One-step method for preparing glycolide or lactide from ethylene glycol or propylene glycol

Abstract

The invention relates to the field of new material fine chemicals, in particular to a method for preparing corresponding glycolide or lactide substances by taking a large amount of high-yield ethylene glycol or propylene glycol and the like as raw materials through one-step direct oxidation. The substance is a key material for preparing biodegradable polyglycolic acid (PGA) or polylactic acid (PLA).

Description

[Technical field]

[0001] The present invention relates to the field of new materials and fine chemicals, and in particular to the one-step direct oxidation of ethylene glycol or propylene glycol, which are in high yield, as raw materials to prepare the corresponding glycolide or lactide substances. Such substances are key materials for preparing biodegradable polyglycolic acid PGA or polylactic acid PLA. [Background technology]

[0002] Polyglycolic acid PGA or polylactic acid PLA are two representative biodegradable new materials that have received increasing attention from the industry in recent years, especially under the supervision of laws and regulations such as the "plastic ban", which have achieved rapid growth. Traditionally, polylactic acid PLA is first fermented from food crops such as corn by biological fermentation to obtain lactic acid monomers, which first generate low molecular weight oligomers, which are then prepared under high vacuum thermal cracking conditions to obtain the so-called lactide key intermediates, and finally lactide ring-opening polymerization to obtain high molecular weight polylactic acid PLA products. In contrast, polyglycolic acid PGA is prepared through the coal chemical route, that is, the synthesis gas obtained from coal gasification and methyl nitrate are coupled under precious metal catalysts to generate dimethyl oxalate, and dimethyl oxalate is further reduced under precious metal catalytic selective hydrogenation conditions to obtain methyl glycolate. Methyl glycolate is initially polymerized into oligomers, which are then prepared under vacuum thermal cracking conditions to obtain the so-called glycolide key intermediates, and finally glycolide is ring-opened to obtain high molecular weight polyglycolic acid PGA products.

[0003] From the above process flow, it can be seen that the existing technology for preparing polyglycolic acid PGA and polylactic acid PLA has a series of bottleneck problems such as lengthy process flow, harsh process conditions, and the use of precious metal catalysts, which makes its production cost high, especially compared with the target it wants to replace in the market competition, that is, non-degradable plastics, the cost is not economically competitive. New technologies for reducing costs and increasing efficiency for polyglycolic acid PGA and polylactic acid PLA are still major industrial issues that need to be solved urgently by technical personnel in the industry. Furthermore, as mentioned above, the current industry's manufacturing processes for coal-based PGA and bio-based PLA involve very different raw materials and technical principles, and the incompatibility of equipment directly leads to high intensity and low returns of fixed asset investment, further reducing the cost-effectiveness competitiveness of terminal products.

[0004] The essence of this application is to break through the inherent mindset that polyglycolic acid must come from glycolic acid monomers, or polylactic acid must come from lactic acid monomers, and unexpectedly start from a class of simple diol substances, especially industrially abundant ethylene glycol and 1,2-propylene glycol, to directly prepare key intermediates of glycolide or lactide through selective oxidation reaction, while realizing for the first time the technical homology of polyglycolic acid PGA or polylactic acid PLA and a new process-sharing manufacturing model.

[0005] This first-disclosed technology has outstanding process safety, environmental friendliness, and overall cost competitiveness, thus providing a new and better solution for the low-cost "flexible shared" efficient manufacturing of polyglycolic acid PGA or polylactic acid PLA. [Summary of the invention]

[0006] The present application has unexpectedly found that, as shown in reaction formula (I), the diol compound shown in formula A and the oxidant [O] 1 react under reaction conditions to obtain a chemical equilibrium mixture of hydroxyaldehyde and / or its hemiacetal dimer B2 isomers shown in formula B1; then the dimer B2 and the oxidant [O] 2 react under reaction conditions to obtain the glycolide or lactide product shown in formula C. The above steps A to B and B to C are performed separately or in separate steps; or preferably, the above two steps can be performed continuously in a "one-step method" or "one-pot" manner without separating and purifying the intermediate B.

[0007]

[0008] Wherein R is hydrogen or a hydrocarbon group containing 1 to 24 carbon atoms; preferably, R is hydrogen or methyl.

[0009] The oxidant [O]1 or [O]2 is independently a reagent capable of oxidizing the corresponding substrate hydroxyl group to the corresponding carbonyl group; preferably, the oxidant [O]1 or [O]2 is independently oxygen, hydrogen peroxide, hydrocarbon peroxide, non-metallic (per)oxide, metal (per)oxide, ozone, halogen, organic peroxy acid, metal heteropoly acid, dialkyl peroxide ketone (such as DMDO), organic NO free radical type oxide (such as 2,2,6,6-tetramethylpiperidinyl oxide TEMPO), oxalyl chloride-DMSO, halogenated amide (such as NCS), metal (sub)nitrite-anhydride, metal (hypo)halite, hydrocarbon hypohalite, etc. At least one of the above. More preferably, the oxidants [O]1 and [O]2 are similar or identical to each other.

