Method for synthesizing furoate

Abstract

The invention provides a method for synthesizing furoate. The method comprises the step that furfural and tetraalkyl ammonium hydroxide react in a solvent in the presence of a metal oxide catalyst and an oxygen source at the temperature of 50-100 DEG C to generate furoate. The method provided by the invention has the advantages of mild reaction, simple operation, low cost and environmental protection, and is easy for industrial popularization.

Description

Technical Field

[0001] The invention relates to the field of fine chemical preparation, in particular to a method for synthesizing furoate from furfural. Background Art

[0002] Methyl furoate is one of the important fine chemical products converted from non-petroleum bases. It can be used as a modifier and flavor enhancer in the food, beverage and cosmetics industries. It can also be used as a gasoline anti-knock agent to improve gasoline quality. It also has anti-tumor activity in the pharmaceutical industry.

[0003] At present, furoic acid esters are mainly prepared by direct esterification reaction of furoic acid and alcohol. The raw material furoic acid of this method is prepared from furfural. The process involves adjusting the alkaline environment to an acidic environment and using an ice bath to crystallize furoic acid. This process produces a large amount of wastewater and waste salt and is relatively energy-consuming. The esterification reaction requires a strong acid as a catalyst and is carried out under high temperature conditions, which will bring about problems such as complicated steps, high energy consumption, and serious environmental pollution.

[0004] Some studies have proposed a one-step direct synthesis of furoate from furfural and alcohol, but these methods have problems such as high precious metal prices, difficulty in recovering homogeneous bases, or complex catalyst preparation processes.

[0005] Therefore, developing a method for synthesizing furoate with mild reaction, simple operation, low cost and green environmental protection has important application value and sustainable development significance. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a method for synthesizing furoate, which uses furfural and tetraalkylammonium hydroxide as raw materials, reacts in a solvent at 50-100°C in the presence of a metal oxide catalyst and an oxygen source to directly generate the target product furoate, and the by-product trialkylamine of the reaction can be made into tetraalkylammonium hydroxide for recycling. The method of the present invention does not require the use of a catalyst containing precious metals, nor does it require a strong acid as a catalyst, has the advantages of simple operation, low cost, and green environmental protection, and is suitable for mass synthesis of furoate.

[0007] Specifically, the method for preparing furoate of the present invention comprises: reacting furfural and tetraalkylammonium hydroxide in a solvent at 50-100° C. in the presence of a metal oxide catalyst and an oxygen source to generate furoate.

[0008] In one or more embodiments, the tetraalkylammonium hydroxide is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0009] In one or more embodiments, the metal oxide catalyst is selected from one or more of copper oxide, cuprous oxide, silver oxide, cerium oxide and manganese oxide, preferably copper oxide.

[0010] In one or more embodiments, the oxygen source is oxygen, air, air enriched with nitrogen, or air enriched with oxygen.

[0011] In one or more embodiments, the solvent is selected from one or more of water, methanol, ethanol, acetonitrile and dimethyl sulfoxide, preferably water.

[0012] In one or more embodiments, the molar ratio of the metal oxide catalyst to furfural is (0.05-1):1, preferably (0.1-1):1.

[0013] In one or more embodiments, the molar ratio of furfural to tetraalkylammonium hydroxide is (0.9-1.1):1.

[0014] In one or more embodiments, the reaction temperature is 60 to 80°C.

[0015] In one or more embodiments, during the reaction, the furfural and the tetraalkylammonium hydroxide are added dropwise to the mixture of the metal oxide catalyst and the solvent.

[0016] In one or more embodiments, the method comprises: mixing the metal oxide catalyst and the solvent, introducing the oxygen source, heating to 50-100° C., and simultaneously dropping the furfural and the tetraalkylammonium hydroxide separately for reaction, wherein the reaction is completed when the dropping is completed.

[0017] In one or more embodiments, the dropping speed of the furfural and the tetraalkylammonium hydroxide is ≤0.9 mol / h, such as 0.1 to 0.9 mol / h.

[0018] In one or more embodiments, the method further comprises: after the reaction is completed, filtering and recovering the metal oxide catalyst, and then distilling the reaction liquid under reduced pressure to obtain separated furoate and trialkylamine.

[0019] In one or more embodiments, the method further comprises: preparing tetraalkylammonium hydroxide from the trialkylamine for reacting with furfural to prepare furoate. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0022] Herein, “comprising”, “including”, “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of”. For example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to be disclosed herein.

[0023] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0024] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0025] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0026] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0027] The present invention provides a new method for synthesizing furoate. The method of the present invention uses furfural and tetraalkylammonium hydroxide as raw materials, and directly synthesizes furoate in a solvent at 50-100° C. in the presence of a metal oxide catalyst and an oxygen source. The method of the present invention does not require the use of a catalyst containing precious metals, nor does it require a strong acid as a catalyst, and has a simple process flow, low cost, green environmental protection, and is suitable for industrial application.

