A process for the preparation of N,N,-di(beta-hydroxypropyl)benzamide

Abstract

This invention discloses a method for preparing N,N,-di(β-hydroxypropyl)benzamide. Using excess methyl benzoate as a raw material, the amino groups are fully converted to obtain a mixture of N,N-di(β-hydroxypropyl)benzamide product and acyl ester byproducts. The acyl ester byproducts in the mixture are then alcoholyzed using an alcoholysis reagent to obtain the N,N-di(β-hydroxypropyl)benzamide product. This method improves reaction selectivity and product yield, achieving a maximum yield of up to 97%.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to a method for preparing N,N,-bis(β-hydroxypropyl)benzamide. Background Technology

[0002] Hydroxyalkylamides are thermosetting polyester powder coating curing agents. Compared with traditional TGIC-type curing agents, they have the advantage of low toxicity and have great application prospects. However, commonly used hydroxyalkylamide curing agents such as N,N,N',N'-tetra(β-hydroxyethyl)hexamethylenediamide and N,N,N',N'-tetra(β-hydroxypropyl)hexamethylenediamide have certain application drawbacks, such as poor yellowing resistance and surface pinholes, and cannot well replace TGIC curing agents in application.

[0003] N,N,-Di(β-hydroxypropyl)benzamide is a bifunctional hydroxyalkylamide product with benzene substituents. This product, when combined with existing commercially available N,N,N',N'-tetra(β-hydroxyethyl)hexamethylenediamide and N,N,N',N'-tetra(β-hydroxypropyl)hexamethylenediamide products, forms a trifunctional curing agent. This can effectively improve the application defects of hydroxyalkylamide curing agents, enhance yellowing resistance, and reduce surface pinholes.

[0004] In the preparation process of hydroxyalkylamides, since alkanolamine raw materials possess both amine and hydroxyl groups, both of which can react with common acylation reagents to generate amides and esters, there is a competitive reaction. From the perspective of product application, it is desirable for the amine group to be fully converted into an amide group while minimizing the occurrence of esterification side reactions. However, for some alkanolamine raw materials, the reactivity of the amine group is affected by factors such as steric hindrance, resulting in low reactivity and incomplete conversion of the amine group into an amide group. For example, diisopropanolamine and methyl benzoate both have low reactivity, making it difficult to efficiently prepare N,N-bis(β-hydroxypropyl)benzamide products.

[0005] Currently, the industry employs two solutions to address the aforementioned issues:

[0006] The first method employs a highly reactive acylation reagent, such as benzoyl chloride as a raw material. Following the method disclosed in CN1351008A, N,N-di(β-hydroxypropyl)benzamide is prepared using diisopropanolamine and benzoyl chloride as raw materials in the presence of toluene solvent. This method has the advantage of low reaction temperature, but because hydrochloric acid is generated as a byproduct during the reaction, it requires high corrosion resistance of the equipment and strict control of chloride ion content in the product. It also generates a significant amount of solid waste that needs to be treated. Furthermore, since the hydroxyl groups in benzoyl chloride and diisopropanolamine molecules also exhibit high reactivity, the problem of low reaction selectivity cannot be fundamentally solved; the product yield of this method is only about 70%.

[0007] The second method involves using an excess of diisopropanolamine in the reaction, which can improve the selectivity of the synthesis reaction to some extent. The excess diisopropanolamine is then separated by crystallization. However, this method still cannot solve the problem of competitive reaction between the amine group and the hydroxyl group, and the yield of the prepared product is only about 85%. Summary of the Invention

[0008] Objective of this invention: To address the shortcomings of existing technologies, this invention provides a method for preparing N,N,-bis(β-hydroxypropyl)benzamide. This method improves reaction selectivity and increases product yield, achieving a maximum yield of 97%.

[0009] Technical solution: The objective of this invention is achieved through the following technical solution:

[0010] This invention provides a method for preparing N,N,-bis(β-hydroxypropyl)benzamide, which uses excess methyl benzoate as a raw material to fully convert the amino groups, thereby obtaining a mixture of N,N-bis(β-hydroxypropyl)benzamide product and acyl ester byproducts. The acyl ester byproducts in the mixture are then alcoholyzed using an alcoholysis reagent to obtain the N,N-bis(β-hydroxypropyl)benzamide product.

