Amino coumarin type fluorescent whitening agent as well as preparation method and application thereof

Abstract

The invention discloses an amino coumarin fluorescent whitening agent, the molecular structural formula of which is shown in the specification, n is a positive integer not more than 10, and m is a positive integer not more than 20. The amino coumarin type fluorescent whitening agent prepared by the method has the advantages of cheap raw materials, simple synthesis operation, mild reaction conditions, no need of harsh conditions such as water-free and oxygen-free conditions, and high total yield. The synthesized amino coumarin derivative has proper fluorescence characteristics, can be used as a fluorescent whitening agent for treating polyethylene plastics, and can achieve a whitening effect. When the amino coumarin derivative is applied to whitening, the special effect is that the derivative has good compatibility with polyethylene, and can chemically react with polyethylene, so that the derivative is combined with polyethylene in a firm covalent bond form, and migration of a fluorescent whitening agent is difficult to occur.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and specifically relates to an aminocoumarin-type fluorescent whitening agent and a preparation method and application thereof. Background Art

[0002] Fluorescent whitening agents (FBAs) are chemical substances that whiten substrate materials by absorbing ultraviolet light and emitting bluish-violet light. Currently, common FBAs used in the plastics industry include benzoxazoles and distyrylbenzenes. In whitened plastics, the FBAs bind to polymer macromolecules primarily through hydrogen bonds, van der Waals forces, and hydrophobic interactions. These binding forces are weak, and under certain conditions, FBA molecules can migrate, degrading product quality. Polyethylene masterbatches contain high levels of FBAs, making migration more likely. The market and consumers are increasingly favoring FBAs with high migration resistance.

[0003] Aminocoumarin-based fluorescent brighteners are a common type of brightener, characterized by their low price and excellent fluorescent properties. They are commonly used to whiten fibers such as nylon, wool, and acetate, and are also used to whiten polyvinyl chloride plastics to a limited extent (see: Complete Dye Variety Collection, Volume 2, edited by He Yanbin, Shenyang Publishing House, 1st edition, 2018). However, when used in polyethylene masterbatches, aminocoumarin-based fluorescent brighteners currently on the market exhibit poor compatibility with polyethylene due to their structure. Polyethylene is a low-polarity substance, while aminocoumarin-based fluorescent brighteners are highly polar. This significant polarity difference between the two makes the brighteners less compatible with polyethylene, making precipitation and migration of the brighteners a common problem. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide an aminocoumarin-type fluorescent whitening agent with high migration resistance for polyethylene masterbatch.

[0005] To achieve the above object, the present invention provides the following technical solutions: An aminocoumarin type fluorescent brightener, Its molecular structure is:

[0006] Wherein, n is a positive integer not exceeding 10, and m is a positive integer not exceeding 20.

[0007] As a further improvement of the present invention, Its molecular structure is: .

[0008] As another object of the present invention, a method for preparing an aminocoumarin-type fluorescent whitening agent is provided. The method comprises the following steps: Step 1: 7-amino-4-methylcoumarin, 1-bromoalkyl alcohol, sodium carbonate, and potassium iodide are added to an acetonitrile solution to react to obtain intermediate 1; Step 2: Add intermediate 1, 1-bromoalkane, sodium carbonate, and potassium iodide to an acetonitrile solution to react to obtain intermediate 2; Step 3: Intermediate 2, monomethyl malonate, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine are added to a dichloromethane solution to react to obtain intermediate 3; Step 4: Add intermediate 3, 4-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene to an acetonitrile solution to react and obtain an aminocoumarin-type fluorescent brightener; The molecular structural formula of the intermediate 1 is: ; The molecular structural formula of the intermediate 2 is: ; The molecular structural formula of the intermediate 3 is: ; Wherein, n is a positive integer not exceeding 10, and m is a positive integer not exceeding 20.

[0009] As a further improvement of the present invention, In the step 1, the molar ratio of 7-amino-4-methylcoumarin, 1-bromoalkyl alcohol, sodium carbonate, and potassium iodide is 1:1.5:4:2; The molar concentration of the 7-amino-4-methylcoumarin in acetonitrile is 0.1 to 1 mol / L; The reaction temperature of step 1 is 80° C. and the reaction time is 12 h.