[0028] In the method for preparing furoate ester of the present invention, furfural undergoes oxidation reaction under the action of a metal oxide catalyst to generate furoic acid, furoic acid reacts with tetraalkylammonium hydroxide to generate furoic acid tetraalkylammonium salt, and furoic acid tetraalkylammonium salt is decomposed at high temperature to generate furoate ester and trialkylamine.

[0029] In the present invention, the available tetraalkylammonium hydroxide can be selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide. In the method of the present invention, the use of tetraalkylammonium hydroxide containing a certain alkyl group can prepare an alkyl furoate containing the corresponding alkyl group, for example, the use of tetramethylammonium hydroxide can prepare methyl furoate. In the present invention, the tetraalkylammonium hydroxide can be provided in the form of a tetraalkylammonium hydroxide solution. Herein, the tetraalkylammonium hydroxide solution refers to an aqueous solution of tetraalkylammonium hydroxide, wherein the mass concentration of the tetraalkylammonium hydroxide can be 10% to 30%, for example, 15%, 20%, 25%.

[0030] In the present invention, the metal oxide catalyst can be selected from one or more of cupric oxide, cuprous oxide, silver oxide, cerium oxide and manganese oxide. In some embodiments, the metal oxide catalyst is cupric oxide and / or cuprous oxide. In some preferred embodiments, the metal oxide catalyst is cupric oxide, which is conducive to improving the yield of the furoate product.

[0031] In the present invention, the solvent can be selected from one or more of water, methanol, ethanol, acetonitrile and dimethyl sulfoxide. In a preferred embodiment, water is used as the solvent, which is conducive to the separation of the product and improves the purity and yield of the product.

[0032] In the present invention, the amount of the solvent can be 1 to 20 times the mass of furfural, for example, 2 times, 5 times, 10 times, or 15 times.

[0033] In the present invention, the oxygen source can be oxygen, air, high nitrogen air, high oxygen air, etc. Preferably, the oxygen source is air, which is conducive to reducing costs and facilitating industrial promotion. In the present invention, the oxygen source can be continuously introduced into the reaction system before adding tetraalkylammonium hydroxide and furfural, or can be continuously introduced into the reaction system at the same time as adding tetraalkylammonium hydroxide and furfural. The oxygen source can be continuously introduced into the reaction system before the temperature of the reaction system is heated to the reaction temperature, or can be continuously introduced into the reaction system after the temperature of the reaction system reaches the reaction temperature.

[0034] In the present invention, the molar ratio of the metal oxide catalyst to furfural can be (0.05-1):1, preferably (0.1-1):1, such as 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1. In some embodiments, the molar ratio of the metal oxidant catalyst to furfural is (0.2-1):1. Controlling the molar ratio of the metal oxide catalyst to furfural to (0.1-1):1, such as (0.2-1):1, is conducive to improving the product yield.

[0035] In the present invention, the molar ratio of furfural to tetraalkylammonium hydroxide may be (0.9-1.1):1, for example 1:1.

[0036] In the present invention, the reaction temperature can be 50-100° C., such as 60° C., 70° C., 80° C., 90° C. Preferably, the reaction temperature is 60-80° C., such as 70±5° C. Controlling the reaction temperature in the range of 60-80° C. is beneficial to improving the product yield.

[0037] In some embodiments, the mixture of the metal oxide catalyst and the solvent is first heated to 50-100° C., and then tetraalkylammonium hydroxide and furfural are added to react. Heating the other materials to the reaction temperature before adding tetraalkylammonium hydroxide and furfural is beneficial to avoid the generation of by-products and improve the yield and purity of the product.

[0038] In the present invention, it is preferred to control the addition speed when adding tetraalkylammonium hydroxide and furfural to avoid too fast a speed causing more side reactions. In the present invention, the addition speed of tetraalkylammonium hydroxide and furfural can be controlled by dripping, and the dripping speed of tetraalkylammonium hydroxide and furfural is preferably ≤0.9mol / h, such as 0.1mol / h, 0.2mol / h, 0.3mol / h, 0.4mol / h, 0.45mol / h, 0.5mol / h, 0.6mol / h, 0.7mol / h, 0.8mol / h, which can effectively reduce the occurrence of side reactions. In some embodiments, the dripping speed of tetraalkylammonium hydroxide and furfural is controlled to 0.4-0.5mol / h, which is conducive to improving the reaction efficiency while reducing the occurrence of side reactions. In some embodiments, for example, when the dripping speed is controlled to ≤0.9mol / h, the reaction is completed when the dripping is completed.

