Method for preparing p-acetoxy-benzoic acid

A technology of acetoxybenzoic acid and p-hydroxybenzoic acid, which is applied in the field of preparation of p-acetoxybenzoic acid, can solve the problems of many by-products, large amount of acetic anhydride used, difficult product refining, etc., and achieve less by-products, The effect of reducing the difficulty of refining products

Active Publication Date: 2013-12-25
CHINA PETROLEUM & CHEM CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0005] Purpose of the invention: In order to overcome the shortcomings of the large amount of acetic anhydride used in the prior art, many by-products, and difficult product purification, the present invention provides a p-hydroxybenzoic acid as a raw material, acetic anhydride as an acylating agent, and pyridine as a catalyst. The preparation method of acetoxybenzoic acid, the method not only uses less acetic anhydride, but also has low by-product content and high product conversion rate

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0019] Embodiment 1: Add 35 grams of acetic anhydride and 26 grams of p-hydroxybenzoic acid in the 100ml there-necked flask equipped with stirrer, thermometer, reflux condenser, stir and be heated to 85 ℃, suspend heating, dropwise add 0.03 gram of pyridine, temperature When the temperature rises to 94°C, the material dissolves completely, and a solid precipitates out quickly to form a suspension, and the reaction temperature is maintained at about 92°C; after 15 minutes, 4 grams of p-hydroxybenzoic acid and 0.03 grams of pyridine are added to the suspension, and the temperature rises to 96°C, stirred at this temperature for 10 minutes, and the material was transformed into crystals; continued to stir for 18 minutes, then added 3 grams of p-hydroxybenzoic acid and 0.03 grams of pyridine, and controlled the temperature at about 98°C; after stirring for 15 minutes, added 3 gram p-hydroxybenzoic acid, insulated and stirred for 2 hours; stop heating and stirring, after the material...

Embodiment 2

[0020] Embodiment 2: Add 27.7 grams of acetic anhydride and 25 grams of p-hydroxybenzoic acid in a 100ml three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, stir and heat to 85° C., suspend heating, and slowly drip 0.06 grams of pyridine, When the temperature rises to 95°C, the material dissolves completely, and a solid precipitates out quickly to form a suspension; control the reaction temperature around 95°C, stir the material fully, and the material changes from a paste to a crystal after 30 minutes; keep the temperature without Change and continue to react for 2 hours; finally, stir at a temperature of 95-98°C for another 1 hour to stop heating and stirring, wait for the material to cool to room temperature, wash and filter it repeatedly with distilled water or deionized water until the pH of the filtrate is 3 ~4, 32.6 g of crude product were obtained. The target product conversion rate is 100%, the melting range recorded by the crude product...

Embodiment 3

[0021] Embodiment 3: Add 175.6 grams of acetic anhydride and 132 grams of p-hydroxybenzoic acid in a 500ml four-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, stir and heat to 80°C, the material is nearly completely dissolved, suspend heating, and drop Add 0.12 g of pyridine. After the temperature of the kettle stabilized at 90°C, 7.9 grams of p-hydroxybenzoic acid was added, and soon a solid precipitated and formed a suspension, then 0.09 grams of pyridine was added dropwise and 9.7 grams of p-hydroxybenzoic acid was added, and a large number of crystals were formed immediately; Control the reaction temperature around 95°C, continue stirring for 15 minutes, add the remaining 30.4 grams of p-hydroxybenzoic acid, and complete the addition within 10 minutes, continue stirring for 3 hours in the temperature range of 95 to 98°C, stop heating and stirring, After the material was cooled to room temperature, it was repeatedly washed and filtered with dis...

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Abstract

The invention discloses a method for preparing p-acetoxy-benzoic acid. The method comprises the following steps of: reacting p-hydroxybenzoic acid as a raw material, acetic anhydride as an acylating agent and pyridine as a catalyst in a condition of 1.2-1.5 times of the excessive acetic anhydride: firstly, adding a certain amount of the p-hydroxybenzoic acid and the acetic anhydride into a reactor; dropwise adding the pyridine while stirring and raising the temperature to 80-85 DEG C; controlling the dropwise adding speed, wherein preferentially the temperature raising speed of a reactant is not beyond 10 DEG C; keeping the reaction temperature and continuously stirring for 2-3 h after adding the p-hydroxybenzoic acid and the pyridine and completely converting the reactant into crystals; and finally, repetitively washing the cooled reactant till the pH value of filtrate is 3-4 so as to obtain a crude product of acetoxy-benzoic acid. Both purities of a liquid chromatogram analysis result and a nuclear magnetic resonance hydrogen analysis result of the p-acetoxy-benzoic acid are more than 99.5%. According to the method disclosed by the invention, the conversion rate of the p-acetoxy-benzoic acid is more than 96%; furthermore, the content of by-products is low; and the difficultly for further refining and purifying the product is greatly reduced.

Description

technical field [0001] The invention relates to a preparation method of p-acetoxybenzoic acid, in particular to a preparation method of p-acetoxybenzoic acid using p-hydroxybenzoic acid as a raw material. Background technique [0002] p-Hydroxybenzoic acid is one of the important raw materials for the synthesis of aromatic polyester liquid crystal polymers, but it is easy to sublimate itself, and the activity of phenolic hydroxyl groups for esterification is low, so it is usually converted into active by acetylation first. Higher intermediate p-acetoxybenzoic acid to increase reactivity. Therefore, the successful preparation of high-purity acetoxybenzoic acid is a prerequisite for the synthesis of liquid crystal polyesters. [0003] The existing technology of preparing p-acetoxybenzoic acid from p-hydroxybenzoic acid mostly uses concentrated sulfuric acid as a catalyst, and acetic anhydride is an acylating agent, and is usually carried out under the conditions of adding sol...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C07C69/157C07C67/08
Inventor 左志俊倪寒秋魏家瑞胡兆麟
Owner CHINA PETROLEUM & CHEM CORP
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