[0010] As a further improvement of the present invention, In the step 2, the molar ratio of intermediate 1, 1-bromoalkane, sodium carbonate, and potassium iodide is 1:1.5:4:2; The concentration of the intermediate 1 in the acetonitrile solution is 0.1-1 mol / L; The reaction temperature of step 2 is 100° C. and the reaction time is 2 h.

[0011] As a further improvement of the present invention, In the step 3, the molar ratio of intermediate 2, monomethyl malonate, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1:1.5:1.5:0.15; The concentration of the intermediate 2 in the acetonitrile solution is 0.1-1 mol / L; The reaction temperature of step 3 is 20-30°C and the reaction time is 2 h.

[0012] As a further improvement of the present invention, In the step 4, the molar ratio of intermediate 3, 4-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene is 1:1.2:1.2; The concentration of the intermediate 3 in the acetonitrile solution is 0.1~1 mol / L; The temperature range of step 4 is 20-30°C; the reaction time is 2 h.

[0013] As a further improvement of the present invention, The molecular structural formula of 1-bromoalkyl alcohol in the step 1 is: ; Wherein, n is a positive integer not exceeding 10; The molecular structural formula of 1-bromoalkane in the step 2 is: ; Wherein, m is a positive integer not exceeding 20.

[0014] As another object of the present invention, an application of an aminocoumarin-type fluorescent brightener is provided, which is applied to low-density polyethylene masterbatch.

[0015] As another object of the present invention, a method for preparing an aminocoumarin-type fluorescent brightener applied to a polyethylene masterbatch is provided, comprising the following steps: An aminocoumarin fluorescent brightener and polyethylene particles were weighed, melt-blended in an internal mixer, and then introduced into a twin-screw extruder. After melt-extrusion and granulation, a polyethylene masterbatch was obtained. The aminocoumarin fluorescent brightener accounted for 10% to 30% by weight. The temperature during the melt blending was 130° C. to 150° C.; and the temperature during the melt extrusion was 180° C. to 220° C.

[0016] To address the issue of poor compatibility, the inventors introduced long alkyl chains into the aminocoumarin structure, reducing the polarity of the brightener and thereby narrowing the polarity difference between the brightener and the polymer. Secondly, the inventors introduced a covalent bond between the brightener molecule and the polyethylene, permanently and firmly binding the brightener to the polyethylene and significantly reducing the probability of brightener migration. To this end, the present invention introduced a carbene precursor into the brightener molecule. After the carbene precursor forms a carbene, it chemically reacts with the carbon-hydrogen bonds in the polyethylene molecule, thereby achieving a covalent bond between the brightener and the polymer.

[0017] However, the carbon-hydrogen bonds on the long alkyl chains in the whitening agent structure may participate in carbene reactions, that is, self-reactions, thereby reducing the reaction probability between the whitening agent and the polymer. The longer the alkyl chain, the more likely this side reaction will occur.

[0018] Therefore, the inventors improved the alkyl groups on the amino structure in the CI fluorescent brightener 206 molecule. First, one of the alkyl groups was changed to a long alkyl chain to increase the compatibility of the brightener with polyethylene. Secondly, a suitable carbene precursor, namely a 2-diazomalonate structure, was introduced into one of the alkyl groups. This structure can form an active carbene intermediate under the action of heat, which can then react chemically with the carbon-hydrogen bonds in the polyethylene structure, thereby firmly bonding the brightener matrix to the polymer via covalent bonds, thereby increasing the migration resistance of the brightener. In order to balance the compatibility and reactivity between the brightener and the polymer, an alkyl chain of a certain length as in the present invention was designed. If the alkyl chain is too long, although it can further improve the compatibility of the brightener with polyethylene, it will increase the reaction of the brightener itself and correspondingly reduce the reaction probability of the brightener with polyethylene. In addition, if the alkyl chain is too long, the reaction yield will decrease during synthesis, increasing product cost.

[0019] The chemical reaction between the fluorescent brightener and polyethylene in this invention occurs because the diazo group introduced into the brightener molecule transforms into a carbene intermediate under specific temperature conditions, which then reacts with the carbon-hydrogen bonds in the polyethylene structure. Therefore, initiating this reaction requires only a specific temperature, without the need for additional chemical reagents. The specific method of this invention involves melt-mixing the brightener and polyethylene and then melt-extruding them, utilizing the high temperature of the melt to promote the reaction between the brightener and polyethylene. The resulting polyethylene masterbatch exhibits excellent migration resistance.

