Method for preparing 2-alkyl-1, 3 propylene glycol from fatty aldehyde

Abstract

The invention provides a method for preparing 2-alkyl-1, 3 propylene glycol from fatty aldehyde, and belongs to the technical field of liquid crystal materials, and the method comprises the following steps: step S1, fatty aldehyde is subjected to a reaction to prepare methoxyl olefin; s2, carrying out condensation reaction on the methoxyl olefin prepared in the step S1 to obtain methylamino methylene fatty aldehyde; s3, carrying out hydrolysis reaction on the methylamino methylene fatty aldehyde prepared in the step S2 to prepare alkyl malondialdehyde; and S4, carrying out a reduction reaction on the alkyl malonaldehyde prepared in the step S3 to prepare the 2-alkyl-1, 3-propylene glycol. The raw materials used in the preparation method are easy to obtain, reaction conditions are easy to operate, and industrialization is realized; the purity of the prepared product reaches 99% or above, and the total yield of the product reaches 70% or above.

Description

Technical Field

[0001] The present invention relates to a method for preparing chemical materials, in particular to a method for preparing 2-alkyl-1,3-propylene glycol, and belongs to the technical field of liquid crystal materials. Background Art

[0002] TFT-LCD is a large-scale semiconductor integrated circuit manufacturing technology that utilizes new materials and processes. It is the foundation of liquid crystal (LC), inorganic and organic thin-film electroluminescent (EL and OEL) flat-panel displays. 2-Alkyl-1,3-propanediol, an important ester liquid crystal intermediate for TFT-LCD, is synthesized using diethyl malonate and alkyl ketone as the main raw materials through addition, hydrogenation, and reduction reactions. This method results in poor reactivity, low product purity, low yield, and high production costs.

[0003] At present, the domestic demand for 2-alkyl-1,3-propanediol is large and the production capacity is insufficient, so the research and development and industrial production of 2-alkyl-1,3-propanediol have become particularly important. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for preparing 2-alkyl-1,3-propanediol using fatty aldehydes to improve the purity and yield of the product.

[0005] To achieve the above object, the technical solution of the present invention is: a method for preparing 2-alkyl-1,3-propanediol using fatty aldehyde, comprising the following steps:

[0006] Step S1: preparing methoxy olefin by reacting fatty aldehyde;

[0007] Step S2: condensing the methoxy olefin prepared in step S1 to obtain methylaminomethylene fatty aldehyde;

[0008] Step S3: hydrolyzing the methylaminomethylene fatty aldehyde prepared in step S2 to obtain alkyl malondialdehyde;

[0009] Step S4: 2-alkyl-1,3-propanediol is prepared by subjecting the alkyl malondialdehyde prepared in step S3 to a reduction reaction.

[0010] Furthermore, the fatty aldehyde is n-butyraldehyde or 4-alkylcyclohexylcarboxaldehyde.

[0011] Furthermore, when the fatty aldehyde is n-butyraldehyde, the methoxy olefin is prepared by the reaction according to the following steps:

[0012] Step S1a-1, condensation reaction: n-butyraldehyde, methanol, and acidic catalyst I are added to a reaction vessel, heated to 60-65°C, refluxed and separated by water for 2-4 hours, cooled to 30-35°C, and neutralized by dropwise addition of sodium methoxide solution. The mixture is then extracted with toluene and water, the lower layer is further extracted with toluene, the organic phases are combined, washed with water, and the solvent methanol is discarded to obtain n-butanol dimethyl acetal; the acidic catalyst I is any one of p-toluenesulfonic acid, sulfuric acid, phosphotungstic acid, or glacial acetic acid;

[0013] Step S1a-2, elimination reaction: heating a mixed solution consisting of n-butanol dimethyl acetal, catalyst II, and reaction solvent I to reflux for 4 to 6 hours, cooling to 30 to 35° C., adding a sodium carbonate aqueous solution for neutralization, separating the liquids, extracting the lower layer with reaction solvent I, then combining the organic phases, washing with sodium carbonate aqueous solution, and discarding the solvent to obtain a methoxy olefin, wherein the methoxy olefin is 1-methoxybut-1-ene; the catalyst II is any one of sodium bisulfate, potassium bisulfate, ammonium dihydrogen phosphate, or phosphoric acid; and the reaction solvent I is any one of toluene, chlorobenzene, o-xylene, or toluene.

