A metal ligand catalyst and a method for preparing lactic acid

Abstract

This invention belongs to the field of catalyst technology, and relates to a metal ligand catalyst and a method for preparing lactic acid. The metal ligand catalyst is a complex formed by a metal and a ligand; the metal is one or more of manganese, copper, zinc, and molybdenum; the ligand is phenanthroline, pyridine, phosphine ligand, or nitrogen-phosphine ligand. The catalyst provided by this invention is low in cost, has relatively mild reaction conditions, is simple to prepare, and exhibits high selectivity for the preparation of lactic acid.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a metal ligand catalyst and a method for preparing lactic acid. Background Technology

[0002] Lactic acid, also known as 2-hydroxypropionic acid, is an important and versatile organic acid. It was first isolated from spoiled milk and has wide applications in food, cosmetics, pharmaceuticals, pesticides, daily chemicals, and biodegradable plastics. In particular, the development and application of biodegradable plastics have greatly increased the demand for polylactic acid (PLA). Currently, my country's lactic acid production falls far short of industrial needs, making the exploration of novel and efficient processes for preparing lactic acid extremely urgent.

[0003] There are two main traditional methods for preparing lactic acid: 1) Microbial fermentation: Biomass resources (such as bagasse, corn starch, lignin, cellulose, cottonseed hulls, corn stalks, sorghum, cellulose, and other sugar-containing substances) are fermented by lactic acid bacteria and filamentous molds to produce a lactic acid mixture. After separation and purification, lactic acid is obtained. However, this method has low fermentation efficiency, consumes a lot of water, and the purification process is cumbersome. It also generates a large amount of biological sludge, causing environmental pollution, making it difficult to produce lactic acid on a large scale. 2) Chemical synthesis: Acetaldehyde and hydrogen cyanide are reacted in a reactor to produce 2-hydroxypropionitrile (lactic acid), which then undergoes hydrolysis under strong acids (such as sulfuric acid, trifluoromethanesulfonic acid, etc.) to obtain a lactic acid mixture. After esterification and hydrolysis, lactic acid is produced. However, chemical synthesis requires the use of catalysts to accelerate the reaction, but since catalysts are generally toxic reagents, their large-scale application is limited.

[0004] In recent years, chemists have been preparing lactic acid using inexpensive raw materials such as sorbitol (containing six carbons) and glycerol (containing three carbons). However, this reaction produces numerous byproducts such as methanol, glycolaldehyde, and formaldehyde, resulting in poor selectivity. Methanol and ethylene glycol are common, inexpensive, and readily available chemicals that can be used to prepare lactic acid with the aid of catalysts. However, currently used catalysts include iridium and rhodium, which are expensive and have complex preparation processes, hindering industrial production. Therefore, exploring inexpensive catalysts for lactic acid preparation is undoubtedly of significant research value. Summary of the Invention

[0005] The purpose of this invention is to provide a metal ligand catalyst and a method for preparing lactic acid. The catalyst has low cost, mild reaction conditions, and simple preparation, and exhibits high selectivity for the preparation of lactic acid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A metal ligand catalyst is a complex formed by a metal and a ligand; the metal is one or more of manganese, copper, zinc and molybdenum; the ligand is phenanthroline, pyridine, phosphine ligand or nitrogen phosphine ligand.

[0008] Furthermore, the ligand is phenanthroline, and the structural formula of the complex is:

[0009]

[0010] Wherein: R is H, aromatic group or alkyl group.

[0011] Furthermore, the ligand is a pyridine, and the structural formula of the complex is:

[0012]

[0013] Where R is H, aromatic or alkyl, and R2 represents two R groups.

[0014] Furthermore, the ligand is a phosphine ligand or a nitrogen-phosphine ligand, and the structural formula of the complex is:

[0015]

[0016] Where: R 1 It is an aromatic group or an alkyl group.

[0017] Application of the aforementioned metal ligand catalyst in the preparation of lactic acid.

[0018] A method for preparing lactic acid based on a metal ligand catalyst includes the following steps:

[0019] 1) Mix A mmol of ethylene glycol, B mmol of methanol, C mol of metal ligand catalyst and D mmol of base, and heat to react and generate a mixture; wherein A:B:C:D = 1:(10-30):(0.01-0.1):(1-3);

[0020] 2) Add acid to the mixture from step 1) to adjust the pH to 1-3, and then distill to separate lactic acid.

