Synthetic method of thermosensitive dye pink pigment

Abstract

The invention discloses a synthesis method of a thermosensitive dye pink pigment, and particularly relates to a synthesis method of 9-(ethyl (isoamyl) amino)-3 'H-spiro [benzo [A] xanthene-12, 1'-isobenzofuran]-3 '-ketone. Comprising the following steps: reacting N-(3-hydroxyphenyl) acetamide with borane tetrahydrofuran at 50 DEG C to prepare N-ethyl-3-methoxyaniline, and reacting the N-ethyl-3-methoxyaniline with isovaleraldehyde and acetic acid sodium borohydride to prepare N-ethyl-N-isopentyl-3-methoxyaniline; then refluxing with an HBr / acetic acid system at 100 DEG C to prepare 3-(ethyl (isoamyl) amino) phenol; then reacting with phthalic anhydride at the temperature of 100 DEG C to prepare 2-(4-(ethyl (isoamyl) amino)-2-hydroxybenzoyl) benzoic acid; and reacting the obtained product in methanesulfonic acid or concentrated sulfuric acid at room temperature, and performing post-treatment to obtain a target product. The method is low in reaction temperature, free of byproducts, low in raw material cost and easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and in particular relates to a method for synthesizing a thermosensitive dye, specifically a method for synthesizing 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one (i.e., the thermosensitive dye, peach pink). Background Technology

[0002] Thermosensitive materials are a class of special materials whose color changes with temperature. They are widely used in daily life and industrial production and are mainly classified into inorganic, organic, polymer, and liquid crystal types. Among them, organic thermosensitive compounds occupy an important position in the field of thermosensitive materials due to their high sensitivity and good color development performance. Common types include spirocyclic compounds, bisanthrone compounds, Schiff bases, fluoresceins, and triphenylmethane compounds.

[0003] 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one belongs to the fluorane class of organic thermosensitive dyes (hereinafter referred to as "thermosensitive dye pink pigment"). It possesses advantages such as high sensitivity, high color density, and a rich chromatographic spectrum, and has been widely used in carbonless copy paper, temperature testing materials, and analytical testing. With technological advancements, the application scenarios of thermosensitive materials have further expanded to food packaging, medical supplies, and smart textiles, leading to continued market demand growth. Simultaneously, increasingly stringent environmental regulations are driving the industry towards "environmentally friendly thermosensitive materials."

[0004] However, the current global market for high-end thermosensitive materials is dominated by foreign companies, which hold a leading position due to their strong R&D capabilities and mature industrialization experience. In the domestic market, the research and development of the thermosensitive dye pink pigment is still in its infancy, and industrial production has not yet been achieved. This has led to a long-term reliance on imports from Japan by related domestic industries, increasing application costs and posing supply chain risks.

[0005] In existing technologies, the synthesis of fluorane dyes generally employs Friedel-Crafts acylation, a process also applicable to the synthesis of the thermosensitive dye peach pink pigment. However, existing synthesis methods for its key intermediate, 3-(ethyl(isopentyl)amino)phenol, such as the method disclosed in patent CN101486658B, have significant drawbacks: the reaction temperature is as high as 160-200℃, requiring extremely high temperature and pressure resistance from the reaction equipment, which not only increases equipment investment costs but also raises safety risks during the reaction process. Furthermore, high-temperature reactions easily generate byproducts, reducing product yield and purity. Therefore, developing a synthesis process for the thermosensitive dye peach pink pigment that features mild reaction conditions, low equipment requirements, is green and economical, safe operation, and easy industrialization is crucial to addressing the technological gap in this material in China. Summary of the Invention

[0006] This invention provides a method for synthesizing the thermosensitive dye peach pink pigment. The purpose is to overcome the shortcomings of the existing technology in the synthesis process of thermosensitive dye peach pink pigment, which involves high temperature, high equipment requirements, and difficulty in industrialization. This invention provides a new synthesis method, fills the industrialization gap of this material in China, and reduces dependence on imports.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0008] The present invention discloses a method for synthesizing a thermosensitive dye, a peach-pink pigment, the chemical name of which is 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one;

[0009]

[0010] Its synthesis method is achieved through five consecutive reaction steps. The selection of raw materials, process parameters, and post-processing methods for each step have been optimized, as detailed below:

[0011] Raw materials and reagents:

[0012] The raw materials used in this invention include N-(3-hydroxyphenyl)acetamide, boranetetrahydrofuran solution (1M), tetrahydrofuran (THF), methanol, N-ethyl-3-methoxyaniline, 1,2-dichloroethane (DCE), isopentaldehyde, sodium borohydride acetate, acetic acid, 36% HBr aqueous solution, potassium bromide, 6N sodium hydroxide aqueous solution, 3-(ethyl(isopentyl)amino)phenol, phthalic anhydride, 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid, 4-naphthol, methanesulfonic acid, concentrated sulfuric acid, petroleum ether, and ethyl acetate; the equipment used includes a three-necked flask, a mechanical stirrer, a constant pressure dropping funnel, and a vacuum concentration device.

[0013] Synthesis steps:

[0014]

[0015] Step 1: Preparation of N-ethyl-3-methoxyaniline. Take a 10L three-necked flask and assemble it with a mechanical stirrer; dissolve 100g of N-(3-hydroxyphenyl)acetamide in 500~1000mL of tetrahydrofuran (THF) to form a homogeneous solution; place the three-necked flask in an ice bath and purge it with nitrogen for protection, and add 2L of 1M boranetetrahydrofuran solution (the molar ratio of N-(3-hydroxyphenyl)acetamide to boranetetrahydrofuran is 1:20) dropwise through a constant pressure dropping funnel at a rate of 20mL / min.

[0016] After the addition is complete, remove the ice bath and place the reaction system at room temperature (25°C) and stir for 2 hours. Then, heat the reaction system to 50°C and continue stirring overnight (about 12-16 hours). After the reaction is complete, stop heating and wait for the reaction solution to cool to room temperature. Place the three-necked flask in the ice bath again and add 300 mL of methanol dropwise through a constant pressure dropping funnel at a rate of 10 mL / min until no bubbles are generated (quenching is complete).

[0017] The quenched reaction solution was transferred to a vacuum concentration apparatus to remove the solvent by vacuum concentration, yielding 82g of colorless oily product N-ethyl-3-methoxyaniline, with a yield of 90%.

[0018] Step 2: Preparation of N-ethyl-N-isopentyl-3-methoxyaniline Take a 2L three-necked flask and assemble it with a mechanical stirrer; dissolve 82g of N-ethyl-3-methoxyaniline in 800mL of 1,2-dichloroethane (DCE) to form a homogeneous solution; place the three-necked flask in an ice bath, add 46g of isopentaldehyde, start stirring and continue stirring for 30 minutes.

[0019] Subsequently, 228g of sodium borohydride acetate was added to the reaction system in batches, with 50g added every half hour (the molar ratio of N-ethyl-3-methoxyaniline, isovaleraldehyde, and sodium borohydride acetate was 1:1:2); after the addition was complete, stirring was continued for 1 hour until the reactants reacted completely (monitored by thin-layer chromatography or LCMS).

[0020] After the reaction was completed, the three-necked flask was placed in an ice bath, and 200 mL of H2O was added to the system for quenching. The reaction solution was then extracted with DCE (200 mL × 3 times), and the organic phases were combined. The organic phase was dried with anhydrous sodium sulfate and then transferred to a vacuum concentration apparatus to remove the solvent by vacuum concentration, yielding 110 g of the oily product N-ethyl-N-isopentyl-3-methoxyaniline, with a yield of 92%.

[0021] Step 3: Preparation of 3-(ethyl(isopentyl)amino)phenol Take a 2L three-necked flask and assemble a mechanical stirrer; dissolve 100g of N-ethyl-N-isopentyl-3-methoxyaniline in a mixture of 200mL of acetic acid and 400mL of 36% HBr aqueous solution, add 27g of potassium bromide (0.5eq.), and start stirring to completely dissolve the solid.

[0022] Wrap the three-necked flask with tin foil (to shield it from light and prevent the formation of byproducts by light exposure), purge with nitrogen for protection, heat the reaction system to 100°C, and reflux for 16 hours. After the reaction is complete, stop heating and allow the reaction solution to cool to room temperature. Place the three-necked flask in an ice bath and slowly add 6N sodium hydroxide aqueous solution dropwise to adjust the pH of the reaction solution to 11.