[0014] Furthermore, when the fatty aldehyde is n-butyraldehyde, step S2 includes the following process:

[0015] Step S2a-1, condensation reaction: adding 1-methoxybut-1-ene and reagent R to reaction solvent II, heating to 55-60°C for reaction for 2-4 hours, cooling to 30-35°C, neutralizing with a potassium carbonate aqueous solution, extracting with toluene and water, re-extracting the lower liquid with toluene, and then combining the organic phases and washing with water to obtain methylaminomethylene fatty aldehyde, wherein the methylaminomethylene fatty aldehyde is 2-(dimethylaminomethylene)butyraldehyde; the reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine;

[0016] The structural formula of the reagent R is shown in Formula I:

[0017]

[0018] Wherein, R is PO2Cl2, Cl or CO2Cl;

[0019] The preparation of the reagent R is carried out according to the following steps: controlling the temperature at -10 to 0°C, adding an acidic chloride dropwise to N,N-dimethylformamide (DMF), keeping the temperature constant for 2 to 4 hours, and filtering under nitrogen protection to obtain a solid reagent R; the acidic chloride is any one of phosphorus oxychloride, thionyl chloride, oxalyl chloride, phosgene, triphosgene, and chlorosuccinimide.

[0020] Furthermore, when the fatty aldehyde is n-butyraldehyde, step S3 includes the following process:

[0021] Step S3a-1, hydrolysis reaction: a toluene solution of 2-(dimethylaminomethylene)butyraldehyde is added dropwise to a sodium hydroxide solution, reacted at 70-80°C with stirring for 4-6 hours, cooled to 30-35°C, adjusted to a pH of 7-8 with hydrochloric acid, and then separated. The lower layer liquid is extracted with toluene, and the organic phases are combined, washed with water, and the solvent is discarded to obtain alkyl malondialdehyde, which is 2-ethyl-1,3-malondialdehyde.

[0022] Furthermore, when the fatty aldehyde is n-butyraldehyde, step S4 includes the following process:

[0023] Step S4a-1, reduction reaction: heating a mixture of tetrahydrofuran and a reducing agent to reflux, then slowly adding 2-ethyl-1,3-propanedialdehyde, continuing to reflux for 12 to 15 hours after the addition, and respectively adding water and hydrochloric acid solution to terminate the reaction, adjusting the pH value to 7, separating and recovering tetrahydrofuran, cooling to 30 to 35° C., and then extracting with toluene and water, extracting the lower layer with toluene, and then combining the organic phases, washing with water, and concentrating under reduced pressure to remove toluene, then continuing to cool to allow crystals to precipitate, filtering at -15 to -10° C., and vacuum drying at 80° C. to obtain the target product 2-alkyl-1,3-propanediol, wherein the 2-alkyl-1,3-propanediol is 2-ethyl-1,3-propanediol; the reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride, or lithium aluminum hydride.

[0024] Furthermore, when the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, the methoxy olefin is prepared by the reaction according to the following steps:

[0025] Step S1b-1, Wittig reaction: chloromethyl ether triphenylphosphine salt and tetrahydrofuran are added to a reaction vessel, cooled to -15 to 5°C, and base I is slowly added thereto to prepare a Wittig reagent. Then, 4-alkylcyclohexylcarboxaldehyde is added dropwise, and the reaction is stirred at -15 to 5°C for 4 to 10 hours. Then, water is added for hydrolysis, and toluene is added for extraction. The separated liquid is washed with an ethanol-water mixture 3 to 4 times, and the solvent is concentrated under reduced pressure to dryness to obtain a methoxy olefin, wherein the methoxy olefin is 4-alkylcyclohexyl vinyl methyl ether; the base I is any one of n-butyl lithium, potassium tert-butoxide, sodium tert-butoxide, or sodium hydroxide.

[0026] Furthermore, when the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S2 includes the following process:

[0027] Step S2b-1, condensation reaction: adding 4-alkylcyclohexyl vinyl methyl ether and reagent R to reaction solvent II, heating to 55-100°C for reaction for 4-6 hours, cooling to 30-35°C, adding potassium carbonate aqueous solution dropwise for neutralization, then extracting with toluene and water, extracting the lower layer with toluene, and then combining the organic phases and washing with water to obtain methylaminomethylene fatty aldehyde, wherein the methylaminomethylene fatty aldehyde is 3-(dimethylamino)-2-(alkylcyclohexyl)propionaldehyde; the reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine;

[0028] The structural formula of the reagent R is shown in Formula I:

[0029]

[0030] Wherein, R is PO2Cl2, Cl or CO2Cl;

[0031] The preparation of the reagent R is carried out according to the following steps: controlling the temperature at -10 to 0°C, adding an acidic chloride dropwise to N,N-dimethylformamide (DMF), keeping the temperature constant for 2 to 4 hours, and filtering under nitrogen protection to obtain a solid reagent R; the acidic chloride is any one of phosphorus oxychloride, thionyl chloride, oxalyl chloride, phosgene, triphosgene, and chlorosuccinimide.