[0010] The conditions refer to at least one of additives, light, heat, microwaves, ultrasound, vacuum or pressure, solvents, and the like.

[0011] The additive is a catalyst, a promoter, or an inhibitor; preferably, the catalyst or promoter is a Lewis acid or Lewis base compound; the amount of the catalyst or promoter added is 0.1-1000% of the reaction raw materials; preferably 1-1000%, more preferably 1-200%, and even more preferably 1-120%.

[0012] Light refers to that the reaction system is carried out under light irradiation conditions, and the wavelength of the light is in the range of 200-780 nanometers.

[0013] Heat means that the reaction system is carried out under heating conditions, and the reaction temperature is -25-450 degrees Celsius, preferably -20-150 degrees Celsius; more preferably -20-100 degrees Celsius.

[0014] Microwave or ultrasonic means using a microwave or ultrasonic generator to irradiate the reaction system.

[0015] Pressure means that the reaction system is carried out under pressurized or certain vacuum conditions. The pressure of the reaction process can be 0.001-200 atmospheres, preferably 0.01-100 atmospheres.

[0016] The solvent is selected from at least one of substituted or unsubstituted aromatic hydrocarbons containing 1 to 24 carbon atoms, linear or branched aliphatic hydrocarbons, (sub)sulfones, amides, ethers, alcohols, esters, ketones, nitriles, carboxylic acids, water, amines, carbonates, ionic liquids, and supercritical carbon dioxide; or the liquid substrate itself simultaneously serves as a solvent medium.

[0017] In some preferred embodiments of the present invention, the solvent is selected from water, dioxane, acetonitrile, ethanol, butanol, ethyl acetate, butyl acetate, dimethyl sulfoxide, dimethyl sulfone, benzyl sulfoxide, benzyl sulfone, cyclobutylene sulfoxide, cyclobutylene, trichlorosilane, dichloromethane, dichloroethane, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, chloroform, carbon tetrachloride, benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, acetonitrile, ethylbenzene, diethylbenzene, chlorobenzene, dichloromethane, chlorobenzene, dichloroethane, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, chloroform, carbon tetrachloride, benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, acetonitrile, ethylbenzene, diethylbenzene, chlorobenzene, di ... At least one of benzene, anisole, nitrobenzene, heptane, hexane, petroleum ether, tetrahydrofuran, methyltetrahydrofuran, methyl tert-butyl ether, ethylene glycol dimethyl ether, bis(ethylene glycol dimethyl ether), triethylene glycol dimethyl ether, propylene glycol methyl ether acetate, triethylamine, tributylamine, dimethylisopropylamine, pyridine, N,N-tetramethylethylenediamine, N-alkylmorpholine, N-alkylpyrrole, N,N-dimethylformamide, formylmorpholine, N,N-diethylformamide and N-methylpyrrolidone.

[0018] The use of solvent is preferred but not essential. Under certain conditions, no solvent may be used, that is, a dissolved body, a melt of the reaction raw materials, or the reaction raw materials may be directly mixed and then reacted under heating, grinding, or gas phase conditions; and supercritical carbon dioxide may be used as the reaction medium. The advantages of using supercritical carbon dioxide as the reaction medium are that it is green and environmentally friendly and is conducive to the occurrence of the reaction and the separation of the products. Such advantages are well known to technicians in this field.

[0019] The raw material A is used as a reference, and the additive is used in a catalytic amount, an equivalent amount, or an over equivalent amount (0.001-100 equivalents).

[0020] Preferably, an exemplary but non-limiting implementation of the general reaction formula (I) is (IA), that is, ethylene glycol as a raw material and an oxidant [O] react in sequence under reaction conditions to generate glycolide:

[0021]

[0022] Preferably, an exemplary but non-limiting implementation of the general reaction formula (I) is (IB), that is, propylene glycol as a raw material and an oxidant [O] react in sequence under reaction conditions to generate lactide:

[0023]

[0024] It is worth noting that the raw material propylene glycol A can be used in the reaction in a chiral optically pure form. This type of optical purity (i.e., about 99% ee enantiomeric excess purity) can be conveniently prepared by the so-called catalytic hydration kinetic resolution HKR (hydrolytic kinetic resolution) of propylene oxide. The corresponding technology was first developed and industrialized by Jacobsen et al. using chiral Schiff base (Salen)-metal complex catalysts (Science, 1997, 277, 936), and is widely used in the functional chemical manufacturing industry. This is well known to the technical personnel in the industry. Therefore, the corresponding optically pure (L, L) configuration lactide C can be directly prepared from the optically pure (S) configuration A; or, the corresponding optically pure (D, D) configuration lactide C can be directly prepared from the optically pure (R) configuration A. Therefore, using diols A of different optical purity can prepare any one of the following three lactides or a mixture of any two or more of them.