[0023] The pH-adjusted reaction solution was extracted with DCE (200 mL × 3 times), and the organic phases were combined. The organic phases were dried with anhydrous sodium sulfate and then transferred to a vacuum concentration apparatus to remove the solvent by vacuum concentration, yielding 82 g of reddish-brown oily product 3-(ethyl(isopentyl)amino)phenol, with a yield of 88%.

[0024] Step 4: Preparation of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid. Take a 1L three-necked flask and assemble it with a mechanical stirrer. Dissolve 80g of 3-(ethyl(isopentyl)amino)phenol and 57g of phthalic anhydride (molar ratio 1:1) in 300mL of acetic acid and start stirring to completely dissolve the solids.

[0025] The reaction system was heated to 100°C and stirred overnight (approximately 12-16 hours). After the reaction was completed, heating was stopped, and the reaction solution was transferred to a vacuum concentration apparatus to remove some of the acetic acid (approximately 1 / 3 of the volume). Subsequently, 100 mL of water was added to the concentrate, and the mixture was extracted with DCE (100 mL × 3 times), and the organic phases were combined.

[0026] After drying the organic phase with anhydrous sodium sulfate, it was transferred to a vacuum concentration apparatus to remove the solvent by vacuum concentration, yielding 120g of the red oily product 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid, with a yield of 88%.

[0027] Step 5: Preparation of the thermosensitive dye peach pink pigment. Take a 1L three-necked flask and assemble a mechanical stirrer; dissolve 100g of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid and 50g of 4-naphthol (molar ratio 1:1) in 500mL of methanesulfonic acid, start stirring, and stir at room temperature (25℃) for 1h.

[0028] After the reaction was completed, the reaction solution was slowly poured into 1L of water and stirred continuously until the solid precipitated. The red solid was collected by filtration and slurryed with a mixture of 300mL of petroleum ether and ethyl acetate (volume ratio 5:1). After filtration, 97g of white solid product (i.e., the thermosensitive dye peach pink pigment) was obtained, with a yield of 75%.

[0029] Alternatively, replace the methanesulfonic acid in Step 5 with concentrated sulfuric acid: Take a 1L three-necked flask, dissolve 50g of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid and 25g of 4-naphthol (molar ratio 1:1) in 250mL of concentrated sulfuric acid, and stir at 25℃ for 1h; slowly pour the reaction solution into 500mL of water, extract with DCE (200mL×3 times), combine the organic phases and concentrate under reduced pressure; add 150mL of methanol to the concentrate, stir at -20℃ until a solid precipitates, filter to obtain 39g of white solid product, yield 60%.

[0030] Product applications:

[0031] The thermosensitive dye pink pigment synthesized in this invention needs to be used in combination with other materials (such as resin, filler, stabilizer, etc.). It is mainly used in the textile field (such as temperature-sensitive fabric), automotive field (such as temperature indicator stickers), art field (such as anti-counterfeiting ink), and ceramic field (such as temperature-sensitive glaze). It can realize functions such as indicating temperature changes, anti-counterfeiting identification, and hidden information display.

[0032] The present invention has the following advantages over the prior art:

[0033] (1) Mild reaction conditions reduce equipment requirements: Step 1 reduces the reaction temperature from 160~200℃ in the existing technology to 50℃, eliminating the need for high temperature and high pressure resistant equipment. This not only reduces equipment investment costs but also avoids the safety risks of high temperature reactions and improves operational safety.

[0034] (2) High reaction selectivity and no by-products: Step 2 achieves a "clean" reaction system with no by-products by optimizing the raw material molar ratio (1:1:2) and the feeding method (adding sodium borohydride acetate in batches). The product yield (92%) and purity are better than those of the existing process.

[0035] (3) Low raw material cost and easy to industrialize: The raw materials used in this invention (such as N-(3-hydroxyphenyl)acetamide, isovaleraldehyde, sodium borohydride acetate, etc.) are all conventional chemical raw materials that are readily available in the market, and the procurement cost is low; the process parameters of each step are stable (such as reaction temperature, time, raw material ratio), the operation process is simple, and it can be directly scaled up to the scale of industrial production.

[0036] (4) Filling the domestic technological gap: This invention realizes the domestic synthesis of the thermosensitive dye pink pigment, breaks the foreign technology monopoly, solves the problem of long-term reliance on imports in China, reduces the application cost of related industries, and ensures the security of the supply chain.

