A method for preparing hydroxy fatty acids with high selectivity

Abstract

The present invention relates to the fields of catalytic chemistry and biomass resource utilization, and in particular to a method for preparing hydroxy fatty acids with high selectivity. The present invention adopts a method for selectively oxidizing diols to prepare hydroxy fatty acids, and utilizes the characteristics of methylal αC-H bonds being easy to oxidize to carry out oxidation reaction, thereby achieving high selectivity and high yield of hydroxy fatty acids under mild conditions, and the total yield of hydroxy fatty acids is as high as more than 80%. The preparation method has the characteristics of simple operation, safety and efficiency, environmental friendliness, low cost, etc., and has good prospects for industrial application.

Description

Technical Field

[0001] The invention relates to the fields of catalytic chemistry and biomass resource utilization, and in particular to a method for preparing hydroxy fatty acids with high selectivity. Background Art

[0002] Polyhydroxyalkanoates (PHA) are a class of polymer materials with excellent processing properties and biodegradability. Because they are completely biodegradable and do not cause any pollution to the environment, they meet the requirements of circular economy and sustainable development in the 21st century and are considered to be the most promising new "ecological materials" in the new century. At present, the synthesis process of PHA is mainly through bacterial fermentation. The biological method has problems such as slow reaction, low raw material conversion rate, easy pollution, and large equipment investment. Although the chemical synthesis method has the advantages of low cost, fast reaction, and high product concentration, the chemical synthesis of the monomer-hydroxy fatty acid for synthesizing PHA still faces many problems, such as expensive raw materials and low selectivity.

[0003] Taking the C3 straight-chain hydroxy fatty acid 3-hydroxypropionic acid (3-HP) as an example, 3-HP is basically produced by microbial conversion in industry, resulting in a small output (about 40 tons / year) and high price (about 30,000 yuan / kg), which is also the main reason for restricting the development of the 3-HP industry and its downstream products. In 2011, Della Pina et al. reviewed the different synthetic pathways of 3-HP (Green Chemistry, 2011, 13, 1624-1632). The cost of using 3-hydroxypropionitrile and 3-hydroxypropionaldehyde as raw materials is relatively high. The selectivity of reactions using propylene alcohol, acrylic acid or 1,3-propylene glycol, levulinic acid, etc. as raw materials is often very low. For example, Yang et al. used propylene alcohol as raw material and Au / CeO2 as catalyst, and the optimal yield of 3-HP was about 50% (Catalysis Science & Technology, 2016, 6, 3616-3622); Mohammad et al. used 1,3-propylene glycol as raw material (AIP Conference Proceedings, 2015, 1649, 58-66), and Au-Pd / HT bimetallic catalyst obtained 42% 3-HP under alkali-free conditions. Therefore, the highly selective oxidation of diols to prepare hydroxy fatty acids under mild conditions is a research direction of great practical significance and has also received widespread attention from scientific researchers.

[0004] In view of this, in view of the above shortcomings of the prior art, the present invention proposes a method for preparing hydroxy fatty acids with high selectivity from diols without using any base or precious metal catalyst. Summary of the invention

[0005] (1) Technical issues to be solved

[0006] The purpose of the present invention is to provide a method for preparing hydroxy fatty acids with high selectivity, so as to solve the problems of low selectivity, low preparation efficiency and high production cost in the prior art for preparing hydroxy fatty acids.

[0007] (2) Technical solution

[0008] In order to solve the above problems, the present invention provides a method for preparing hydroxy fatty acids with high selectivity, the specific steps are:

[0009] S1, dissolving paraformaldehyde in diol, adding a first type of catalyst, heating to carry out acetalization reaction, performing reduced pressure distillation after the reaction, and collecting fractions to obtain diol formal;

[0010] S2, dissolving the diol formal in a solvent, adding a second type of catalyst, and then dropping an oxidant to carry out a chemical reaction to obtain a formyloxyalkyl acid;

[0011] S3, diluting the formyloxyalkyl acid solution obtained in step S2, and then fully hydrolyzing it through an acidic ion exchange resin, and then distilling under reduced pressure to remove water and formic acid to obtain a crude hydroxy fatty acid product.

