Regarding the issue of the secondary condensation conversion rate of H acid
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The company has recently synthesized a red dye; specifically, it is obtained by a single condensation reaction between H-acid and tricyano compound, followed by two more condensation reactions with H-acid. The resulting product is then coupled with an ortho-ester diazonium salt in a molar ratio of two to one. As a result, the color produced is always bluer and darker compared to the standard sample. Chromatographic analysis of the product revealed the presence of mono-condensation products. I would like to ask experts how to increase the conversion rate of secondary condensation using H acid?
The ratio of H acid to trichlorocyanuric acid must be carefully controlled. The first condensation step is relatively easy, but during the second condensation step, the mixture becomes very thick if the temperature is not managed properly. If the ratio is not controlled correctly, excess H acid can react with the para-ester diazohydrchloride to form KN-B, resulting in a dye with a darker color and a bluer tone. It is recommended to analyze the residual H acid in the product of the second condensation step using HPLC; ideally, this level should be below 1%
The residual amount of H acid after the first condensation is around 0.5%; in the second condensation, the amount of H acid is 3% less compared to the product obtained after the first condensation. Even after 6 hours of reaction (when the pH stabilizes and no further decrease occurs), the residual amount of H acid in the dimer is still around 5%, with little difference when the ratio of reactants is reduced. I was wondering if there are any additives that can improve the conversion rate?
Can’t you add both amounts of H acid at once during the condensation? It’s easy to reach the end point after one shrinkage; keep the material at that temperature for an hour and then proceed with the second shrinkage, and it will take about three hours to reach the end point