[0037] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The liquid chromatogram of N-ethyl-3-methoxyaniline as shown in Formula 2 of this invention;

[0040] Figure 2 The 1H NMR spectrum of N-ethyl-3-methoxyaniline as shown in Formula 2 of this invention;

[0041] Figure 3 The liquid chromatogram of N-ethyl-N-isopentyl-3-methoxyaniline as shown in Formula 3 of this invention;

[0042] Figure 4 The 1H NMR spectrum of N-ethyl-N-isopentyl-3-methoxyaniline as shown in Formula 3 of this invention;

[0043] Figure 5 The liquid chromatogram of 3-(ethyl(isopentyl)amino)phenol as shown in Formula 4 of this invention;

[0044] Figure 6 The 1H NMR spectrum of 3-(ethyl(isopentyl)amino)phenol as shown in Formula 4 of this invention;

[0045] Figure 7 The liquid chromatogram of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid as shown in Formula 5 of this invention;

[0046] Figure 8 The 1H NMR spectrum of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid as shown in Formula 5 of this invention;

[0047] Figure 9 The liquid chromatogram of 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one as shown in Formula 6 of this invention;

[0048] Figure 10 The 1H NMR spectrum of 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one, as shown in Formula 6 of this invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention discloses a method for synthesizing a thermosensitive dye, a peach-pink pigment, the chemical name of which is 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one; its structure is shown below:

[0051]

[0052] Its synthesis method is achieved through five consecutive reaction steps. The selection of raw materials, process parameters, and post-processing methods for each step have been optimized, as detailed below:

[0053] Raw materials and reagents:

[0054] The raw materials used in this invention include N-(3-hydroxyphenyl)acetamide, boranetetrahydrofuran solution (1M), tetrahydrofuran (THF), methanol, N-ethyl-3-methoxyaniline, 1,2-dichloroethane (DCE), isopentaldehyde, sodium borohydride acetate, acetic acid, 36% HBr aqueous solution, potassium bromide, 6N sodium hydroxide aqueous solution, 3-(ethyl(isopentyl)amino)phenol, phthalic anhydride, 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid, 4-naphthol, methanesulfonic acid, concentrated sulfuric acid, petroleum ether, and ethyl acetate; the equipment used includes a three-necked flask, a mechanical stirrer, a constant pressure dropping funnel, and a vacuum concentration device.

[0055] Example 1:

[0056]

[0057] The synthesis steps are as follows:

[0058] Step 1: Preparation of N-ethyl-3-methoxyaniline. Take a 10L three-necked flask and add mechanical stirring. Dissolve 100g of N-(3-hydroxyphenyl)acetamide in 1000mL of THF. Under ice bath and nitrogen protection, add 2L of 1M borate tetrahydrofuran solution (molar ratio 1:20) dropwise at 20mL / min. After the addition is complete, stir at room temperature for 2h, and then stir at 50℃ overnight. After the reaction solution is cooled, quench it with 300mL of methanol dropwise at 10mL / min in an ice bath. Concentrate under reduced pressure to obtain 82g of colorless oily product, yield 90%.

[0059] like Figure 1 The image shown is a liquid chromatogram of N-ethyl-3-methoxyaniline of Formula 2 of this invention; as shown... Figure 2 The image shown is the 1H NMR spectrum of N-ethyl-3-methoxyaniline according to Formula 2 of this invention.

[0060] Characterization data:

[0061] LCMS: m / z152.0[m+H]+;1H NMR(400MHz,DMSO-d6)δ6.99 (t, J=8.4Hz, 1H),6.23–6.12(m,3H),3.69 (s,3H),3.03(d, J=7.1Hz,2H),1.18(t, J=7.1Hz,3H).

[0062] Step 2: Preparation of N-ethyl-N-isopentyl-3-methoxyaniline. Take a 2L three-necked flask, dissolve 82g of N-ethyl-3-methoxyaniline in 800mL of DCE, add 46g of isopentaldehyde in an ice bath and stir for 30 minutes; add 228g of sodium borohydride acetate in portions (50g every half hour), and react for 1 hour; quench with 200mL of H2O in an ice bath, extract with DCE (200mL×3), dry the organic phase and concentrate under reduced pressure to obtain 110g of oily product, yield 92%.