[0012] S4, subjecting the crude hydroxy fatty acid product to reduced pressure distillation, and collecting fractions to obtain pure hydroxy fatty acid.

[0013] Preferably, in step S1, the diol is one or more of 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-n-propylpropane-1,3-diol, and 2-n-butyl-1,3-propylene glycol.

[0014] Preferably, in step S1, the first type of catalyst is trifluoromethanesulfonic acid or trifluoromethanesulfonate.

[0015] Preferably, in step S1, the reaction temperature of the acetalization reaction is 50°C-90°C, and the reaction time is 5h-8h.

[0016] Preferably, in step S2, the solvent is one or more of acetonitrile, acetone, 1,2-dichloromethane, and 1,2-dichloroethane, and the second type of catalyst is an oxidizing catalyst, and the oxidizing catalyst is one or more of ferric oxide, nickel oxide, cobalt oxide, and copper oxide.

[0017] Preferably, in step S2, the oxidant is one or more of hydrogen peroxide, tert-butyl hydroperoxide, 3-chloroperbenzoic acid, di-tert-butyl peroxide, etc., and the molar ratio of the oxidant to the substrate is 1.1-4.5.

[0018] Preferably, in step S2, the reaction temperature of the chemical reaction is 90°C-130°C, and the reaction time is 1h-12h.

[0019] Preferably, in step S3, the acidic ion exchange resin is a strong acidic ion exchange resin, and the strong acidic ion exchange resin is one or more of Amberlyst 15, Amberlyst 45, Amberlyst 70, and Nafion NR50.

[0020] Preferably, in step S3, the volume of water added during the dilution is 1-100 times of the reaction solution, the pressure of the vacuum distillation is 0-1 bar, and the temperature of the vacuum distillation is 40°C-60°C.

[0021] Preferably, in step S4, the temperature of the reduced pressure distillation is 90°C-150°C.

[0022] (3) Beneficial effects

[0023] The above technical solution of the present invention has the following advantages:

[0024] The method of the present invention is based on a protection strategy, firstly, a diol and polyformaldehyde are subjected to an acetal reaction to form a ring, and then an oxidation reaction is carried out by utilizing the easy oxidation characteristic of the αC-H bond of acetal, thereby protecting one end of the diol to obtain a formyloxyalkyl acid, and finally the formyloxyalkyl acid is hydrolyzed to obtain a hydroxy fatty acid.

[0025] (a) The preparation method is simple to operate, environmentally friendly, and can achieve high selectivity in the preparation of hydroxy fatty acids without using alkali and precious metal catalysts;

[0026] (b) Safe and efficient, the acetalization and oxidation reaction temperatures are relatively low, resulting in good process safety and high product yield (>80%);

[0027] (c) It does not require high-pressure gas, has low requirements on production equipment, and complies with the principle of safe production.

[0028] In summary, compared with the existing technical routes, the method for preparing hydroxy fatty acids provided by the present invention has significant advantages such as simplicity, greenness, safety, high efficiency, and low equipment requirements, and has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process of preparing hydroxy fatty acid reaction with high selectivity by using diol in an embodiment of the present invention.

[0030] Figure 2 The liquid chromatography of the reaction separation product 3-hydroxypropionic acid in the embodiment of the present invention is Figure 2 (A), H1-NMR Figure 2 (B) and C13-NMR Figure 2 (C) Spectrum. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0033] The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments.

[0034] like Figure 1 As shown, the present invention provides a method for preparing hydroxy fatty acids with high selectivity, and the specific steps are:

[0035] S1. dissolving polyformaldehyde in diol, adding the first type of catalyst, heating to carry out acetalization reaction, performing reduced pressure distillation after the reaction, and collecting fractions to obtain diol formal.

[0036] Preferably, the diol is one or more of 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-n-propylpropane-1,3-diol, and 2-n-butyl-1,3-propylene glycol.

[0037] Preferably, the first type of catalyst is trifluoromethanesulfonic acid or trifluoromethanesulfonic acid salt.

[0038] Preferably, the reaction temperature of the acetalization reaction is 50° C.-90° C., and the reaction time is 5 h-8 h.