[0011] The present invention provides a preferred method for preparing N,N,-bis(β-hydroxypropyl)benzamide, comprising the following steps:

[0012] (1) Add an inorganic base catalyst to diisopropanolamine, apply negative pressure, react at 80-120℃ until the catalyst is completely dissolved, add excess methyl benzoate PMA dropwise, stir the reaction and discharge the product to obtain crude product.

[0013] (2) After mixing the crude product obtained in step (1) with the alcoholysis reagent evenly, add the alkaline catalyst, stir, and carry out the alcoholysis reaction;

[0014] (3) After the reaction is completed, the alkaline catalyst is removed by neutralization and filtration; excess alcoholysis reagent and excess methyl benzoate are removed by evaporation separation to obtain N,N,-bis(β-hydroxypropyl)benzamide product.

[0015] Further, in step (1), the inorganic base is an alkali metal hydroxide.

[0016] Furthermore, the inorganic base is sodium hydroxide, potassium hydroxide, barium hydroxide, or calcium hydroxide.

[0017] Furthermore, the inorganic base is preferably sodium hydroxide or potassium hydroxide.

[0018] Furthermore, in step (1), the molar ratio of methyl benzoate to diisopropanolamine is 1.1-4.0:1.

[0019] Furthermore, the molar ratio of methyl benzoate to diisopropanolamine is 2.0-3.0:1. Too low a molar ratio will not completely convert the amine groups; too high a molar ratio, although it can fully convert the amine groups, will result in a large excess of methyl benzoate, which will increase the energy consumption of the separation process and reduce the economic efficiency of the process.

[0020] Furthermore, in step (1), the reaction time is 2-3 hours. Within this time range, the raw materials can be fully converted, while improving process efficiency.

[0021] Furthermore, in step (1), the reaction is carried out at 90-105°C. Too low a reaction temperature is not conducive to the rapid conversion of the raw materials; too high a reaction temperature makes the raw materials easy to evaporate under vacuum conditions, thereby reducing the conversion rate of the raw materials, especially the conversion rate of amine groups.

[0022] Furthermore, in step (1), the vacuum degree of the negative pressure is -0.05 to -0.099 MPa.

[0023] Furthermore, the vacuum degree of the negative pressure is -0.08 to -0.095 MPa. Too low a vacuum degree is detrimental to the effective evaporation of the byproduct methanol, thus affecting the reaction equilibrium and causing it to proceed to the right, reducing the raw material conversion rate. Simultaneously, the presence of a large amount of unremoved methanol in the reaction system can easily accelerate the saponification reaction between the catalyst and methyl benzoate, thereby quenching the catalyst and preventing the reaction from proceeding effectively. Too high a vacuum degree can also easily evaporate and carry methyl benzoate raw material out of the reaction system, which is not conducive to the complete conversion of the amine groups.

[0024] Further, in step (2), the alcoholysis reagent is methanol, ethanol, isopropanol or n-propanol.

[0025] Furthermore, the alcoholysis reagent is methanol. Methanol has higher alcoholysis activity, and the product after alcoholysis is methyl benzoate, which can be fully recovered and reused. Using other alcoholysis reagents, corresponding benzoate ester byproducts will be generated, such as ethyl benzoate, isopropyl benzoate, and propyl benzoate, which are not conducive to recovery and reuse. In addition, methanol has a lower boiling point, which also facilitates the subsequent separation of the alcoholysis reagent.

[0026] Further, in step (2), the mass ratio of the alcoholysis reagent to the crude product is 0.5-4.0:1.

[0027] Furthermore, the mass ratio of the alcoholysis reagent to the crude product is 1.0-2.0. A lower proportion of alcoholysis reagent is not conducive to the full conversion of acyl ester byproducts; while an excessively high proportion of alcoholysis reagent will increase the alcoholysis conversion of amide groups, thereby generating free amines and reducing the yield of the target product.

[0028] Furthermore, in step (2), the temperature of the alcoholysis reaction is 20-80℃.