[0025]

[0026] We also claim the use of glycolide or lactide synthesized by the process technology flow (I) disclosed in the present invention in the preparation of corresponding polyglycolic acid PGA or polylactic acid PLA polymers by ring-opening polymerization. The process disclosed in the present invention does not involve harsh reaction conditions such as precious metal catalysis or high temperature vacuum, the process flow is mild and controllable, and the quality of the obtained product, especially key indicators such as color and metal ion residue, is significantly better than that of traditional processes, which is widely favored by downstream applications and customers.

[0027] This will be further explained in the examples. [Specific implementation method]

[0028] The gist of the present invention is further described below in conjunction with specific embodiments:

[0029] Example:

[0030] At room temperature, using the oxidation reaction conditions of Akira Aso, 36.7 g of ethylene glycol, 9.2 g of TEMPO, 24.0 g of ferric nitrate nonahydrate, 3.5 g of sodium chloride and 400 ml of dichloroethane DCE were added to a reaction flask in an oxygen balloon atmosphere. The mixture was stirred for reaction overnight and then the reaction solution was filtered. The filtrate was concentrated to dryness and diluted with 80 ml of dioxane. After stirring for 2 hours, it was concentrated again. The system was placed in a refrigerator to precipitate 30.6 g of ethanolaldehyde dimer crystals.

[0031] The above 30.0 g of ethanolaldehyde dimer, 0.2 g of TEMPO and 250 ml of dichloroethane DCE were added to the reaction bottle, the reaction temperature was lowered and maintained at -10°C under continuous stirring, 56.5 ml of tert-butyl hypochlorite was slowly dripped into the reaction solution, and the reaction was maintained at -10°C and protected from light for 6 hours. After the reaction was completed, the reaction solution was filtered, and the obtained filtrate was directly mixed with 250 ml of -10°C n-hexane, mixed and stirred evenly, and then allowed to stand for 5 minutes, and then filtered to separate the precipitated pale yellow solid glycolide crude product; the obtained filter residue was put into 15 ml of ethyl acetate at room temperature, stirred to fully dissolve the glycolide in the filter residue, and then filtered to separate the unreacted ethanolaldehyde dimer and the ethyl acetate solution of glycolide, and the ethanolaldehyde dimer was recovered for reuse. The solid crude glycolide obtained from the above filtrate and the glycolide ethyl acetate solution obtained from the filter residue were mixed, slightly heated to completely dissolve the solid, then cooled to below 0°C to recrystallize the glycolide, and filtered to obtain 25.2 grams of pure white and colorless transparent glycolide crystals. The yield of a single oxidation reaction was 86%.

[0032] Example:

[0033] 30.3 g of glycolaldehyde dimer, 0.78 g of TEMPO and 500 ml of dichloromethane were added to the reaction flask, the reaction temperature was lowered and maintained at -10 ° C under continuous stirring. 65 g of sodium hypochlorite solid with an effective chlorine content of 60% was weighed and slowly added to the reaction solution in batches, and the reaction was kept at 0 ° C and protected from light for 6 hours. After the reaction was completed, the reaction solution was filtered, and the filtrate was directly mixed with 500 ml of -10 ° C n-hexane, mixed and stirred evenly, and then allowed to stand for 5 minutes, and then filtered to separate the precipitated pale yellow solid glycolide crude product. The obtained glycolide crude product was dissolved in 25 ml of ethyl acetate, lowered to below 0 ° C until glycolide was completely precipitated, and filtered to obtain 26.7 g of pure white and colorless transparent glycolide crystals with a yield of 91%.

[0034] Example:

[0035] At room temperature and in an oxygen balloon atmosphere, 55 g of (S)-propylene glycol (commercially available with an enantiomeric excess of 99.6% ee), 11.2 g of TEMPO, 29.0 g of ferric nitrate nonahydrate, 4.2 g of sodium chloride and 450 ml of dichloroethane DCE were added to a reaction flask. The mixture was stirred for reaction overnight and then the reaction solution was filtered. The filtrate was concentrated to dryness and diluted with 75 ml of dioxane. After stirring for 6 hours, it was concentrated again. The system was placed in a refrigerator to precipitate 43.1 g of (S,S)-propanol aldehyde dimer crystals.

