High-light-fastness red dye intermediate and preparation method thereof

Abstract

The invention provides a high-light-fastness red dye intermediate and a preparation method thereof. The preparation method comprises the following steps: step 1, mixing aniline and 2, 6-dichloro-4-methyl-3-cyanopyridine in an inorganic solvent to obtain a mixed product; step 2, carrying out condensation reaction on aniline and 2, 6-dichloro-4-methyl-3-cyanopyridine in the mixed product to obtain a condensation reaction product; and step 3, azeotropic the condensation reaction product, and removing and recovering an azeotrope of aniline and water to obtain a product containing the red dye intermediate. According to the preparation method of the high-light-fastness red dye intermediate, the reaction is carried out in the inorganic solvent, compared with an organic solvent, wastewater is easier to treat, and the cost is lower; after the reaction is finished, redundant aniline is recovered through azeotropy with the inorganic solvent, and the recovered aniline can be reused, so that the comprehensive utilization rate of aniline is improved, and meanwhile, the treatment difficulty of wastewater is reduced.

Description

Technical Field

[0001] The invention relates to a high-solarization red dye intermediate and a preparation method thereof, and belongs to the field of dye intermediate synthesis. Background Art

[0002] Dyes prepared with pyridone derivatives as azo components have the advantage of strong light fastness. Traditional pyridone azo dyes generally have a color distribution range mainly concentrated in yellow and orange due to structural disadvantages. By replacing the hydroxyl and ketone carbonyl groups in pyridone, darker red high-sun fastness dyes can be obtained. One of the coupling components is prepared by replacing the 2nd and 6th positions of pyridine with aniline and diglycolamine.

[0003] The product of the first step condensation of the coupling components is a mixture of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine and 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine, which are monophenylamino substituents at the 2nd and 6th positions, hereinafter referred to as condensed nicotinonitrile. In the prior art, the preparation of condensed nicotinonitrile mainly includes the following methods:

[0004] (1) Aniline and 2,6-dichloro-4-methyl-3-cyanopyridine are heated to 90-100°C in an organic solvent such as dimethylformamide (DMF), and the generated hydrogen chloride is removed by an acid-binding agent such as sodium carbonate / baking soda to promote the reaction. The reaction is kept at the temperature until the reaction end point, and then diluted hydrochloric acid is added dropwise until the temperature is slightly acidic to precipitate a condensed nicotinonitrile.

[0005] (2) Aniline, sodium carbonate and 2,6-dichloro-4-methyl-3-cyanopyridine are added to water, and the temperature is raised to react to obtain a condensed nicotinonitrile. After the reaction is completed, the temperature is lowered to room temperature, and dilute hydrochloric acid is added dropwise to precipitate a solid product, a condensed nicotinonitrile.

[0006] In the above method, the feeding amount of aniline is excessive. After the reaction is completed, the excess aniline reacts with hydrochloric acid to generate aniline hydrochloride which is taken into the mother liquor. This process not only wastes aniline, but also consumes unnecessary hydrochloric acid, making the subsequent wastewater treatment process more difficult. Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In view of the technical problems existing in the prior art, the present invention first provides a method for preparing a high-sun red dye intermediate. The preparation method of the present invention improves the comprehensive utilization rate of aniline, reduces the difficulty of treating mother liquor wastewater, effectively reduces production costs, and has significant practicality, economic benefits and environmental benefits.

[0009] Furthermore, the present invention also provides a high-sun red dye intermediate. The high-sun red dye intermediate of the present invention is brown in color and has high purity and yield.

[0010] Solutions for solving problems

[0011] The present invention first provides a method for preparing a red dye intermediate, which comprises the following steps:

[0012] Step 1: mixing aniline and 2,6-dichloro-4-methyl-3-cyanopyridine in an inorganic solvent to obtain a mixed product;

[0013] Step 2: subjecting the aniline and 2,6-dichloro-4-methyl-3-cyanopyridine in the mixed product to a condensation reaction to obtain a condensation reaction product;

[0014] Step 3: subjecting the condensation reaction product to azeotropy, removing and recovering the azeotrope of aniline and water to obtain a product containing a red dye intermediate.

[0015] According to the preparation method of the present invention, wherein in the step 1, the molar ratio of aniline to 2,6-dichloro-4-methyl-3-cyanopyridine is 1.2 to 2.0:1; and / or,

[0016] The volume ratio of the inorganic solvent to aniline is 2.0-10.0:1.0.