[0032] Furthermore, when the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S3 includes the following process:

[0033] Step S3b-1, hydrolysis reaction: a toluene solution of 3-(dimethylamino)-2-(alkylcyclohexyl)propanal is added dropwise to a sodium hydroxide solution, reacted at 70-80°C with stirring for 4-6 hours, cooled to 30-35°C, adjusted to a pH of 7-8 with hydrochloric acid, and then separated. The lower layer of liquid is extracted with toluene, and the organic phases are combined, washed with water, and the solvent is discarded to obtain alkyl malondialdehyde, which is 2-alkylcyclohexyl-1,3-propanedial.

[0034] Furthermore, when the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S4 includes the following process:

[0035] Step S4b-1, reduction reaction: heating the mixture of tetrahydrofuran and the reducing agent to reflux, then slowly adding 2-alkylcyclohexyl-1,3-propanedialdehyde, continuing to reflux for 6 to 15 hours after the addition, respectively adding water and hydrochloric acid solution to terminate the reaction, adjusting the pH to 7, separating and recovering tetrahydrofuran, cooling to 30 to 35° C., and then extracting with toluene and water, extracting the lower layer with toluene again, and then combining the organic phases, washing with water, and concentrating under reduced pressure to remove toluene, then continuing to cool to precipitate crystals, filtering at -15 to 0° C., and vacuum drying at 80° C. to obtain the target product 2-alkyl-1,3-propanediol, wherein the 2-alkyl-1,3-propanediol is 2-alkylcyclohexyl-1,3-propanediol; the reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride or lithium aluminum hydride.

[0036] The beneficial effects of the method for preparing 2-alkyl-1,3-propanediol from fatty aldehydes of the present invention are:

[0037] 1. The raw materials used in the present invention are all conventional chemicals, which are easily available, the finished product is moderate, and the reaction conditions used are easy to operate and industrialize;

[0038] 2. The product prepared by the present invention has a high purity of more than 99%;

[0039] 3. The total yield of the product prepared by the present invention reaches more than 70% (the total yield of the old technology is only about 30%);

[0040] 4. The reagent R used in the condensation reaction process of the present invention is independently developed and synthesized, involving the Vilsmeier reaction. The raw materials used are cheap and easily available, the reaction conditions are mild, the post-processing is simple, the yield and quality are high, and it is suitable for industrial production. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0042] A method for preparing 2-alkyl-1,3-propanediol using fatty aldehydes comprises the following steps:

[0043] Step S1: preparing methoxy olefin by reacting fatty aldehyde;

[0044] Step S2: condensing the methoxy olefin prepared in step S1 to obtain methylaminomethylene fatty aldehyde;

[0045] Step S3: hydrolyzing the methylaminomethylene fatty aldehyde prepared in step S2 to obtain alkyl malondialdehyde;

[0046] Step S4: 2-alkyl-1,3-propanediol is prepared by subjecting the alkyl malondialdehyde prepared in step S3 to a reduction reaction.

[0047] Preparation Example 1

[0048] Reagent R structural formula:

[0049] wherein R is PO2Cl2, Cl, or CO2Cl; and the synthesis comprises the following steps: controlling the temperature at -10 to 0°C, dropwise adding an acidic chlorinated compound to N,N-dimethylformamide (DMF), maintaining the temperature for 2 to 4 hours, and filtering under nitrogen protection to obtain reagent R; the acidic chlorinated compound is any one of phosphorus oxychloride, thionyl chloride, oxalyl chloride, phosgene, triphosgene, and chlorosuccinimide; and monitoring the quality of reagent R by TLC.

[0050] Among them, when R is PO2Cl2, the corresponding product reagent is R1; when R is PO2Cl2, the corresponding product reagent is R2; and of course, when R is CO2Cl, the corresponding product reagent is R3.

