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Salicylic acid recrystallization in gel and oils
I am trying to understand why Salicylic acid recrystallizing and why stops when I mix with
Sodium Citrate 1.00% Sodium Bicarbonate 0.066% And what can I do if I want to mix it with oils(anhydrous), how can I stop recrystallization? Many thanks
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19 Replies
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Anyone knows if it is possible to stop recrystallization of SA with anything else but a salt like Sodium Citrate? I am using Polyacrylate Crosspolymer-6 and it is failing with this much salt in this ‘serum’
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Hi Alan. Both Sodium citrate and Bicarbonate are salts of strong bases, which means that in solution, they will form Sodium hydroxide.
So, what might be happening is that your Salicylic acid that is not very water soluble (that’s why the recrystallization), will react with the Sodium hydroxide, forming as a result of neutralization, Sodium salicylate, which is more water soluble.
You could replace both salts (Sodium citrate and bicarbonate) with a bit of Sodium hydroxide.
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Thank you @ketchito
From what I understand I can neutralize salicylic acid with sodium bicarbonate and make sodium salicylate and this will stop recrystallization. Is that correct?
I can do the gel. Mix salicylic acid with sodium bicarbonate and water.. wait to react and add it to the gel.
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Hi! That should work, but you need to check the amount of Bicarbonate you’d need.
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@ketchito Sweet!! Is it any equation on how much Bicarbonate to add to salicylic acid or is it just a matter of ph?
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ketchito said:Hi Alan. Both Sodium citrate and Bicarbonate are salts of strong bases, which means that in solution, they will form Sodium hydroxide.
So, what might be happening is that your Salicylic acid that is not very water soluble (that’s why the recrystallization), will react with the Sodium hydroxide, forming as a result of neutralization, Sodium salicylate, which is more water soluble.
You could replace both salts (Sodium citrate and bicarbonate) with a bit of Sodium hydroxide.
Hi @ketchito, I have a question. When the Salicylic acid react with Sodium hydroxide and be neutralized, does it still be effective?
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@1501 It is no longer as effective but it is alright. I tried to keep it as salicylic acid in the serum but apparently it isnt that easy to integrate.
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@Microformulation Thank you
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@alan123 Hi! As @Microformulation mentioned, there are ways to solubilize Salicylic acid. One is to use some solvents (ethanol, glycols and non ionic ethoxylated fatty alcohols). Another is to neutralize it to form Sodium salicylate (either using a base like Sodium hydroxide, or basic salts like Sodium bicarbonate, citrate, phosphate, etc.). Or, you could buy Sodium salicylate instead, which is more soluble in water.
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1501 said:ketchito said:Hi Alan. Both Sodium citrate and Bicarbonate are salts of strong bases, which means that in solution, they will form Sodium hydroxide.
So, what might be happening is that your Salicylic acid that is not very water soluble (that’s why the recrystallization), will react with the Sodium hydroxide, forming as a result of neutralization, Sodium salicylate, which is more water soluble.
You could replace both salts (Sodium citrate and bicarbonate) with a bit of Sodium hydroxide.
Hi @ketchito, I have a question. When the Salicylic acid react with Sodium hydroxide and be neutralized, does it still be effective?
Hi! It depends on the final pH of your system. You can use Sodium salicylate at the start, to incorporate it in your system, and then lower the pH a bit, to have part of the molecule as its active form (Salicylic acid). Only, don’t lower the pH too much to prevent solubility issues.
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At the allowable Cosmetic levels (avoiding OTC drugs) of 2%, you should have little issues solubulizing Salicylic acid. -
@Microformulation Yes - It easily dissolves in PG, etc or octyldodecanol.
I am trying to make something like 0.15% salicylic acid in gel (sepizen) without recrystallization.
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So a polyol like propylene glycol is not an option?
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It will recrystallize
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Polyols such as Propylene Glycol and Propanediol are an option but they are needed in large amount.
I responded to THIS a few minutes ago.
There is a study which states neutralised (near ph 7) Salicylic Acid is as good as Salicylic Acid at low pH. It is a common knowledge that ALL acids must be in low pH to be effective. Salicylic Acid is an exception to the rule.
I made both Salicylic Acid and Sodium Salicylate solutions. Difference is negligible. But Sodium Salicylate is way less irritating than Salicylic Acid due to pH not crazy low.
Use this page to help you with the neutralisation. It is all set up for you, just punch in the numbers. But you still need to check with pH strip or metre! Purity of the substance, temperature, and so forth, can influence the actual numbers.
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@Cst4Ms4Tmps4 Thank you. Can you give me the link of this study? (about Salicylic Acid at pH 7)
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Here you go!
https://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2009.00501_2.x
You are welcome!
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Cst4Ms4Tmps4 said:@1501
Here you go!
https://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2009.00501_2.x
You are welcome!
thanh you very much
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