[0017] According to the preparation method of the present invention, wherein in step 1, the inorganic solvent contains an acid binding agent, preferably, the acid binding agent comprises a metal inorganic salt or a metal oxide;

[0018] Preferably, the molar ratio of the acid binding agent to 2,6-dichloro-4-methyl-3-cyanopyridine is 0.5 to 1.0:1.

[0019] According to the preparation method of the present invention, wherein, in the step 2, the temperature of the condensation reaction is 85-105° C., and the time of the condensation reaction is 20-72 hours.

[0020] According to the preparation method of the present invention, wherein in the step 3, the condensation reaction product is azeotropically prepared by distillation; preferably, the distillation temperature is 105-140° C.;

[0021] Preferably, the distillation is terminated when no aniline drips out for more than 15 minutes to obtain a product containing a red dye intermediate.

[0022] According to the preparation method of the present invention, after step 3, a step of precipitating the red dye intermediate is further included; preferably, the red dye intermediate is precipitated by cooling.

[0023] According to the preparation method of the present invention, the precipitation temperature is 0-25° C.; and / or,

[0024] When the temperature drops below 60°C, the cooling rate is 5 to 10 min / °C.

[0025] According to the preparation method of the present invention, before the precipitation, the step of using an acidic substance to adjust the pH to below 7, preferably 4 to 7 is also included.

[0026] The present invention also provides a red dye intermediate, wherein the red dye intermediate is prepared by the preparation method of the present invention; preferably, the purity of the red dye intermediate is above 90%, preferably above 94%; the yield of the red dye intermediate is above 90%, preferably above 94%.

[0027] According to the red dye intermediate of the present invention, the red dye intermediate comprises 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine and 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine;

[0028] Preferably, based on the total mass of the red dye intermediate, the content of the 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine is 40-70%, and the content of the 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine is 30-60%.

[0029] Effects of the Invention

[0030] The preparation method of the high-sun red dye intermediate of the present invention carries out the reaction in an inorganic solvent, and compared with an organic solvent, wastewater is easier to treat and the cost is lower; after the reaction is completed, the excess aniline is recovered by azeotropic reaction with the inorganic solvent, and the recovered aniline can be reused, thereby improving the comprehensive utilization rate of the aniline and reducing the difficulty of treating the wastewater.

[0031] Furthermore, the high-sun-durability red dye intermediate of the present invention is brown in color and has high purity and yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention shows a process flow chart of the preparation of a high-sun red dye intermediate, condensed nicotinonitrile. DETAILED DESCRIPTION

[0033] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0034] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0035] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0036] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0037] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0038] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0039] The present invention first provides a method for preparing a red dye intermediate, which comprises the following steps:

[0040] Step 1: mixing aniline and 2,6-dichloro-4-methyl-3-cyanopyridine in an inorganic solvent to obtain a mixed product;

[0041] Step 2: subjecting the aniline in the mixed product and 2,6-dichloro-4-methyl-3-cyanopyridine to a condensation reaction to obtain a condensation reaction product;

[0042] Step 3: The condensation reaction product is subjected to azeotropy, and the azeotrope of aniline and water is removed and recovered to obtain a product containing a red dye intermediate.

[0043] The preparation method of the high-sun red dye intermediate of the present invention is to carry out the reaction in an inorganic solvent, and the wastewater is easier to handle and the cost is lower than that of an organic solvent; after the reaction, the excess aniline is recovered by azeotropy with the inorganic solvent, and the recovered aniline can be used, thereby improving the comprehensive utilization rate of aniline and reducing the difficulty of wastewater treatment. In addition, the red dye intermediate of the present invention can also be referred to as a condensed nicotinonitrile. Specifically, the inorganic solvent includes water.

[0044] In some specific embodiments, in step 1, the molar ratio of aniline to 2,6-dichloro-4-methyl-3-cyanopyridine is 1.2 to 2.0:1, for example, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, etc. When the molar ratio of aniline to 2,6-dichloro-4-methyl-3-cyanopyridine is 1.2 to 2.0:1, a condensation reaction can occur to prepare a red dye intermediate.

[0045] Furthermore, in the present invention, in order to better prepare the red dye intermediate, the volume ratio of the inorganic solvent to aniline is 2.0 to 10.0:1.0, for example: 3.0:1, 4.0:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, 9.0:1, etc.

[0046] In some specific embodiments, in step 1, the inorganic solvent contains an acid binding agent, preferably, the acid binding agent includes an inorganic metal salt and / or a metal oxide; preferably, the inorganic metal salt includes a carbonate and / or a bicarbonate, for example: sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, etc., and the metal oxide can be magnesium oxide, zinc oxide, etc.