[0020] The synthesis method provided by the present invention utilizes inexpensive raw materials, is simple to operate, and employs relatively mild reaction conditions, eliminating the need for harsh conditions such as anhydrous and oxygen-free conditions, resulting in a high overall yield. The synthesized aminocoumarin derivatives exhibit suitable fluorescent properties and can be used as fluorescent brighteners to treat polyethylene plastics, achieving a whitening effect. The aminocoumarin derivatives of the present invention exhibit a unique advantage in whitening applications: they exhibit good compatibility with polyethylene and can chemically react with the polyethylene, forming a strong covalent bond that prevents migration of the fluorescent brightener. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the hydrogen nuclear magnetic resonance spectrum of intermediate 1 in Example 1 of the present invention; Figure 2 is the carbon NMR spectrum of intermediate 1 in Example 1 of the present invention; Figure 3 is the hydrogen nuclear magnetic resonance spectrum of intermediate 2 in Example 1 of the present invention; Figure 4 is the carbon NMR spectrum of intermediate 2 in Example 1 of the present invention; Figure 5 is the hydrogen nuclear magnetic resonance spectrum of intermediate 3 in Example 1 of the present invention; Figure 6 is the carbon NMR spectrum of intermediate 3 in Example 1 of the present invention; Figure 7 is the hydrogen nuclear magnetic resonance spectrum of the aminocoumarin-type fluorescent whitening agent in Example 1 of the present invention; Figure 8 is the carbon NMR spectrum of the aminocoumarin fluorescent whitening agent in Example 1 of the present invention; Figure 9 The UV-visible absorption spectrum and fluorescence emission spectrum of the aminocoumarin-type fluorescent whitening agent in dichloromethane in Example 1 of the present invention are shown; Figure 10 This is the thermogravimetric curve of the aminocoumarin fluorescent whitening agent in Example 1 of the present invention; Figure 11 is a differential scanning calorimetry curve of the aminocoumarin fluorescent whitening agent in Example 1 of the present invention; Figure 12 Schematic diagram of the process for preparing polyethylene masterbatch from the fluorescent whitening agents of Examples 2 to 4 and Comparative Examples 1 to 6 of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0023] Raw materials such as 7-amino-4-methylcoumarin, 1-bromopropanol, 1-bromodecane, monomethyl malonate, p-acetamidobenzenesulfonyl azide (p-ABSA), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), potassium iodide, sodium carbonate, N,N'-dicyclohexylcarbodiimide (DCC), and 4-dimethylaminopyridine (DMAP); solvents such as acetonitrile and dichloromethane; and substrates such as low-density polyethylene particles were all commercially available. Room temperature in the following examples refers to 20 ± 5°C.

[0024] Example 1: Step 1: Synthesis of Intermediate 1 The reaction equation is as follows:

[0025] To a three-necked flask equipped with a reflux condenser and a magnetic bar, 7-amino-4-methylcoumarin (10 mmol, 1.75 g) and acetonitrile (20 mL) were added sequentially at room temperature. After stirring and dissolution, sodium carbonate (40 mmol, 4.24 g), potassium iodide (20 mmol, 3.32 g), and 1-bromopropanol (15 mmol, 2.09 g) were added. The flask was then placed in an 80°C oil bath and stirred for 12 h. After the reaction, the flask was removed and cooled to room temperature. The mixture was then filtered through a Büchner funnel filled with approximately 0.5 cm thick diatomaceous earth. The filter cake was rinsed with dichloromethane until the eluent showed no visible fluorescence under 365 nm fluorescent light. All filtrates were combined and the low-boiling organic solvents (dichloromethane and acetonitrile) were removed using a rotary evaporator. The residue was separated by 100-200 mesh silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 1 / 3, v / v) to obtain intermediate 1 as an off-white solid, 2.28 g, in a yield of 78%. 1 H NMR (CDCl3, 400 MHz) δ 7.34 (d, J = 8.8 Hz, 1H), 6.51 (dd, J 1 = 8.8 Hz, J 2 = 2.0 Hz, 1H), 6.46 (d, J = 2.0 Hz,1H), 5.97 (s, 1H), 3.84 (t, J = 6.0 Hz, 2H), 3.34 (t, J = 6.4 Hz, 2H), 2.33(s, 3H), 1.94-1.88 (m, 2H). 13 C NMR (CDCl3, 100 MHz) δ 162.15, 156.01, 153.11,151.69, 125.49, 110.49, 110.44, 109.31, 97.99, 61.21, 41.35, 31.33, 18.57.ESI-MS: m / z = 234.1 [M+H]. H NMR and C NMR spectra of intermediate 1 are shown in Figure 1 and Figure 2 .

