Process for the preparation of macromolecular hindered amine uv absorbers

Abstract

The application discloses a preparation method of a macromolecular hindered amine ultraviolet absorber, which comprises the following steps: under the catalysis of a synthetic hydrotalcite catalyst, ultraviolet absorber UV-3 and 1,2,2,6,6-pentamethylpiperidinol are subjected to an ester exchange reaction to obtain N,N'-bis(pentamethylpiperidyl benzoate)-N-benzylformamidine; the molar ratio of the ultraviolet absorber UV-3 to the 1,2,2,6,6-pentamethylpiperidinol is 1:2-1:4; the amount of the synthetic hydrotalcite is 0.1-10% of the weight of the ultraviolet absorber UV-3; the ester exchange reaction temperature is 100-200 DEG C; and the ester exchange reaction time is 5-10 h. The method of the application adopts the synthetic hydrotalcite as the catalyst for the ester exchange reaction, the catalyst is not only cheap and easy to obtain, but also can achieve the effect equivalent to that of the organic tin catalyst, so that the target product with high purity can be obtained, and the residual tin element in the target product can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet absorber technology, specifically relating to a method for preparing a macromolecular hindered amine ultraviolet absorber. Background Technology

[0002] Since their introduction, hindered amine light stabilizers have attracted widespread attention from scholars around the world due to their excellent photostability, which has also sparked extensive interest in exploring their photostability mechanisms.

[0003] In terms of product development, the goal is to further improve the photostability of hindered amine UV absorbers and overcome their application limitations. For example, although early hindered amine UV absorbers had excellent photostability, most of them had disadvantages such as low average relative molecular weight and high alkalinity. The biggest drawback of low molecular weight hindered amine UV absorbers is that they are not resistant to extraction and are easily lost during use. Their high alkalinity also makes them difficult to compound with acidic additives and cannot be used in acidic environments such as polyvinyl chloride and coatings. Therefore, the development of new hindered amine UV absorbers is ultimately aimed at improving or not losing their photostability, while striving for a more reasonable structure, better performance, and lower cost.

[0004] NPTP, a novel macromolecular hindered amine ultraviolet absorber, has the chemical name N,N'-bis(pentamethylpiperidinyl benzoate)-N-benzylformamidinium, CAS number 2640365-84-8, and molecular formula C1. 42 H 56 N4O4, with a molecular weight of 680.92, has the following structural formula:

[0005] .

[0006] Chinese patent document CN112679415A discloses a method for preparing ultraviolet absorber NPTP. The method involves the transesterification reaction of ultraviolet absorber UV-3 (chemical name N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidinium) with 1,2,2,6,6-pentamethylpiperidinol under the catalysis of a catalyst to obtain UV-3N (i.e., ultraviolet absorber NPTP). The catalyst is methanesulfonic acid, zinc chloride, or tetraisopropyl titanate.

[0007] The drawback of this method is that the catalyst has poor catalytic effect and produces a large number of incomplete esterification byproducts (i.e., monosubstituted byproducts), resulting in low purity of the target product.

[0008] Currently, organotin compounds are the most effective catalysts for this type of transesterification. However, the use of organotin compounds can lead to residual tin in the product. Since both domestic and international standards require that ultraviolet absorbers be tin-free, this method is becoming increasingly restricted. Summary of the Invention

[0009] The purpose of this invention is to solve the above-mentioned problems and provide a method for preparing a macromolecular hindered amine ultraviolet absorber that not only has a better catalytic effect and thus a higher purity of the target product, but also does not leave any tin residue.

[0010] The technical solution to achieve the objective of this invention is: a method for preparing a macromolecular hindered amine ultraviolet absorber, which involves the transesterification reaction of N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidinium [hereinafter referred to as ultraviolet absorber UV-3] and 1,2,2,6,6-pentamethylpiperidinol under the catalysis of a catalyst to obtain N,N'-bis(pentamethylpiperidinium benzoate)-N-benzylformamidinium [hereinafter referred to as ultraviolet absorber NPTP]; characterized in that: the catalyst is synthetic hydrotalcite.

[0011] The reaction formula is as follows:

[0012] .

[0013] 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.

[0014] Excessive use of 1,2,2,6,6-pentamethylpiperidinol not only increases production costs but also reduces reaction yield.

[0015] If the amount of 1,2,2,6,6-pentamethylpiperidinol is too small, it will lead to a high content of monosubstituted byproducts, which will affect the purity of the product.

