A highly selective preparation method for hexanoic acid

Abstract

This application discloses a highly selective method for preparing hexonic acid. This method uses hexuronic acid as a substrate and prepares hexonic acid through a three-step process of esterification, oxidation, and hydrolysis. The first step involves protecting the hydroxyl groups on hexuronic acid with an organic acid / anhydride. The second step uses molecular oxygen as an oxygen source to oxidize hexuronic acid to hexonic acid ester under the synergistic catalytic oxidation of metal ions and halogens. The third step hydrolyzes the hexonic acid ester to obtain hexonic acid. This invention offers high selectivity and is environmentally friendly, providing a novel method for the preparation of hexonic acid.

Description

Technical Field

[0001] This invention relates to a highly selective preparation method for hexanoic acid, belonging to the field of biomass chemical technology. Background Technology

[0002] Hexonic acid can be used to synthesize biodegradable polymers, possessing enormous potential application value. Gluconic acid is the most widely used type of hexonic acid, and it and its derivatives can help enhance the body's natural immunity and reduce the risk of cancer. It also has broad applications in the chemical industry, and has been identified by the U.S. Department of Energy as one of the 12 "most valuable biorefining products," capable of synthesizing polyamides, hydroxylated nylon, biodegradable materials, and slow-release fertilizers.

[0003] Currently, gluconic acid is mainly obtained through the oxidation of glucose, primarily through fermentation, nitric acid oxidation, and TEMPO oxidation. Fermentation suffers from low gluconic acid concentration, difficult separation and purification, and long processing times, hindering large-scale production. Nitric acid oxidation exhibits poor selectivity, low gluconic acid yield, and significant pollution, making it unsuitable for large-scale industrial production. CN 112010752 A describes the oxidation of glucose to calcium gluconic acid under alkaline conditions using nitrogen oxides and bromides as catalysts, and peroxides and sodium hypochlorite as oxidants. The yield of calcium gluconic acid is approximately 80%, requiring further improvement. Furthermore, the production of 1 kg of calcium gluconic acid requires 30–40 kg of wastewater, a substantial amount that is detrimental to industrial production. In the oxidation of glucose to gluconic acid, the oxidation of glucuronic acid to gluconic acid is the most difficult step and the rate-limiting step of the entire reaction. Therefore, developing a highly selective oxidation method for hexuronic acid to hexonic acid would significantly promote the development of the hexonic acid industry. Summary of the Invention

[0004] According to one aspect of this application, a method for preparing hexonic acid is provided, the operation steps of which are as follows:

[0005] (1) Mix hexose uronic acid, organic acid and / or organic acid anhydride, and carry out reaction I to obtain hexose uronic acid ester reaction solution;

[0006] (2) Add water, catalyst A and catalyst B to the hexose uronic acid ester reaction solution, and introduce an oxygen source containing CO2 to carry out reaction II to obtain hexose diester.

[0007] (3) Hydrolyze the hexanoic acid ester to obtain the hexanoic acid.

[0008] The purpose of this method to prepare hexonic acid is to first protect the C2-C5 hydroxyl groups through esterification to prevent oxidation and chain scission of the C2-C5 hydroxyl groups during oxidation. Then, the aldehyde group in hexonic uronic acid is oxidized to a carboxyl group by the formation of free radicals using metal ions to catalyze the halogen ions. After the reaction is completed, the aldehyde group is hydrolyzed to finally obtain hexonic acid.

[0009] Optionally, the hexose uronic acid includes at least one of glucuronic acid, mannuronic acid, galacturonic acid, iduronic acid, and guluronic acid.

[0010] Optionally, the organic acid is a monocarboxylic acid, and the organic acid anhydride is a monocarboxylic acid anhydride;

[0011] Preferably, the monocarboxylic acid is selected from at least one of acetic acid, propionic acid, and butyric acid, and the monocarboxylic anhydride is selected from at least one of acetic anhydride, propionic anhydride, and butyric anhydride;

[0012] Preferably, the monocarboxylic acid is acetic acid, and the monocarboxylic acid anhydride is acetic anhydride.

[0013] Optionally, the mass ratio of hexose uronic acid to reactants in step (1) is (0.05-0.3):1, and the temperature of reaction I is 30-100℃.