[0029] Furthermore, the alcoholysis reaction temperature is 40-60°C. Too low an alcoholysis temperature will prolong the reaction time and result in lower process efficiency; while too high an alcoholysis temperature will increase the alcoholysis of amide groups, thereby reducing the yield of the target product.

[0030] Furthermore, in step (2), the alcoholysis reaction time is 0.5-3.0 h. If the alcoholysis time is too short, the acyl ester byproducts cannot be fully converted; if the alcoholysis reaction time is too long, the conversion of amide groups will increase, reducing the yield of the target product.

[0031] Further, in step (2), the alkaline catalyst is one or more of calcium oxide, barium oxide, sodium oxide, potassium oxide, supported lanthanide catalyst, sodium methoxide, or potassium methoxide.

[0032] Furthermore, the alkaline catalyst is calcium oxide, sodium methoxide, or potassium methoxide. Calcium oxide catalysts, while ensuring catalytic efficiency, also exhibit relatively high stability, facilitating recycling. Alkali metal catalysts, due to their reaction with hydroxyl groups to produce corresponding water molecules, can convert some methyl benzoate feedstock into benzoic acid, which is difficult to separate from the product, thus reducing product quality. Sodium methoxide and potassium methoxide do not cause this problem. Although supported lanthanide catalysts also have good catalytic effects, they require large quantities and are relatively expensive, resulting in high application costs.

[0033] Further, in step (2), the amount of alkaline catalyst added is 0.01-10.0% of the crude product mass.

[0034] For soluble sodium methoxide and potassium methoxide, the preferred catalyst dosage is 0.03-0.05%. For insoluble calcium oxide, the preferred catalyst dosage is 3.0-5.0%.

[0035] Furthermore, in step (3), when the alkaline catalyst is a soluble catalyst, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, magnesium hydroxide, sodium methoxide, or potassium methoxide, it is removed by neutralization; the neutralizing agent is sulfuric acid, nitric acid, or phosphoric acid.

[0036] When the alkaline catalyst is an insoluble catalyst, it can be removed by filtration.

[0037] The purpose of catalyst removal is to quench alkaline catalysts or separate catalysts to prevent the amide groups from being decomposed and destroyed in subsequent high-temperature separation processes, thereby effectively ensuring the process yield.

[0038] Furthermore, in step (3), the evaporation separation method is a known separation technology such as simple distillation, rectification, or falling film evaporation.

[0039] Beneficial effects:

[0040] This invention employs an ester-excess preparation technique. By fully converting excess ester into amino groups, a crude product containing N,N,-di(β-hydroxypropyl)benzamide and acyl ester byproducts is obtained. Then, through alcoholysis with a catalyst, using alcohol as the alcoholysis reagent, the acyl ester byproducts are converted into N,N,-di(β-hydroxypropyl)benzamide and methyl benzoate raw material. By separating the excess alcoholysis reagent and methyl benzoate, high-purity N,N,-di(β-hydroxypropyl)benzamide can be obtained in high yield. Compared to existing acyl chloride methods, this invention is more environmentally friendly, generates no corrosive gases, and has lower requirements for equipment corrosion resistance. Compared to amine-excess processes, this invention offers higher amino group conversion rates, improved process yield, and product purity. Furthermore, since methyl benzoate raw material has a lower boiling point and latent heat of vaporization than diisopropanolamine, energy consumption in post-processing steps can also be reduced. Detailed Implementation

[0041] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0042] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the experimental materials used in the following examples are commercially available products.

[0044] Example 1

[0045] Weigh 133.15g of diisopropanolamine into a four-necked flask, and add 1.22g of [unspecified ingredient]. NaOH catalyst was used, and the mixture was stirred and heated to 90℃. A vacuum was applied to -0.095 MPa. After the catalyst was completely dissolved, 272.3 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.0:1). After the addition was complete, the mixture was stirred for 2.5 h. After the reaction was complete, the temperature was lowered to 40℃, and 374.6 g of methanol (methanol to crude product mass ratio 1:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 0.11 g of sodium methoxide (0.03% of the crude product mass) catalyst was added for alcoholysis. The mixture was stirred for 0.5 h. After the reaction was complete, 0.099 g of concentrated sulfuric acid was added to neutralize the alcoholysis catalyst. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by distillation using evaporation separation technology to obtain 214.5 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 90.5%, and the product purity was 94.3%.

