Preparation method of macromolecular hindered amine ultraviolet light absorber

Abstract

The invention discloses a preparation method of a macromolecular hindered amine ultraviolet light absorber, which comprises the following steps: carrying out transesterification on an ultraviolet light absorber UV-3 and 1, 2, 2, 6, 6-pentamethylpiperidinol under the catalysis of a synthetic hydrotalcite catalyst to obtain N, N '-bis (pentamethylpiperidine benzoate)-N-benzyl formamidine; wherein the molar ratio of the ultraviolet light absorber UV-3 to the 1, 2, 2, 6, 6-pentamethylpiperidinol is (1: 2)-(1: 4); the dosage of the synthetic hydrotalcite is 0.1-10% of the weight of the ultraviolet light absorber UV-3; the transesterification temperature is 100-200 DEG C, and the transesterification time is 5-10 hours. According to the method disclosed by the invention, the synthetic hydrotalcite is used as the catalyst for the transesterification reaction, and the catalyst is cheap and easy to obtain and can achieve the effect equivalent to that of an organic tin catalyst, so that the target product with relatively high purity can be obtained, and the residual tin element in the target product can be avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of ultraviolet absorbers, and in particular relates to a method for preparing a macromolecular hindered amine ultraviolet absorber. Background Art

[0002] Since its introduction, hindered amine light stabilizers have attracted widespread attention from scholars around the world due to their excellent light stabilization performance, and have also stimulated widespread interest in exploring their light stabilization mechanism.

[0003] In terms of product development, the goal is to further improve the photostability of hindered amine UV absorbers and break through their application limitations. For example, although early hindered amine UV absorbers have excellent photostability, most of them have disadvantages such as low average relative molecular weight and high alkalinity. The biggest defect of low molecular weight hindered amine UV absorbers is that they are not resistant to extraction and are easily lost during use. The high alkalinity makes it difficult to compound with acidic additives and cannot be used in acidic environments such as polyvinyl chloride and coatings. Therefore, the development trend of new types of hindered amine UV absorbers is mainly to improve or not lose their photostability, and strive to have a more reasonable structure, better performance and lower cost.

[0004] UV absorber NPTP is a new type of macromolecular hindered amine UV absorber. Its chemical name is N,N'-bis(pentamethylpiperidinylbenzoate)-N-benzylformamidine, CAS No. 2640365-84-8, and its molecular formula is C 42 H 56 N4O4, molecular weight is 680.92, structural formula is as follows: .

[0005] Chinese patent document CN112679415A discloses a method for preparing an ultraviolet absorber NPTP, which comprises the following steps: an ultraviolet absorber UV-3 [chemical name: N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine] and 1,2,2,6,6-pentamethylpiperidinol are reacted under the catalysis of a catalyst to obtain UV-3N [also known as ultraviolet absorber NPTP] through an ester exchange reaction; wherein the catalyst is methanesulfonic acid, zinc chloride or tetraisopropyl titanate.

[0006] The disadvantage of this method is that the catalytic effect of the above catalyst is not good, there will be more incomplete esterification by-products (ie, monosubstituted by-products), resulting in low purity of the target product.

[0007] At present, organic tin compounds have the best catalytic effect for this type of ester exchange method. However, the use of organic tin compounds will cause residual tin in the product. Currently, both domestic and foreign requirements for ultraviolet absorbers do not contain tin, resulting in this method being increasingly restricted. Summary of the invention

[0008] The object of the present invention is to solve the above problems and provide a method for preparing a macromolecular hindered amine ultraviolet absorber which has not only good catalytic effect, so that the target product has high purity, but also no residual tin element.

[0009] The technical scheme for achieving the purpose of the present invention is: a method for preparing a macromolecular hindered amine ultraviolet absorber, which comprises the following steps: N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine [hereinafter referred to as ultraviolet absorber UV-3] and 1,2,2,6,6-pentamethylpiperidinol are reacted under the catalysis of a catalyst to obtain N,N'-bis(benzoic acid pentamethylpiperidinyl ester)-N-benzylformamidine [hereinafter referred to as ultraviolet absorber NPTP] through an ester exchange reaction; the characteristic of the method is that the catalyst is synthetic hydrotalcite.

[0010] The reaction formula is as follows: .

[0011] The molar ratio of the ultraviolet absorber UV-3 to the 1,2,2,6,6-pentamethylpiperidinol is 1:2 to 1:4, preferably 1:2.2 to 1:2.5.

[0012] Using too much 1,2,2,6,6-pentamethylpiperidinol will not only increase the production cost, but also reduce the reaction yield.

[0013] If the amount of 1,2,2,6,6-pentamethylpiperidinol used is too small, it will lead to a high content of monosubstituted by-products and affect the purity of the product.

[0014] The synthetic hydrotalcite is also called aluminum-magnesium hydrotalcite, and its molecular formula is Mg6Al2(CO3)(OH) 16 4H2O, molecular weight is 603.98, and its CAS number is 12304-65-3.

