A preparation method of 2-(2-naphthyl)-5-chloro-benzoxazole

Abstract

The present invention provides a preparation method of 2-(2-naphthyl)-5-chloro-benzoxazole, characterized in that the method includes: 2-naphthoic acid and p-chloro-o-aminophenol are subjected to condensation reaction in a solvent under the action of a catalyst, and the solvent is: 1-methylnaphthalene, and the catalyst is boric acid. 2-(2-naphthyl)-5-chloro-benzoxazole produced by the method of the present invention, the yield of 2-(2-naphthyl)-5-chloro-benzoxazole can reach more than 95%, and industrialized large-scale production can be achieved. Therefore, the method provided by the present invention can meet the market demand for inexpensive fluorescent whitening agents.

Description

Technical Field

[0001] The invention relates to a method for preparing 2-(2-naphthyl)-5-chloro-benzoxazole. Background Art

[0002] The fluorescent brightener KCB, namely 1,4-dibenzoxazolylnaphthalene, currently used in the market has a high price of 500,000 yuan / ton due to the high price of its intermediate 1,4-naphthalene dicarboxylic acid, which is as high as 300,000 yuan / ton. Customers feel that they cannot afford it.

[0003] Therefore, how to develop a high-quality and low-cost upgraded product to meet customer needs? After nearly a year of research and development, the applicant prepared 2-(2-naphthyl)-5-chloro-benzoxazole, which is priced at 300,000 yuan / ton. The fluorescence quantum yield of this product reaches more than 95%, which is higher than KCB's 89%, and the whitening effect is better, which meets the customer's requirements for high quality and low price. Summary of the invention

[0004] Based on the problem of relatively high prices of fluorescent whitening agents in the current market, the present invention develops a method for preparing 2-(2-naphthyl)-5-chloro-benzoxazole as a fluorescent whitening agent. The 2-(2-naphthyl)-5-chloro-benzoxazole prepared by the method has high yield, low preparation process cost and can be industrialized for mass production.

[0005] The invention provides a method for preparing 2-(2-naphthyl)-5-chloro-benzoxazole as a fluorescent whitening agent. The method uses 2-naphthoic acid as a starting raw material, and adds 4-chloro-o-aminophenol in a certain ratio, uses 1-methylnaphthalene as a solvent, and uses boric acid as a catalyst, and undergoes a condensation reaction to obtain a crude 2-(2-naphthyl)-5-chloro-benzoxazole product. The crude 2-(2-naphthyl)-5-chloro-benzoxazole product is then recrystallized through xylene and decolorized with a decolorizing agent to obtain a finished 2-(2-naphthyl)-5-chloro-benzoxazole product.

[0006] Chemical reaction principle:

[0007]

[0008] The yield of 2-(2-naphthyl)-5-chloro-benzoxazole produced by the method of the present invention can reach more than 95%, and industrialized large-scale production can be achieved. Therefore, the method provided by the present invention can meet the market demand for high-quality and low-cost fluorescent whitening agents. DETAILED DESCRIPTION

[0009] The present invention provides a method for preparing 2-(2-naphthyl)-5-chloro-benzooxazole, which is characterized in that the method comprises: allowing 2-naphthoic acid and p-chloro-o-aminophenol to undergo a condensation reaction in a solvent under the action of a catalyst, wherein the solvent is 1-methylnaphthalene and the catalyst is boric acid.

[0010] The chemical reaction principle is:

[0011]

[0012] Among them, the present invention has no particular limitation on the amount of the 2-naphthoic acid and the p-chloro-o-aminophenol used, as long as a condensation reaction can occur. However, from the perspective of more efficient reaction, the molar ratio of the 2-naphthoic acid to the p-chloro-o-aminophenol is preferably 1:(1-1.1).

[0013] The present invention has no particular limitation on the amounts of the solvent and the catalyst. The amount of the solvent is preferably 9-11 times the mass of 2-naphthoic acid, and the amount of the catalyst is preferably 0.2-0.3 times the mass of 2-naphthoic acid.

[0014] In the present invention, the condensation reaction is preferably carried out under a nitrogen atmosphere, and the ventilation volume is preferably 2-4 cubic meters per hour.

[0015] In order to accelerate the condensation reaction, the condensation reaction preferably includes: first reacting at 120-140° C. for 3-5 hours, and then reacting at 180-200° C. for 4-5 hours.