[0051] Example 1

[0052] Product 2-ethyl-1,3-propanediol synthesis route:

[0053]

[0054] The specific preparation steps are as follows:

[0055] S1a-1, condensation reaction: add the reactants n-butyraldehyde and methanol, and acidic catalyst I to a reaction vessel, the molar ratio of n-butyraldehyde to methanol is 1:4-5, and the amount of acidic catalyst I added is 5-8% of the total mass fraction of the reactants, heat to 60-65°C, reflux and separate water for 2-4 hours, cool to 30-35°C, add 28% sodium methoxide solution dropwise for neutralization, the molar ratio of the added sodium methoxide solution to acidic catalyst I is 1:2-2.5, then use toluene and water with a mass ratio of 1:2-3 to extract, the lower liquid is extracted again with half the amount of toluene used last time, then the organic phases are combined, and then washed three times with half the amount of water used last time, and the solvent methanol is evaporated to dryness to obtain n-butyraldehyde dimethyl acetal with a gas phase purity of 99-99.8% and a yield of 95-100%. Acidic catalyst I is any one of p-toluenesulfonic acid, sulfuric acid, phosphotungstic acid or glacial acetic acid. The gas phase detection conditions are as follows (the same below):

[0056] Gas chromatograph: Aglient 7820

[0057] Chromatographic column: HP-5MS 30m*0.32mm*0.25μm

[0058] Column temperature: 50℃(4min)-20℃ / min-290℃

[0059] Split: 40:1

[0060] Flow rate: about 1ml / min

[0061] INJ:300℃

[0062] FID:300℃.

[0063] S1a-2, elimination reaction: a mixture of n-butyraldehyde dimethyl acetal, catalyst II, and reaction solvent I is heated to reflux for 4-6 hours, cooled to 30-35°C, neutralized by adding 10% sodium carbonate aqueous solution, the molar ratio of sodium carbonate to catalyst II being 1:1-1.5, separated, the lower liquid extracted once with half the amount of reaction solvent I used in the reaction, then the organic phases are combined, washed three times with half the volume of the sodium carbonate aqueous solution, and the solvent is evaporated to dryness to obtain 1-methoxybut-1-ene with a vapor phase purity of 95-98% and a yield of 93-96%. Catalyst II is any one of sodium bisulfate, potassium bisulfate, ammonium dihydrogen phosphate, or phosphoric acid, and the amount of catalyst II is 2-5% by weight of the n-butyraldehyde methylal; reaction solvent I is any one of toluene, chlorobenzene, or o-xylene, and the amount of reaction solvent I is 3-6 times the weight of the n-butyraldehyde methylal.

[0064] S2a-1, condensation reaction: add 1-methoxybut-1-ene and reagent R to reaction solvent II, heat to 55-60°C for reaction for 2-4 hours, cool to 30-35°C, add 10% potassium carbonate aqueous solution dropwise for neutralization, the molar ratio of the added potassium carbonate solution to reagent R is 1:2.5-3, then separate and extract with toluene and water in a mass ratio of 1:3-4, extract the lower layer liquid again with half the amount of toluene used last time, then combine the organic phases, and wash three times with half the amount of water used last time to obtain a toluene solution of 2-(dimethylaminomethylene)butyraldehyde with a gas phase purity of 95.5-97.5% and a yield of 92-96%. The reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine; the reagent R is any one of R1, R2, or R3; the mass ratio of 1-methoxybut-1-ene to the reaction solvent II is 1:3-4; and the molar ratio of 1-methoxybut-1-ene to the reagent R is 1:1.2-1.4.

[0065] Reagent R structural formula:

[0066] Where R is one of the following:

[0067] R1=PO2Cl2;

[0068] R2=Cl;

[0069] R3=CO2Cl

[0070] S3a-1, hydrolysis reaction: a toluene solution of 2-(dimethylaminomethylene)butyraldehyde is added dropwise to a sodium hydroxide solution having a concentration of 15-20%, and the mixture is reacted at 70-80°C with stirring for 4-6 hours. The mixture is cooled to 30-35°C, and the pH value is adjusted to a range of 7-8 with hydrochloric acid. The liquid is then separated, and the lower layer is extracted once with half the amount of toluene used last time. The organic phases are then combined and washed three times with half the amount of water used last time. The solvent is evaporated to dryness to obtain 2-ethyl-1,3-propanedial with a gas phase purity of 93-96% and a yield of 95-98%.

