Al-Salen catalyst, preparation method thereof and synthesis method of di-tert-amyl succinate

Abstract

The present invention provides an Al-Salen catalyst, a preparation method thereof and a synthesis method of di-tert-amyl succinate, and belongs to the field of fine chemical technology. The Al-Salen catalyst provided is used as a catalyst for preparing di-tert-amyl succinate by ester exchange reaction, and the yield of high-purity di-tert-amyl succinate can reach 55.1%-94.3%. At the same time, the Al-Salen catalyst has good chemical and thermal stability. More importantly, the Al-Salen catalyst is easily grafted onto a solid support containing an amino group to prepare a solid catalyst that is easily recyclable, so that it can be separated from the system when preparing di-tert-amyl succinate, which is conducive to further improving the purity of di-tert-amyl succinate.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemicals, and in particular relates to an Al-Salen catalyst, a preparation method thereof, and a synthesis method of di-tert-amyl succinate. Background Art

[0002] DPP organic pigments, derivatives of diketopyrrolopyrrole compounds, are a new class of high-performance organic pigments developed by Ciba, Switzerland, in 1983. Dialkyl succinate is a key intermediate in the production of DPP. Different dialkyl succinates reacting with the same benzonitrile or its derivatives yield varying pigment yields and qualities. Di-tert-amyl succinate has been shown to be a precursor that can further reduce costs, simplify the production process, and be environmentally friendly.

[0003] Di-tert-amyl succinate is different from other alkyl esters. Due to the large steric hindrance of tert-amyl alcohol, it is difficult to obtain the target product through the acid-alcohol esterification reaction between it and succinic acid. The transesterification method is currently a relatively mature method and is easy to operate and control. For example, in 1990, Ciba Company reported a method for synthesizing di-tert-amyl succinate by transesterification of dimethyl succinate and tert-amyl alcohol under the action of metallic lithium. This method is relatively simple to operate, the reaction is also easy to control, and the yield of high-purity di-tert-amyl succinate is about 77%. Publication number CN103804190A is a Chinese invention patent that provides a synthetic method for di-tert-alkyl succinate and proposes to use a mixture of metallic lithium hydroxide and cesium salt as a catalyst. Because these catalysts have moderate solubility in the alcohol used in the reaction, the yield of di-tert-amyl succinate can be increased, reaching 92%, and reducing the operating requirements of separation and purification. However, although lithium-based catalysts have achieved good catalytic effects, they are expensive and cannot be reused, which increases the preparation cost.

[0004] The catalytic activity of salen complexes depends primarily on the coordination environment and structural flexibility of the active center (metal center). Salen typically occupies only four coordination sites within the metal plane, leaving the axial sites vacant. This allows for highly tunable stereoelectronic properties of salen complexes, making it possible for metal-salen complexes to catalyze tertiary alcohol systems with significant steric hindrance. Research by Takashi et al. demonstrated that using a dinuclear Fe-salen catalyst with a bridged oxygen structure to catalyze the transesterification reaction of ethylbenzene with tert-butyl alcohol, tert-butyl ethylbenzene can be obtained under relatively mild conditions. However, experiments and theory have shown that using dinuclear Fe-salen as a catalyst to prepare di-tert-amyl succinate results in a low yield of the target product, with mono-tert-amyl succinate being the main product. This is due to the fact that, on the one hand, mono-tert-amyl succinate has significant steric hindrance, making further reactions difficult. On the other hand, the catalyst is relatively unstable, as dinuclear Fe-salen is easily hydrolyzed to mononuclear Fe-salen in the presence of acid. Furthermore, the C=N bond in salen is further hydrolyzed in the presence of acid, and a small amount of acid is unavoidable in dimethyl succinate. Therefore, the development of new metal-salen catalysts is needed. Summary of the Invention

[0005] Based on this, the present invention provides an Al-Salen catalyst, which has good chemical and thermal stability, is easy to be grafted onto a solid catalytic carrier containing amino groups, and is used to prepare a solid catalyst that is easily recyclable. The catalyst is used as a catalyst for preparing di-tert-amyl succinate through an ester exchange reaction, and the yield of high-purity di-tert-amyl succinate can reach 55.1%-94.3%.