[0026] Step 2: Preparation of intermediate 2 The specific reaction equation is as follows:

[0027] To a three-necked flask equipped with a reflux condenser and a magnetic bar, intermediate 1 (7 mmol, 2.04 g) and acetonitrile (20 mL) were added sequentially at room temperature. After stirring and dissolution, sodium carbonate (28 mmol, 2.97 g), potassium iodide (14 mmol, 2.32 g), and 1-bromodecane (10.5 mmol, 2.33 g) were added. The flask was then placed in an oil bath at 100°C and stirred for 24 h. After the reaction, the flask was removed and allowed to cool to room temperature. The mixture was then filtered through a Büchner funnel filled with approximately 0.5 cm thick diatomaceous earth. The filter cake was rinsed with dichloromethane until the eluent showed no visible fluorescence under 365 nm fluorescent light. All filtrates were combined and the low-boiling organic solvents (dichloromethane and acetonitrile) were removed using a rotary evaporator. The residue was separated by 100-200 mesh silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 1 / 1, v / v) to obtain intermediate 2 as a pale yellow liquid, 1.18 g, in a 45% yield. 1 H NMR (CDCl3, 400 MHz) δ 7.34 (d, J = 8.8 Hz,1H), 6.60 (dd, J 1 = 9.2 Hz, J 2 = 2.4 Hz, 1H), 6.48 (d, J = 2.4 Hz, 1H), 5.90(s, 1H), 3.72 (t, J = 6.0 Hz, 2H), 3.48 (t, J = 7.2 Hz, 2H), 3.31 (t, J = 7.6Hz, 2H), 2.30 (s, 3H), 2.17 (br, 1H), 1.88~1.81 (m, 2H), 1.58 (m, 2H), 1.29~1.24 (m, 14H), 0.86 (t, J = 6.4 Hz, 3H). 13 C NMR (CDCl3, 100 MHz) δ162.47,155.90, 153.17, 151.00, 125.48, 109.09, 108.73, 108.55, 97.79, 60.00, 51.19,47.73, 31.87, 29.99, 29.63, 29.54, 29.51, 29.30, 27.05, 22.67, 18.42, 14.12.ESI-MS: m / z = 374.3 [M+H]. H NMR and C NMR spectra of intermediate 2 are shown in Figure 2. Figure 3 and Figure 4 .

[0028] Step 3: Synthesis of intermediate 3 The specific reaction equation is as follows:

[0029] To a three-necked flask equipped with a magnetic rod, intermediate 2 (3 mmol, 1.12 g) and dichloromethane (10 mL) were added sequentially at room temperature. After stirring and dissolution, monomethyl malonate (4.5 mmol, 531 mg), DCC (4.5 mmol, 928 mg), and DMAP (0.45 mmol, 55 mg) were added, and the mixture was stirred for 2 h. After completion of the reaction, the mixture was filtered through a Buchner funnel filled with approximately 0.5 cm thick diatomaceous earth. The filter cake was rinsed with dichloromethane until the eluent showed no significant fluorescence under 365 nm fluorescent light. All filtrates were combined and the low-boiling organic solvent (dichloromethane) was removed using a rotary evaporator. The residue was separated by chromatography on a 100-200 mesh silica gel column (eluent: petroleum ether / ethyl acetate = 2 / 1, v / v) to afford intermediate 3 as a pale yellow liquid, 1.38 g, in a 97% yield. 1 H NMR (CDCl3, 400 MHz) δ 7.37 (d, J = 8.8 Hz,1H), 6.56 (dd, J 1 = 8.8 Hz, J 2 = 2.4 Hz, 1H), 6.47 (d, J = 2.4 Hz, 1H), 5.93(s, 1H), 4.21 (t, J = 6.0 Hz, 2H), 3.76 (s, 3H), 3.46~3.43 (m, 4H), 3.30 (t, J= 7.6 Hz, 2H), 2.32 (s, 3H), 1.99~1.93 (m, 2H), 1.58 (m, 2H), 1.30~1.25 (m,14H), 0.86 (t, J = 6.4 Hz, 3H). 13 C NMR (CDCl3, 100 MHz) δ 3, 14.11, 16.96, 166.41,162.09, 155.93, 152.84, 150.64, 125.57, 109.41, 109.06, 108.56, 98.01, 63.00,52.60, 51.28, 47.55, 41.29, 31.86, 29.62, 29.53, 29.48, 29.29, 27.08, 27.03,26.29, 22.66, 18.42, 14.11. ESI-MS: m / z = 474.3 [M+H]. H NMR and C NMR spectra of intermediate 3 are shown in Figure 2. Figure 5 and Figure 6 .