[0016] The method further comprises: post-processing the product liquid obtained by the condensation reaction, wherein the post-processing comprises the following steps:

[0017] (1) distilling off the 1-methylnaphthalene solvent in the product solution to obtain a crude 2-(2-naphthyl)-5-chloro-benzoxazole product;

[0018] (2) The crude 2-(2-naphthyl)-5-chloro-benzoxazole is washed with methanol and water, and then purified with xylene.

[0019] The post-treatment further comprises: decolorizing with a decolorizing agent during the refining to obtain a finished 2-(2-naphthyl)-5-chloro-benzoxazole product.

[0020] The decolorizing agent includes: activated carbon and activated clay.

[0021] The present invention is described in more detail below by way of examples. In the following examples, the raw materials are all conventional raw materials in the art and are purchased commercially.

[0022] Example

[0023] Embodiment 1:

[0024] Into a clean 2000L stainless steel reactor (with nitrogen pipe, condenser, thermometer, water separator, etc.), add 1400L of 1-methylnaphthalene, 137.6kg of 2-naphthoic acid, 114.8kg of p-chloro-o-aminophenol, and 28kg of boric acid. At this time, the molar ratio of 2-naphthoic acid to p-chloro-o-aminophenol is 1:1, the amount of 1-methylnaphthalene is 10 times the mass of 2-naphthoic acid, and the amount of boric acid is 0.2 times the mass of 2-naphthoic acid.

[0025] After the addition is completed, nitrogen is introduced at a uniform rate of 3 cubic meters per hour, stirring is started, and the temperature is slowly raised to 120°C with heat transfer oil, and the reaction is kept at 120°C for 3 hours, then the temperature is raised to 180°C, and the reaction is kept at 180°C for 4 hours. A total of about 28.8 kg of water is distilled during the reaction.

[0026] After the reaction is completed, the 1-methylnaphthalene solvent is distilled out under negative pressure by a water pump until no distillation is left. The distilled 1-methylnaphthalene is reused for the next batch of reactions. Cool to 80°C, turn off the nitrogen, dropwise add 1000L of methanol, heat and reflux for 1 hour, cool to room temperature, filter to obtain a crude product and mother liquor, and the crude product needs to be washed with methanol and water, and then refined; the methanol recovered from the mother liquor can be reused, and the kettle residue is concentrated to distill out 1-methylnaphthalene in several batches and then put down while hot, and it becomes solid waste after cooling. Among them, the method of washing the crude product with methanol and water and refining is as follows:

[0027] Washing of crude product with methanol: Add the above crude product and 1000L methanol into a 2000L glass-lined reactor, stir and reflux for 1 hour, cool to room temperature, filter the crude product washed with methanol, and the methanol recovered from the mother liquor can be reused.

[0028] Washing of crude product: Add alcohol to wash crude product in a 2000L glass-lined reactor, and add 1000L water, stir and heat to 60°C, wash for 1 hour, spin dry while hot, and obtain 270kg of crude product.

[0029] Crude product refining: add half of the crude product (135 kg), activated carbon (17 kg), activated clay (28 kg), and xylene (2600 kg) into a clean 5000L glass-lined reactor (with thermometer, condenser, water separator, etc.). After adding, stir, heat and reflux for 2 hours, distill water while reflux, stop heating, filter while hot into another 5000L glass-lined reactor, cool the mother liquor to room temperature and spin dry, and directly pump the mother liquor into the refining reactor for the next batch of refining; rinse with about 70 kg of methanol on a centrifuge, spin dry and dry, and obtain 106.3 kg of white needle-shaped crystalline finished product 2-(2-naphthyl)-5-chloro-benzoxazole, with a melting range of 166-167°C and a yield of 95%.

[0030] After dozens of batches of methanol mother liquor used for elution are concentrated, a small amount of crude product is filtered out and refined as the crude product, and the methanol is recovered from the mother liquor and reused; after dozens of batches of xylene mother liquor are used, xylene is recovered and used as new xylene, and a small amount of finished product is washed with methanol and then dried and refined as the crude product, and the methanol is recovered.