[0039] S2. Dissolve the diol formal in a solvent, add a second type of catalyst, and then drop an oxidant to carry out a chemical reaction to obtain a formyloxyalkyl acid.

[0040] Preferably, the solvent is one or more of acetonitrile, acetone, 1,2-dichloromethane, and 1,2-dichloroethane, and the second type of catalyst is an oxidative catalyst, and the oxidative catalyst is one or more of ferric oxide, nickel oxide, cobalt oxide, and copper oxide.

[0041] Preferably, the oxidant is one or more of hydrogen peroxide, tert-butyl hydroperoxide, 3-chloroperbenzoic acid, di-tert-butyl peroxide, etc., and the molar ratio of the oxidant to the substrate is 1.0-4.5, more preferably, the molar ratio of the oxidant to the substrate is 1.1-3.0.

[0042] Preferably, the reaction temperature of the chemical reaction is 90° C.-130° C., and the reaction time is 1 h-12 h.

[0043] S3, diluting the formyloxyalkyl acid solution obtained in step S2, and then fully hydrolyzing it through an acidic ion exchange resin, and then distilling under reduced pressure to remove water and formic acid to obtain a crude hydroxy fatty acid product.

[0044] Preferably, the acidic ion exchange resin is a strong acidic ion exchange resin, and the strong acidic ion exchange resin is one or more of Amberlyst 15, Amberlyst 45, Amberlyst 70, and Nafion NR50.

[0045] Preferably, the volume of water added during the dilution is 1-100 times of the reaction solution, the pressure of the vacuum distillation is 0-1 bar, and the temperature of the vacuum distillation is 40°C-60°C.

[0046] S4, subjecting the crude hydroxy fatty acid product to reduced pressure distillation, and collecting fractions to obtain pure hydroxy fatty acid.

[0047] Preferably, the temperature of the reduced pressure distillation is 90°C-150°C.

[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0049] Unless otherwise specified, the materials and reagents used in the following examples can be purchased from commercial sources.

[0050] Raw materials: 1,3-propylene glycol (Innochem, product number A59183, purity 98%);

[0051] 2-Methyl-1,3-propanediol (Innochem, product number A82900, purity 98%);

[0052] 2-Ethyl-1,3-propanediol (Key organics, product number AS-44730, purity >95%);

[0053] 2-n-propyl-1,3-propanediol (Alfa, product number B22152, purity 98%);

[0054] 2-n-Butyl-1,3-propanediol (Alfa, product number B21739, purity 97%);

[0055] Paraformaldehyde (Innochem, product number A34195, purity >96%);

[0056] p-Toluenesulfonic acid (Innochem, product number I04218, purity>99%);

[0057] Trifluoromethanesulfonic acid (Acros, product number 169890500, purity 99%);

[0058] Scandium trifluoromethanesulfonate (Alfa, product number 040566, purity 98%);

[0059] Bismuth trifluoromethanesulfonate (Merck, Catalog No. 633305-5G, purity 99%);

[0060] Ferrous oxide (Innochem, product number A67206, purity 99.5%);

[0061] Nickel oxide (Alfa, product number 010819, purity 99.998%);

[0062] Cobalt oxide (Macklin, product number C804716-100g, purity>98%);

[0063] Copper oxide (Innochem, product number A76603, purity 98%);

[0064] Hydrogen peroxide (Acros, product number 411885000, purity 30%);

[0065] Tert-butyl hydroperoxide (Acros, product number 180342500, purity 70%);

[0066] 3-Chloroperbenzoic acid (Innochem, product number A21126, purity 75%);

[0067] Di-tert-butyl peroxide (Acros, product number 349931000, purity 99%);

[0068] Amberlyst 15 (Alfa, Cat. No. 044079);

[0069] Amberlyst 45 and Amberlyst 70;

[0070] Nafion NR50 (Alfa, Catalog No. 040802).

[0071] Example 1

[0072] A method for preparing hydroxy fatty acids with high selectivity, comprising the following steps:

[0073] (1) 6.1 g of paraformaldehyde, 1.0 g of trifluoromethanesulfonic acid, and 12.5 g of 1,3-propylene glycol were placed in a 50 ml reactor. After the reactor was assembled, the temperature was raised to 90°C with stirring, and the reaction was continued for 8 hours before cooling to room temperature. The reaction solution was then subjected to vacuum rotary evaporation (50°C, 10 Psi) to collect the fractions to obtain crude 1,3-dioxane.

