My experimental product is soap base shower cream by mixing the fatty acid with KOH at 75 degrees Celsius and other ingredients (emulsion chemical, salt,...) and using Patent Blue V (CI 42051) as color at below 45 degree Celsius. However, the blue color changed to green after more than six months. Is the reason for the oxidation of pigments or from the temperature?
Patent Blue V has a phenolic group. Your soap has KOH, which deprotonates this group. Phenolates are oxidized by air. The reaction proceeds faster with temperature increase.
Yurii V Geletii Dear Sir, thank you for your answer. Do you have any references related to this reaction?
And my soap also has fragrance, but I add fragrance (also has the phenolic group) after cooling to below 45 degrees Celsius and before adding the Patent Blue V. Does the fragrance also affect the oxidation process and make the color unstable?
Thank you very much.
Phenolics are easily oxidized in water by air. There are tons of literature, start from
https://en.wikipedia.org/wiki/Patent_Blue_V
https://en.wikipedia.org/wiki/Phenolates
The oxidation might be triggered by light. So keep your sample protected from light.
If there are two phenolics in solution, they might be oxidized much faster than each one separately.
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