A novel fluorane compound and its preparation method

Abstract

The present invention relates to a novel fluoran compound and a preparation method thereof, belonging to the technical field of thermosensitive dyes. The compound is intended to address at least one of the following problems with existing pink dyes: a high color development temperature, a dull color after development, low color density, a complex synthesis method, and low purity. The present invention synthesizes a novel fluoran compound having a conjugated structure with a parent core. The compound has a relatively low color development temperature, developing color at temperatures of approximately 70°C, enhancing the color development ability of the fluoran core, resulting in a pink color that is more vivid and has a higher color density.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosensitive dyes, and in particular to a novel fluorane compound and a preparation method thereof. Background Art

[0002] Fluoran compounds are widely used in thermal and pressure-sensitive printing due to the unique properties of their lactone ring structure. The color-developing raw material, the lactone ring, is in a closed loop, typically producing a hidden or non-coloring color. Once the lactone ring is broken, it comes into contact with a developer, revealing a different color within the visible light range, enabling the printing of text and images in various colors.

[0003] The diversity of colors of fluorane thermosensitive materials mainly comes from the different substituents on the fluorane parent core, as shown in formula (III):

[0004]

[0005] The substituents R1 to R8 are completely different or partially identical, and the lactone ring opens upon contact with a color developer to exhibit different colors. Existing pink thermosensitive materials have problems such as a high color development temperature, a dull color, low color density, complex synthesis methods, and low purity. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a novel fluoran compound and a preparation method thereof, which can be used to solve at least one of the problems of the prior art pink dyes, such as high color development temperature, dull color after development, low color density, complex synthesis method, and low purity.

[0007] In a first aspect, the present invention provides a novel fluoran compound, wherein the compound has a structural formula as shown in Formula (I) or Formula (II), and the specific structural formula is as follows:

[0008]

[0009] In a second aspect, the present invention provides a method for preparing a novel fluoran compound, comprising the following steps:

[0010] (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling to obtain a reaction solution;

[0011] (2) adding the reaction solution to water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate;

[0012] (3) adding a crystallizing agent to dissolve the concentrate, cooling and crystallizing, filtering, and drying to obtain the novel fluorane compound.

[0013] Furthermore, in step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2.

[0014] Furthermore, in step (1), the acid is sulfuric acid, methanesulfonic acid, or nitric acid.

[0015] Furthermore, in step (1), the reaction temperature is 60-160° C., and the reaction time is 0.5-6 h.

[0016] Furthermore, in step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

[0017] Furthermore, in step (2), the alkaline water includes but is not limited to sodium hydroxide and potassium hydroxide strong inorganic alkaline solutions.

[0018] Furthermore, in step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

[0019] Furthermore, in step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20.

[0020] In a third aspect, the present invention provides a thermosensitive dye comprising the fluoran compound.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The present invention synthesizes a novel fluorane compound having a conjugated structure with a fluorescent parent nucleus. The compound has a relatively low color development temperature and can develop color at a temperature of about 70°C, thereby enhancing the color development ability of the fluorane parent nucleus. The color is pink, and the color after development is more vivid and the color density value is higher. The color density value at 160°C is 0.96-1.0.

[0023] (2) The preparation method of the novel fluorane compound of the present invention is simple, the production cost is low, and the purity of the product can reach above 97.1%, which is suitable for large-scale industrial production.

[0024] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the subsequent description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. DETAILED DESCRIPTION

[0025] A specific embodiment of the present invention discloses a novel fluoran compound, the structural formula of the compound is shown in Formula (I) or Formula (II), and the specific structural formula is as follows:

[0026]

[0027] Compared with the prior art, the present invention discloses a novel fluoran compound having a conjugated structure with a fluorescent mother nucleus. The present invention synthesizes a novel fluoran compound having a conjugated structure with a fluorescent mother nucleus. The compound has a relatively low color development temperature and can develop color at a temperature of about 70°C, thereby enhancing the color development ability of the fluoran mother nucleus, developing a pink color, and having a brighter color and a higher color density after development.