[0074] The conversion rate of 1,3-propylene glycol and the yield of the product 1,3-dioxane are calculated according to the following formula: Formula 1: Conversion rate [mol%] = (n0-n) / n0×100%;

[0075] Formula 2: Yield [mol%] = ni / n0 × 100%.

[0076] Wherein, n0 is the molar amount of 1,3-propylene glycol before the reaction;

[0077] n is the molar amount of 1,3-propylene glycol after the reaction;

[0078] ni is the molar amount of 1,3-dioxane produced.

[0079] The calculation results show that after the reaction, the conversion rate of 1,3-propylene glycol is >99%, and the yield of the product 1,3-dioxane is 95%.

[0080] (2) Dissolve 2 g of crude 1,3-dioxane in 10 mL of acetone, add 0.5 g of iron oxide catalyst and 6.6 g of di-tert-butyl peroxide, and heat to 100°C for 3 h. After removing the solvent acetone by vacuum distillation, the reaction solution is diluted with 20 mL of water, and the aqueous phase is passed through an Amberlyst 15 column. The solution is collected, and water and formic acid are removed by vacuum distillation. The distillation temperature is further increased to 110°C, and the fractions are collected to obtain pure 3-hydroxypropionic acid.

[0081] The conversion rate of 1,3-dioxane and the yield of the product 3-hydroxypropionic acid are calculated according to the following formula:

[0082] Formula 1: Conversion rate [mol%] = (n0-n) / n0×100%;

[0083] Formula 2: Yield [mol%] = ni / n0 × 100%.

[0084] Wherein, n0 is the molar amount of 1,3-dioxane before the reaction;

[0085] n is the molar amount of 1,3-dioxane after the reaction;

[0086] ni is the molar amount of 3-hydroxypropionic acid produced.

[0087] The calculation results show that the conversion rate of 1,3-dioxane after the reaction is >99%, and the yield of the product 3-hydroxypropionic acid is 90%. The purity of the product 3-hydroxypropionic acid by NMR analysis is >98% (such as Figure 2 shown).

[0088] Example 2

[0089] A method for preparing hydroxy fatty acids with high selectivity, comprising the following steps:

[0090] (1) 6.1 g of paraformaldehyde, 0.5 g of bismuth trifluoromethanesulfonate, and 12.5 g of 1,3-propylene glycol were placed in a 50 ml reactor. After the reactor was installed, the temperature was raised to 90° C. with stirring, and the reaction was continued for 8 h before cooling to room temperature. The reaction solution was then subjected to vacuum rotary evaporation (50° C., 10 Psi) to collect the fractions to obtain a crude 1,3-dioxane product.

[0091] The conversion rate of 1,3-propylene glycol and the yield of the product 1,3-dioxane are calculated according to the following formula:

[0092] Formula 1: Conversion rate [mol%] = (n0-n) / n0×100%;

[0093] Formula 2: Yield [mol%] = ni / n0 × 100%.

[0094] Wherein, n0 is the molar amount of 1,3-propylene glycol before the reaction;

[0095] n is the molar amount of 1,3-propylene glycol after the reaction;

[0096] ni is the molar amount of 1,3-dioxane produced.

[0097] The calculation results show that after the reaction, the conversion rate of 1,3-propylene glycol is 80%, and the yield of the product 1,3-dioxane is 77%.

[0098] (2) Dissolve 2 g of crude 1,3-dioxane in 10 mL of acetone, add 0.5 g of cobalt oxide catalyst and 4.2 g of tert-butyl hydroperoxide, and heat to 110°C for 3 h. After removing the solvent acetone by vacuum distillation, the reaction solution is diluted with 20 mL of water, and the aqueous phase is passed through an Amberlyst 45 column. The solution is collected, and water and formic acid are removed by vacuum distillation. The distillation temperature is further increased to 110°C, and the fractions are collected to obtain pure 3-hydroxypropionic acid.