[0030] Step 4: Synthesis of aminocoumarin fluorescent whitening agent The specific reaction equation is as follows:

[0031] To a three-necked flask equipped with a magnetic rod, intermediate 3 (1 mmol, 473 mg) and acetonitrile (10 mL) were added sequentially at room temperature. After stirring and dissolution, DBU (1.5 mmol, 228 mg) and p-ABSA (1.5 mmol, 360 mg) were added, and the mixture was stirred for 2 h. After completion of the reaction, water (20 mL) was added, and the mixture was extracted three times with ethyl acetate (20 mL x 3). All organic phases were combined and dried over anhydrous sodium sulfate. After filtration, the filtrate was evaporated using a rotary evaporator to remove the low-boiling organic solvent (ethyl acetate). The residue was separated by 100-200 mesh silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 4 / 1, v / v) to obtain an aminocoumarin-type fluorescent brightener. The product was an orange-yellow oily liquid, yielding 415 mg in 83% yield. 1 H NMR (CDCl3, 400 MHz) δ 7.36 (d, J = 9.2 Hz, 1H), 6.58 (dd, J 1 = 8.8 Hz, J 2= 2.4 Hz, 1H), 6.48 (d, J = 2.4 Hz, 1H), 5.93 (s, 1H), 4.29 (t, J = 6.0 Hz, 2H), 3.85 (s, 3H), 3.48 (t, J = 7.2 Hz, 2H), 3.30 (t, J = 7.6 Hz, 2H), 2.32 (s, 3H), 2.01~1.96 (m, 2H), 1.58 (m, 2H), 1.30~1.25 (m, 14H), 0.86 (t, J = 6.4 Hz, 3H). 13 C NMR (CDCl3, 100 MHz) δ 162.07, 161.26, 161.16, 155.93, 152.82, 150.64, 125.57, 109.43,109.08, 108.57, 98.02, 63.07, 52.57, 51.26, 47.46, 31.87, 29.63, 29.53,29.48, 29.29, 27.06, 27.03, 26.49, 22.67, 18.43, 14.12. ESI-MS: m / z = 499.3[M+H]. The H and C NMR spectra of aminocoumarin-type fluorescent whitening agents are shown in Figure 2. Figure 7 and Figure 8 .

[0032] The UV-visible absorption spectrum and fluorescence emission spectrum of aminocoumarin type fluorescent whitening agents are shown in Figure 9 As can be seen, the compound has a strong absorption peak in the ultraviolet region of 300-400 nm, with the maximum absorption wavelength at 364 nm. When excited by light at a wavelength of 364 nm, the compound exhibits a strong emission peak in the 400-500 nm region, with the maximum emission wavelength at 420 nm.

[0033] Thermogravimetric curve of aminocoumarin fluorescent whitening agent is shown in Figure 10 , differential scanning calorimetry curves are shown in Figure 11 It can be seen that the starting temperature for the compound to transform into a carbene intermediate is about 150 ℃. Below this temperature, the aminocoumarin-type fluorescent whitening agent will not change; above this temperature, the diazo group in the structure of the aminocoumarin-type fluorescent whitening agent will transform into a carbene intermediate.

[0034] Example 2: Weigh 10% by weight of the aminocoumarin fluorescent brightener prepared in Example 1 and 90% by weight of polyethylene particles, fully melt-mix them in an internal mixer at a roller temperature of 140°C, introduce them into a twin-screw extruder with an aspect ratio of 60, and melt-extrude them at an extrusion temperature of 200°C. After water cooling, blow dry them with a fan, and cut them into pellets to obtain fluorescent whitening polyethylene masterbatch. The application process diagram is shown in the figure below. Figure 12 shown.