[0071] S4a-1, reduction reaction: heat the mixture of tetrahydrofuran and the reducing agent to reflux, then slowly add 2-ethyl-1,3-propanedialdehyde, continue to reflux after the addition, and add water and 10% hydrochloric acid solution respectively under slight reflux to terminate the reaction, adjust the pH value to 7, continue heating to separate and recover the tetrahydrofuran by distillation, cool to 30-35°C, and then extract with toluene and water in a mass ratio of 1:3-4. Extract the lower layer of liquid again with half the amount of toluene used last time, then combine the organic phases, wash three times with half the amount of water used last time, concentrate under reduced pressure to remove part of the toluene, and then continue to cool to allow crystals to precipitate, filter at -15--10°C, and vacuum dry at 80°C to obtain the target product 2-ethyl-1,3-propanediol with a gas phase purity of 99-99.5% and a yield of 91-95%. The reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride or lithium aluminum hydride; wherein the added amount of tetrahydrofuran is 3-6w% of 2-ethyl-1,3-propanedial, and the amount of the reducing agent is 1-3 times the molar amount of 2-ethyl-1,3-propanedial.

[0072] The yields in the above steps refer to the yields of the current step.

[0073] The types and amounts of substances used in each step of the reaction in this embodiment, as well as the test indicators of the obtained products are detailed as follows (the remaining parameters not detailed are consistent with the above):

[0074] Table 1: 2-Ethyl-1,3-Propanediol Synthesis Example 1-1

[0075]

[0076]

[0077] Table 2: 2-ethyl-1,3-propanediol synthesis example 1-2

[0078]

[0079]

[0080] Table 3: 2-Ethyl-1,3-Propanediol Synthesis Examples 1-3

[0081]

[0082]

[0083] Example 2

[0084] The synthetic route of the product 2-alkylcyclohexyl-1,3-propanediol:

[0085]

[0086] R represents an alkyl group of 2 to 5 carbon atoms.

[0087] The specific preparation steps are as follows:

[0088] S1b-1, Wittig reaction: chloromethyl ether triphenylphosphine salt and tetrahydrofuran are added to a reaction vessel, cooled to -15 to 5°C, and base I is slowly added thereto to prepare a Wittig reagent. Then, 4-alkylcyclohexylcarboxaldehyde is added dropwise, and the reaction is carried out under stirring at a temperature of -15 to 5°C for 4 to 10 hours. Then, water is added for hydrolysis, and the amount of water added is 10% of the mass of chloromethyl ether triphenylphosphine salt. Then, toluene is added for extraction, and the amount of toluene added is 3 to 4 times the mass of 4-alkylcyclohexylcarboxaldehyde. The separated liquid is repeatedly washed with an ethanol-water mixture for 3 to 4 times, and the solvent is concentrated under reduced pressure to obtain 4-alkylcyclohexyl vinyl methyl ether with a gas phase purity of 96 to 99% and a yield of 95 to 98%. Base I is any one of n-butyl lithium, potassium tert-butoxide, sodium tert-butoxide or sodium hydroxide; the molar ratio of the main materials used is chloromethyl ether triphenylphosphine salt: base I: 4-alkylcyclohexylcarboxaldehyde = 1-1.1:1.1-1.2:1; the amount of tetrahydrofuran used is twice the mass of the phosphine salt.

[0089] S2b-1, condensation reaction: add 4-alkylcyclohexyl vinyl methyl ether and reagent R to reaction solvent II, heat to 55-100°C for reaction for 4-6 hours, cool to 30-35°C, add 10% potassium carbonate aqueous solution dropwise for neutralization, the molar ratio of the added potassium carbonate solution to reagent R is 1:3-5, then separate and extract with toluene and water in a mass ratio of 1:3-5, extract the lower layer liquid again with half the amount of toluene used last time, then combine the organic phases, and wash three times with half the amount of water used last time to obtain a toluene solution of 3-(dimethylaminomethylene)-2-(alkylcyclohexyl)propanal with a gas phase purity of 93-95% and a yield of 90-94%. The reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine; the reagent R is any one of R1, R2, or R3; the mass ratio of 4-alkylcyclohexyl vinyl methyl ether to the reaction solvent II is 1:3-6; and the molar ratio of 4-alkylcyclohexyl vinyl methyl ether to the reagent R is 1:1.2-1.6.