[0028] In the structure of formula (I) of the present invention, the two bridging carbons C13 and C14 form a large conjugated structure of a fluorane compound, and in the structure of formula (II), the two bridging carbons C12 and C13 form a large conjugated structure of a fluorane compound.

[0029] The spectral absorption and color development properties of the dye are determined by the combined effects of factors such as the molecular structure with a fluorane structure as the parent core, the length and symmetry of the conjugated system, the polar groups within the molecule, the coplanarity of the molecule, and steric hindrance. The presence of the diethylamine group in the parent core structure has the above-mentioned properties, thereby affecting the color development temperature and effect of the dye.

[0030] The presence of a conjugated structure and an increase in the number of conjugated double bonds have a significant impact on the color of the substance. By affecting the mobility of the electron cloud and reducing the energy level difference between molecules, the conjugated structure enables the substance to absorb and transmit more light energy, thereby affecting the color performance of the substance. At the same time, the color of the conjugated system is also affected by certain functional groups and substituents. The introduction of certain substituents can change the electron cloud density distribution and spatial configuration in the conjugated system, thereby affecting the light absorption capacity of the system. Therefore, different substituents can lead to different color changes, and the presence of a methoxynaphthalene ring increases the number of conjugated double bonds of the parent nucleus. At the same time, the electron donation effect of the methoxy group makes the electron cloud density on the conjugated structure higher, thereby making the color of the dye relatively more vivid. The color development temperature of the compound prepared by the present invention is 69.3-70.3°C, and the color density value at 160°C is 0.96-1.0.

[0031] Another specific embodiment of the present invention discloses a method for preparing the novel fluoran compound, comprising the following steps:

[0032] (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling to obtain a reaction solution;

[0033] (2) adding the reaction solution to water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate;

[0034] (3) adding a crystallizing agent to dissolve the concentrate, cooling and crystallizing, filtering, and drying to obtain the novel fluorane compound.

[0035] The chemical equation of the above reaction in the present invention is as follows:

[0036]

[0037] In a specific embodiment, in step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2. For example, the molar ratio is 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2.

[0038] In a specific embodiment, further, in step (1), the acid is sulfuric acid, methanesulfonic acid, or nitric acid.

[0039] In a specific embodiment, in step (1), the reaction temperature is 60-160°C, and the reaction time is 0.5-6h. For example, the reaction temperature is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or 160°C, and the reaction time is 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h.

[0040] In a specific embodiment, in step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

[0041] In a specific embodiment, in step (2), the alkaline water includes but is not limited to strong inorganic alkaline solutions such as sodium hydroxide and potassium hydroxide. Exemplarily, the mass fraction of sodium hydroxide in the sodium hydroxide solution is 10%.

[0042] In a preferred embodiment, in step (2), the layers are specifically divided into an aqueous layer and an organic solvent layer. The aqueous layer needs to be extracted with an organic solvent at least once until the color of the organic solvent layer becomes lighter. The organic solvent layers are combined each time and extracted with clean water until the pH value of the aqueous layer is 7 to 8.

[0043] In a specific embodiment, in step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

[0044] In a specific embodiment, in step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20. For example, the mass ratio is 1:5, 1:7, 1:9, 1:11, 1:13, 1:15, 1:17, 1:19, or 1:20.

[0045] In a specific embodiment, in step (3), the temperature for crystallization is -15 to 25°C. For example, the temperature is -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, or 25°C.

[0046] The purity of the compound prepared by the method of the invention is greater than 97.1%, and the yield is greater than 25.4%.

[0047] In a third aspect, the present invention provides a thermosensitive dye comprising the fluoran compound.

[0048] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0049] Example 1

[0050] The present embodiment provides a method for preparing a fluoran compound represented by formula (I), as follows:

[0051] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 80° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution.