[0035] Example 3: 20% by weight of aminocoumarin fluorescent brightener and 80% by weight of polyethylene particles were weighed and thoroughly mixed in an internal mixer at a roller temperature of 140°C. The mixture was then introduced into a twin-screw extruder with a length-to-diameter ratio of 60, melt-extruded at 200°C, water-cooled, blown dry with a fan, and pelletized to obtain fluorescent whitening polyethylene masterbatch.

[0036] Example 4: 30% by weight of aminocoumarin fluorescent brightener and 70% by weight of polyethylene particles were weighed and thoroughly mixed in an internal mixer at a roller temperature of 140°C. The mixture was then introduced into a twin-screw extruder with a length-to-diameter ratio of 60, melt-extruded at 200°C, water-cooled, blown dry with a fan, and pelletized to obtain fluorescent whitening polyethylene masterbatch.

[0037] Comparative Example 1: The aminocoumarin fluorescent brightener was replaced with the commercial brightener CI fluorescent brightener 206 (7-diethylamino-4-methylcoumarin), and the other steps were the same as in Example 2; The molecular structure of the brightener CI fluorescent brightener 206 (7-diethylamino-4-methylcoumarin) is (i.e., comparative compound 1): .

[0038] Comparative Example 2: Reference was made to the method in the literature (Chem. Pharm. Bull. 1983, 31(9), 3014-3023) to synthesize comparative compound 2 (m / z: 257.1[M]+), except that the aminocoumarin fluorescent whitening agent was replaced by comparative compound 2. The other steps were the same as those in Example 2.

[0039] The molecular structure of comparative compound 2 is: .

[0040] Comparative Example 3: In step 2 of Example 1, 1-bromodecane was replaced with bromoethane, and the rest was as in Example 1 to synthesize comparative compound 3 (m / z: 387.1 [M] + ). The aminocoumarin fluorescent brightener was replaced with comparative compound 3, and the rest was as in Example 2. The molecular structure of comparative compound 3 is: .

[0041] Comparative Example 4: In step 2 of Example 1, 1-bromodecane was replaced with bromohexane, and the rest was as in Example 1 to synthesize compound 4 (m / z: 443.2 [M] + ). The aminocoumarin fluorescent brightener was replaced with comparative compound 4, and the rest was as in Example 2. The molecular structure of comparative compound 4 is: .

[0042] Comparative Example 5 In step 2 of Example 1, 1-bromodecane was replaced with 1-bromoeicosane, and the rest was as in Example 1 to synthesize comparative compound 5 (m / z: 639.4 [M] + ). The aminocoumarin fluorescent brightener was replaced with compound 5, and the rest was as in Example 2. The molecular structure of comparative compound 5 is: .

[0043] Comparative Example 6 In step 3 of Example 1, monomethyl malonate was replaced with p-methoxyphenylacetic acid, and the rest was as in Example 1 to synthesize comparative compound 6 (m / z: 547.3 [M] + ). The aminocoumarin-type fluorescent whitening agent was replaced with comparative compound 6, and the rest was as in Example 2. The molecular structure of comparative compound 6 is: .

[0044] Ingredients:

[0045] Test method: Test 1: 20 g of the fluorescent whitening polyethylene masterbatch prepared in Examples 2 to 4 and Comparative Examples 1 to 6 were weighed and processed using an injection molding machine to produce polyethylene blocks. These blocks were placed in an 80°C oven for 24 hours. The color uniformity of the polyethylene blocks was then observed under a 365 nm UV light source. The test results are shown in Table 1.

[0046] Table 1:

[0047] As can be seen from Table 1, Examples 2 and 3 show that the high-concentration fluorescent whitening polyethylene masterbatch prepared using the fluorescent whitening agent of the present invention has good color uniformity, indicating that the fluorescent whitening agent of the present invention has good compatibility with polyethylene.

[0048] Comparative Example 1 shows that the polyethylene masterbatch prepared using the existing coumarin-based commercial fluorescent brightener has poor color uniformity and poor compatibility between the brightener and polyethylene.