[0047] The present invention can consume the hydrogen chloride generated during the reaction by using an acid binding agent, promote the forward reaction, and increase the reaction rate. Preferably, the molar ratio of the acid binding agent to 2,6-dichloro-4-methyl-3-cyanopyridine is 0.5 to 1.0:1, for example: 0.6:1, 0.7:1, 0.8:1, 0.9:1, etc.

[0048] In the present invention, the reaction formula of the condensation reaction is as follows:

[0049]

[0050] In some specific implementation schemes, in step 2, the temperature of the condensation reaction is 85-105°C, for example: 88°C, 90°C, 92°C, 95°C, 98°C, 100°C, 102°C, etc.; the time of the condensation reaction is 20-72h, for example: 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, etc. When the temperature of the condensation reaction is 85-105°C and the time of the condensation reaction is 20-72h, the condensation reaction can be effectively carried out. For the end of the reaction, the condensation reaction can be considered to be completed when the peak detected by high performance liquid chromatography of the raw material is less than 0.5%.

[0051] In some specific embodiments, in step 3, the condensation reaction product is azeotropically reacted by distillation. In fact, aniline and water have an azeotropic point. After the reaction is completed, the aniline is recovered by adding water and distilling to recover the aniline-water azeotrope. This not only reuses the recovered aniline, but also removes the aniline in the mother liquor boiling water, thereby reducing the difficulty of wastewater treatment. Further, the recovered aniline can be applied to subsequent synthesis.

[0052] Preferably, the distillation temperature is 105-140°C, for example, 108°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, etc. When the distillation temperature is 105-140°C, the azeotrope of aniline and water can be distilled out by azeotropy. Further, the distillation is terminated when no aniline drips out for more than 15 minutes to obtain a product containing a red dye intermediate.

[0053] In some specific embodiments, after step 3, a step of precipitating the red dye intermediate is further included; preferably, the red dye intermediate is precipitated by cooling. The precipitation and purification process of the red dye intermediate of the present invention does not require acid precipitation, which reduces the amount of raw materials and saves costs.

[0054] In some specific embodiments, the precipitation temperature is 0-25°C, for example: 2°C, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C, 20°C, 22°C, etc. The inventors of the present invention have found that when the temperature is reduced to 0-25°C, the red dye intermediate can be precipitated without the use of other additives.

[0055] The inventors of the present invention have found that as the temperature decreases, the slower the cooling rate, the more concentrated the particle size distribution of the red dye intermediate. In order to obtain a red dye intermediate with a suitable particle size, when the temperature drops below 60°C, the cooling rate is 5 to 10 min / °C, for example: 6 min / °C, 7 min / °C, 8 min / °C, 9 min / °C, etc.

[0056] In some specific embodiments, optionally, before precipitating the red dye intermediate, a step of adjusting the pH using an acidic substance is further included, preferably, the pH may be below 7, preferably 4 to 7, for example: 4.5, 5, 5.5, 6, 6.5, etc. By adjusting the pH value using an acidic substance, the solid of the precipitated red dye intermediate can be made more uniform.

[0057] Furthermore, the precipitated red dye intermediate is post-treated, and the post-treatment includes washing, drying, etc., so as to obtain a dry product of the red dye intermediate.

[0058] The present invention does not specifically limit the acidic substance, and it can be any acidic substance commonly used in the art, such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, etc. Preferably, the present invention can use dilute hydrochloric acid with a mass concentration of 1-10% to adjust the pH value.

[0059] The red dye intermediate of the invention can realize resource recycling, reduce production costs and reduce the difficulty of wastewater treatment.

[0060] <Second Aspect>

[0061] The second aspect of the present invention provides a red dye intermediate, which is prepared by the preparation method described in the first aspect of the present invention; preferably, the purity of the red dye intermediate is above 90%, preferably above 94%; the yield of the red dye intermediate is above 90%, preferably above 94%.

[0062] In some specific embodiments, the red dye intermediate includes 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine and 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine; preferably, based on the total mass of the red dye intermediate, the content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine is 40-70%, for example: 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, etc.; the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine is 30-60%, for example: 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, etc.;.

[0063] The high-sun-durability red dye intermediate of the invention is brown in color and has high purity and yield.