[0090] Reagent R structural formula:

[0091] Where R is one of the following:

[0092] R1=PO2Cl2;

[0093] R2=Cl;

[0094] R3=CO2Cl

[0095] S3b-1, hydrolysis reaction: a toluene solution of 3-(dimethylaminomethylene)-2-(alkylcyclohexyl)propanal is added dropwise to a sodium hydroxide solution with a concentration of 15-30%, and the mixture is reacted at 70-80°C with stirring for 4-6 hours. The mixture is cooled to 30-35°C, and the pH value is adjusted to a range of 7-8 with hydrochloric acid. The liquid is then separated, and the lower layer is extracted again with half the amount of toluene used last time. The organic phases are then combined and washed three times with half the amount of water used last time. The solvent is evaporated to dryness to obtain 2-alkylcyclohexyl-1,3-propanedial with a gas phase purity of 91.5-95% and a yield of 93-98%.

[0096] S4b-1, reduction reaction: The mixture of tetrahydrofuran and the reducing agent is heated to reflux, and then 2-alkylcyclohexyl-1,3-propanedialdehyde is slowly added. After the addition is complete, reflux is continued for 6 to 15 hours. Water and 10% hydrochloric acid solution are respectively added under slight reflux to terminate the reaction. The pH value is adjusted to 7. The tetrahydrofuran is separated and recovered by distillation while continuing heating. The mixture is cooled to 30 to 35° C. and then extracted with toluene and water in a mass ratio of 1:3 to 6. The lower layer liquid is extracted again with half the amount of toluene used in the previous extraction. The organic phases are then combined and washed three times with half the amount of water used in the previous extraction. Part of the toluene is concentrated under reduced pressure, and the temperature is continued to be lowered to allow crystals to precipitate. The mixture is filtered at -15 to 0° C. and dried in vacuo at 80° C. to obtain the target product, 2-alkylcyclohexyl-1,3-propanediol, with a vapor phase purity of 99 to 99.5% and a yield of 88 to 93.5%. The reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride or lithium aluminum hydride; wherein the amount of tetrahydrofuran is 3-6w% of 2-alkylcyclohexyl-1,3-propanedial, and the amount of the reducing agent is 1-3 times the molar amount of 2-alkylcyclohexyl-1,3-propanedial.

[0097] The types and amounts of substances used in each step of the reaction in this embodiment, as well as the test indicators of the obtained products are detailed as follows (the remaining parameters not detailed are consistent with the above):

[0098] Table 4: 2-Ethyl-1,3-propanediol Synthesis Example 2-1

[0099]

[0100] Table 5: 2-ethyl-1,3-propanediol synthesis example 2-2

[0101]

[0102]

[0103] Table 6: 2-Ethyl-1,3-Propanediol Synthesis Example 2-3

[0104]

[0105]

[0106] Comparative Example 1

[0107] Comparative Example 1 is a method for preparing 2-alkyl-1,3-propanediol using diethyl malonate and alkyl ketone in the prior art, which is as follows:

[0108] 1. Diethyl malonate and alkyl ketone react with Lewis acid to produce diethyl 2-alkyl-1,3-malonate. This product contains impurities such as decarboxylation, hydrolysis, and polymerization, and has low purity, requiring distillation and purification. After distillation, the purity of diethyl 2-alkyl-1,3-malonate is only about 89-94%, with a yield of 60-70%.

[0109] 2. After distillation and purification, diethyl 2-alkylenyl-1,3-propanedioate is first hydrogenated to reduce the alkenyl group, and then the ester group is reduced using a reducing agent such as lithium aluminum hydride to obtain the final product, 2-alkyl-1,3-propanediol. Hydrogenation is a key regulated process, and the use of lithium aluminum hydride and other reducing agents is highly hazardous, which is not conducive to safe production. After the two-step reduction and repeated crystallization and purification, the yield of the product with a gas phase purity of ≥99% is only 20-30%, generating a large amount of waste that cannot be recycled and low production efficiency.

[0110] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for preparing 2-alkyl-1,3-propanediol using fatty aldehydes, characterized in that: The steps include: Step S1: preparing methoxy olefin by reacting fatty aldehyde; Step S2: condensing the methoxy olefin prepared in step S1 to obtain methylaminomethylene fatty aldehyde; Step S3: hydrolyzing the methylaminomethylene fatty aldehyde prepared in step S2 to obtain alkyl malondialdehyde; Step S4: 2-alkyl-1,3-propanediol is prepared by subjecting the alkyl malondialdehyde prepared in step S3 to a reduction reaction.

2. The method for preparing 2-alkyl-1,3-propanediol by utilizing fatty aldehyde according to claim 1, characterized in that: The aliphatic aldehyde is n-butyraldehyde or 4-alkylcyclohexylcarboxaldehyde.

