent the wire from electrochemically reacting and is pierced through the spacer to hold the Pt electrode in place. The Ni cathode is notched so that the Pt coil can be seen. The distance between the two electrodes is 3mm

[0097] No reference electrode or stirring is used.

[0098] • Reactor was filled with 5 ml of lysine monohydrochloride (1 M) and NaBr (0.14 M). The pH was measured to be about 6.

[0099] Reaction parameters: Total experimental time: 72 h, current = 41 mA (current density = 15 mA / cm 2 ).

[0100] During the reaction, samples were taken and analyzed by NMR. The results are summarized in Table 1.

[0101] Example 4 (Bromide Mediator, 2M Lysine Monohydrochloride (Saturated), Cu Cathode)

[0102] As a batch reactor, a 10 ml glass container (2.5 cm in diameter) was used. A Pt coil (height = 1.5 cm, diameter = 1 cm, circumference = 3.1 cm, surface area = 4.7 cm) was placed. 2 ) was used as anode. As cathode, Cu foam was bent into a cylinder (dimensions = 5.5 cm x 5.5 cm - long enough to extend out of the reactor). It was bent into a cylinder and wrapped around a cylindrical foam (diameter = 2 cm). Cathode surface area = 5.5 cm x 0.5 cm (Pt coil height) = 2.75 cm 2 The Pt wire above the coil is insulated by a PTFE tube to prevent the wire from electrochemically reacting and is pierced through the spacer to hold the Pt electrode in place. The Cu cathode is notched so that the Pt coil can be seen. The distance between the two electrodes is 3mm

[0103] No reference electrode or stirring is used.

[0104] • Reactor was filled with 8 ml of lysine monohydrochloride (2 M) and NaBr (0.2 M). The pH was measured to be about 6.

[0105] Reaction parameters: Total experimental time: 31 h, current = 113 mA (15 mA / cm 2 ).

[0106] During the reaction, samples were taken and analyzed by NMR. The results are summarized in Table 1.

[0107] Example 5 (Fe 3+ \Fe 2+Mediator, 1 M lysine monohydrochloride, Cu cathode)

[0108] As a batch reactor, a 20 ml glass reactor was used. A Pt cylindrical mesh (height = 2 cm, diameter = 1 cm, circumference = 3.1 cm, surface area = 6.3 cm) was placed in the reactor. 2 ) was used as anode. As cathode, Cu foam was bent into a cylinder (thickness = 2 cm, size = 4 cm x 8 cm - long enough to extend out of the reactor). It was bent into a cylinder and wrapped around a cylindrical polymer foam (diameter = 2 cm). Cathode surface area = 4 cm x 2 cm (Pt coil height) = 8 cm 2 The Pt wire above the coil is insulated by a PTFE tube to prevent the wire from electrochemically reacting and is pierced through the spacer to hold the Pt electrode in place. The Cu cathode is notched so that the Pt electrode can be seen.

[0109] No reference electrode and stirring were used. The distance between the two electrodes was 3 mm.

[0110] The reactor was filled with 10 ml of a reaction solution containing 1 M lysine monohydrochloride and 0.14 M ferric sulfate heptahydrate. During the preparation of 10 ml of the solution, the pH was adjusted to 1 with 1 M sulfuric acid.

[0111] Reaction parameters: Total reaction time is 96h. Current = 120mA (equivalent to 15mA / cm at the anode) 2 of current density).

[0112] During the reaction, samples were taken and analyzed by NMR. The results are summarized in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] Conversion = 100%. Examples 1, 2 and 3 used Ni cathodes. Examples 4 and 5 used Cu cathodes.

[0117] APN = 5-aminovaleronitrile

[0118] DAP = 1,5-diaminopentane

[0119] APA = aminovaleramide.

Claims

1. An electrochemical method for converting an amino acid salt into an amine and a nitrile in the presence of a solvent and a compound that generates a reduced mediator in the solvent, wherein the concentration of the amino acid salt in the solvent is equal to or greater than 0.15 mol / L, wherein the compound that generates a reduced mediator in the solvent is an iron salt.

2. The method according to claim 1, wherein: The concentration of the amino acid salt in the solvent is in the range of 0.15 mol / L to 2 mol / L.

3. The method according to claim 1, wherein: The concentration of the compound generating the reduced mediator in the solvent is in the range of 0.01 mol / L to 1 mol / L.

4. The method according to claim 1, wherein: The compound that generates the reduced mediator in the solvent is iron (II) sulfate.

5. The method according to claim 1, wherein: The amino acid is selected from the group consisting of lysine, cysteine, leucine, serine, tyrosine, arginine, histidine and isoleucine.

6. The method according to claim 1, wherein: The amino acid salt is selected from the group consisting of hydrochloride, hydrobromide and hydroiodide.

7. The method according to claim 1, wherein: The conversion is carried out in a reactor comprising both an anode and a cathode, and the distance between the anode and the cathode is in the range of 1 mm to 10 cm.

8. The method according to claim 7, wherein: The anode and / or the cathode comprises a catalyst.

9. The method according to claim 7, wherein: The catalyst of the anode is Pt, and the catalyst of the cathode is Ni or Cu.

10. The method according to claim 1, wherein: The concentration of the amino acid salt in the solvent is in the range of 0.50 mol / L to 1.0 mol / L.

11. The method according to claim 1, wherein: The concentration of the compound generating the reduced mediator in the solvent is in the range of 0.05 mol / L to 0.2 mol / L.

12. The method according to claim 1, wherein: The conversion is carried out in a reactor comprising both an anode and a cathode, and the distance between the anode and the cathode is in the range of 3 mm to 1 cm.

Images