[0064] Example

[0065] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0066] Example 1

[0067] (1) Add 250 mL of water to a 500 mL three-necked flask, start stirring, and heat to 30°C. Add 37.1 g (0.35 mol) of sodium carbonate powder and stir until the sodium carbonate is completely dissolved. Pour 60.5 g (0.65 mol) of aniline, stir for 15 minutes, then pour 93.5 g (0.5 mol) of 2,6-dichloro-4-methyl-3-cyanopyridine, heat to 95°C, and keep warm for 72 hours to obtain a condensation reaction product. The content of 2,6-dichloro-4-methyl-3-cyanopyridine in the condensation reaction product was measured by high performance liquid chromatography to be 0.2980%, the content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine to be 47.8156%, and the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine to be 33.8365%.

[0068] (2) The temperature was raised to 115° C. and kept at this temperature for 45 minutes to recover the azeotrope of aniline and water by distillation. The distillation was terminated when no aniline dripped out for more than 15 minutes. The total weight of the obtained fraction was 85 g. After standing and stratification, 10.0 g of aniline was obtained. The comprehensive recovery rate was 71.33%.

[0069] (3) Cooling to 60°C at a rate of 5°C / min, and then cooling to 25°C at a rate of about 2.5°C / min, brown solid particles of condensed nicotinonitrile precipitate, vacuum filtration to obtain a crude condensed nicotinonitrile, washing with 60°C hot water until the washing liquid is neutral to obtain a wet condensed nicotinonitrile. Drying at 80°C for 12 hours to obtain a dry condensed nicotinonitrile. Using high performance liquid chromatography to measure the content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine in the dry condensed nicotinonitrile is 44.3345%, the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine is 52.0059%, the content of by-products is 1.6769%, and the comprehensive purity is 96.34%. The calculated yield is 92.95%.

[0070] (4) A total of 2250 g of mother liquor and washing liquid wastewater were recovered, and the aniline content was measured by high performance liquid chromatography to be 0.011 mg / L, which is lower than the industry wastewater discharge standard of 0.3 mg / L.

[0071] Example 2

[0072] (1) Add 400 mL of water into a 1000 mL three-necked flask, start stirring, and heat to 30°C. Add 74.2 g (0.7 mol) of sodium carbonate powder and stir until the sodium carbonate is completely dissolved. Pour 130.2 g (1.4 mol) of aniline, stir for 15 minutes, then pour 187.0 g (1.0 mol) of 2,6-dichloro-4-methyl-3-cyanopyridine, heat to 92°C, and keep warm for 64 hours to obtain a condensation reaction product. The content of the raw material 2,6-dichloro-4-methyl-3-cyanopyridine in the condensation reaction product was measured by high performance liquid chromatography to be 0.3721%, the content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine to be 29.4765%, and the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine to be 27.7545%.

[0073] (2) The temperature was raised to 115° C. and kept warm for 1 hour, and the azeotrope of aniline and water was recovered by distillation. The distillation was terminated when no aniline was dripped out for more than 15 minutes. The total weight of the obtained fraction was 200 g. After standing and stratification, 29.5 g of aniline was obtained. The comprehensive recovery rate was 73.75%.

[0074] (3) The temperature was lowered to 60°C at a rate of 5°C / min, and then lowered to 25°C at a rate of about 2.5°C / min. A brown solid particle, condensed nicotinonitrile, was precipitated. The crude condensed nicotinonitrile was filtered under reduced pressure to obtain a condensed nicotinonitrile. The crude condensed nicotinonitrile was washed with 60°C hot water until the washing liquid was neutral to obtain a wet condensed nicotinonitrile. The condensed nicotinonitrile was dried at 80°C for 12 hours to obtain a dry condensed nicotinonitrile. The content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine in the dry condensed nicotinonitrile was 61.2661% and the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine was 34.7353% by high performance liquid chromatography. The content of by-products was 2.9218%, and the comprehensive purity was 96.00%. The yield was calculated to be 94.70%.

[0075] (4) A total of 4000 g of mother liquor and washing liquid wastewater were recovered, and the aniline content was measured by high performance liquid chromatography to be 0.009 mg / L, which is lower than the industry wastewater discharge standard of 0.3 mg / L.