[0046] Example 2

[0047] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. NaOH catalyst was used, and the mixture was stirred and heated to 105℃. A vacuum was applied to -0.08 MPa. After the catalyst was completely dissolved, 408.45 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 3.0:1). After the addition was complete, the mixture was stirred for another 2.0 h. After the reaction was complete, the temperature was lowered to 60℃, and 1021.6 g of methanol (methanol to crude product mass ratio of 2:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 0.26 g of sodium methoxide (0.05% of the crude product mass) catalyst was added for alcoholysis. The mixture was stirred for another 3.0 h. After the reaction was complete, 0.24 g of concentrated sulfuric acid was added to neutralize the alcoholysis catalyst. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by distillation to obtain 216.9 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 91.2%, and the product purity was 95.4%.

[0048] Example 3

[0049] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was stirred and heated to 95℃, then evacuated to -0.09 MPa. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the reaction was stirred for another 2.0 h. After the reaction was completed, the temperature was lowered to 50℃, and 664.0 g of methanol (methanol to crude product mass ratio of 1.5:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 0.18 g of sodium methoxide (0.04% of the crude product mass) catalyst was added for alcoholysis. The reaction was stirred for 1.5 h. After the reaction was completed, 0.16 g of concentrated sulfuric acid was added to neutralize the alcoholysis catalyst. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by distillation to obtain 228.0 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 96.2%, and the product purity was 97.8%.

[0050] Example 4

[0051] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was used, and the mixture was stirred and heated to 90℃. A vacuum of -0.09 MPa was applied. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the mixture was stirred for another 2.0 h. After the reaction was complete, the temperature was lowered to 50℃, and 664.0 g of methanol (methanol to crude product mass ratio of 1.5:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 0.18 g of potassium methoxide (0.04% of the crude product mass) catalyst was added for alcoholysis. The mixture was stirred for 1.5 h. After the reaction was complete, 0.13 g of concentrated sulfuric acid was added to neutralize the alcoholysis catalyst. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by distillation to obtain 229.2 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 96.7%, and the product purity was 98.0%.

[0052] Example 5

[0053] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was used, and the mixture was stirred and heated to 90℃. A vacuum was applied to -0.09 MPa. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the mixture was stirred for another 2.0 h. After the reaction was complete, the temperature was lowered to 50℃, and 949.48 g of methanol (methanol to crude product mass ratio of 2.0:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 0.18 g of potassium methoxide (0.04% of the crude product mass) catalyst was added for alcoholysis. The mixture was stirred for 1.5 h. After the reaction was complete, 0.13 g of concentrated sulfuric acid was added to neutralize the alcoholysis catalyst. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed using a falling film evaporator to obtain 220.6 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 93.1%, and the product purity was 96.2%.

[0054] Example 6

[0055] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was used, and the mixture was stirred and heated to 90℃, then evacuated to -0.09 MPa. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the reaction was stirred for another 2.0 h. After the reaction was completed, the temperature was lowered to 50℃, and 664.0 g of methanol (methanol to crude product mass ratio of 1.5:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 13.28 g of calcium oxide (3.0% of the crude product mass) catalyst was added for alcoholysis. The reaction was stirred for 1.5 h. After the reaction was completed, the calcium oxide catalyst was removed by filtration. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by falling film evaporation to obtain 230.1 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 97.1%, and the product purity was 97.5%.

[0056] Example 7

[0057] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was used, and the mixture was stirred and heated to 90℃, then evacuated to -0.09 MPa. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the reaction was stirred for another 2.0 h. After the reaction was completed, the temperature was lowered to 50℃, and 664.0 g of methanol (methanol to crude product mass ratio of 1.5:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 13.28 g of barium oxide (3.0% of the crude product mass) catalyst was added for alcoholysis. The reaction was stirred for 1.5 h. After the reaction was completed, the barium oxide catalyst was removed by filtration. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by falling film evaporation to obtain 230.1 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 96.4%, and the product purity was 95.3%.