[0006] The present invention also provides a method for preparing the Al-Salen catalyst.

[0007] The present invention also provides a method for synthesizing di-tert-amyl succinate using the Al-Salen catalyst. The reaction conditions are mild and a high yield of di-tert-amyl succinate can be achieved with a small amount of catalyst.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] An Al-Salen catalyst, whose structural formula is shown in Formula I or Formula II:

[0010]

[0011] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0012] A method for preparing the Al-Salen catalyst as described above comprises the following steps:

[0013] When the structural formula of the Al-Salen catalyst is as shown in Formula I:

[0014] The H4-Salen ligand shown in the structural formula III is reacted with Al(NO3)3·9H2O in a solvent to obtain an Al-Salen catalyst shown in the structural formula I;

[0015] When the structural formula of the Al-Salen catalyst is as shown in Formula II:

[0016] The H4-Salen ligand represented by the structural formula III is reacted with aluminum triethoxide in a solvent to obtain an Al-Salen catalyst represented by the structural formula II;

[0017]

[0018] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0019] Preferably, when the structural formula of the Al-Salen catalyst is as shown in Formula I:

[0020] The molar ratio of the H4-Salen ligand having the structural formula shown in Formula III to Al(NO3)3·9H2O is 1:(1-1.3);

[0021] When the structural formula of the Al-Salen catalyst is as shown in Formula II:

[0022] The molar ratio of the H4-Salen ligand with a structural formula as shown in Formula III to aluminum triethanolate is 1:(1-1.3).

[0023] Preferably, the H2-Salen ligand having the structural formula shown in Formula IV is subjected to a reduction reaction with sodium borohydride in a solvent to obtain the H4-Salen ligand having the structural formula shown in Formula III;

[0024]

[0025] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0026] Preferably, the molar ratio of the H2-Salen ligand represented by the structural formula IV to sodium borohydride is 1:(1-1.3).

[0027] Preferably, a salicylaldehyde compound having a structural formula as shown in Formula V is subjected to a condensation reaction with ethylenediamine in a solvent to obtain an H2-Salen ligand having a structural formula as shown in Formula IV;

[0028]

[0029] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0030] Preferably, the molar ratio of the salicylaldehyde substance represented by the structural formula V to ethylenediamine is (2-2.5):1.

[0031] Preferably, the solvent is selected from one of dichloroethane, hexane, ethyl acetate, ethanol, cyclohexane, n-butanol and toluene.

[0032] A method for synthesizing di-tert-amyl succinate comprises the following steps: dimethyl succinate and tert-amyl alcohol undergo an ester exchange reaction in the presence of a catalyst to generate di-tert-amyl succinate; the catalyst comprises a main catalyst, and the main catalyst is the Al-Salen catalyst described above.

[0033] Preferably, the catalyst further comprises a co-catalyst, and the co-catalyst is selected from one of tetrabutylammonium bromide and hexadecylammonium bromide.

[0034] Preferably, in the catalyst, the molar ratio of the main catalyst to the co-catalyst is 1:1.

[0035] Preferably, the catalyst further comprises a carrier, and the carrier has amino groups.

[0036] Preferably, the carrier is selected from one of Fe3O4-NH2, molecular sieve-NH2 and alumina-NH2.

[0037] Preferably, the synthesis method of di-tert-amyl succinate comprises the following steps:

[0038] S01 dimethyl succinate, tert-amyl alcohol and the catalyst are mixed to obtain a reaction solution;

[0039] S02. The reaction solution is heated to reflux temperature, and the generated methanol and part of tert-amyl alcohol are continuously distilled off;

[0040] S03. Add tert-amyl alcohol, keeping the added amount equal to the distilled amount;

[0041] S04. Detecting the dimethyl succinate content in the reaction solution. When the dimethyl succinate content is not greater than a predetermined value, the reaction is stopped and the reaction solution is cooled to room temperature;

[0042] S05. The reaction solution was distilled under reduced pressure to obtain di-tert-amyl succinate product.

[0043] Preferably, in the reaction solution, the molar ratio of dimethyl succinate to tert-amyl alcohol is 1:(10-12).