[0049] Comparative Example 2 shows that the polyethylene masterbatch prepared using the reported diazomethane coumarin derivative has poor color uniformity, which is due to the poor compatibility of the compound with polyethylene and the poor reactivity of the compound with polyethylene.

[0050] Comparative Examples 3 and 4 demonstrate that insufficient alkyl chain length in the brightener molecules of the present invention leads to a certain degree of decline in the color uniformity of the product. Comparative Example 5 demonstrates that further increasing the alkyl chain length in the brightener molecules of the present invention results in a polyethylene masterbatch having good color uniformity. Comparative Example 6 demonstrates that when the ortho-position of the diazo group in the brightener molecules of the present invention is replaced by a phenyl group, the color uniformity of the product does not change significantly.

[0051] Test 2: 1 g of polyethylene masterbatch prepared in Examples 2 to 4 and Comparative Example 1 to 6 was placed in a non-woven bag. The bag was then placed in a Soxhlet extractor and subjected to reflux extraction at 50°C for 24 hours using 200 mL of dichloromethane. 1 mL of the extract was measured using a pipette, and the UV-visible absorption spectrum of the brightener in the extract was measured using a UV-spectrophotometer. The brightener content in the extract was calculated, and the retention rate of the brightener in the polyethylene masterbatch was then calculated. A higher retention rate indicates a better migration resistance of the fluorescent whitening polyethylene masterbatch. The specific test results are shown in Table 2.

[0052] Table 2:

[0053] As can be seen from Table 2, Examples 2 to 4 show that the high-concentration fluorescent whitening polyethylene masterbatch prepared using the fluorescent whitening agent of the present invention has excellent migration resistance.

[0054] Comparative Example 1 shows that the polyethylene masterbatch prepared using the existing coumarin-based commercial fluorescent brightener has poor migration resistance. This is because the existing commercial brightener has no reactivity with polyethylene and poor compatibility.

[0055] Comparative Example 2 shows that the polyethylene masterbatch prepared using the reported diazomethane coumarin derivative has poor migration resistance, which may also be caused by poor compatibility and poor reactivity.

[0056] Comparative Examples 3 and 4 show that when the alkyl chain length in the whitening agent molecule of the present invention is insufficient, the migration resistance of the prepared polyethylene masterbatch is slightly reduced.

[0057] Comparative Example 5 shows that when the alkyl chain length in the whitening agent molecule of the present invention is too long, the migration resistance of the polyethylene masterbatch will decrease. This may be due to the increase in side reactions of the whitening agent itself caused by the long alkyl chain.

[0058] Comparative Example 6 shows that when the ortho position of the diazo group in the brightener molecule of the present invention is replaced by a phenyl group, the migration resistance of the product is significantly reduced. This is because the temperature for converting phenyl diazo ester to carbene is low. When the polyethylene has not yet been completely melted and uniform, the brightener has already undergone conversion, resulting in a worse reaction between the brightener and polyethylene.

[0059] It should be noted that the inventors found that the literature (Chem. Pharm. Bull. 1983, 31(9), 3014-3023) reported aminocoumarin derivatives containing diazo groups, which are similar in chemical structure to the aminocoumarin-type fluorescent whitening agent prepared by the present invention. Therefore, Comparative Example 2 was designed. The whitening agent prepared in Comparative Example 2 is significantly different from the substance of the present invention in terms of design concept, structural form, effect, etc. First, the substance appears as a reaction intermediate and is used to react with carboxylic acid to synthesize coumarin ester derivatives. This is different from the purpose of the present invention. Therefore, the combination form of coumarin and diazo groups in the substance is significantly different from that of the present invention. The diazo group in the substance exists as a diazomethane derivative, while the present invention is a 2-diazo diester type structure. That is, the temperature at which the diazo group is converted into carbene, that is, the thermal response temperature, is much lower than the 2-diazo diester type structure of the present invention. Therefore, even if the brightener prepared in Comparative Example 2 is used in the preparation of polyethylene masterbatches, its reactivity with polyethylene is poor due to its insufficient heat resistance and premature carbene formation. Furthermore, since it lacks long alkyl chains, its compatibility with polyethylene is inferior to that of the present invention, which also affects the reactivity of the prepared masterbatch. Furthermore, the test results in Tables 1 and 2 demonstrate poor compatibility with polyethylene, poor reactivity, and poor migration resistance. These differences are also confirmed by comparing Comparative Example 2 with Example 2.