[0076] Example 3

[0077] (1) Add 200 mL of water to a 1000 mL three-necked flask, pour in 300 mL of the recovered aniline and water mixture, start stirring, and heat to 30°C. Add 74.2 g (0.7 mol) of sodium carbonate powder and stir until the sodium carbonate is completely dissolved. Pour in 93.0 g (about 1.0 mol) of aniline, stir for 15 minutes, then pour in 187.0 g (1.0 mol) of 2,6-dichloro-4-methyl-3-cyanopyridine, heat to 92°C, and keep warm for 60 hours to obtain a condensation reaction product. The condensation reaction product was measured by high performance liquid chromatography to obtain a 0.4365% content of the raw material 2,6-dichloro-4-methyl-3-cyanopyridine, a 37.5514% content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine, and a 36.7759% content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine.

[0078] (2) The temperature was raised to 115° C. and kept at this temperature for 1 hour, and the azeotrope of aniline and water was recovered by distillation. The distillation was terminated when no aniline was dripped out for more than 15 minutes. The total weight of the obtained fraction was 200 g. After standing and stratification, 32.0 g of aniline was obtained.

[0079] (3) Cooling to 60°C at a rate of 5°C / min, and then cooling to 25°C at a rate of about 2.5°C / min, adding 6% dilute hydrochloric acid to adjust the pH to 6.0, a brown solid powder-condensed nicotinonitrile is precipitated, and vacuum filtration is performed to obtain a crude condensed nicotinonitrile, and washing with 60°C hot water until the washing liquid is neutral to obtain a wet condensed nicotinonitrile. Drying at 80°C for 12 hours obtains a dry condensed nicotinonitrile. Using high performance liquid chromatography, the content of 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine in the dry condensed nicotinonitrile is 56.5173%, the content of 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine is 39.4300%, the content of by-products is 3.5470%, the comprehensive purity is 95.95%, and the yield is 95.10%.

[0080] (4) A total of 4000 g of mother liquor and washing liquid wastewater were recovered, and the aniline content was measured by high performance liquid chromatography to be 0.014 mg / L, which is lower than the industry wastewater discharge standard of 0.3 mg / L.

[0081] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0082] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a red dye intermediate, characterized in that: The following steps are involved: Step 1: mixing aniline and 2,6-dichloro-4-methyl-3-cyanopyridine in an inorganic solvent to obtain a mixed product; Step 2: subjecting the aniline and 2,6-dichloro-4-methyl-3-cyanopyridine in the mixed product to a condensation reaction to obtain a condensation reaction product; Step 3: subjecting the condensation reaction product to azeotropy, removing and recovering the azeotrope of aniline and water to obtain a product containing a red dye intermediate.

2. The preparation method according to claim 1, characterized in that: In the step 1, the molar ratio of aniline to 2,6-dichloro-4-methyl-3-cyanopyridine is 1.2 to 2.0:1; and / or, The volume ratio of the inorganic solvent to aniline is 2.0-10.0:1.

0.

3. The preparation method according to claim 1 or 2, characterized in that: In the step 1, the inorganic solvent contains an acid binding agent, and preferably, the acid binding agent comprises a metal inorganic salt or a metal oxide; Preferably, the molar ratio of the acid binding agent to 2,6-dichloro-4-methyl-3-cyanopyridine is 0.5 to 1.0:

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step 2, the temperature of the condensation reaction is 85 to 105° C., and the time of the condensation reaction is 20 to 72 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the step 3, the condensation reaction product is azeotropically reacted by distillation; preferably, the distillation temperature is 105-140° C.; Preferably, the distillation is terminated when no aniline drips out for more than 15 minutes to obtain a product containing a red dye intermediate.

6. The preparation method according to any one of claims 1 to 5, characterized in that: After step 3, the method further comprises the step of precipitating the red dye intermediate; preferably, the red dye intermediate is precipitated by cooling.

7. The preparation method according to claim 6, characterized in that: The precipitation temperature is 0 to 25° C.; and / or, When the temperature drops below 60°C, the cooling rate is 5 to 10 min / °C.

8. The preparation method according to claim 6 or 7, characterized in that: Before the precipitation, the method further comprises the step of using an acidic substance to adjust the pH to below 7, preferably 4 to 7.

9. A red dye intermediate, characterized in that: The red dye intermediate is prepared by the preparation method according to any one of claims 1 to 8; preferably, the purity of the red dye intermediate is above 90%, preferably above 94%; the yield of the red dye intermediate is above 90%, preferably above 94%.

10. The red dye intermediate according to claim 9, characterized in that The red dye intermediate includes 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine and 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine; Preferably, based on the total mass of the red dye intermediate, the content of the 2-phenylamino-6-chloro-4-methyl-3-cyanopyridine is 40-70%, and the content of the 6-phenylamino-2-chloro-4-methyl-3-cyanopyridine is 30-60%.

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