[0044] Preferably, in the reaction solution, the molar percentage of the catalyst relative to dimethyl succinate is 0.2%-2%.

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

[0046] The present invention provides an Al-Salen catalyst in which C=N is reduced to CN, thereby increasing the catalyst's basicity and flexibility, changing the Al coordination space environment, and making it suitable for sterically hindered tertiary amyl alcohol to participate in an ester exchange reaction. The catalyst can be used as a catalyst for preparing di-tert-amyl succinate through an ester exchange reaction, and the yield of high-purity di-tert-amyl succinate can reach 55.1%-94.3%. Furthermore, the Al-Salen catalyst has excellent chemical and thermal stability. More importantly, the Al-Salen catalyst can be easily grafted onto a solid support containing an amino group, thereby preparing an easily recyclable solid catalyst. This facilitates separation from the system during the preparation of di-tert-amyl succinate, thereby further improving the purity of the di-tert-amyl succinate.

[0047] The present invention also provides a method for preparing an Al-Salen catalyst, which is prepared by a coordination reaction between an H4-Salen ligand and an Al compound. The preparation process is simple and the yield of the Al-Salen catalyst is high.

[0048] The present invention also provides a method for synthesizing di-tert-amyl succinate. Dimethyl succinate and tert-amyl alcohol are used as reaction raw materials. In the presence of a small amount of the above-mentioned Al-Salen catalyst, di-tert-amyl succinate is prepared. The method not only has a yield of 55.1% to 94.3%, but also has a certain solubility in the reaction system due to the small amount of Al-Salen catalyst, eliminating the need for subsequent separation, thereby simplifying the reaction steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the preparation of Al-Salen catalyst in one embodiment. DETAILED DESCRIPTION

[0050] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The following will further describe the technical solution of the present invention in conjunction with the embodiments of the present invention, and the present invention is not limited to the following specific implementation methods.

[0051] In one embodiment of the present invention, an Al-Salen catalyst has a structural formula as shown in Formula I or Formula II:

[0052]

[0053] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0054] In the Al-Salen catalyst, C=N is reduced to CN, increasing the catalyst's basicity and flexibility, changing the Al coordination steric environment, and making it suitable for the sterically hindered tert-amyl alcohol to participate in the transesterification reaction. Furthermore, the Al-Salen catalyst exhibits excellent chemical and thermal stability. More importantly, the Al-Salen catalyst can be easily grafted onto a solid support containing amino groups (e.g., Fe3O4-NH2, molecular sieve-NH2, and alumina-NH2), allowing for the preparation of an easily recyclable solid catalyst. This facilitates separation from the system during the preparation of di-tert-amyl succinate, further improving the purity of the di-tert-amyl succinate.

[0055] In another embodiment of the present invention, please refer to Figure 1 A method for preparing the Al-Salen catalyst as described above comprises the following steps:

[0056] When the structural formula of the Al-Salen catalyst is as shown in Formula I:

[0057] The H4-Salen ligand shown in the structural formula III is reacted with Al(NO3)3·9H2O in a solvent to obtain an Al-Salen catalyst shown in the structural formula I;

[0058] When the structural formula of the Al-Salen catalyst is as shown in Formula II:

[0059] The H4-Salen ligand represented by the structural formula III is reacted with aluminum triethoxide in a solvent to obtain an Al-Salen catalyst represented by the structural formula II;

[0060]

[0061] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0062] Preferably, when the structural formula of the Al-Salen catalyst is as shown in Formula I:

[0063] The molar ratio of the H4-Salen ligand represented by the structural formula III to Al(NO3)3·9H2O is 1:(1-1.3); for example, the molar ratio of the H4-Salen ligand represented by the structural formula III to Al(NO3)3·9H2O is 1:1.1.

[0064] When the structural formula of the Al-Salen catalyst is as shown in Formula II:

[0065] The molar ratio of the H4-Salen ligand represented by the structural formula III to aluminum triethanolate is 1:(1-1.3). For example, the molar ratio of the H4-Salen ligand represented by the structural formula III to aluminum triethanolate is 1:1.1.