[0099] The conversion rate of 1,3-dioxane and the yield of the product 3-hydroxypropionic acid are calculated according to the following formula:

[0100] Formula 1: Conversion rate [mol%] = (n0-n) / n0×100%;

[0101] Formula 2: Yield [mol%] = ni / n0 × 100%.

[0102] Wherein, n0 is the molar amount of 1,3-dioxane before the reaction;

[0103] n is the molar amount of 1,3-dioxane after the reaction;

[0104] ni is the molar amount of 3-hydroxypropionic acid produced.

[0105] The calculation results show that the conversion rate of 1,3-dioxane after the reaction is >99%, the yield of the product 3-hydroxypropionic acid is 64%, and the purity of the product 3-hydroxypropionic acid by nuclear magnetic resonance analysis is >98%.

[0106] Example 3

[0107] In other embodiments of the present invention, in order to verify the universality of the substrate, the reaction conditions of Example 1 were adjusted: except for the different substrate 1,3-propylene glycol, the other reaction conditions were the same as Example 1. The reaction results are shown in Table 1 below.

[0108] Table 1 Effect of different substrates on product yield

[0109]

[0110]

[0111] a The product has a high boiling point and can be separated by a silica gel column.

[0112] As can be seen from Table 1, with the increase of the carbon chain length of the functional group, the acetalization reaction and the oxidation reaction are affected, and the final yield of the hydroxy fatty acid product is significantly reduced.

[0113] In summary, the hydroxyl protection strategy provided by the present invention can achieve high selectivity in the preparation of hydroxy fatty acids from diols, and achieves high selectivity and high yield of hydroxy fatty acids under mild conditions in the absence of alkali and precious metal catalysts, with the total yield of hydroxy fatty acids reaching more than 80%.

[0114] It should be clear that the present invention is not limited to the specific steps and structures described above. In addition, for the sake of brevity, detailed descriptions of known methods and technologies are omitted here.

[0115] The above is only an embodiment of the present application and is not limited to the present application. For those skilled in the art, the present application may have various changes and variations without departing from the scope of the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for preparing hydroxy fatty acids with high selectivity, characterized in that: The following steps are involved: S1, dissolving paraformaldehyde in diol, adding a first type of catalyst, heating to carry out acetalization reaction, performing reduced pressure distillation after the reaction, and collecting fractions to obtain diol formal; S2, dissolving the diol formal in a solvent, adding a second type of catalyst, and then dropping an oxidant to carry out a chemical reaction to obtain a formyloxyalkyl acid; S3, diluting the formyloxyalkyl acid solution obtained in step S2, and then fully hydrolyzing it with an acidic ion exchange resin, and then distilling under reduced pressure to remove water and formic acid to obtain a crude hydroxy fatty acid product; S4, subjecting the crude hydroxy fatty acid product to vacuum distillation, and collecting fractions to obtain a pure hydroxy fatty acid product; In step S1, the diol is any one of 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-n-propyl-1,3-propylene glycol, and 2-n-butyl-1,3-propylene glycol, and the first type of catalyst is trifluoromethanesulfonic acid or bismuth trifluoromethanesulfonate; In step S2, the second type of catalyst is iron oxide or cobalt oxide, and the oxidant is di-tert-butyl peroxide or tert-butyl hydroperoxide.

2. The method for preparing hydroxy fatty acids with high selectivity according to claim 1, characterized in that: In step S1, the reaction temperature of the acetalization reaction is 50°C-90°C, and the reaction time is 5h-8h.

3. The method for preparing hydroxy fatty acids with high selectivity according to claim 1, characterized in that: In step S2, the solvent is acetone.

4. The method for preparing hydroxy fatty acids with high selectivity according to claim 1, characterized in that: In step S2, the reaction temperature of the chemical reaction is 90°C-130°C, and the reaction time is 1h-12h.

5. The method for preparing hydroxy fatty acids with high selectivity according to claim 1, characterized in that: In step S3, the acidic ion exchange resin is a strong acidic ion exchange resin, and the strong acidic ion exchange resin is Amberlyst 15 or Amberlyst 45.

6. The method for preparing hydroxy fatty acids with high selectivity according to claim 1, characterized in that: In step S4, the temperature of the reduced pressure distillation is 90°C-150°C.

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