[0052] (2) Add 60 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, and extract the aqueous layer twice with dichloroethane, 200 ml each time, until the color of the dichloroethane layer becomes lighter, combine the dichloroethane, extract the dichloroethane with clean water, measure the pH value of the aqueous layer to be 7-8, and concentrate the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0053] (3) 30 g of the concentrate was added to 150 g of methanol, and the mixture was heated and refluxed for 30 min to completely dissolve the solid. The mixture was then crystallized at -5°C for 3 h, filtered, and dried to obtain 20.74 g of a light pink solid with a yield of 71.9% and a content of 98.52%.

[0054] The fluorane compounds obtained in this example were subjected to nuclear magnetic resonance testing, and the results were as follows:

[0055] Mp:200.1-201.3℃;1HNMR(400MHz,DMSO)δ8.02(dd,1H),7.72–7.66(m,1H),7.67–7.62(m,1H),7.59–7.52(m,2H),7.50(d d,1H),7.44–7.34(m,2H),7.22(d,1H),6.90(dd,1H),6.67(dd,1H),6.31(d,1H),3.92(s,2H),3.52(q,4H),1.16(t,6H).

[0056] After ultraviolet scanning testing, the compound prepared in this example has an absorption wavelength of 518 nm, which is in the pink absorption band.

[0057] Example 2

[0058] The present embodiment provides a method for preparing a fluoran compound represented by formula (I), as follows:

[0059] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 11.2 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 85° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution.

[0060] (2) The reaction solution was added to 60 ml of a 10% sodium hydroxide aqueous solution and stirred for 10 min. 200 ml of dichloroethane was then added and stirred for 10 min. The solution was transferred to a separatory funnel and allowed to stand for stratification. The aqueous layer was extracted twice with dichloroethane, 200 ml each time, until the color of the dichloroethane layer became lighter. The dichloroethanes were combined and extracted with clean water. The pH value of the aqueous layer was measured to be 7-8. The dichloroethane layer was concentrated to dryness under reduced pressure at 45-70° C. to obtain a concentrate.

[0061] (3) 30 g of the concentrate was added to 360 g of methanol, and the temperature was raised to reflux for 30 min to completely dissolve the solid. The solid was then crystallized at -5°C for 3 h, filtered, and dried to obtain 16.24 g of a light pink solid with a yield of 56.35% and a content of 99.34%.

[0062] The nuclear magnetic resonance and ultraviolet scanning tests of the fluorane compounds obtained in this example were basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0063] Example 3

[0064] The present embodiment provides a method for preparing a fluoran compound represented by formula (I), as follows:

[0065] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 90° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution.

[0066] (2) Add 60 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, and extract the aqueous layer twice with dichloroethane, 200 ml each time, until the color of the dichloroethane layer becomes lighter, combine the dichloroethane, extract the dichloroethane with clean water, measure the pH value of the aqueous layer to be 7-8, and concentrate the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0067] (3) 30 g of the concentrate was added to 450 g of toluene, and the mixture was heated and refluxed for 30 min to completely dissolve the solid. The mixture was then crystallized at -5°C for 3 h, filtered, and dried to obtain 13.64 g of a light pink solid with a yield of 47.3% and a content of 99.43%.

[0068] The nuclear magnetic resonance and ultraviolet scanning tests of the fluorane compounds obtained in this example were basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0069] Example 4

[0070] The present embodiment provides a method for preparing a fluoran compound represented by formula (I), as follows:

[0071] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 100° C. for 6 h. After the reaction was completed, the temperature was lowered to obtain a reaction solution;

[0072] (2) Add 60 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, and extract the aqueous layer twice with dichloroethane, 200 ml each time, until the color of the dichloroethane layer becomes lighter, combine the dichloroethane, extract the dichloroethane with clean water, measure the pH value of the aqueous layer to be 7-8, and concentrate the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0073] (3) 30 g of the concentrate was added to 600 g of toluene, and the mixture was heated and refluxed for 30 min to completely dissolve the solid. The mixture was then crystallized at -5 °C for 3 h, filtered, and dried to obtain 10.58 g of a light pink solid with a yield of 36.71% and a content of 99.85%.

