ascorbic acid and propilenglycol

[bpl]

Hi

Does anyone know the stability of ascorbic acid in pure propilenglycol??
Does propilenglycol help to stop oxidation?

Thanks
Beatriz

[Bill Tindall]

I have not studied ascorbic acid oxidation in propylene glycol but I am sure that oxygen dissolves in this solvent and that UV light easily penetrates it, so I would assume that the degredation reactions that occur in water will to a greater or lesser extent occur in proplyene glycol too.

[HW Mueller]

Funny, I had planned to say the same thing as what Bill said on this, but then remembered that ascorbic is quite stable in water if the solution is acidic (as an example, if you dissolve ascorbic in pure water). Oxidation is quite rapid in a nearly neutral solution or especially in basic ones. Most likely, oxygen is more soluble in the glycol than in H2O, UV is not needed (of course it will speed it up), metal ions (transition metals) are, but these are present everywhere. Polarity of the reaction medium is important here, but how much? So... I still have to pass.

[bpl]

so, oxidation is quicker in propylenglycol than in water!!
What a surprise!!
Because we are analizing ascorbic acid in pure propylenglycol (8%,10% and 15%), after a week, three months and six months by HPLC to study stability as mi boss told me that propylenglycol is good to stabilize ascorbic acid in cosmetics.

Thanks
Beatriz

[Tim]

I am curious why you are trying to stabilise one antioxidant with another antioxidant. What purpose is the one that is not acting as the antioxidant there for?

It would seem to me that if you are using the proylene glycol to stabilise the ascorbic acid and the ascorbic acid is degrading, the propylene gylcol isn't doing its job and you should look to finding something that oxidises more easily than the ascorbic acid.

[bpl]

I don´t really know if ascorbic acid is stable with propylenglycol and I´ve been told to study, by HPLC, if propylenglycol helps to stop the oxidation of vit C in cosmetic serums, because one of my jobmates really believes that propylenglycol works stopping it!!
Maybe it is obvious, but I am new working on this! I don´t know how to handdle it!!
Thank you very much

[HW Mueller]

Now this is getting to be confusing, nobody said that Asc oxidizs faster in propyleneglycol if I read this correctly, Beatriz, do your experiments show this? If they do, why ask? Certainly, propylenglycol is an extremely weak radical scavenger or antioxident. There are other properties influenzing radical reactions, these are difficult to predict.

[Bill Tindall]

I spent several years analyzing solutions of ascorbic acid. There isn't one answer to the question of how fast it goes away in propylene glycol, or any other solvent, because so many other factors will affect the rate. As has been mentioned-light, temperature, oxygen, metal impurities, pH, solvent, the container it is in, as well as the concentration of acorbic acid all affect decomposition rate. Dilute solutions are extremely difficult to stabilize at any pH.

[Einar Ponten]

It is obvious that a cosmetic product may be marketed as "Vitamin C rich" while "propylene glycol enriched" probably don't sell at all. See, http://www.dsmnutrafacts.com/cosmetics/ ... p?vitamins
http://www.collabo.com/Vitagen.htm
http://www.uniqueimage.com/skin_care_vi ... _serum.asp

Even though I don't think propylene glycol stabilise ascorbic acid to a significant extent. I bet there are patents in this area. From my experience, preserving easily oxidised thiols in pharmaceutical formulations, I agree with Bill. It is too complicated to predict and experiments are required.

However, electrochemist will claim that stability constants and red/ox potentials will give valuable hints.

[bpl]

Thank you to all of you

I am going to carry on working on this acid, this is the only way to find out stability and you are right, it depends on conditions!

Beatriz