Standard test method for free acid content in polybasic organic carboxylic acid products

Abstract

The present invention provides a standard detection method for the free acid content in a polybasic organic carboxylic acid product, and in particular, provides a standard detection method for the free acid content in a cyclic acid product, in order to provide a detection basis and detection standard for impurity free acid for polybasic organic carboxylic acid products such as cyclic acid products. The standard detection method for the free acid content in the polybasic organic carboxylic acid product of the present invention is to mix the polybasic organic acid with a high boiling point solvent and heat it to reflux, use a reflux water separation device to collect water, and use an alkali titration method to detect the free acid content of the collected water. The free acid hydrochloric acid content standard in the water separated by the free acid detection of the present invention is ≤0.3%, which can relatively guarantee the better quality and better production requirements of the cyclic acid product, is more conducive to ensuring the quality of the downstream products of the cyclic acid, and can produce the cyclic acid at a lower cost and relatively reduce environmental pressure.

Description

Technical Field

[0001] The present invention relates to a standard test method for the free acid content in polybasic organic carboxylic acid products. Background Art

[0002] Carboxylic acids (RCOOH) are the most important class of organic acids. A class of compounds with the general formula RCOOH or R(COOH)n, where R is an aliphatic or aromatic group, are called fatty acids or aromatic acids, respectively. They can be divided into monobasic acids, dibasic acids, and polybasic acids according to the number of carboxyl groups.

[0003] Cyclic acid, chemical name 1,3-dibenzyl imidazoline-2-one-cis-4,5-dicarboxylic acid, can be used as an intermediate for the drug biotin (vitamin H). Cyclic acid products are prone to produce free acid (mainly hydrochloric acid) during production. Although a large part of it can be removed by washing with water, some of it still remains in the cyclic acid product. The effects of excessive free acid in cyclic acid include: (1) affecting the yield of cyclic acid products. Excessive free acid leads to low yield of cyclic acid products; (2) affecting the equipment in the production workshop. Excessive free acid is highly corrosive to the equipment, making it easy to corrode; (3) affecting the solvent recovery of production. Xylene is used in the dehydration process of cyclic acid production. If the free acid is too high, the recovered xylene is acidic. The acidic xylene cannot be recycled for reuse in production, which increases the production cost of cyclic acid and also increases environmental pressure, because it is difficult to handle so many organic solvents; (4) affecting the quality of downstream products of cyclic acid. Therefore, the control of free acid content is more important. However, if you want to detect this free acid content index, direct titration is definitely not enough, because cyclic acid is also an acid, and direct titration cannot obtain reliable free acid content. In addition, at present, the production and application industries of cyclic acid products do not involve free acid index requirements, that is, there is no such standard. Summary of the invention

[0004] Based on the above background technology, in order to solve the problem that there is no basis for detecting the free acid content in the current polybasic organic carboxylic acid products, the present invention provides a standard detection method for the free acid content in polybasic organic carboxylic acid products, and in particular, provides a standard detection method for the free acid content in cyclic acid products, in order to provide a basis and standard for detecting the impurity free acid in polybasic organic carboxylic acid products such as cyclic acid products.

[0005] The standard detection method for the free acid content in the polybasic organic carboxylic acid product of the present invention is to mix the polybasic organic acid with a high boiling point solvent and heat it to reflux, collect water using a reflux water separation device, and detect the free acid content of the collected water using an alkali titration method. Among them, it is preferred that the polybasic carboxylic acid groups in the polybasic organic carboxylic acid can form intramolecular acid anhydrides; the polybasic organic carboxylic acid can be a dibasic carboxylic acid, a tetrabasic carboxylic acid, etc., especially a cyclic acid; the high boiling point solvent is preferably an organic solvent with a boiling point of 130-200°C, such as xylene, ethylbenzene, etc., and the xylene used can be industrial xylene, which is a mixture of three isomers of o-xylene, m-xylene, and p-xylene. The present invention does not need to specifically distinguish the three isomers. Of course, if o-xylene, m-xylene or p-xylene that are specially distinguished are used, it is obviously feasible and should be within the scope of protection of the present invention. However, from the perspective of actual production, such as cost, the use of industrial xylene is more practical. In addition, since xylene is used in the dehydration process of cyclic acid production, the present invention also uses xylene, which is better, on the one hand, reducing the use of new solvents, and on the other hand, reducing new impurities and facilitating the recovery of a single solvent. In addition, the inventors have found through experimental research that it is difficult to achieve the purpose of the free acid content determination of the present invention by using toluene as a solvent for the reflux reaction of the present invention, because the boiling point of toluene is relatively low, so that the proportion of acid anhydride formed by the reaction of carboxylic acid is relatively low, and the formation of acid anhydride is not complete.