[0063] like Figure 3 The image shown is a liquid chromatogram of N-ethyl-N-isopentyl-3-methoxyaniline of Formula 3; as shown... Figure 4 The image shown is the 1H NMR spectrum of N-ethyl-N-isopentyl-3-methoxyaniline of Formula 3 of this invention.

[0064] Characterization data:

[0065] LCMS: m / z222.0[m+H]+;1H NMR(400MHz,DMSO-d6)δ7.05(t, J=8.1Hz, 1H),6.25(dd, J=8.4,2.3Hz,1H),6.20–6.14(m,2H),3.71(s,3H),3.31(q, J=7.0Hz,2H),3.26–3.21(m,2H),1.65–1.56(m,1H),1.47–1.39(m,2H), 1.10(t, J=7.0Hz,3H),0.96(s,3H),0.94(s,3H).

[0066] Step 3: Preparation of 3-(ethyl(isopentyl)amino)phenol. Take a 2L three-necked flask, dissolve 100g of N-ethyl-N-isopentyl-3-methoxyaniline in 200mL of acetic acid and 400mL of 36% HBr aqueous solution, add 27g of potassium bromide; reflux at 100℃ for 16h under nitrogen protection with tin foil shielding; adjust the pH to 11 with 6N sodium hydroxide in an ice bath, extract with DCE (200mL×3), dry the organic phase and concentrate under reduced pressure to obtain 82g of reddish-brown oily product, yield 88%.

[0067] like Figure 5 The image shows a liquid chromatogram of 3-(ethyl(isopentyl)amino)phenol as shown in Formula 4 of this invention; as... Figure 6 The image shown is the 1H NMR spectrum of 3-(ethyl(isopentyl)amino)phenol as shown in Formula 4 of this invention.

[0068] Characterization data:

[0069] LCMS: m / z208.0[m+H]+;1H NMR(400MHz,DMSO-d6)δ6.76 (t, J=8.1Hz, 1H),6.03(t, J=2.3Hz,1H),5.99–5.90 (m,1H),5.90–5.83 (m,1H),3.20(t, J=7.0Hz,2H),3.18–3.10(m,2H),1.55(m,1H),1.43–1.33 (m,2H),1.03(t, J=7.0Hz,3H),0.92(s,3H),0.90(s,3H).

[0070] Step 4: Preparation of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid. Take a 1L three-necked flask, dissolve 80g of 3-(ethyl(isopentyl)amino)phenol and 57g of phthalic anhydride in 300mL of acetic acid, and stir overnight at 100℃; concentrate part of the acetic acid under reduced pressure, add water and extract with DCE (100mL×3), dry the organic phase and concentrate under reduced pressure to obtain 120g of red oily product, yield 88%.

[0071] like Figure 7 The image shows the liquid chromatogram of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid as shown in Formula 5 of this invention; Figure 8 The image shown is the 1H NMR spectrum of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid as shown in Formula 5 of this invention. Characterization data: LCMS: m / z 356.0[m+H]+;1H NMR(400 MHz, DMSO-d6)δ12.57 (s,1H),7.98 (dd,J= 7.9,1.3 Hz, 1H),7.73-7.69 (m,1H),7.65-7.61(m,1H),7.40(dd, J=7.5,1.3Hz,1H),6.82 (d, J=9.2Hz,1H),6.18(dd, J=9.2,2.5Hz,1H),6.06 (d, J=2.4Hz,1H),3.35-3.31(m,4H),1.60(m,1H),1.43(m,2H),1.11(t, J=7.0 Hz,3H),0.94(d, J = 6.6 Hz, 6 Hz.

[0072] Step 5: Preparation of the thermosensitive dye peach pink pigment. Take a 1L three-necked flask, dissolve 100g of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid and 50g of 4-naphthol in 500mL of methanesulfonic acid, and stir at 25℃ for 1h; pour the reaction solution into 1L of water, filter to obtain a red solid; slurry with 300mL (petroleum ether: ethyl acetate = 5:1) to obtain 97g of white product, yield 75%.

[0073] like Figure 9 The image shown is a liquid chromatogram of 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one, as shown in Formula 6 of this invention; Figure 10 The image shown is the 1H NMR spectrum of 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one, as shown in Formula 6 of this invention.