[0021] Furthermore, in step 1), the base is a hydroxide, carbonate, phosphate, alcohol base, or organic base.

[0022] Furthermore, the hydroxide is sodium hydroxide, potassium sodium hydroxide, calcium hydroxide, barium hydroxide, or lithium hydroxide; the carbonate is sodium carbonate, potassium carbonate, cesium carbonate, or sodium bicarbonate; the phosphate is potassium phosphate, sodium phosphate, or disodium hydrogen phosphate; the alcohol base is lithium methoxide, sodium methoxide, potassium methoxide, sodium ethoxide, sodium tert-butoxide, or potassium tert-butoxide; and the organic base is pyridine and its derivatives, triethylenediamine, diisopropylethylamine, or tetramethylguanidine.

[0023] Furthermore, in step 1), the heating reaction conditions are: temperature 90℃~150℃, time 2h~4h.

[0024] Furthermore, in step 2), the acid is sulfuric acid, hydrochloric acid, or nitric acid, and the concentration of the acid is 1 mol / L.

[0025] The beneficial effects of this invention are:

[0026] 1. The metal ligand catalyst of the present invention is a complex formed by a metal and a ligand; the metal is one or more of manganese, copper, zinc and molybdenum; the ligand is phenanthroline, pyridine, phosphine ligand or nitrogen phosphine ligand, the raw materials are readily available, the cost is low, and it has high selectivity for the preparation of lactic acid.

[0027] 2. This invention uses methanol and ethylene glycol as raw materials. Under the catalysis of metal ligand catalysts, the reaction conditions are mild and the operation process is simple. Furthermore, the acidification post-treatment is simple and mild, with minimal environmental pollution, laying the foundation for industrial production. Attached Figure Description

[0028] Figure 1 The 1H NMR spectrum of lactic acid was obtained.

[0029] Figure 2 The carbon NMR spectrum of lactic acid was prepared.

[0030] Figure 3 This is the ion chromatogram of a lactic acid standard.

[0031] Figure 4 This is the ion chromatogram of the lactic acid reaction solution. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] The metal ligand catalyst of the present invention is a complex formed by a metal and a ligand; the metal is one or more of manganese, copper, zinc and molybdenum; the ligand is phenanthroline, pyridine, phosphine ligand or nitrogen-phosphine ligand. Both phenanthroline and pyridine are nitrogen ligands.

[0034] The ligand in this invention is phenanthroline, and the structural formula of the complex is as follows:

[0035]

[0036] Wherein: R is H, aromatic group or alkyl group.

[0037] The ligands in this invention are pyridines, and the structural formula of the complex is as follows:

[0038]

[0039] Where R is H, aromatic or alkyl, and R2 represents two R groups.

[0040] The ligand in this invention is a phosphine ligand or a nitrogen-phosphine ligand, and the structural formula of the complex is as follows:

[0041]

[0042] Where: R 1 It is an aromatic group or an alkyl group.

[0043] Specifically, several structures of some metal ligand catalysts are shown below.

[0044]

[0045] Where: Aryl is an aromatic group, Alkyl is an alkyl group, X is a halogen, phosphate ion or borate ion, Y is N-alkylated N-alkyl, N-aryl-aryl or alkylalkyl; M is a metal, and R2 represents two Rs.

[0046] Preferably, the metal is manganese.

[0047] The application of the metal ligand catalyst provided by this invention in the preparation of lactic acid.

[0048] The synthetic mechanism for preparing lactic acid using ethylene glycol and methanol in this invention is as follows:

[0049]

[0050] The method for preparing lactic acid based on metal ligand catalysts includes the following steps:

[0051] 1) Mix A mmol ethylene glycol, B mmol methanol, C mol metal ligand catalyst and D mmol base, and heat to react to generate a mixed solution; wherein A:B:C:D = 1:(10-30):(0.01-0.1):(1-3).

[0052] In step 1), the heating reaction conditions are: temperature 90℃~150℃, time 2h~4h.