3. The method for preparing 2-alkyl-1,3-propanediol by utilizing fatty aldehyde according to claim 2, characterized in that: When the fatty aldehyde is n-butyraldehyde, the methoxy olefin is prepared by the reaction according to the following steps: Step S1a-1, condensation reaction: n-butyraldehyde, methanol, and acidic catalyst I are added to a reaction vessel, heated to 60-65°C, refluxed and separated by water for 2-4 hours, cooled to 30-35°C, and neutralized by dropwise addition of sodium methoxide solution. The mixture is then extracted with toluene and water, the lower layer is further extracted with toluene, the organic phases are combined, washed with water, and the solvent methanol is discarded to obtain n-butanol dimethyl acetal; the acidic catalyst I is any one of p-toluenesulfonic acid, sulfuric acid, phosphotungstic acid, or glacial acetic acid; Step S1a-2, elimination reaction: heating a mixture of n-butanol dimethyl acetal, catalyst II, and reaction solvent I under reflux for 4 to 6 hours, cooling to 30 to 35° C., adding a sodium carbonate aqueous solution for neutralization, separating the liquids, extracting the lower layer with reaction solvent I, then combining the organic phases, washing with sodium carbonate aqueous solution, and discarding the solvent to obtain a methoxy olefin, wherein the methoxy olefin is 1-methoxybut-1-ene; the catalyst II is any one of sodium bisulfate, potassium bisulfate, ammonium dihydrogen phosphate, or phosphoric acid; and the reaction solvent I is any one of toluene, chlorobenzene, o-xylene, or toluene.

4. The method for preparing 2-alkyl-1,3-propanediol by utilizing fatty aldehyde according to claim 3, characterized in that: When the fatty aldehyde is n-butyraldehyde, step S2 includes the following process: Step S2a-1, condensation reaction: 1-methoxybut-1-ene and reagent R are added to reaction solvent II, heated to 55-60°C for reaction for 2-4 hours, cooled to 30-35°C, and neutralized by dropwise addition of an aqueous potassium carbonate solution. The mixture is extracted with toluene and water, the lower layer is re-extracted with toluene, and the organic phases are combined and washed with water to obtain a methylaminomethylene fatty aldehyde, which is 2-(dimethylaminomethylene)butyraldehyde; the reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine; The structural formula of the reagent R is shown in Formula I: Where R is PO2Cl2, Cl or CO2Cl ； The preparation of the reagent R is carried out according to the following steps: controlling the temperature at -10 to 0°C, dropwise adding an acidic chlorinated compound to N,N-dimethylformamide, keeping the temperature constant for 2 to 4 hours, and filtering under nitrogen protection to obtain a solid reagent R; the acidic chlorinated compound is any one of phosphorus oxychloride, thionyl chloride, oxalyl chloride, phosgene, triphosgene, and chlorosuccinimide.

5. The method for preparing 2-alkyl-1,3-propanediol by utilizing fatty aldehyde according to claim 4, characterized in that: When the fatty aldehyde is n-butyraldehyde, step S3 includes the following process: Step S3a-1, hydrolysis reaction: a toluene solution of 2-(dimethylaminomethylene)butyraldehyde is added dropwise to a sodium hydroxide solution, reacted at 70-80°C with stirring for 4-6 hours, cooled to 30-35°C, adjusted to a pH of 7-8, and then separated. The lower layer of liquid is extracted with toluene, and then the organic phases are combined, washed with water, and the solvent is discarded to obtain alkyl malondialdehyde, which is 2-ethyl-1,3-malondialdehyde.

6. The method for preparing 2-alkyl-1,3-propanediol by using fatty aldehyde according to claim 5, characterized in that: When the fatty aldehyde is n-butyraldehyde, step S4 includes the following process: Step S4a-1, reduction reaction: heating a mixture of tetrahydrofuran and a reducing agent to reflux, then slowly adding 2-ethyl-1,3-propanedialdehyde, continuing to reflux for 12 to 15 hours after the addition, and respectively adding water and hydrochloric acid solution to terminate the reaction, adjusting the pH value to 7, separating and recovering tetrahydrofuran, cooling to 30 to 35° C., and then extracting with toluene and water, extracting the lower layer with toluene, and then combining the organic phases, washing with water, and concentrating under reduced pressure to remove toluene. The temperature is continued to be lowered to allow crystals to precipitate, filtering at -15 to -10° C., and vacuum drying at 80° C. to obtain the target product 2-alkyl-1,3-propanediol, wherein the 2-alkyl-1,3-propanediol is 2-ethyl-1,3-propanediol; the reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride, or lithium aluminum hydride.