[0036] 38.6 g of (S, S)-propanol aldehyde dimer, 0.86 g of TEMPO and 500 ml of dichloromethane were added to the reaction bottle, the reaction temperature was lowered and maintained at -10 ° C under continuous stirring. 68 g of sodium hypochlorite solid with an effective chlorine content of 60% was weighed and slowly added to the reaction solution in batches, and the reaction was kept at 0 ° C and protected from light for 6 hours. After the reaction was completed, the reaction solution was filtered, and the filtrate was directly mixed with 500 ml of -10 ° C n-hexane, mixed and stirred evenly, and then allowed to stand for 5 minutes, and then filtered to separate the precipitated light yellow solid lactide crude product. The obtained lactide crude product was dissolved in 28 ml of ethyl acetate, lowered to below 0 ° C, and filtered to obtain 27.2 g of pure white and colorless transparent optically pure lactide crystals with a yield of 74%.

[0037] It should be emphasized that the above embodiments are merely illustrative and not restrictive. Based on the disclosure of this application, any adjustment or change in reaction conditions or parameters that may be commonly adopted by practitioners will not deviate from the gist of the present invention. The scope of protection of this patent shall be based on the relevant rights record items.

Claims

1. A process technology for preparing the corresponding glycolide or lactide substance by direct oxidation using ethylene glycol or propylene glycol as raw materials. As shown in reaction formula (I), the diol compound shown in structural formula A and the oxidant [O] 1 react under reaction conditions to obtain a chemical equilibrium mixture of hydroxyaldehyde and / or its hemiacetal dimer B2 isomers shown in structural formula B1; then the dimer B2 and the oxidant [O] 2 react under reaction conditions to obtain the glycolide or lactide product shown in structural formula C: Wherein R is hydrogen or a hydrocarbon group containing 1 to 24 carbon atoms; preferably, R is hydrogen or methyl; the oxidant [O]1 or [O]2 is independently a reagent capable of oxidizing the corresponding substrate hydroxyl group (OH) to the corresponding carbonyl group (C=O); the reaction conditions refer to at least one of additives, light, heat, microwaves, ultrasound, vacuum or pressure, solvents and the like.

2. According to claim (1), preferably, the oxidant [O]1 or [O]2 is independently oxygen, hydrogen peroxide, hydrocarbon peroxide, non-metallic (per)oxide, metal (per)oxide, ozone, halogen, organic peroxy acid, metal heteropoly acid, dialkyl peroxy ketone, organic NO free radical type oxide, halogenated amide, metal (sub)nitrite-anhydride, oxalyl chloride-DMSO, metal (hypo)halite, hydrocarbon hypohalite at least one. More preferably, the oxidants [O]1 and [O]2 are similar or identical to each other.

3. According to claim (1), the catalyst or promoter in the conditions is a Lewis acid or Lewis base compound; the amount of the catalyst or promoter added is 0.1-1000% of the reaction raw materials; preferably 1-1000%, more preferably 1-200%, and further more preferably 1-120%. Light means that the reaction system is carried out under light irradiation conditions, and the wavelength of the light ranges from 200 to 780 nanometers. Heat means that the reaction system is carried out under heating conditions, and the reaction temperature is -25-450 degrees Celsius, preferably -20-150 degrees Celsius; more preferably -20-100 degrees Celsius. Microwave or ultrasound means that the reaction system is irradiated with a microwave or ultrasound generator. Pressure means that the reaction system is carried out under pressurized or certain vacuum conditions, and the pressure of the reaction process can be 0.001-200 atmospheres, preferably 0.01-100 atmospheres. The solvent is an aromatic or aliphatic hydrocarbon, a halogenated aromatic or aliphatic hydrocarbon, or various esters, alcohols, ethers, nitriles, ketones, amides, sulfones, carbonates, or water, or so-called green solvents such as the emerging "ionic liquids" or supercritical carbon dioxide (Supercritical CO2); or a mixed solvent system of any two or more of the above.

4. According to claim (1), preferably, an exemplary but non-limiting execution mode of the general reaction formula (I) is (IA), that is, ethylene glycol as a raw material and an oxidant [O] react in sequence under reaction conditions to generate glycolide:

5. According to claim (1), preferably, an exemplary but non-limiting execution mode of the general reaction formula (I) is (IB), that is, propylene glycol as a raw material and an oxidant [O] react in sequence under reaction conditions to generate lactide:

6. According to claims (1 and 5), any one of the following three lactides or a mixture of any two or more thereof is prepared using propylene glycol A of different optical purity:

7. According to claims (1, 4, and 5), the steps A to B and B to C are performed separately; or preferably, the two steps can be performed continuously in a "one-step" or "one-pot" manner without separating and purifying the intermediate B.

8. According to claims (1, and 4-6), the use of glycolide or lactide compounds or mixtures thereof synthesized by the process technology disclosed in the present invention in the preparation of corresponding polyglycolic acid PGA or polylactic acid PLA polymers by ring-opening polymerization.

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