[0015] The amount of the synthetic hydrotalcite used is 0.1-10% by weight of the ultraviolet absorber UV-3, preferably 0.5-2% by weight.

[0016] The transesterification reaction temperature is 100-200°C, preferably 140-160°C.

[0017] The transesterification reaction time is 5 to 10 hours.

[0018] The present invention has positive effects: the method of the present invention adopts synthetic hydrotalcite as a catalyst for ester exchange reaction, which is not only cheap and easy to obtain, but also can achieve the same effect as organic tin catalysts, so that not only a target product with high purity can be obtained, but also the residual tin element in the target product can be avoided. DETAILED DESCRIPTION

[0019] (Example 1) The preparation method of the macromolecular hindered amine ultraviolet absorber of this embodiment is as follows: Into a 1L four-necked flask, add 100g of ultraviolet absorber UV-3 (0.232, 1eq), 88g of 1,2,2,6,6-pentamethylpiperidinol (0.514mol, 2.2eq) and 1g of synthetic hydrotalcite, then introduce nitrogen, stir and heat to 150°C, keep the temperature for 8h, and take samples to detect the content of monosubstituted by-products ≤1%.

[0020] After the reaction, first cool to 100 ° C, add 500 mL of toluene, stir to dissolve, then wash twice with 100 mL of water, concentrate the organic phase under reduced pressure, add 600 mL of methanol after dehydration, heat to reflux to dissolve, cool and crystallize, add a small amount of seed crystals [i.e., the target product] at 45 ° C, cool to 10 ° C, filter, rinse the filter cake with 50 mL of methanol, drain and dry in an oven to obtain 144.6 g of a macromolecular hindered amine UV absorber with a yield of 91.4% and an HPLC purity of 97.9%.

[0021] (Example 2 to Example 9) The preparation methods of each embodiment are basically the same as that of embodiment 1, and the differences are shown in Table 1.

[0022] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Ultraviolet absorber UV-3 100g 100g 100g 100g 100g 100g 100g 100g 100g Pentamethylpiperidinol 88g, 2.2eq 80g, 2.0eq 100g, 2.5eq 88g, 2.2eq 88g, 2.2eq 88g, 2.2eq 88g, 2.2eq 88g, 2.2eq 88g, 2.2eq Synthetic hydrotalcite 1g 1g 1g 2g 0.5g 1g 1g 1g 1g Reaction temperature 150℃ 150℃ 150℃ 150℃ 150℃ 120℃ 180℃ 150℃ 150℃ Reaction time 8h 8h 8h 8h 8h 8h 8h 10h 6h UV absorber NPTP 144.6g 142.8g 144.7g 144.3g 142.4g 140.9g 139.7g 143.2g 141.6g Yield 91.4% 90.3% 91.5% 91.2% 90.0% 89.1% 88.3% 90.5% 89.5% HPLC purity 97.9% 95.7% 98.2% 98.1% 95.5% 97.1% 96.8% 97.5% 95.8%

[0023] (Comparative Example 1 to Comparative Example 4) The preparation methods of the comparative examples are basically the same as those of Example 1, and the differences are shown in Table 2.

[0024] Table 2 Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 catalyst Synthetic hydrotalcite 1g Methanesulfonic acid 1g Zinc chloride 1g Tetraisopropyl titanate 1g Dibutyltin oxide 1g UV absorber NPTP 144.6g 133.3g 142.6g 138.4g 145.6g Yield 91.4% 84.3% 90.2% 87.5% 92.1% HPLC purity 97.9% 88.8% 91.5% 90.3% 97.1%

Claims

1. A method for preparing a macromolecular hindered amine ultraviolet absorber, which is to obtain N,N'-bis(pentamethylpiperidinylbenzoate)-N-benzylformamidine by ester exchange reaction of N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine and 1,2,2,6,6-pentamethylpiperidinol under the catalysis of a catalyst; characterized in that: The catalyst is synthetic hydrotalcite.

2. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 1, characterized in that: The molar ratio of the ultraviolet absorber UV-3 to the 1,2,2,6,6-pentamethylpiperidinol is 1:2 to 1:

4.

3. The method for preparing the macromolecular hindered amine ultraviolet absorber according to claim 2, characterized in that: The molar ratio of the ultraviolet absorber UV-3 to the 1,2,2,6,6-pentamethylpiperidinol is 1:2.2 to 1:2.

5.

4. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 1, characterized in that: The amount of the synthetic hydrotalcite used is 0.1 to 10% by weight of the ultraviolet absorber UV-3.

5. The method for preparing the macromolecular hindered amine ultraviolet absorber according to claim 4, characterized in that: The amount of the synthetic hydrotalcite used is 0.5-2% by weight of the ultraviolet absorber UV-3.

6. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 1, characterized in that: The transesterification reaction temperature is 100-200°C.

7. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 6, characterized in that: The transesterification reaction temperature is 140-160°C.

8. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 1, characterized in that: The transesterification reaction time is 5 to 10 hours.