[0074] Characterization data:

[0075] LCMS: m / z 464.0 [m+H]+; 1H NMR (400 MHz, DMSO-d6)δ8.19–8.13 (m,2H),7.99(d, J=7.7 Hz,1H),7.79–7.73(m,2H),7.59(d, J=9.0 Hz,1H), 7.39 (q, J=7.7 Hz,2H),7.29–7.21(m,3H), 6.97(d, J=8.7Hz,1H),6.55–6.42(m,3H),3.30(d, J=5.6Hz,2H),1.63 (dt, J=13.2,6.6 Hz,1H),1.44(q, J =7.3 Hz,2H),1.11(t, J=7.0Hz,3H),0.96(s,3H),0.94(s,3H).

[0076] Example 2:

[0077] Step 1: The preparation of N-ethyl-3-methoxyaniline is the same as Step 1 in Example 1, yielding 82g of colorless oily product with a yield of 90%.

[0078] Step 2: Preparation of N-ethyl-N-isopentyl-3-methoxyaniline. Take a 2L three-necked flask, dissolve 20g of N-ethyl-3-methoxyaniline in 200mL of DCE, add 16g of isovaleraldehyde and 1.3g of triethylamine in an ice bath and stir for 30 minutes; add 56g of sodium borohydride acetate in portions (20g every half hour), and react for 1 hour; quench with 100mL of H2O in an ice bath, extract with DCE (100mL×3), dry the organic phase and concentrate under reduced pressure to obtain 26g of oily product, yield 90%.

[0079] Step 3: The preparation of 3-(ethyl(isopentyl)amino)phenol is the same as in Step 3 of Example 1, yielding 82g of reddish-brown oily product, with a yield of 88%.

[0080] Step 4: The preparation of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid is the same as Step 4 of Example 1, yielding 120g of red oily product with a yield of 88%.

[0081] Step 5: The preparation of the thermosensitive dye pink pigment is the same as Step 5 of Example 1, yielding 97g of white product with a yield of 75%.

[0082] Example 3:

[0083] Step 1: The preparation of N-ethyl-3-methoxyaniline is the same as Step 1 in Example 1, yielding 82g of colorless oily product with a yield of 90%.

[0084] Step 2: The preparation of N-ethyl-N-isopentyl-3-methoxyaniline is the same as Step 2 of Example 1, yielding 110g of oily product with a yield of 92%.

[0085] Step 3: The preparation of 3-(ethyl(isopentyl)amino)phenol is the same as Step 3 in Example 1, yielding 82g of reddish-brown oily product, with a yield of 88%.

[0086] Step 4: The preparation of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid is the same as Step 4 of Example 1, yielding 120g of red oily product, with a yield of 88%.

[0087] Step 5: Preparation of the thermosensitive dye peach pink pigment. Take a 1L three-necked flask, dissolve 50g of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid and 25g of 4-naphthol in 250mL of concentrated sulfuric acid, and stir at 25℃ for 1h; pour the reaction solution into 500mL of water, and extract with DCE (200mL×3); concentrate the organic phase under reduced pressure, add 150mL of methanol, and stir at -20℃ to precipitate the solid; filter to obtain 39g of white product, yield 60%.

[0088] Step 1 of this invention reduces the reaction temperature from 160-200℃ in existing technologies to 50℃, eliminating the need for high-temperature and high-pressure resistant equipment. This not only reduces equipment investment costs but also avoids the safety risks of high-temperature reactions, improving operational safety. The mild reaction conditions lower equipment requirements. Step 2 of this invention optimizes the raw material molar ratio (1:1:2) and the feeding method (adding sodium borohydride acetate in batches) to achieve a "clean" reaction system with no by-products. The product yield (92%) and purity are superior to existing processes, with high reaction selectivity and no by-products. The raw materials used in this invention (such as N-(3-hydroxyphenyl)acetamide, isovaleraldehyde, sodium borohydride acetate, etc.) are all readily available conventional chemical raw materials with low procurement costs. The process parameters of each step are stable (such as reaction temperature, time, and raw material ratio), the operation process is simple, and it can be directly scaled up to industrial production scale. The raw material cost is low and it is easy to industrialize. This invention realizes the domestic synthesis of the thermosensitive dye peach pink pigment, breaking the foreign technology monopoly, solving the problem of long-term reliance on imports in China, reducing application costs in related industries, and ensuring supply chain security.