[0066] In some specific embodiments, the H2-Salen ligand represented by the structural formula IV is subjected to a reduction reaction with sodium borohydride in a solvent to obtain the H4-Salen ligand represented by the structural formula III;

[0067]

[0068] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0069] Preferably, the molar ratio of the H2-Salen ligand shown in Formula IV to sodium borohydride is 1:(1-1.3), for example, the molar ratio of the H2-Salen ligand to sodium borohydride is 1:1.1.

[0070] In some embodiments, a salicylaldehyde compound represented by the structural formula V is subjected to a condensation reaction with ethylenediamine in a solvent to obtain an H2-Salen ligand represented by the structural formula IV;

[0071]

[0072] Wherein, R is selected from one of H, halogen, and tert-butyl.

[0073] Preferably, the molar ratio of the salicylaldehyde substance represented by the structural formula V to ethylenediamine is (2-2.5): 1. For example, the molar ratio of the salicylaldehyde substance represented by the structural formula V to ethylenediamine is 2.2:1.

[0074] In one embodiment, the preparation method of the Al-Salen catalyst comprises the following steps:

[0075] S10. A salicylaldehyde compound represented by formula V is reacted with ethylenediamine in ethanol by heating under reflux to obtain an H2-Salen ligand represented by formula IV;

[0076] S20. The H2-Salen ligand of the structural formula shown in Formula IV is reduced with sodium borohydride in ethanol by heating under reflux to obtain the H4-Salen ligand of the structural formula shown in Formula III;

[0077] S31. The H4-Salen ligand of the structural formula shown in Formula III is reacted with Al(NO3)3.9H2O in dichloroethane by heating under reflux to obtain an Al-Salen catalyst of the structural formula shown in Formula I;

[0078] S32. The H4-Salen ligand with the structural formula shown in Formula III is reacted with aluminum triethanolate in toluene by heating under reflux to obtain an Al-Salen catalyst with the structural formula shown in Formula II.

[0079] Meanwhile, in the present invention, the H2-Salen ligand having the structural formula shown in Formula IV is substituted for the H4-Salen ligand having the structural formula shown in Formula III, and steps S31 and S32 are repeated to obtain comparative catalyst 1 and comparative catalyst 2, respectively.

[0080] In some specific embodiments, during the above process, the heating reflux temperature is 30°C-90°C, preferably 60°C; the heating reflux time is 2h-8h, preferably 5h.

[0081] Preferably, the solvent is selected from one of dichloroethane, hexane, ethyl acetate, ethanol, cyclohexane, n-butanol and toluene.

[0082] In some specific embodiments, 13.4 g (0.11 mol) of salicylaldehyde and 3 g (0.05 mol) of ethylenediamine were dissolved in 100 ml of ethanol, heated under reflux at 60 ° C for 5 h, cooled to 0 ° C, and pale yellow crystals were precipitated. The crystals were filtered, washed with ethanol, and vacuum dried to remove the solvent. The crystals were recrystallized from ethanol to obtain 11.9 g of H2-Salen ligand with the structural formula shown in Formula IV. The yield was 89%, and the elemental analysis (%) was C, 71.01; H, 6.10; N, 10.03 (C 16 H 16 N2O2 calculated values (C, 71.64; H, 5.97; N, 10.44).

[0083] 11.9 g H2-Salen ligand (0.0444 mol) and 18.5 g (0.0488 mol) were dissolved in 100 ml ethanol, heated under reflux at 60°C for 5 h, cooled to 0°C, and pale yellow crystals were precipitated. The crystals were filtered, washed with ethanol, and vacuum-dried to remove the solvent. The crystals were recrystallized from ethanol to obtain 10.9 g H4-Salen ligand with the structural formula shown in Formula III. The yield was 91%. The elemental analysis (%) was C, 70.92; H, 6.98; N, 10.01 (C 16 H 18 N2O2 calculated values (C, 71.11; H, 6.66; N, 10.37).