[0058] Example 8

[0059] Add 133.15g of diisopropanolamine to a four-necked flask, and then add 1.22g of [unspecified ingredient]. KOH catalyst was used, and the mixture was stirred and heated to 90℃, then evacuated to -0.09 MPa. After the catalyst was completely dissolved, 340.37 g of methyl benzoate (PMA) was slowly added dropwise to the mixture using a constant pressure funnel (the molar ratio of methyl benzoate to diisopropanolamine was 2.5:1). After the addition was complete, the reaction was stirred for another 2.0 h. After the reaction was completed, the temperature was lowered to 50℃, and 664.0 g of methanol (methanol to crude product mass ratio of 1.5:1) was added to a four-necked flask. After the methanol and the synthesized sample were completely dissolved, 22.14 g of calcium oxide (5.0% of the crude product mass) catalyst was added for alcoholysis. The reaction was stirred for 1.5 h. After the reaction was completed, the calcium oxide catalyst was removed by filtration. After removing the catalyst, excess alcoholysis reagent and excess methyl benzoate were removed by falling film evaporation to obtain 230.1 g of N,N,-bis(β-hydroxypropyl)benzamide product. The yield was 95.6%, and the product purity was 97.7%.

[0060] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A process for the preparation of N,N,-di(β-hydroxypropyl)benzamide, characterized in that, Using diisopropanolamine and excess methyl benzoate as raw materials, the amino groups are fully converted to obtain a mixture of N,N-di(β-hydroxypropyl)benzamide product and acyl ester byproduct. The acyl ester byproduct in the mixture is then alcoholyzed with an alcoholysis reagent to obtain the N,N-di(β-hydroxypropyl)benzamide product. The molar ratio of methyl benzoate to diisopropanolamine is 2.0-4.0:

1.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: (1) Add an inorganic base catalyst to diisopropanolamine, apply negative pressure, react at 80-120℃ until the catalyst is completely dissolved, add excess methyl benzoate PMA dropwise, stir the reaction and discharge the product to obtain crude product. (2) After mixing the crude product obtained in step (1) with the alcoholysis reagent evenly, add the alkaline catalyst, stir, and carry out the alcoholysis reaction; (3) After the reaction is completed, the alkaline catalyst is removed by neutralization and filtration; excess alcoholysis reagent and excess methyl benzoate are removed by evaporation separation to obtain N,N,-bis(β-hydroxypropyl)benzamide product.

3. The preparation method according to claim 2, characterized in that, In step (1), the inorganic base is an alkali metal hydroxide; the alkali metal hydroxide is selected from sodium hydroxide, potassium hydroxide, barium hydroxide or calcium hydroxide.

4. The preparation method according to claim 2, characterized in that, In step (1), the reaction time is 2-3 hours; the reaction temperature is 90-105°C; and the vacuum degree of the negative pressure is -0.05 to -0.099 MPa.

5. The preparation method according to claim 2, characterized in that, In step (2), the alcoholysis reagent is methanol, ethanol, isopropanol or n-propanol; the mass ratio of the alcoholysis reagent to the crude product is 0.5-4.0:

1.

6. The preparation method according to claim 2, characterized in that, In step (2), the temperature of the alcoholysis reaction is 20-80℃; the time of the alcoholysis reaction is 0.5-3.0h.

7. The preparation method according to claim 2, characterized in that, In step (2), the alkaline catalyst is one or more of calcium oxide, barium oxide, supported lanthanide catalyst, sodium methoxide or potassium methoxide; the amount of alkaline catalyst added is 0.01-10.0% of the crude product mass.

8. The preparation method according to claim 2, characterized in that, In step (3), if the alkaline catalyst is a soluble catalyst, it is removed by neutralization; the neutralizing agent is sulfuric acid, nitric acid or phosphoric acid; if the alkaline catalyst is an insoluble catalyst, it is removed by filtration.

9. The preparation method according to claim 2, characterized in that, In step (3), the evaporation separation method is simple distillation, rectification or falling film evaporation.