[0060] In summary, the synthesis method provided by the present invention has cheap raw materials, simple synthesis operation, mild reaction conditions, no need to use harsh conditions such as anhydrous and oxygen-free conditions, and a high total yield. The synthesized aminocoumarin derivative has suitable fluorescent properties and can be used as a fluorescent whitening agent to treat polyethylene plastics to achieve a whitening effect. The special effect of the aminocoumarin derivative of the present invention in whitening applications is that the derivative first has good compatibility with polyethylene and secondly can react chemically with polyethylene, thereby binding to polyethylene in the form of a strong covalent bond, making it difficult for the fluorescent whitening agent to migrate.

[0061] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An aminocoumarin-type fluorescent whitening agent, characterized in that Its molecular structure is: ； Wherein, n is a positive integer not exceeding 10, and m is a positive integer not exceeding 20.

2. An aminocoumarin-type fluorescent whitening agent according to claim 1, characterized in that, Its molecular structure is: 。 3. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 1 or 2, wherein: The method comprises the following steps: Step 1: 7-amino-4-methylcoumarin, 1-bromoalkyl alcohol, sodium carbonate, and potassium iodide are added to an acetonitrile solution to react to obtain intermediate 1; Step 2: Add intermediate 1, 1-bromoalkane, sodium carbonate, and potassium iodide to an acetonitrile solution to react to obtain intermediate 2; Step 3: Intermediate 2, monomethyl malonate, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine are added to a dichloromethane solution to react to obtain intermediate 3; Step 4: Add intermediate 3, 4-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene to an acetonitrile solution to react and obtain an aminocoumarin-type fluorescent brightener; The molecular structural formula of the intermediate 1 is: ； The molecular structural formula of the intermediate 2 is: ； The molecular structural formula of the intermediate 3 is: ； Wherein, n is a positive integer not exceeding 10, and m is a positive integer not exceeding 20.

4. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 3, wherein: In the step 1, the molar ratio of 7-amino-4-methylcoumarin, 1-bromoalkyl alcohol, sodium carbonate, and potassium iodide is 1:1.5:4:2; The molar concentration of the 7-amino-4-methylcoumarin in acetonitrile is 0.1 to 1 mol / L; The reaction temperature of step 1 is 80° C. and the reaction time is 12 h.

5. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 3, wherein: In the step 2, the molar ratio of intermediate 1, 1-bromoalkane, sodium carbonate, and potassium iodide is 1:1.5:4:2; The concentration of the intermediate 1 in the acetonitrile solution is 0.1-1 mol / L; The reaction temperature of step 2 is 100° C. and the reaction time is 2 h.

6. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 3, wherein: In the step 3, the molar ratio of intermediate 2, monomethyl malonate, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1:1.5:1.5:0.15; The concentration of the intermediate 2 in the acetonitrile solution is 0.1-1 mol / L; The reaction temperature of step 3 is 20-30°C and the reaction time is 2 h.

7. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 3, wherein: In the step 4, the molar ratio of intermediate 3, 4-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene is 1:1.2:1.2; The concentration of the intermediate 3 in the acetonitrile solution is 0.1~1 mol / L; The temperature range of step 4 is 20-30°C; the reaction time is 2 h.

8. The method for preparing an aminocoumarin fluorescent whitening agent according to claim 3, wherein: The molecular structural formula of 1-bromoalkyl alcohol in the step 1 is: ； Wherein, n is a positive integer not exceeding 10; The molecular structural formula of 1-bromoalkane in the step 2 is: ； Wherein, m is a positive integer not exceeding 20.

9. The use of the aminocoumarin fluorescent whitening agent according to claim 1, wherein Applied to low density polyethylene masterbatch.

10. The method for preparing the aminocoumarin fluorescent whitening agent according to claim 9, wherein: The following steps are included: An aminocoumarin fluorescent brightener and polyethylene particles were weighed, melt-blended in an internal mixer, and then introduced into a twin-screw extruder. After melt-extrusion and granulation, a polyethylene masterbatch was obtained; the weight proportion of the aminocoumarin fluorescent brightener was 10% to 30%; the temperature during the melt blending was 130°C to 150°C; and the temperature during the melt extrusion was 180°C to 220°C.

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