[0089] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for synthesizing a thermosensitive dye, pink pigment, characterized in that, The pink pigment is 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one; The synthesis method includes the following steps: Step 1: Dissolve N-(3-hydroxyphenyl)acetamide, the compound shown in Formula 1, in tetrahydrofuran (THF). Add 1M boranetetrahydrofuran solution dropwise at 20 mL / min under ice bath and nitrogen protection. After the addition is complete, stir at room temperature for 2 h, then heat to 50 °C and stir overnight. After cooling the reaction solution, quench with methanol dropwise in an ice bath and concentrate under reduced pressure to obtain the compound shown in Formula 2: N-ethyl-3-methoxyaniline. The molar ratio of N-(3-hydroxyphenyl)acetamide to boranetetrahydrofuran in the boranetetrahydrofuran solution is 1:

20. Step 2: Dissolve the compound shown in Formula 2, N-ethyl-3-methoxyaniline, in 1,2-dichloroethane (DCE). Add isopentaldehyde to the solution in an ice bath and stir for 30 minutes. Then add sodium borohydride acetate in batches and react for 1 hour. Quench the reaction in an ice bath with H2O, extract with DCE, and concentrate under reduced pressure to obtain the compound shown in Formula 3, N-ethyl-N-isopentyl-3-methoxyaniline. The molar ratio of N-ethyl-3-methoxyaniline, isopentaldehyde, and sodium borohydride acetate in sodium borohydride acetate is 1:1:

2. Step 3: Dissolve the compound shown in Formula 3, N-ethyl-N-isopentyl-3-methoxyaniline, in a mixture of acetic acid and 36% HBr aqueous solution, add 0.5 eq. potassium bromide, reflux at 100℃ for 16 h under nitrogen protection, during which the reaction solution must be protected from light; adjust the pH to 11 with 6N sodium hydroxide aqueous solution in an ice bath, extract with DCE, and concentrate under reduced pressure to obtain the compound shown in Formula 4, 3-(ethyl(isopentyl)amino)phenol; Step 4: Dissolve the compound shown in Formula 4, 3-(ethyl(isopentyl)amino)phenol, and phthalic anhydride in acetic acid at a molar ratio of 1:1, and stir overnight at 100°C; concentrate part of the acetic acid under reduced pressure, add water and extract with DCE, and concentrate under reduced pressure to obtain the compound shown in Formula 5, 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid; Step 5: Take the compound shown in Formula 5, 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid and 4-naphthol, and dissolve them in methanesulfonic acid at a molar ratio of 1:

1. Stir at 25°C for 1 hour. Pour the reaction solution into water and filter to obtain a red solid. Slurry the solid with a mixture of petroleum ether and ethyl acetate to obtain the target pink pigment shown in Formula 6, namely 9-(ethyl(isopentyl)amino)-3'H-spiro[benzo[A]oxanthracene-12,1'-isobenzofuran]-3'-one.

2. The synthesis method according to claim 1, characterized in that, In Step 1, the ratio of N-(3-hydroxyphenyl)acetamide to tetrahydrofuran is 100g:500~1000mL.

3. The method for synthesizing a thermosensitive dye, peach pink pigment, according to claim 1, is characterized in that, In Step 2, sodium borohydride acetate is added in batches every half hour.

4. The method for synthesizing a thermosensitive dye, pink pigment, according to claim 1, characterized in that, In Step 3, the method of shading off the light is to wrap the reaction vessel with tin foil.

5. The method for synthesizing a thermosensitive dye, peach pink pigment, according to claim 1, characterized in that, In Step 5, the volume ratio of petroleum ether to ethyl acetate is 5:1, and the amount used is 300 mL, calculated based on 100 g of 2-(4-(ethyl(isopentyl)amino)-2-hydroxybenzoyl)benzoic acid.

6. The method for synthesizing a thermosensitive dye, peach pink pigment, according to claim 1, characterized in that, In Step 5, methanesulfonic acid can be replaced with concentrated sulfuric acid. After the reaction solution is poured into water, it must first be extracted by DCE, then concentrated under reduced pressure and methanol is added. The solid is then precipitated by stirring at -20°C.

7. A method for synthesizing a thermosensitive dye, peach pink pigment, according to any one of claims 1-6, characterized in that, The thermosensitive dye pink pigment synthesized by this method can be used in textiles, automobiles, artworks, or ceramics to achieve indication, anti-counterfeiting, or concealment functions.

Images