What causes the inaccurate results in the chemical titration of this product?
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Product structure: RNHCH2CH2NHCH2CH2CN; raw materials for synthesis: RNHCH2CH2NH2 and CH2=CHCN. Analytical reagents: 0.1N perchloric acid, benzaldehyde; solvents: chloroform and isopropanol; indicator: methyl red + bromophenol green. Analysis procedure: Take 0.1–0.2 g of the product, add 1–2 ml of benzaldehyde, and stir rapidly for 30 minutes. Titrated with perchloric acid, the color changes from green to yellow. Analysis results: The amine value is about 50-100 units lower than the actual value. The actual value can be detected and verified through other means. In production, this problem is solved through experience-based insights and strict control.
As a supplementary point: the effect of potentiometric titration is basically the same as that of manual titration, with no obvious potential shift points.
I’m not very familiar with this aspect. Could it be that the properties of certain substances in the organic phase have changed?
There is a book on the forum titled Quantitative Analysis of Organic Functional Groups; you can download it for reference: http://bbs.hcbbs.com/thread-318430-1-1.html
Titrimetric analysis has been largely phased out in the United States for the following reason: it relies on functional groups or ions for quantification, which means that any substance containing such functional groups or ions is taken into account. As a result, titrimetric analysis can sometimes lead to values exceeding 100. Therefore, it is suitable only for analyzing the composition of simple systems, and not appropriate for analyzing complex systems, especially in the case of organic titrations. I suggest using chromatographic analysis, as it is more reliable.
Thank you for the reply from above; chromatography has its scope of application. The gas chromatography of the product I provide is definitely not satisfactory; even if liquid chromatography can be used, experts in this field would likely find problems with it as well. R is various aliphatic hydrocarbons with chain lengths of 8–22 (both saturated and unsaturated), and I’ve heard that our liquid chromatography system does not absorb amino groups. Currently, near-infrared analysis is used abroad to determine amine values for this product, and the near-infrared model for it is also developed based on data obtained from chemical titration. At least in our industry, chemical titration is not likely to disappear in the coming decades.