[0074] The nuclear magnetic resonance and ultraviolet scanning tests of the fluorane compounds obtained in this example were basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0075] Example 5

[0076] The preparation method of the fluorane compound represented by formula (II) in this embodiment is as follows:

[0077] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 12.8 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid aqueous solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 80° C. for 5 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0078] (2) adding 100 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of ethyl acetate, stirring for 10 min, transferring the solution to a separatory funnel, allowing the layers to stand, and extracting the aqueous layer twice with ethyl acetate (200 ml / time) until the color of the ethyl acetate layer becomes lighter, combining the ethyl acetate, extracting the ethyl acetate with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the ethyl acetate layer under reduced pressure at 35-70° C. to dryness to obtain a concentrate;

[0079] (3) 30 g of the concentrate was added to 150 g of methanol, and the temperature was raised to reflux for 30 min to completely dissolve the solid. The solid was then crystallized at -5°C for 3 h, filtered, and dried to obtain 13.65 g of a light pink solid with a yield of 47.36% and a content of 97.1%.

[0080] The fluorane compounds obtained in this example were subjected to nuclear magnetic resonance testing, and the results were as follows:

[0081] Mp:198.3-199.2℃; 1H-NMR(400MHz,DMSO)δ8.02(dd,1H),7.77(s,1H),7.72–7.66(m,1H),7.64(ddd,1H),7.56(td,1 H),7.52–7.44(m,3H),7.22(d,1H),7.00(dd,1H),6.67(dd,1H),6.31(d,1H),3.95(s,2H),3.52(q,4H),1.16(t,6H).

[0082] After ultraviolet scanning testing, the compound prepared in this example has an absorption wavelength of 526 nm, which is in the pink absorption band.

[0083] Example 6

[0084] The preparation method of the fluorane compound represented by formula (II) in this embodiment is as follows:

[0085] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 12.8 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution was added, and the mixture was reacted at 85° C. for 6 h. After the reaction was complete, the mixture was cooled to obtain a reaction solution.

[0086] (2) Add 100 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, and extract the aqueous layer twice with dichloroethane, 200 ml each time, until the color of the dichloroethane layer becomes lighter, combine the dichloroethane, extract the dichloroethane with clean water, measure the pH value of the aqueous layer to be 7-8, and concentrate the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0087] (3) 30 g of the concentrate was added to 450 g of toluene, and the mixture was heated and refluxed for 30 min to completely dissolve the solid. The mixture was then crystallized at -15°C for 4 h, filtered, and dried to obtain 10.28 g of a light pink solid with a yield of 35.32% and a content of 97.8%.

[0088] The nuclear magnetic resonance and ultraviolet scanning tests of the fluorane compounds obtained in this example were basically consistent with those in Example 5, and are not listed one by one due to limited space.

[0089] Example 7

[0090] The preparation method of the fluorane compound represented by formula (II) in this embodiment is as follows:

[0091] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 15.5 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked flask, 180 g of a 75% sulfuric acid solution was added, and the mixture was reacted at 90° C. for 8 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution.

[0092] (2) Add 100 ml of a 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, and extract the aqueous layer twice with dichloromethane, 200 ml / time, until the color of the dichloromethane layer becomes lighter, combine the dichloromethane, extract the dichloromethane with clean water, measure the pH value of the aqueous layer to be 7-8, and concentrate the dichloromethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0093] (3) 30 g of the concentrate was added to 600 g of toluene, and the mixture was heated and refluxed for 30 min to completely dissolve the solid. The mixture was then crystallized at -5°C for 5 h, filtered, and dried to obtain 7.32 g of a light pink solid with a yield of 25.4% and a content of 99.1%.

[0094] The nuclear magnetic resonance and ultraviolet scanning tests of the fluorane compounds obtained in this example were basically consistent with those in Example 5, and are not listed one by one due to limited space.