[0084] 2.7 g (0.01 mol) of H4-Salen ligand was dissolved in 10 ml of dichloromethane, and 100 ml of ethanol solution of 4.125 g (0.011 mol) of Al(NO3)3·9H2O was added. The mixture was heated under reflux at 60°C for 5 h, cooled to 0°C, and yellow-green crystals were precipitated. The crystals were filtered, washed with ethanol, and vacuum-dried to remove the solvent. The crystals were recrystallized from ethanol to obtain 2.535 g of Al-Salen catalyst with the structural formula shown in Formula I. The yield was 71%. The elemental analysis (%) was C, 54.03; H, 4.99; N, 12.01 (C 16 H 16 N3O5Al calculated values C, 53.78; H, 4.48; N, 11.76).

[0085] 2.7 g (0.01 mol) of H4-Salen ligand was dissolved in 10 ml of dichloromethane, and 100 ml of a toluene solution of 1.782 g (0.011 mol) of Al(OCH2CH3)3 was added. The mixture was heated under reflux at 60°C for 5 h, cooled to 0°C, and yellow crystals were precipitated. The crystals were filtered, washed with toluene, and vacuum dried to remove the solvent. The crystals were recrystallized from toluene solvent to obtain 1.97 g of Al-Salen catalyst with the structural formula shown in Formula II. The yield was 65%, and the elemental analysis (%) was C, 63.98; H, 5.87; N, 9.02 (C 32 H 32 N4O5Al2 calculated values C, 63.34; H, 5.28; N, 9.24).

[0086] 2.68 g (0.01 mol) of H2-Salen ligand was dissolved in 10 ml of dichloromethane, and 100 ml of ethanol solution of 4.12 g (0.011 mol) of Al(NO3)3.9H2O was added. The mixture was heated under reflux at 60°C for 5 h, cooled to 0°C, and yellow-green crystals were precipitated. The crystals were filtered, washed with ethanol, and vacuum-dried to remove the solvent. The crystals were recrystallized from ethanol to obtain 2.627 g of comparative catalyst 1 with a yield of 74%. The elemental analysis (%) was C, 53.72; H, 5.23; N, 12.12 (C 16 H 14 N3O5Al calculated values C, 54.08; H, 4.97; N, 11.83).

[0087] 2.68 g (0.01 mol) of H2-Salen ligand was dissolved in 10 ml of dichloromethane, and 100 ml of a toluene solution of 1.782 g (0.011 mol) of Al(OCH2CH3)3 was added. The mixture was heated under reflux at 60°C for 5 h, cooled to 0°C, and yellow crystals were precipitated. The crystals were filtered, washed with toluene, and dried under vacuum to remove the solvent. The crystals were recrystallized from toluene solvent to obtain 1.97 g of comparative catalyst 2 with a yield of 68%. The elemental analysis (%) was C, 63.22; H, 4.98; N, 9.13 (C 32 H 28 N4O5Al2 calculated values C, 63.57; H, 4.65; N, 9.30).

[0088] In another specific embodiment of the present invention, a method for synthesizing di-tert-amyl succinate is provided. Specifically, dimethyl succinate and tert-amyl alcohol undergo an ester exchange reaction in the presence of a catalyst to produce di-tert-amyl succinate. The catalyst includes a main catalyst, and the main catalyst is the Al-Salen catalyst described above.

[0089] In order to further improve the catalytic efficiency and increase the yield of di-tert-amyl succinate, preferably, the catalyst also includes a co-catalyst, and the co-catalyst is selected from one of tetrabutylammonium bromide and hexadecylammonium bromide.

[0090] In a preferred embodiment, in the catalyst, the molar ratio of the main catalyst to the co-catalyst is 1:1.

[0091] To facilitate separation of the Al-Salen catalyst from the system, in a preferred embodiment, the catalyst further comprises a carrier having amino groups.

[0092] Preferably, the carrier is selected from one of Fe3O4-NH2, molecular sieve-NH2 and alumina-NH2.

[0093] In a specific embodiment, the synthesis method of di-tert-amyl succinate comprises the following steps:

[0094] S01 dimethyl diacid, tert-amyl alcohol and the catalyst are mixed to obtain a reaction solution;

[0095] S02. The reaction solution is heated to reflux temperature, and the generated methanol and part of tert-amyl alcohol are continuously distilled off;

[0096] S03. Add tert-amyl alcohol, keeping the added amount equal to the distilled amount;

[0097] S04. Detecting the dimethyl succinate content in the reaction solution. When the dimethyl succinate content is not greater than a predetermined value, the reaction is stopped and the reaction solution is cooled to room temperature;

[0098] S05. The reaction solution was distilled under reduced pressure to obtain di-tert-amyl succinate product.

