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Allantoin or betaine cause of ammonia smell?
Yesterday I tried to neutralize an O/W emulsion with NaOH 18% to a pH of around 6, quite soon after emulsification. I was about to use sodium ascorbyl phosphate in a predispersion in the cool down, and the SAP needs a pH of about 6.5 to remain stable.
But before I could even get to that (luckily no actives wasted) an ammonia smell came from the emulsion when I mixed the first few drops of NaOH 18%. The temperature was around 38C.The formula:
Phase A
Water, distilled/deionized ad 100
0.5% Allantoine
3.0% Betaine (trimethylglycine)
0.1% Dinatrium EDTAPhase B
4.5% GMS + PEG-100 Stearate
2.0% Cetyl Alcohol
1.5% Myristyl Myristate
1.0% Shea Butter
3.0% Squalane (olive derived)
5.0% Isoamyl Laurate
1.0% Dimethicon 350 cSt.
0.85% Sepimax ZenPhase C
NaOH 18% q.s. pH 6 - 6.5 (the first few drops unto the emulsion at <38C, mixing and => whiff of ammonia
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A
Dissolve individually EDTA, allantoin and finally the betaine. Heat to 70C.B
Add individually heat to 70C. Disperse the Zen.Add B to A while stirring or A to B without stirring. Homogenize.
C
Dissolve 3,6 grams of NaOH in 16,4 ml/gr water. Let cool down.
q.s. to pH of at least 6
________________________________________________________________________________________To avoid misunderstandings, I don’t mention the cool down phase, as I didn’t even get to that. The reason that the Sepimax Zen is so high, is because of the relatively high level of electrolytes I would be adding in the cool down.
The release of ammonia. I don’t know why, but I had to think immediately of the allantoin. Which is odd, because I use allantoin all the time and neutralize also many times with NaOH, only not so soon in the process. Or would it be the betaine? I read that betain is a zwitterion and anionic at a pH > 5.5, so no interactions there, or so I hoped.
What would be the culprit for the sudden forming of ammonia?
Thanks!!
edited: typos
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18 Replies
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Up! That’s an interesting question. Can professionals help please?
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Pour NaOH on some allantoin in water and see if you get an interesting reaction? For science!
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@KateCreates
I am planning to do a few experiments and that is indeed one of them!
Thanks for thinking along with me! :+1: -
LOL. I was worried you’d think I’m trolling but it’s the first thing I would do.
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Strong bases cause allantoin to decompose.Also, that’s a lot of allantoin! It will probably recrystallize over time (even though betaine improves its solubility).If you used less, you could add it after neutralizing the polymer.
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most likely the allantoin; it’s got a terminal amide group (-C(
)-NH2), and if that’s hydrolysed, e.g. by a strong base, it’d release ammonia -
@Vnnil
Thanks for your reply.
Do you think that 0.5% allantoin is a lot? I’ve never had 0.5% allantoin recrystallize over time even without betaine? What would you say is a ‘normal’ amount?
It’s so weird that I use allantoin all the time in the heated water phase and neutralize with a NaOH solution (in the end of the process). I will be more cautious next time! -
@Bill_Toge
Thanks for your answer and explanation!One more question if you don’t mind:
What if I add the allantoin (in solution) later on in the cool down and I need to adjust the pH just a bit more?
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Doreen said:@Bill_Toge
Thanks for your answer and explanation!One more question if you don’t mind:
What if I add the allantoin (in solution) later on in the cool down and I need to adjust the pH just a bit more?
I’d suggest putting the sodium ascorbyl phosphate and allantoin in first, then adjusting the pH at room temperature; not only will this reduce the probability of any hydrolysis reactions, SAP itself is very basic, so you’ll need less caustic soda to get the desired pHor you could use something like TEA or AMP instead of caustic soda, as they are non-nucleophilic and can’t hydrolyse amides -
@Bill_Toge
So the temperature of around 38C has increased the rate of the hydrolysis reaction?
That must be the reason why I’ve never had this happen before with both allantoin and NaOH in a formula, I always alter the pH at the very end of the process, at room temperature.Much obliged! :+1: :blush:
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Doreen said:@Bill_Toge
So the temperature of around 38C has increased the rate of the hydrolysis reaction?
That must be the reason why I’ve never had this happen before with both allantoin and NaOH in a formula, I always alter the pH at the very end of the process, at room temperature.absolutely: for relatively simple chemical reactions, the dependence of rate on temperature is exponential, so there’s a huge difference between 28 and 38 °C -
@Bill_Toge
Thanks so much for all the information!
Glad that the lotion fail happened, now I’ve learnt a bit more! -
@Doreen, I do not have betaine available at home, so I cannot try it myself, but it could have been that one as well. Quaternary ammoniums tend to do weird things in presence of a base. One of the weird things is that they can degrade to trialkylamines (fishy/ammonia smell).
If you can spare some and try it at different pHs you might see what happens, especially if you compare it with allantoin. It is true that allantoin has an amide-like group, however it is a urea group, which can hydrolyze as well, if not even faster than amides (because one of the final products is bicarbonate/CO2, and also because of the pH drift to higher values, which promotes the reaction).This is interesting. Sorry for the lotion fail
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@lmosca
Thanks a lot for your information! I’ll do some experiments. -
UPDATE
I’ve been thinking it over and the probable reason for the ammonia smell was that I put too much drops of NaOH 18% solution to my emulsion, which I think raised the pH way too high (maybe around 10 or even higher, if only I had some left to test). Before adding the drops the pH must have already been above 5 so I needed really a tiny tiny bit. And I remember using several drops right after eachother in one time.
I’ve been making an exfoliating toner for a few years now, this toner contains both allantoin and betaine and I raise the pH with sodium hydroxide at a high temperature (65C) without problems. The difference between this toner and the forementioned emulsion is the pH. The toner, before adding the NaOH, is around pH 2.8. After adding NaOH it is around 3.8, so still acidic.
To raise the pH from 2.8 to 3.8 with NaOH 18%, quite a bit is needed (around 2%). Because I make the toner quite often (way more often than emulsions that I neutralize with NaOH), I think it was force of habit using a larger quantity of several drops in one time rather than a single tiny drop first and measure the pH before going any further.@Bill_Toge
I hope you don’t mind me asking one more question here.
You mentioned TEA and AMP not being able to hydrolyze amides as these are non-nucleophilic.
But if I used TEA or AMP and raised the pH to e.g.10 or higher, wouldn’t there be an alkaline hydrolysis anyway?
(The toner that I mention in this post as example, is the same as the one that turned into a gel yesterday. I raise the pH to at least 3 while it is still hot, because I’ve had the SA precipitate when I waited too long in the cool down without raising the pH. When it’s at room temperature I raise it further to around 3.8.) -
@Doreen you’d struggle to get a pH above 9 with TEA or AMP, they’re just not that strong as bases
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I believe that betaine sooner or later is doomed to get a fishy smell by itself, you just accelerated somehow the process.
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