[0014] Optionally, the weight ratio of water in step (2) is 5-10% of the total weight of the hexose uronic acid ester reaction solution, water, catalyst A, and catalyst B.

[0015] Optionally, catalyst A in step (2) is a metal ion compound catalyst;

[0016] Preferably, the metal in the metal ion compound catalyst is selected from at least one of palladium, cobalt, cerium, ruthenium, zirconium, manganese, iron, copper, and vanadium;

[0017] Preferably, the total mass ratio of the metal ion compound catalyst is 200-2000 ppm, calculated as metal ions.

[0018] Optionally, catalyst B in step (2) contains halogen elements;

[0019] Preferably, the halogen element is selected from at least one of fluorine, chlorine, bromine, and iodine;

[0020] Preferably, the halogen element is bromine;

[0021] Preferably, the total content of catalyst B is 100-1000 ppm, calculated as halide ions.

[0022] Optionally, the oxygen source in step (2) is empty oxygen, oxygen-enriched oxygen, or pure oxygen;

[0023] Preferably, the volume ratio of the oxygen source to CO2 is (1-10):5.

[0024] Optionally, in step (2), the conditions for reaction 2 are: temperature 130-200℃, pressure 2-5MPa;

[0025] Optionally, in step (3), the conditions for the hydrolysis reaction can be selected from one of pH = 10-14 and temperature of 60-150℃, or pH = 0.5-3 and temperature of 60-150℃.

[0026] The beneficial effects that this application can produce include:

[0027] 1) The method for producing hexonic acid provided in this application protects the hydroxyl groups at the C2-C5 positions through esterification, preventing them from being oxidized to ketone groups or forming by-products during oxidation, thereby improving the selectivity of oxidation.

[0028] 2) The method for producing hexuronic acid provided in this application eliminates the hydroxyl groups in the solvent through esterification, thereby increasing the solubility of hexuronic acid in organic acids and accelerating the reaction rate.

[0029] 3) The method for producing hexonic acid provided in this application can reduce the oxidation energy barrier in this step by using free radicals formed by halogen ions catalyzed by metal ions, thereby accelerating the oxidation process.

[0030] 4) The method for producing hexonic acid provided in this application inhibits the decarboxylation of hexuronic acid by introducing CO2, thereby improving the selectivity of hexonic acid.

[0031] 5) The method for producing hexonic acid provided in this application allows for the recycling and reuse of solvents and organometallic catalysts, reducing the preparation cost of hexonic acid and generating no waste. It is a green and environmentally friendly process for preparing hexonic acid. Detailed Implementation

[0032] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0033] Unless otherwise specified, the raw materials and catalysts used in the embodiments of this application were all purchased from Sinopharm Chemical Reagent Co., Ltd.

[0034] The analysis method and selective calculation formula in the embodiments of this application are as follows:

[0035] The contents of hexuronic acid and hexonic acid were detected by high performance liquid chromatography (HPLC).

[0036] Hexonidia selectivity = (molar amount of hexonidia / (molar amount of hexuronic acid before reaction - molar amount of hexuronic acid after reaction)) × 100%.

[0037] Example 1

[0038] 5g of glucuronic acid was weighed and added to 90g of acetic acid, and the mixture was heated to 90℃ and reacted for 1 hour. Then, 5g of water, 0.02g of cobalt acetate, 0.05g of cerium acetate, 0.03g of manganese acetate, and 0.02g of hydrobromic acid were added to the reaction solution, and the mixture was heated to 150℃. Air and CO2 were bubbled through the solution at a 2:1 ratio to 3.0 MPa, and the reaction was allowed to proceed for 150 minutes. After bubbling, the mixture was cooled and distilled to recover the acetic acid. 20g of a pH 1 hydrochloric acid aqueous solution was added to the distillation residue, and the mixture was heated to 80℃ for 120 minutes to hydrolyze the solution, followed by cooling. The concentrations of glucuronic acid and gluconic acid in the solid and solution were measured, and the glucuronic acid selectivity was calculated to be 96.6%.

