Allantoin: in which phase?

Today I was reading a document (of International Specialty Products) about allantoin.
I read that allantoin is amphoteric and anionic at basic conditions.

- Does that mean that it is dipolar at a neutral pH?

The supplier suggests to suspend it in emulsions in the cool down phase <50°C. According to them recrystallization can occur later when it has been solubilized >50°C.
I never suspend allantoin, I always dissolve it in the water phase ≥70°C and luckily I've never had recrystallization problems so far.
I read that the solubility in water is 0.45 g/100 g at 25°C, so I guess that if you mix well and let it be, 0.45% of the suspended particles will dissolve later on anyway at room temperature?

A prototype formula was attached: 1% allantoin suspended in an anhydrous, lipophilic body balm.

- Does that actually work, suspending a water soluble, fine powder like allantoin in a lipophilic base?

- Are there other reasons than crystallization alone, to suspend allantoin in the cool down phase?


    May I ask you what phase you would suggest? Thanks a lot in advance!
  • DoreenDoreen Member
    edited June 2018

    I'v got answers on my questions above and would like to share it, hopefully it might be of help for you too.

    About suspending allantoin to a lipophilic product: this is probably useful indeed. Apparently it doesn't need to be in a dissolved state per se for it's soothing properties. I have attached the document with the lipophilic treatment stick with 1% allantoin formula (on page three).

    Here is the answer I got:
    "Allantoin is an amphoteric molecule. It can have a positive charge under acidic conditions, but could only have a negative charge under very basic conditions. Betaine on the other hand can only have a positive charge under very acidic conditions, and it's usually present as a zwitterion (both anionic and cationic charges at the same time, with a net carge of zero). It could never be anionic since it has a permanent positive charge. At the pH of 5.32, allantoin is cationic, so it might actually interact with the anionic emulsifier. You basically suspend allantoin due to its low solubility and recrystallization risk. Incorporation into an emulsion during the cool down phase is done in the same way as you do with many other ingredients, only that you need vigorous mixing."

    So the minor pilling issues I had recently, could indeed be due to the allantoin interacting with the glyceryl stearate citrate.
  • DoreenDoreen Member
    edited June 2018
    p.s. About the pH of 5.32: this was the pH of the emulsion with the allantoin, betaine and glyceryl stearate citrate I had made. So there's nothing important about this exact pH, only that it's acidic and allantoin is indeed cationic when in an acidic product.
  • PerryPerry Administrator, Professional Chemist
    Thanks for the updates
  • DoreenDoreen Member
    You're welcome! :-) 
  • Doreen  Sorry didn't see your question until now.We dissolve the allantoin in the water phase prior to heating to 70C and have not had any problems.
  • DoreenDoreen Member
    edited June 2018
    No problem! :-) I've also had a few times that my name was tagged, but I didn't get a notification.

    Glad to see you also don't put it in the cool down! I've never had problems with allantoin either, well up to now maybe (the 'gritty deodorant' discussion). But maybe that was due to a too fast cool down.
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