[0039] In some embodiments, the metal oxide catalyst and the solvent are mixed, an oxygen source is introduced, the temperature is raised to 50-100° C., and furfural and tetraalkylammonium hydroxide are added dropwise at a rate of ≤0.9 mol / h to carry out the reaction of the present invention.

[0040] In the present invention, after the reaction is completed, the furoate can be separated from the reaction solution by distillation. The distillation can be reduced pressure distillation.

[0041] The method for synthesizing furoate of the present invention may further include: after the reaction is completed, filtering and recovering the metal oxide catalyst, and then distilling the reaction liquid under reduced pressure to obtain separated furoate and trialkylamine.

[0042] The method for synthesizing furoate of the present invention may further include: preparing tetraalkylammonium hydroxide from trialkylamine, and using the tetraalkylammonium hydroxide for reacting with furfural to prepare furoate.

[0043] In the present invention, the method for preparing tetraalkylammonium hydroxide from trialkylamine can be: reacting dialkyl carbonate and trialkylamine in a solvent to obtain alkyl carbonate tetraalkylamine, the solvent can be an alcohol solvent, such as methanol; after the reaction, firstly performing reduced pressure distillation to remove the solvent and unreacted trialkylamine and dialkyl carbonate, then adding water for hydrolysis reaction, and performing reduced pressure distillation after the hydrolysis reaction to obtain tetraalkylammonium bicarbonate; adding tetraalkylammonium bicarbonate to an excess calcium hydroxide suspension for replacement reaction to generate tetraalkylammonium hydroxide, and filtering to obtain a tetraalkylammonium hydroxide solution. Dialkyl carbonate and trialkylamine containing a specific alkyl group can be used to prepare tetraalkylammonium hydroxide containing the corresponding alkyl group, for example, tetramethylammonium hydroxide can be prepared using dimethyl carbonate and trimethylamine.

[0044] In the present invention, the metal oxide catalyst obtained by filtration and the tetraalkylammonium hydroxide obtained by regeneration of the trialkylamine obtained by vacuum distillation can be returned to the reaction cycle for reuse, which avoids the generation of waste materials, is conducive to reducing costs and being environmentally friendly.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] (1) The present invention directly synthesizes the product furoate by a one-step method, does not require a strong acid as a catalyst, has mild reaction conditions, and is simple and convenient to operate;

[0047] (2) The catalyst and by-products in the present invention can be recycled and reused, which is green and environmentally friendly;

[0048] (3) The catalyst used in the present invention is relatively cheap compared to precious metals and is easy to recycle and process compared to strong acids, thus significantly reducing production costs;

[0049] (4) The yield of furoate prepared by the method of the present invention can reach 56% or more, preferably 74% or more, more preferably 86% or more, for example 89% or more, and the product purity can reach 96% or more, preferably 98% or more.

[0050] The present invention will be described below in the form of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents and materials used in the examples are, unless otherwise stated, conventional methods, reagents and materials in the art. The raw material compounds in the examples can all be purchased through commercial routes.

[0051] Example 1

[0052] 5g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively loaded into the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was distilled under reduced pressure. The oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 92.4% and a purity of 99.3%.

[0053] The remaining liquid after vacuum distillation is trimethylamine, and trimethylamine is prepared into tetramethylammonium hydroxide by the following method: the molar ratio of dimethyl carbonate and trimethylamine is 1:1.2, the amount of methanol is 10 times the molar number of trimethylamine, and the reaction is carried out at a pressure of 1.5MPa and a temperature of 125°C for 4 hours. After the reaction is completed, the reaction mixture is taken out and vacuum distilled to remove the solvent methanol and unreacted trimethylamine and dimethyl carbonate. Then, 6 times the mass of water is added to the distillation residue to carry out hydrolysis reaction at 70°C for 2h, and water is removed by vacuum distillation to obtain tetramethylammonium bicarbonate. Tetramethylammonium bicarbonate is added to the excess calcium hydroxide suspension to carry out a replacement reaction to generate tetramethylammonium hydroxide, and the calcium carbonate precipitate generated by the reaction is removed by filtration, and the filtrate is a tetramethylammonium hydroxide solution. The obtained tetramethylammonium hydroxide solution is prepared into a tetramethylammonium hydroxide solution with a mass concentration of 20%.