[0053] In step 1) of this invention, the base is a hydroxide, carbonate, phosphate, alcohol base or organic base.

[0054] The hydroxide is sodium hydroxide, potassium sodium hydroxide, calcium hydroxide, barium hydroxide, or lithium hydroxide.

[0055] The carbonates are sodium carbonate, potassium carbonate, cesium carbonate, or sodium bicarbonate.

[0056] The phosphate is potassium phosphate, sodium phosphate, or disodium hydrogen phosphate.

[0057] The alcohol base is lithium methoxide, sodium methoxide, potassium methoxide, sodium ethoxide, sodium tert-butoxide, or potassium tert-butoxide.

[0058] The organic base is pyridine and its derivatives, triethylenediamine, diisopropylethylamine, or tetramethylguanidine.

[0059] 2) Add acid to the mixture from step 1) to adjust the pH to 1-3, and then distill to separate lactic acid.

[0060] In step 2), the acid is sulfuric acid, hydrochloric acid, or nitric acid, and the concentration of the acid is 1 mol / L.

[0061] In this invention, the reaction process is monitored using a TLC plate.

[0062] Specifically, bromocresol green is used as the colorimetric reagent, and carboxylic acids turn yellow, thus detecting the formation of lactic acid. The developing solvent used in the TLC plate is a mixture of ethyl acetate and petroleum ether in a volume ratio of 2:1.

[0063] The present invention will now be described in detail with reference to specific embodiments.

[0064] Example 1

[0065] The metal ligand catalyst provided in this embodiment is shown below.

[0066]

[0067] i Pr2 represents two isopropyl groups.

[0068] The lactic acid preparation method in this embodiment includes the following steps:

[0069] (1) In a 25 mL sealed tube containing a magnetic magnet, add catalyst (1 mol%), potassium hydroxide (560 mg, 10 mmol), ethylene glycol (310 mg, 5 mmol) and methanol (3200 mg, 100 mmol) to the reaction tube, heat the reaction tube to 120 °C, and react for 2 h to obtain a reaction mixture.

[0070] (2) Add 1 mol / L sulfuric acid to the mixture after the reaction to adjust the pH to 2, and then distill to separate lactic acid.

[0071] In this embodiment, the reaction was monitored by gas chromatography and TLC plates, and the yield of lactic acid was determined to be 38% by high-pressure ion chromatography.

[0072] The lactic acid prepared in Example 1 was subjected to performance analysis. According to industry standard testing methods, the 1H NMR spectrum, 1C NMR spectrum, and ion chromatography of the reaction solution were obtained. See [link to relevant documentation] for details. Figure 1 , Figure 2 and Figure 4And a lactic acid standard curve was used for comparison, as shown in the standard curve. Figure 3 As shown.

[0073] See Figure 1 and Figure 2 It can be seen that, 1 H NMR (400MHz, CDCl3): δ = 4.37 (q, J = 8.0Hz, 1H), 1.48 (d, J = 8.0Hz, 3H); 13 C NMR (100MHz, CDCl3): δ=179.7, 66.5, 20.1.

[0074] See Figure 3 and Figure 4 This indicates that, under the action of the catalyst in this embodiment, ethanol and methanol react to synthesize lactic acid.

[0075] Example 2

[0076] The metal ligand catalyst provided in this embodiment is as follows.

[0077]

[0078] The lactic acid preparation method in this embodiment includes the following steps:

[0079] (1) In a 25 mL sealed tube containing a magnetic magnet, add catalyst (2 mol%), sodium carbonate (1060 mg, 10 mmol), ethylene glycol (310 mg, 5 mmol) and methanol (3200 mg, 100 mmol) to the reaction tube, heat the reaction tube to 130 °C, and react for 2 h to obtain a reaction mixture.

[0080] (2) Add 1 mol / L sulfuric acid to the mixture after the reaction to adjust the pH to 2, and then distill to separate lactic acid.

[0081] In this embodiment, the reaction was monitored by gas chromatography and TLC plates, and the yield of lactic acid was detected by high-pressure ion chromatography as 41%.

[0082] Example 3

[0083] The metal ligand catalyst provided in this embodiment is as follows.

[0084]

[0085] Pr2 represents two isopropyl groups.