[0095] Comparative Example 1

[0096] The structural formula of the fluorane compound of this comparative example is as follows:

[0097]

[0098] Test Example 1

[0099] The compounds prepared in Examples 1-7 and Comparative Example 1 were respectively prepared into coating solutions;

[0100] (1) Preparing a first mixed solution: 10.5 g of PVA-205MB, 160 g of ultrapure water, and 70 g of the compounds prepared in Examples 1-7 and Comparative Example 1 were mixed to prepare a mixed solution with a mass fraction of 29.1%, and then ground in a wet grinder until the solid particles in the mixed solution had a particle size of 0.8 μm to obtain a first mixed solution;

[0101] (2) preparing a second mixed solution: 12.0 g of PVA-205MB, 168.0 g of ultrapure water, 60.0 g of F-108 (D-8, 4-isopropoxy-4'-hydroxydiphenyl sulfone, color developer), and 0.3 g of SN-522 coating agent were mixed to form a mixed solution with a mass fraction of 24.9%, and then ground in a wet grinder until the solid particles in the mixed solution had a particle size of 0.8 μm to obtain a second mixed solution;

[0102] (3) Preparation of auxiliary agent emulsion: PVA-205MB 0.3g, ultrapure water 12.7g, kaolin 12.0g were mixed to a mixture with a mass fraction of 48.0%, and stirred at high speed for later use;

[0103] (4) Coating liquid: 24.0 g of the first mixed liquid, 22.0 g of the second mixed liquid and 25.0 g of the auxiliary agent emulsion were mixed, and mechanically stirred for 30 minutes to obtain a coating liquid.

[0104] Use a coating machine to coat the prepared base paper surface with a coating of 4.5g / m 2 The top coating liquid is applied in a coating amount of , and after drying, a top coating layer is formed to obtain thermal paper.

[0105] The thermal papers obtained in Examples 1-7 and Comparative Example 1 were subjected to thermal color development tests at 70-160° C., and the colors after development were all pink. The color development temperature and color density values ​​at 160° C. are shown in Table 1.

[0106] Table 1

[0107]

[0108] As can be seen from the table above, the compound in Comparative Example 1 has a higher color development temperature and lower color density than the compound of the present invention. This is because the compound in Comparative Example 1 contains a dibutylamino group and a nitrogen heterocyclic ring on the parent nucleus, resulting in a higher color development temperature and lower color density compared to the compound of the present invention. This is because the nitrogen heterocyclic ring and the benzene ring are connected by a sigma bond, which is rotatable, causing the plane of the nitrogen heterocyclic ring to be different from the plane of the benzene ring, resulting in a lower color density. Furthermore, the dibutylamino group has more carbon atoms than the diethylamino group, which increases the melting point of the compound, thereby affecting the color development temperature of the compound.

[0109] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A fluoran compound, characterized in that The structural formula of the compound is shown in formula (I) or formula (II), and the specific structural formula is as follows: Formula (I); Formula (II).

2. A method for preparing a fluoran compound, characterized in that: The steps include: (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling the reaction mixture to obtain a reaction solution; (2) adding the reaction solution to water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate; (3) adding a crystallizing agent to dissolve the concentrate, cooling the concentrate to crystallize, filtering the concentrate, and drying the concentrate to obtain the fluorane compound.

3. The method for preparing a fluoran compound according to claim 2, wherein: In step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2.

4. The method for preparing a fluoran compound according to claim 2, wherein: In step (1), the acid is sulfuric acid, methanesulfonic acid, or nitric acid.

5. The method for preparing a fluoran compound according to claim 2, wherein: In step (1), the reaction temperature is 60-160°C and the reaction time is 0.5-6h.

6. The method for preparing a fluoran compound according to any one of claims 2 to 5, wherein: In step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

7. The method for preparing a fluoran compound according to any one of claims 2 to 5, wherein: In step (2), the alkaline water is selected from a strong inorganic alkaline solution of sodium hydroxide or potassium hydroxide.

8. The method for preparing a fluoran compound according to claim 2, wherein: In step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

9. The method for preparing a fluoran compound according to claim 2, wherein: In step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20.

10. A thermosensitive dye, characterized in that: The invention comprises the compound according to claim 1 or the compound prepared by the method according to any one of claims 2 to 9.

Images