[0054] The regenerated tetramethylammonium hydroxide and the filtered copper oxide powder are put into the reaction again: 4.5g of the copper oxide powder filtered and recovered after the previous batch of reaction and 100mL of deionized water are added to a 500mL four-necked flask with two constant pressure dropping funnels and a gas guide tube. The two constant pressure dropping funnels are respectively filled with a 20% mass concentration of tetramethylammonium hydroxide solution (wherein the tetramethylammonium hydroxide is regenerated from the trimethylamine generated by the previous batch of reactions) and 10g of freshly steamed furfural, and the molar ratio of furfural to tetramethylammonium hydroxide is 1:1. Ventilate the air, heat to 70°C, and simultaneously drip furfural and tetramethylammonium hydroxide solution for 15min. After the reaction is completed, the copper oxide powder is filtered out, and the filtered reaction solution is decompressed and distilled, and the oil phase is collected to obtain a light yellow methyl furoate liquid with a yield of 89.8% and a purity of 98.5%.

[0055] Example 2

[0056] 5g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetraethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetraethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetraethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was distilled under reduced pressure. The oil phase was collected to obtain a light yellow ethyl furoate liquid with a yield of 90.8% and a purity of 98.8%.

[0057] Example 3

[0058] 5g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetrabutylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetrabutylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetrabutylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was distilled under reduced pressure. The oil phase was collected to obtain a light yellow butyl furoate liquid with a yield of 86.6% and a purity of 98.4%.

[0059] Example 4

[0060] 5g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 50°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was distilled under reduced pressure. The oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 74.9% and a purity of 98.6%.

[0061] Example 5

[0062] 5g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 100°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was decompressed and distilled, and the oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 76.1% and a purity of 96.7%.

[0063] Example 6

[0064] 0.6g of copper oxide powder and 100mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively loaded into the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was distilled under reduced pressure. The oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 56.4% and a purity of 98.5%.

[0065] Example 7

[0066] 11.9g of copper oxide powder and 250mL of deionized water were added to a 500mL four-necked flask equipped with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of freshly distilled furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the copper oxide powder was filtered out, and the filtered reaction solution was decompressed and distilled, and the oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 90.9% and a purity of 99.2%.

[0067] Example 8

[0068] 5g of cuprous oxide and 100mL of deionized water were added to a 500mL four-necked flask with two constant pressure dropping funnels and an air guide tube. A 20% tetramethylammonium hydroxide solution and 14.4g of furfural were respectively placed in the two constant pressure dropping funnels. The molar ratio of furfural to tetramethylammonium hydroxide was 1:1. The air was ventilated, the temperature was raised to 70°C, and furfural and tetramethylammonium hydroxide solution were added dropwise at the same time. The addition time was 20min. After the reaction was completed, the cuprous oxide powder was filtered out, and the filtered reaction solution was decompressed and distilled, and the oil phase was collected to obtain a light yellow methyl furoate liquid with a yield of 69.6% and a purity of 98.6%.

Claims

1. A method for synthesizing furoate, characterized in that, The method comprises reacting furfural and tetraalkylammonium hydroxide in the presence of a metal oxide catalyst and an oxygen source in a solvent at 50-100° C. to generate furoate.

2. The method according to claim 1, characterized in that The tetraalkylammonium hydroxide is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

3. The method according to claim 1, characterized in that The metal oxide catalyst is selected from one or more of cupric oxide, cuprous oxide, silver oxide, cerium oxide and manganese oxide, preferably cupric oxide.

4. The method according to claim 1, characterized in that The oxygen source is oxygen, air, enriched nitrogen air or enriched oxygen air.

5. The method according to claim 1, characterized in that The solvent is selected from one or more of water, methanol, ethanol, acetonitrile and dimethyl sulfoxide, preferably water.

6. The method according to claim 1, characterized in that The molar ratio of the metal oxide catalyst to furfural is (0.05-1):1, preferably (0.1-1):1; and / or The molar ratio of furfural to tetraalkylammonium hydroxide is (0.9-1.1):

1.

7. The method according to claim 1, characterized in that The reaction temperature is 60 to 80°C; and / or During the reaction, the furfural and the tetraalkylammonium hydroxide are added dropwise to the mixture of the metal oxide catalyst and the solvent; preferably, the dropping speed of the furfural and the tetraalkylammonium hydroxide is ≤0.9 mol / h.

8. The method according to claim 1, characterized in that The method comprises: mixing the metal oxide catalyst and the solvent, introducing the oxygen source, heating to 50-100° C., and simultaneously dropping the furfural and the tetraalkylammonium hydroxide respectively for reaction, wherein the reaction is completed when the dropping is completed.

9. The method according to claim 1, characterized in that The method further comprises: after the reaction is finished, filtering and recovering the metal oxide catalyst, and then distilling the reaction liquid under reduced pressure to obtain separated furoate and trialkylamine.

10. The method according to claim 9, characterized in that The method further comprises: preparing tetraalkylammonium hydroxide from the trialkylamine for reacting with furfural to prepare furoate.