[0099] Furthermore, dimethyl succinate, tert-amyl alcohol, the Al-Salen catalyst, and a co-catalyst are added to a reactor, the reaction solution is heated to reflux temperature, and the generated methanol and part of the tert-amyl alcohol are continuously evaporated; tert-amyl alcohol is added at regular intervals, and the added amount is kept substantially equal to the evaporated amount; after a period of time, gas chromatography detection shows that the dimethyl succinate is completely reacted, and the reaction is stopped; the reaction solution is cooled to room temperature, and since the amount of the catalyst used is very small and has a certain solubility in the reaction system, subsequent separation is not required; the reaction solution is distilled under reduced pressure (65° C., 10 Pa) to remove the tert-amyl alcohol in the reaction solution, thereby obtaining di-tert-amyl succinate with a purity of 98.5%.

[0100] Preferably, in the reaction solution, the molar ratio of dimethyl succinate to tert-amyl alcohol is 1:(10-12), for example, the molar ratio of dimethyl succinate to tert-amyl alcohol is 1:11.

[0101] Preferably, in the reaction solution, the molar percentage of the catalyst relative to dimethyl succinate is 0.2%-2%, preferably 1%.

[0102] The following is a detailed description of the technical solutions and effects of the present invention through specific experimental examples.

[0103] 146 g (1 mol) of dimethyl succinate and 969.7 g (1.1 mol) of tert-amyl alcohol were added to the reactor. Catalysts were added according to the catalyst compositions and amounts specified in the experimental examples shown in Table 1. The reaction solution was heated to reflux at 100°C, and the resulting methanol and some tert-amyl alcohol were continuously distilled off. Additional tert-amyl alcohol was added at regular intervals, maintaining the added amount substantially equal to the amount distilled off. After 24 hours, gas chromatography indicated complete reaction of the dimethyl succinate, and the reaction was stopped. The reaction solution was cooled to room temperature, and the tert-amyl alcohol was removed by vacuum distillation (65°C, 10 Pa) to obtain di-tert-amyl succinate with a purity of 98.5%. The yields of di-tert-amyl succinate for each catalyst system are shown in Table 1.

[0104] Table 1 Di-tert-amyl succinate yields in various catalytic systems

[0105]

[0106] As shown in Table 1, comparative catalysts 1 and 2 obtained based on the coordination reaction of H2-Salen ligand and Al compound participate in the transesterification reaction of dimethyl succinate and tert-amyl alcohol, and the yield of di-tert-amyl succinate is only 5.1%-6.5%. Even in the presence of a co-catalyst, the yield of di-tert-amyl succinate is only 9.7%-10.1%.

[0107] Al-Salen catalysts, represented by the structural formulas I and II, obtained by reacting the H4-Salen ligand with an Al compound, directly participate in the transesterification reaction between dimethyl succinate and tert-amyl alcohol, achieving yields of 55.1%-65.6% for di-tert-amyl succinate. In the presence of co-catalysts such as tetrabutylammonium bromide or hexadecylammonium bromide, the yields of di-tert-amyl succinate reach 85.2%-94.3%, demonstrating high catalytic efficiency. This is likely due to the reduction of the C=N in the H4-salen ligand to CN, which increases the catalyst's basicity and flexibility, altering the Al coordination steric environment and making it suitable for the transesterification reaction with the sterically hindered tert-amyl alcohol.

[0108] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. An Al-Salen catalyst, characterized in that Its structural formula is shown in Formula I or Formula II: Wherein, R is selected from one of H, halogen, and tert-butyl.

2. A method for preparing the Al-Salen catalyst according to claim 1, characterized in that: The following steps are involved: When the structural formula of the Al-Salen catalyst is as shown in Formula I: The H4-Salen ligand shown in the structural formula of formula III is reacted with Al(NO3)3·9H2O in a solvent to obtain an Al-Salen catalyst shown in the structural formula of formula I; When the structural formula of the Al-Salen catalyst is as shown in Formula II: The H4-Salen ligand represented by the structural formula III is reacted with aluminum triethoxide in a solvent to obtain an Al-Salen catalyst represented by the structural formula II; Wherein, R is selected from one of H, halogen, and tert-butyl.

