Method for determining amino value by automatic potentiometric titration

Abstract

The invention discloses a method for determining an amino value by automatic potentiometric titration, wherein by using the principle of a diazotization reaction between an aromatic primary amine compound and nitrite, taking a sodium nitrite standard solution as a titrant and a Pt electrode as an indicator electrode, and determining the titration end point by the maximum value of the first derivative of the titration curve, the quantitative analysis of the amino value is realized. The introduction of hydrobromic acid in the system and the control of the titration temperature solve the problemthat the potential titration end points of some low-active aromatic primary amine compounds do not jump significantly, enable control of the rate of the titration reaction, and can obtain test data more quickly and accurately. The method provided by the invention is convenient in operation, simple and fast, and reliable in results.

Description

technical field [0001] The invention belongs to the technical field of analytical chemistry, in particular to a method for testing the amino value of primary aromatic amines with a potentiometric titrator. Background technique [0002] Aromatic primary amine compounds are common pesticides and pharmaceutical intermediates, such as p-aminophenol, 2,5-dichloroaniline, 3,3’-dichlorobenzidine, p-aminosalicylate sodium and so on. This type of compound is characterized by the presence of primary aryl amino groups (Ar-NH 2 ), can carry out quantitative diazotization reaction with sodium nitrite under acidic conditions, and generate diazonium salt. Using this principle, the amino value of the compound can be determined, and then the absolute content can be obtained. Amino value is an important test index for the product quality of aromatic primary amine compounds, and is often used to judge the product grade of such compounds. At present, the determination of the amino value of mo...

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Problems solved by technology

At present, the determination of the amino value of most aromatic primary amine compounds is carried out according to the manual titration method in the relevant national standards. Potassium iodide test paper turns blue to indicate the titration end point, and the end point indication sensitivity is poor, especially for some samples with a certain color, it is difficult to control the parallelism and accuracy of the results measured by this method. There are two main reasons: (1) The diazotization reaction activity of some primary aramides themselves is low, and the diazotization rate is slow, resulting in low sensitivity of the endpoint indication; (2) The diazotization reaction temperature is generally low, resulting in some primary aramides with low activity. reaction rate is slower

Patent CN108375620A describes a method for determining the content of 2,4,5-triamino-6-hydroxypyrimidine sulfate by automatic potentiometric titration. The Pt electrode is used as the indicator electrode for redox potential titration, and the first order derivative of the titration curve ERC is the largest The end point of the titration can be judged by the titration value, and the quantitative analysis can be realized, which avoids the disadvantage of the indicator method that the end point is not obvious, but this method cannot solve the problem of the determination of the amino value of the low activity primary aramide.

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