[0039] Example 2

[0040] 15g of galacturonic acid was weighed and added to a mixed solution of 70g acetic acid and 10g acetic anhydride, and heated to 30℃ for 1h. Then, 10g water, 0.01g cobalt acetate, 0.01g ferric chloride, 0.1g ruthenium acetate, and 0.1g potassium bromide were added to the above reaction solution, and the mixture was heated to 200℃. Pure oxygen and CO2 were bubbled through the solution at a ratio of 1:5 to 2.0 MPa, and the reaction was allowed to proceed for 80min. After bubbling, the solution was cooled and distilled to recover acetic acid. 50g of a pH 0.5 sulfuric acid aqueous solution was added to the distillation residue, and the mixture was heated to 60℃ for 90min to hydrolyze the solution, followed by cooling. The concentrations of galactoic acid and galacturonic acid in the solid and solution were measured, and the selectivity of galactoic acid was calculated to be 94.3%.

[0041] Example 3

[0042] 20g of glucuronic acid was weighed and added to a mixed solution of 50g propionic acid and 15g propionic anhydride, and heated to 40℃ for 0.5h. Then, 8g of water, 0.03g of palladium acetate, 0.15g of copper chloride, 0.01g of zirconium acetate, and 0.15g of potassium chloride were added to the above reaction solution, and the mixture was heated to 150℃. Air and CO2 were bubbled through the solution at a 1:2 ratio to 5.0 MPa, and the reaction was allowed to proceed for 120min. After bubbling, the mixture was cooled and distilled to recover propionic acid. 60g of a pH=3 sulfuric acid aqueous solution was added to the distillation residue, and the mixture was heated to 100℃ for 100min to hydrolyze the residue, followed by cooling. The concentrations of gluconic acid and glucuronic acid in the solid and solution were measured, and the gluconic acid selectivity was calculated to be 95.8%.

[0043] Example 4

[0044] 15g of glucuronic acid was weighed and added to a mixed solution of 65g acetic acid and 5g acetic anhydride, and heated to 60℃ for 0.5h. Then, 7g of water, 0.05g of cobalt acetate, 0.15g of manganese acetate, and 0.15g of hydrobromic acid were added to the above reaction solution, and the mixture was heated to 130℃. Pure oxygen and CO2 were bubbled through the solution at a 1:1 ratio to 3.0 MPa, and the reaction was allowed to proceed for 180min. The bubbling was then stopped, and the mixture was cooled and distilled to recover acetic acid. 60g of a pH 2 nitric acid aqueous solution was added to the distillation residue, and the mixture was heated to 90℃ for 120min to hydrolyze the residue, followed by cooling. The concentrations of glucuronic acid and glucuronoic acid in the solid and solution were measured, and the glucuronic acid selectivity was calculated to be 96.8%.

[0045] Example 5

[0046] 10g of mannulic acid was weighed and added to a mixed solution of 70g acetic acid and 5g acetic anhydride, and heated to 70℃ for 0.5h. Then, 8g of water, 0.03g of cerium acetate, 0.02g of cobalt acetate, and 0.05g of hydrobromic acid were added to the above reaction solution, and the mixture was heated to 160℃. Pure oxygen and CO2 were bubbled through the solution at a ratio of 1:3 to 4.0 MPa, and the reaction was allowed to proceed for 90min. After bubbling, the mixture was cooled and distilled to recover acetic acid. 40g of a pH=3 nitric acid aqueous solution was added to the distillation residue, and the mixture was heated to 80℃ for 120min to hydrolyze the solution, followed by cooling. The concentrations of mannulic acid and mannuronic acid in the solid and solution were measured, and the selectivity of mannulic acid was calculated to be 95.3%.

[0047] Example 6

[0048] 15g of glucuronic acid was weighed and added to a mixed solution of 75g acetic acid and 5g acetic anhydride, and heated to 60℃ for 0.5h. Then, 15g of water, 0.03g of palladium acetate, 0.1g of ruthenium chloride, and 0.1g of calcium chloride were added to the above reaction solution, and the mixture was heated to 170℃. Air and CO2 were bubbled through the solution at a ratio of 1:3 to 5.0 MPa, and the reaction was allowed to proceed for 110min. After bubbling, the mixture was cooled and distilled to recover acetic acid. 50g of a pH 2 sulfuric acid aqueous solution was added to the distillation residue, and the mixture was heated to 90℃ for 100min to hydrolyze the residue, followed by cooling. The concentrations of glucuronic acid and gluconic acid in the solid and solution were measured, and the glucuronic acid selectivity was calculated to be 95.5%.