[0006] In the standard detection method for the free acid content in the polybasic organic carboxylic acid product of the present invention, when the polybasic organic carboxylic acid is cyclic acid, the following detection method can be specifically used: take a certain amount of cyclic acid, add solvent xylene, heat to solvent reflux, use a reflux water separation device to collect water, detect the water separated by reflux, and determine the free acid content therein. Wherein, the amount of solvent xylene used is 2-6 times, preferably 4-5 times, of the mass of the cyclic acid; when the amount of water collected basically no longer increases, the water separated by reflux is detected, generally 2-5 hours is appropriate. If the time is too short, the water separation is not thorough, the detection result is inaccurate, and if the time is too long, the energy consumption is large. Cyclic acid will completely turn into cyclic anhydride and water during the heating process, and a small amount of hydrochloric acid remaining in the cyclic acid will flow out with the solvent and the water generated by the cyclic acid. The refluxed solvent brings out hydrochloric acid, while the cyclic acid will not be brought out, and then the refluxed part is detected, thereby achieving the determination of the free hydrochloric acid content therein. More specifically, the standard detection method for the free acid content in the cyclic acid product of the present invention is as follows: use a three-necked flask to build a reflux water separation device, take 100-200 grams of cyclic acid and add it to the three-necked flask; add 300-500 milliliters of xylene to the three-necked flask; start heating reflux to perform water separation operation, use a reflux water separation device, and reflux water separation is performed simultaneously; reflux for 2-5 hours, and observe the amount of water separated from the bottom of the reflux water separation device; when the water volume reaches 5-7 milliliters, stop heating and reflux; take out about 5 grams of separated water, and titrate with 0.1 molar sodium hydroxide solution to determine the concentration of hydrochloric acid in the water.

[0007] The present invention aims at the problem that the prior art does not involve the detection of free acid content. The present invention adopts the method of first subjecting the cyclic acid to anhydride reaction, then separating the reaction solvent from the aqueous solution of the free acid, and then detecting the separated free acid aqueous solution. The standard of the free hydrochloric acid content in the separated water is preferably ≤0.3%, which can relatively ensure the better quality of the cyclic acid product and better production requirements, is more conducive to ensuring the quality of the downstream products of the cyclic acid, and can produce the cyclic acid at a lower cost and relatively reduce the environmental pressure. If the free acid content is too high, the cyclic acid needs to be re-slurried and washed. DETAILED DESCRIPTION

[0008] The following embodiments are further descriptions of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention.

[0009] Example 1

[0010] The standard test method for free acid content in the cyclic acid product of the present invention is as follows:

[0011] (1) A reflux water separation device was built using a three-necked flask, and 100 g of 5 different batches of cyclic acid products (as shown in Table 1 below) were taken and added to the three-necked flask;

[0012] (2) Add 500 ml of industrial xylene into a three-necked flask and stir;

[0013] (3) heating the three-necked flask to control the temperature so that the solvent refluxes and performs a water separation operation;

[0014] (4) Reflux for about 4 hours and observe the amount of water discharged from the bottom;

[0015] (5) When the water volume reaches 5-7 ml and the collected water volume basically stops increasing, stop heating and reflux;

[0016] (6) Take out 5 g of the separated water and titrate it with 0.1 M sodium hydroxide solution to determine the concentration of free acid in the water;

[0017] (7) Calculate the free acid content in the cyclic acid product based on the free acid concentration in water.

[0018] Table 1 Cyclic acid product indicators of different batches

[0019]

[0020] From Table 1, the free acid content standard of the water separated by the present invention is preferably ≤0.3%, which can relatively guarantee the better quality of the cyclic acid product and the better production demand, especially the ability to produce the cyclic acid at a lower cost and relatively reduce the environmental pressure. If the free acid content is too high, the cyclic acid needs to be re-slurried and washed. The application of the index detection method for the free acid content in the cyclic acid of the present invention can further enhance the quality of the downstream products of the cyclic acid, and also contribute to the recovery and reuse of the solvent xylene in the production, saving production costs.

[0021] It should be noted that the above-mentioned technical contents of the present invention are only for explanation and clarification to enable those skilled in the art to understand the technical essence of the present invention, so the technical contents are not used to limit the substantial protection scope of the present invention. The substantial protection scope of the present invention shall be subject to the claims. Those skilled in the art should know that any modification, equivalent substitution and improvement based on the substantial spirit of the present invention shall be within the substantial protection scope of the present invention.

Claims

1. A standard detection method for the free acid content in a polybasic organic carboxylic acid product, which comprises mixing a polybasic organic acid with a high boiling point solvent and heating the mixture to reflux, collecting water using a reflux water separation device, and detecting the free acid content of the collected water using an alkali titration method; the polybasic organic carboxylic acid is a cyclic acid, and the cyclic acid is 1,3-dibenzylimidazoline-2-one-cis-4,5-dicarboxylic acid; the high boiling point solvent is an organic solvent having a boiling point of 130-200°C; and the free acid is hydrochloric acid.

2. The standard detection method according to claim 1, characterized in that The high boiling point solvent has a boiling point of 135-160°C.

3. The standard detection method according to claim 1, characterized in that The high boiling point solvent is xylene.

4. The standard detection method according to claim 1, characterized in that Take a certain amount of cyclic acid, add solvent xylene, heat until the solvent refluxes, use a reflux water separation device to collect water, and perform alkaline titration on the refluxed water to determine the free acid content therein.

5. The standard detection method according to claim 4, characterized in that The amount of the solvent xylene used is 2-6 times the mass of the cyclic acid.

6. The standard detection method according to claim 4, characterized in that When the amount of water collected stops increasing, the water separated by reflux is tested by alkali titration.

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