[0031] Embodiment 2:

[0032] Into a clean 2000L stainless steel reactor (with nitrogen pipe, condenser, thermometer, water separator, etc.), add 1-methylnaphthalene 1240L, 2-naphthoic acid 137.6kg, p-chloro-o-aminophenol 117kg, boric acid 28kg. At this time, the molar ratio of 2-naphthoic acid to p-chloro-o-aminophenol is 1:1.02, the amount of 1-methylnaphthalene is 9 times the mass of 2-naphthoic acid, and the amount of boric acid is 0.2 times the mass of 2-naphthoic acid.

[0033] After the addition is completed, nitrogen is introduced at a uniform rate of 2 cubic meters per hour, stirring is started, and the temperature is slowly raised to 130°C with heat transfer oil, and the reaction is kept at 130°C for 4 hours. The temperature is then raised to 190°C and the reaction is kept at 190°C for 4 hours. A total of about 28.8 kg of water is distilled during the reaction.

[0034] After the reaction is completed, the 1-methylnaphthalene solvent is distilled out under negative pressure by a water pump until no distillation is left. The distilled 1-methylnaphthalene is reused for the next batch of reactions. Cool to 80°C, turn off the nitrogen, dropwise add 1000L of methanol, heat and reflux for 1 hour, cool to room temperature, filter to obtain a crude product and mother liquor, and the crude product needs to be washed with methanol and water, and then refined; the methanol recovered from the mother liquor can be reused, and the kettle residue is concentrated to distill out 1-methylnaphthalene in several batches and then put down while hot, and it becomes solid waste after cooling. Among them, the method of washing the crude product with methanol and water and refining is as follows:

[0035] Washing of crude product with methanol: Add the above crude product and 1000L methanol into a 2000L glass-lined reactor, stir and reflux for 1 hour, cool to room temperature, filter the crude product washed with methanol, and the methanol recovered from the mother liquor can be reused.

[0036] Washing of crude product: Add alcohol to wash crude product in a 2000L glass-lined reactor, and add 1000L water, stir and heat to 65°C, wash for 1 hour, spin dry while hot, and obtain 276kg of crude product.

[0037] Crude product refining: add half of the dry crude product (138 kg), activated carbon (17 kg), activated clay (28 kg), and xylene (2600 kg) into a clean 5000L glass-lined reactor (with thermometer, condenser, water separator, etc.). After adding, stir, heat and reflux for 2 hours, distill water while reflux, stop heating, filter while hot into another 5000L glass-lined reactor, cool the mother liquor to room temperature and spin dry, and directly pump the mother liquor into the refining reactor for the next batch of refining; rinse with about 70 kg of methanol on a centrifuge, spin dry and dry, and obtain 107.3 kg of white needle-shaped crystalline finished product 2-(2-naphthyl)-5-chloro-benzoxazole, with a melting range of 166-167°C and a yield of 96%.

[0038] After dozens of batches of methanol mother liquor used for elution are concentrated, a small amount of crude product is filtered out and refined as the crude product, and the methanol is recovered from the mother liquor and reused; after dozens of batches of xylene mother liquor are used, xylene is recovered and used as new xylene, and a small amount of finished product is washed with methanol and then dried and refined as the crude product, and the methanol is recovered.

[0039] Embodiment 3:

[0040] Into a clean 2000L stainless steel reactor (with nitrogen pipe, condenser, thermometer, water separator, etc.), add 1500L of 1-methylnaphthalene, 137.6kg of 2-naphthoic acid, 124.8kg of p-chloro-o-aminophenol, and 40kg of boric acid. At this time, the molar ratio of 2-naphthoic acid to p-chloro-o-aminophenol is 1:1.09, the amount of 1-methylnaphthalene is 11 times the mass of 2-naphthoic acid, and the amount of boric acid is 0.3 times the mass of 2-naphthoic acid.

[0041] After the addition is completed, nitrogen is introduced at a uniform rate of 3 cubic meters per hour, stirring is started, and the temperature is slowly raised to 120°C with heat transfer oil, and the reaction is kept at 140°C for 5 hours. The temperature is then raised to 200°C and the reaction is kept at 200°C for 5 hours. A total of about 28.8 kg of water is distilled during the reaction.