[0016] The synthetic hydrotalcite, also known as aluminum-magnesium hydrotalcite, has the molecular formula Mg6Al2(CO3)(OH). 16 ·4H2O, with a molecular weight of 603.98, has a CAS number of 12304-65-3.

[0017] The amount of the synthetic hydrotalcite is 0.1 to 10% of the weight of the ultraviolet absorber UV-3, preferably 0.5 to 2%.

[0018] The transesterification reaction temperature is 100–200°C, preferably 140–160°C.

[0019] The transesterification reaction time is 5–10 h.

[0020] The positive effects of this invention are as follows: The method of this invention uses synthetic hydrotalcite as a catalyst for transesterification reaction. This catalyst is not only inexpensive and readily available, but also achieves effects comparable to organotin catalysts. Thus, it can not only obtain the target product with high purity, but also avoid the presence of tin residue in the target product. Detailed Implementation

[0021] (Example 1)

[0022] The specific preparation method of the macromolecular hindered amine ultraviolet absorber in this embodiment is as follows:

[0023] 100g of UV absorber UV-3 (0.232, 1 eq), 88g of 1,2,2,6,6-pentamethylpiperidinol (0.514 mol, 2.2 eq), and 1g of synthetic hydrotalcite were added to a 1L four-necked flask. Nitrogen gas was then introduced, and the mixture was stirred and heated to 150℃. The reaction was maintained at this temperature for 8 hours. Samples were taken to test the content of monosubstituted byproducts, which was ≤1%.

[0024] After the reaction was completed, the temperature was lowered to 100℃, 500mL of toluene was added, and the mixture was stirred until dissolved. Then, the mixture was washed twice with 100mL of water. The organic phase was concentrated under reduced pressure, dried, and then 600mL of methanol was added. The mixture was heated to reflux until dissolved, cooled, and crystals were precipitated. A small amount of seed crystals (i.e., the target product) was added at 45℃, and the temperature was lowered to 10℃. The mixture was filtered, and the filter cake was washed with 50mL of methanol. After drying under vacuum, the mixture was placed in an oven to dry, yielding 144.6g of a macromolecular hindered amine ultraviolet absorber with a yield of 91.4% and an HPLC purity of 97.9%.

[0025] (Examples 2 to 9)

[0026] The preparation methods of each embodiment are basically the same as those of Example 1, and the differences are shown in Table 1.

[0027] Table 1

[0028] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 UV-3 ultraviolet absorber 100g 100g 100g 100g 100g 100g 100g 100g 100g Pentamethylpiperidine 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%

[0029] (Comparative Examples 1 to 4)

[0030] The preparation methods of each comparative example are basically the same as those of Example 1, with the differences shown in Table 2.

[0031] Table 2

[0032] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 catalyst 1g of synthetic hydrotalcite 1g of mesylate 1g of zinc chloride 1g tetraisopropyl titanate 1g of dibutyltin oxide 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 N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine and 1,2,2,6,6-pentamethylpiperidinol are subjected to an ester exchange reaction in the presence of a catalyst to obtain N,N'-bis(pentamethylpiperidyl benzoate)-N-benzylformamidine; characterized in that: The catalyst is a synthetic hydrotalcite.

2. The method for preparing a macromolecular hindered amine ultraviolet absorber according to claim 1, characterized by: The molar ratio of the N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine to the 1,2,2,6,6-pentamethylpiperidinol is 1:2-1:

4.

3. The method for preparing a macromolecular hindered amine UV absorber according to claim 2, characterized by: The molar ratio of the N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine to the 1,2,2,6,6-pentamethylpiperidinol is 1:2.2-1:2.

5.

4. The method of making a macromolecular hindered amine UV absorber according to claim 1, characterized in that: The amount of the synthetic hydrotalcite is 0.1-10% by weight of the N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine.

5. The method for preparing a macromolecular hindered amine UV absorber according to claim 4, characterized by: The amount of the synthetic hydrotalcite is 0.5-2% by weight of the N,N'-bis(4-ethoxycarbonylphenyl)-N-benzylformamidine.

6. The method of making a macromolecular hindered amine UV absorber according to claim 1, wherein: The transesterification reaction temperature is 100-200℃.

7. The method of making a macromolecular hindered amine UV absorber according to claim 6, characterized in that: The transesterification reaction temperature is 140-160℃.

8. The method of making a macromolecular hindered amine UV absorber according to claim 1, wherein: The transesterification reaction time is 5-10h.