[0086] The lactic acid preparation method in this embodiment includes the following steps:

[0087] (1) In a 25 mL sealed tube containing a magnetic magnet, add catalyst (2 mol%), sodium hydroxide (2 mmol), ethylene glycol (1 mmol) and methanol (20 mmol) to the reaction tube, heat the reaction tube to 120 °C, and react for 2 h to obtain a reaction mixture.

[0088] (2) Add 1 mol / L sulfuric acid to the mixture after the reaction to adjust the pH to 2, and then distill to separate lactic acid.

[0089] In this embodiment, the reaction was monitored by gas chromatography and TLC plates, and the yield of lactic acid was detected as 26% by high-pressure ion chromatography.

[0090] Example 4

[0091] The metal ligand catalyst provided in this embodiment is shown below.

[0092]

[0093] The lactic acid preparation method in this embodiment includes the following steps:

[0094] (1) In a 25 mL sealed tube containing a magnetic magnet, add catalyst (3 mol%), calcium hydroxide (2 mmol), ethylene glycol (1 mmol) and methanol (20 mmol) to the reaction tube, heat the reaction tube to 130 °C, and react for 4 h to obtain a reaction mixture.

[0095] (2) Add 1 mol / L sulfuric acid to the mixture after the reaction to adjust the pH to 2, and then distill to separate lactic acid.

[0096] In this embodiment, the reaction was monitored by gas chromatography and TLC plates, and the yield of lactic acid was detected by high-pressure ion chromatography as 36%.

[0097] Example 5

[0098] The metal ligand catalyst provided in this embodiment is shown below.

[0099]

[0100] The lactic acid preparation method in this embodiment includes the following steps:

[0101] (1) In a 25 mL sealed tube containing a magnetic magnet, add catalyst (2 mol%), sodium methoxide (2 mmol), ethylene glycol (1 mmol) and methanol (20 mmol) to the reaction tube, heat the reaction tube to 140 °C, and react for 3 h to obtain a reaction mixture.

[0102] (2) Add 1 mol / L sulfuric acid to the mixture after the reaction to adjust the pH to 2, and then distill to separate lactic acid.

[0103] In this embodiment, the reaction was monitored by gas chromatography and TLC plates, and the yield of lactic acid was detected by high-pressure ion chromatography as 31%.

Claims

1. A method for preparing lactic acid, characterized in that, The method for preparing lactic acid includes the following steps: 1) Mix A mmol of ethylene glycol, B mmol of methanol, C mol of metal ligand catalyst and D mmol of base, and heat to react and generate a mixture; wherein A:B:C:D = 1:(10-30):(0.01-0.1):(1-3); 2) Add acid to the mixture from step 1) to adjust the pH to 1-3, and then distill to separate and obtain lactic acid; The structural formula of the metal ligand catalyst is as follows: Where: R is an aromatic or alkyl group, X is a halide or borate ion, Y is N-alkylation, N-arylation, or alkylation; M is a metal, and R2 in NR2 represents two R groups; PR2 ， R2 ， It represents 2 isopropyl groups; the metal is one or more of manganese, copper, zinc and molybdenum.

2. The method for preparing lactic acid according to claim 1, characterized in that, In step 1), the base is a hydroxide, carbonate, alcohol base, organic base, potassium phosphate, sodium phosphate, or disodium hydrogen phosphate.

3. The method for preparing lactic acid according to claim 2, characterized in that, The hydroxide is sodium hydroxide, calcium hydroxide, barium hydroxide, or lithium hydroxide; the carbonate is sodium carbonate, potassium carbonate, cesium carbonate, or sodium bicarbonate; the alcohol base is lithium methoxide, sodium methoxide, potassium methoxide, sodium ethoxide, sodium tert-butoxide, or potassium tert-butoxide; the organic base is pyridine and its derivatives, triethylenediamine, diisopropylethylamine, or tetramethylguanidine.

4. The method for preparing lactic acid according to claim 3, characterized in that, In step 1), the heating reaction conditions are: temperature 90℃~150℃, time 2h~4h.

5. The method for preparing lactic acid according to claim 4, characterized in that, In step 2), the acid is sulfuric acid, hydrochloric acid, or nitric acid, and the concentration of the acid is 1 mol / L.

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