3. The preparation method of the Al-Salen catalyst as claimed in claim 2, characterized in that, When the structural formula of the Al-Salen catalyst is as shown in Formula I: The molar ratio of the H4-Salen ligand shown in Formula III to Al(NO3)3·9H2O is 1:(1-1.3); when the Al-Salen catalyst has the structural formula shown in Formula II: The molar ratio of the H4-Salen ligand with the structural formula shown in Formula III to aluminum triethanolate is 1:(1-1.3).

4. The preparation method of the Al-Salen catalyst according to claim 2, wherein The H2-Salen ligand represented by the structural formula IV is subjected to a reduction reaction with sodium borohydride in a solvent to obtain the H4-Salen ligand represented by the structural formula III; Wherein, R is selected from one of H, halogen, and tert-butyl.

5. The method for preparing the Al-Salen catalyst according to claim 4, wherein The structural formula is shown in Formula IV, and the molar ratio of the H2-Salen ligand to sodium borohydride is 1:(1-1.3).

6. The method for preparing the Al-Salen catalyst according to claim 4, wherein A salicylaldehyde compound represented by the structural formula V is subjected to a condensation reaction with ethylenediamine in a solvent to obtain an H2-Salen ligand represented by the structural formula IV; Wherein, R is selected from one of H, halogen, and tert-butyl.

7. The method for preparing the Al-Salen catalyst according to claim 6, wherein The molar ratio of the salicylaldehyde substance with the structural formula shown in Formula V to ethylenediamine is (2-2.5):

1.

8. The method for preparing the Al-Salen catalyst according to claim 2, 4 or 6, wherein: The solvent is selected from one of dichloroethane, hexane, ethyl acetate, ethanol, cyclohexane, n-butanol and toluene.

9. A method for synthesizing di-tert-amyl succinate, wherein dimethyl succinate and tert-amyl alcohol undergo an ester exchange reaction in the presence of a catalyst to produce di-tert-amyl succinate, characterized in that: The catalyst includes a main catalyst, and the main catalyst is the Al-Salen catalyst as claimed in claim 1.

10. The method for synthesizing di-tert-amyl succinate according to claim 9, wherein The catalyst further comprises a co-catalyst, and the co-catalyst is selected from one of tetrabutylammonium bromide and hexadecylammonium bromide.

11. The method for synthesizing di-tert-amyl succinate according to claim 10, wherein In the catalyst, the molar ratio of the main catalyst to the co-catalyst is 1:

1.

12. The method for synthesizing di-tert-amyl succinate according to claim 10, wherein The catalyst further includes a carrier having amino groups thereon.

13. The method for synthesizing di-tert-amyl succinate according to claim 12, wherein: The carrier is selected from one of Fe3O4-NH2, molecular sieve-NH2 and alumina-NH2.

14. The method for synthesizing di-tert-amyl succinate according to any one of claims 9 to 13, wherein: The following steps are involved: S01 dimethyl succinate, tert-amyl alcohol and the catalyst are mixed to obtain a reaction solution; S02. The reaction solution is heated to reflux temperature, and the generated methanol and part of tert-amyl alcohol are continuously distilled off; S03. Add tert-amyl alcohol, keeping the added amount equal to the distilled amount; S04. Detecting the dimethyl succinate content in the reaction solution. When the dimethyl succinate content is not greater than a predetermined value, the reaction is stopped and the reaction solution is cooled to room temperature; S05. The reaction solution was distilled under reduced pressure to obtain di-tert-amyl succinate product.

15. The method for synthesizing di-tert-amyl succinate as claimed in claim 14, wherein: In the reaction solution, the molar ratio of dimethyl succinate to tert-amyl alcohol is 1:(10-12).

16. The method for synthesizing di-tert-amyl succinate as claimed in claim 14, wherein: In the reaction solution, the molar percentage of the catalyst relative to dimethyl succinate is 0.2%-2%.

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