[0042] After the reaction is completed, the 1-methylnaphthalene solvent is distilled out under negative pressure by a water pump until no distillation is left. The distilled 1-methylnaphthalene is reused for the next batch of reactions. Cool to 80°C, turn off the nitrogen, dropwise add 1000L of methanol, heat and reflux for 1 hour, cool to room temperature, filter to obtain a crude product and mother liquor, and the crude product needs to be washed with methanol and water, and then refined; the methanol recovered from the mother liquor can be reused, and the kettle residue is concentrated to distill out 1-methylnaphthalene in several batches and then put down while hot, and it becomes solid waste after cooling. Among them, the method of washing the crude product with methanol and water and refining is as follows:

[0043] Washing of crude product with methanol: Add the above crude product and 1000L methanol into a 2000L glass-lined reactor, stir and reflux for 1 hour, cool to room temperature, filter the crude product washed with methanol, and the methanol recovered from the mother liquor can be reused.

[0044] Washing of crude product: Add alcohol to wash crude product in a 2000L glass-lined reactor, and add 1000L water, stir and heat to 70°C, wash for 1 hour, spin dry while hot, and obtain 282kg of crude product.

[0045] Crude product refining: add half of the dry crude product (141 kg), activated carbon (17 kg), activated clay (28 kg), and xylene (2600 kg) into a clean 5000L glass-lined reactor (with thermometer, condenser, water separator, etc.). After adding, stir, heat and reflux for 2 hours, distill water while reflux, stop heating, filter while hot into another 5000L glass-lined reactor, cool the mother liquor to room temperature and spin dry, and directly pump the mother liquor into the refining reactor for the next batch of refining; rinse with about 70 kg of methanol on a centrifuge, spin dry and dry, and obtain 108 kg of white needle-shaped crystalline finished product 2-(2-naphthyl)-5-chloro-benzoxazole, with a melting range of 166-167°C and a yield of 96.6%.

[0046] After dozens of batches of methanol mother liquor used for elution are concentrated, a small amount of crude product is filtered out and refined as the crude product, and the methanol is recovered from the mother liquor and reused; after dozens of batches of xylene mother liquor are used, xylene is recovered and used as new xylene, and a small amount of finished product is washed with methanol and then dried and refined as the crude product, and the methanol is recovered.

[0047] The yield of 2-(2-naphthyl)-5-chloro-benzoxazole in the above example is shown in Table 1 below:

[0048] Table 1

[0049] Example 1 Example 2 Example 3 Yield of 2-(2-naphthyl)-5-chloro-benzoxazole 95％ 96％ 96.6％

[0050] From the data of Examples 1-3 above, it can be seen that the yield of 2-(2-naphthyl)-5-chloro-benzoxazole produced by the method of the present invention can reach more than 95%. Therefore, the method provided by the present invention can meet the market demand for high-quality and low-cost fluorescent whitening agents.

Claims

1. A method for preparing 2-(2-naphthyl)-5-chloro-benzoxazole, characterized in that: The method comprises: making 2-naphthoic acid and p-chloro-o-aminophenol undergo condensation reaction in a solvent under the action of a catalyst, wherein the solvent is 1-methylnaphthalene and the catalyst is boric acid. The chemical reaction principle is: ； The prepared 2-(2-naphthyl)-5-chloro-benzoxazole is used as a fluorescent brightener; The molar ratio of the 2-naphthoic acid to the p-chloro-o-aminophenol is 1:(1-1.1); the amount of the solvent is 9-11 times the mass of the 2-naphthoic acid, and the amount of the catalyst is 0.2-0.3 times the mass of the 2-naphthoic acid; First react at 120-140℃ for 3-5 hours, then react at 180-200℃ for 4-5 hours; The method further comprises: post-processing the product liquid obtained by the condensation reaction, wherein the post-processing comprises the following steps: (1) distilling off the 1-methylnaphthalene solvent in the product solution to obtain a crude 2-(2-naphthyl)-5-chloro-benzoxazole product; (2) The crude 2-(2-naphthyl)-5-chloro-benzoxazole was washed with methanol and water, and then purified with xylene.

2. The method according to claim 1, wherein: The condensation reaction was carried out under a nitrogen atmosphere.

3. The method according to claim 2, wherein: The nitrogen gas introduction rate is 2-4 cubic meters per hour.

4. The method according to claim 1, wherein: The post-treatment further comprises: decolorizing with a decolorizing agent during the refining to obtain a finished 2-(2-naphthyl)-5-chloro-benzoxazole product.

5. The method according to claim 4, wherein: The decolorizing agent includes: activated carbon and activated clay.

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