I am currently studying the problem with the quality of distilled glycerin. When stored, it acquires a pink tint (see photo). We analyzed glycerol on a gas chromatography mass spectrometer. In the sample 1099/2, the following impurities were found:
1,2,3-Propanetriol, 1-acetate CAS No. 106-61-6;
3-Methoxy-1,2-propanediol CAS No. 623-39-2;
1,3-Dimethoxypropan-2-ol CAS No. 623-69-8;
2-tert-butylhydroquinone CAS No. 1948-33-0.
Which of these substances can give a pink color and why?
Maybe the last one. What is the probability of identyfication.
You can make a preparative LC with glass column or monitored by UV and collect the fraction causing this colour. In this case the identyf. will less difficult.
Regards
G
Thanks for the answer and recommendations. The analysis was done GC-MS. Vapor phases above the samples and methanol solutions of the samples were investigated. Apply still liquid chromatography.
There are indications in the literature that quinone can give a pink color. Hydroquinone is found in our sample. It should be colorless. How to remove color from glycerin, while I have no thoughts.
Regards,
Tatyana
You may consider to purify glycerol from coloured impurities by washing (liquid-liquid extraction) with 2,2,4-trimethylpentane (iso-octane); possibly repeatedly. You could also select a suitable adsorbent, such as activated alumina or activated charcoal ― followed by filtering. Also possible would be purification by fractional distillation under vacuum.
Thank you very much for the recommendations. We tried powder activated carbon cleaning. The effect is. The question remains - how does this impurity get into crude glycerin or is it formed during processing?
Could it be a breakdown product of tocopherol or vitamin K that has been converted to glycerin from vegetable oil?
TBHQ is a common anti-oxidant. It may have been added to the commercial glycerol you started out with.
Dear Folks, I work as an advisor to a glycerol refining plant and we have just found something very similar to Tatyana's issue - distilled glycerin getting pink. I don't think it is formed during purification process. It is a contamination from the crude glycerol that we have started with. Tatyana, in the end, do you think was a TBHP contamination? thanks for your help
TBHQ reacts with various materials to give a pink color: https://books.google.com/books?id=3wpHj3mvra8C&pg=PA168&lpg=PA168&dq=tbhq+pink
The reaction seems to be catalyzed by alkali, so lowering the pH (e.g. with a trace of acetic acid) might prevent it.
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