7. The method for preparing 2-alkyl-1,3-propanediol by using fatty aldehyde according to claim 2, characterized in that: When the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, the methoxy olefin is prepared by the reaction according to the following steps: Step S1b-1, Wittig reaction: chloromethyl ether triphenylphosphine salt and tetrahydrofuran are added to a reaction vessel, cooled to -15 to 5°C, and base I is slowly added thereto to prepare a Wittig reagent. Then, 4-alkylcyclohexylcarboxaldehyde is added dropwise, and the reaction is carried out under stirring at -15 to 5°C for 4 to 10 hours. Water is then added for hydrolysis, and toluene is added for extraction. The separated liquid is washed with a mixture of ethanol and water, and the solvent is discarded to obtain a methoxy olefin, wherein the methoxy olefin is 4-alkylcyclohexyl vinyl methyl ether; the base I is any one of n-butyl lithium, potassium tert-butoxide, sodium tert-butoxide, or sodium hydroxide.

8. The method for preparing 2-alkyl-1,3-propanediol by using fatty aldehyde according to claim 7, characterized in that: When the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S2 includes the following process: Step S2b-1, condensation reaction: adding 4-alkylcyclohexyl vinyl methyl ether and reagent R to reaction solvent II, heating to 55-100°C for reaction for 4-6 hours, cooling to 30-35°C, adding potassium carbonate aqueous solution dropwise for neutralization, then extracting with toluene and water, extracting the lower layer with toluene, and then combining the organic phases and washing with water to obtain methylaminomethylene fatty aldehyde, wherein the methylaminomethylene fatty aldehyde is 3-(dimethylamino)-2-(alkylcyclohexyl)propionaldehyde; the reaction solvent II is any one of dimethylformamide, dimethyl sulfoxide, triethylamine, and pyridine; The structural formula of the reagent R is shown in Formula I: Where R is PO2Cl2, Cl or CO2Cl ； The preparation of the reagent R is carried out according to the following steps: controlling the temperature at -10 to 0°C, adding an acidic chloride dropwise to N,N-dimethylformamide (DMF), keeping the temperature constant for 2 to 4 hours, and filtering under nitrogen protection to obtain a solid reagent R; the acidic chloride is any one of phosphorus oxychloride, thionyl chloride, oxalyl chloride, phosgene, triphosgene, and chlorosuccinimide.

9. The method for preparing 2-alkyl-1,3-propanediol by using fatty aldehyde according to claim 8, characterized in that: When the fatty aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S3 includes the following process: Step S3b-1, hydrolysis reaction: a toluene solution of 3-(dimethylamino)-2-(alkylcyclohexyl)propanal is added dropwise to a sodium hydroxide solution, reacted at 70-80°C with stirring for 4-6 hours, cooled to 30-35°C, adjusted to a pH of 7-8, and then separated. The lower layer of liquid is extracted with toluene, and the organic phases are combined, washed with water, and the solvent is discarded to obtain alkyl malondialdehyde, which is 2-alkylcyclohexyl-1,3-propanedial.

10. The method for preparing 2-alkyl-1,3-propanediol by using fatty aldehyde according to claim 9, characterized in that: When the aliphatic aldehyde is 4-alkylcyclohexylcarboxaldehyde, step S4 includes the following process: Step S4b-1, reduction reaction: heating the mixture of tetrahydrofuran and the reducing agent to reflux, then slowly adding 2-alkylcyclohexyl-1,3-propanedialdehyde, continuing to reflux for 6 to 15 hours after the addition, respectively adding water and hydrochloric acid solution to terminate the reaction, adjusting the pH to 7, separating and recovering tetrahydrofuran, cooling to 30 to 35° C., and then extracting with toluene and water, extracting the lower layer with toluene again, and then combining the organic phases, washing with water, and concentrating under reduced pressure to remove toluene, then continuing to cool to precipitate crystals, filtering at -15 to 0° C., and vacuum drying at 80° C. to obtain the target product 2-alkyl-1,3-propanediol, wherein the 2-alkyl-1,3-propanediol is 2-alkylcyclohexyl-1,3-propanediol; the reducing agent is any one of sodium borohydride, potassium borohydride, lithium borohydride, zinc borohydride or lithium aluminum hydride.

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