[0049] Example 7

[0050] 10g of glucuronic acid was weighed and added to 80g of butyric acid, and the mixture was heated to 100℃ and reacted for 1 hour. Then, 10g of water, 0.05g of ruthenium acetate, 0.01g of copper nitrate, and 0.1g of magnesium bromide were added to the reaction solution, and the mixture was heated to 180℃. Air and CO2 were bubbled through the solution at a ratio of 1:2 to 3.0 MPa, and the reaction was allowed to proceed for 100 minutes. After bubbling, the mixture was cooled and distilled to recover acetic acid. 50g of a pH=1 sulfuric acid aqueous solution was added to the distillation residue, and the mixture was heated to 90℃ for 60 minutes to hydrolyze the solution, followed by cooling. The concentrations of gluconic acid and glucuronic acid in the solid and solution were measured, and the gluconic acid selectivity was calculated to be 94.8%.

[0051] Through the above embodiments, the selectivity of preparing hexonic acid (gluconic acid) according to this application is at least 94.3% (Example 2), and the product contains fewer impurities, mainly glucuronic acid, which is also beneficial for purification and impurity removal.

[0052] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing hexonic acid, characterized in that, The preparation method involves the following steps: (1) Mix hexose uronic acid, organic acid and / or organic acid anhydride, and carry out reaction I at 30-100℃ to esterify the hydroxyl groups at C2-C5 to obtain hexose uronic acid ester reaction solution; (2) Add water, catalyst A and catalyst B to the hexose uronic acid ester reaction solution, and introduce an oxygen source containing CO2. Carry out reaction II at 130-200℃ and 2-5MPa to obtain hexose diester. Catalyst A is a metal ion compound catalyst; The total mass ratio of the metal ion compound catalyst is 200-2000 ppm, calculated as metal ions; The metal in the metal ion compound catalyst A is selected from at least one of palladium, cobalt, cerium, ruthenium, zirconium, manganese, iron, copper, and vanadium; The catalyst B contains halogen elements; the total content of the catalyst B is 100-1000 ppm, calculated as halide ions. (3) Hydrolyze the hexanoic acid ester at 60-150℃ to obtain the hexanoic acid.

2. The method according to claim 1, characterized in that, The hexose uronic acid is selected from at least one of glucuronic acid, mannuronic acid, galacturonic acid, iduronic acid, and guluronic acid.

3. The method according to claim 1, characterized in that, The organic acid is a monocarboxylic acid, and the organic acid anhydride is a monocarboxylic acid anhydride.

4. The method according to claim 3, characterized in that, The monocarboxylic acid is selected from at least one of acetic acid, propionic acid, and butyric acid, and the monocarboxylic acid anhydride is selected from at least one of acetic anhydride, propionic anhydride, and butyric anhydride.

5. The method according to claim 3, characterized in that, The monocarboxylic acid is acetic acid, and the monocarboxylic acid anhydride is acetic anhydride.

6. The method according to claim 1, characterized in that, The mass ratio of hexose uronic acid to organic acid and / or organic acid anhydride in step (1) is 1:20 to 60:20, and the temperature of reaction I is 30-100℃.

7. The method according to claim 1, characterized in that, The weight ratio of water in step (2) is 5-10% of the total weight of the hexose uronic acid ester reaction solution, water, catalyst A and catalyst B.

8. The method according to claim 1, characterized in that, The halogen element in step (2) is selected from at least one of fluorine, chlorine, bromine and iodine.

9. The method according to claim 8, characterized in that, The halogen element is bromine.

10. The method according to claim 1, characterized in that, The oxygen source in step (2) is either empty oxygen or oxygen-enriched oxygen.

11. The method according to claim 1, characterized in that, The volume ratio of the oxygen source to CO2 is 1:5 to 10:

5.

12. The method according to claim 1, characterized in that, In step (3), the conditions for the hydrolysis reaction are selected from one of pH=10-14 and temperature=60-150℃, or pH=0.5-3 and temperature=60-150℃.

13. The method according to claim 12, characterized in that, In step (3), the conditions for the hydrolysis reaction are selected from pH=0.5-3 and temperature=60-150℃.