Alternatives to propylene glycol as a salicylic acid solubilizer?

Formulating

Alternatives to propylene glycol as a salicylic acid solubilizer?

Posted by Zink on July 16, 2014 at 6:51 pm

Propylene glycol solubilizes salicylic acid at an about 7 to 1 ratio, but are there other good alternatives?

Cst4Ms4Tmps4 replied 4 years ago 11 Members · 25 Replies
25 Replies

DavidW

Member
July 16, 2014 at 10:21 pm

SD Alcohol
DavidW

Member
July 16, 2014 at 10:22 pm

Would be helpful to know what type of product it is going into.
ozgirl

Member
July 17, 2014 at 1:16 am

These tables might be useful for you

http://lxsrv7.oru.edu/~alang/onsc/solubility/allsolvents.php?solute=salicylic%20acid

http://www.asiapharmaceutics.info/viewimage.asp?img=AsianJPharm_2010_4_1_60_63981_t2.jpg

Hope this helps
Zink

Member
July 17, 2014 at 4:07 am

Damn I forgot I had posted those tables before, no formula yet, just wondering about solubility and if there are any good direct replacements to PG.

Here’s the sorted data, can share spreadsheet if needed.
DavidW

Member
July 18, 2014 at 3:20 pm

Well, suggestion really depends on the type of product and other chemicals you can use.

PEG-400
SLES if you heat it first
Add sodium citrate to your water first will help solubility
Adjusting pH up will help depending on what your final pH will be
SD alcohol

There is a start for ya.
Zink

Member
July 18, 2014 at 4:10 pm

Thanks, when you say help re sodium citrate and adjusting ph, do you have any (ballpark) numbers on that?
Microformulation

Member
July 18, 2014 at 4:39 pm

I have solubulized SA numerous times. Just takes a little practice and getting the right solute. I will say I have used the Salvona SalSpheres product successfully in the past and avoided the whole issue. It is a bit $$$ but it does have less irritation and is incredibly easy to use. So easy a marketer can use it…..
MakingSkincare

Member
July 19, 2014 at 6:15 am

To add to the above, some more solubilisers:-

- isopentadiol,

- betaine (this isn’t cocamidopropyl betaine)

and buffer (using citric acid and sodium citrate) to a pH of 3-4.
DavidW

Member
July 20, 2014 at 10:12 am

Without my notes which are in my office I would day try 1% sodium citrate to start. Mic it into water first and make sure it totally dissolves.

Again, not to be rude but until I know what type of product you are making and your other ingredients I won’t be responding to this anymore. It would be a waste of time to throw out all different possibilities when most may not apply.
Microformulation

Member
July 20, 2014 at 1:31 pm

@davidW I agree. It really is a different exercise if it is a Shampoo, Facial Wash, or even a peel.
Zink

Member
July 20, 2014 at 5:40 pm

@Makingskincare : Thanks! Is the choice of buffer important or only the end pH? How many g/100ml of SA is soluble at pH4? And do you have numbers for isopentadioal and betaine?
Zink

Member
May 21, 2015 at 5:45 pm

To revisit this issue for a specific formula!

I’m making a water free thick “anti acne” concealer paste, and wondering if I could perhaps use castor seed oil in conjunction with alcohol to solubilize the SA, instead of say proyplene glycol?
chemist1

Member
May 21, 2015 at 8:11 pm

Finsolv EMG-20
MarkBroussard

Member
May 21, 2015 at 9:19 pm

@Zink

Hard to answer your question without some idea of what is in the water-free paste? Is it oil based?

You could try Octyldodecanol or 1,3-Propanediol, but it all depends on what you’re trying to incorporate it into.
Zink

Member
May 21, 2015 at 11:06 pm

Ah yes forgot to mention, It’s oil based, I used castor seed oil and alcohol and that worked well (both are on the charts).

Cheers,

Johan
Zink

Member
May 22, 2015 at 1:54 am

What I’m not as sure of is how effective SA is in a mostly oil based formula.
cherri

Member
May 26, 2015 at 8:29 pm

isoprene glycol worked well for solubilizing salicylic acid
DavidW

Member
May 31, 2015 at 3:21 am

IF you have an idea, try it and then let us know.
Doreen

Member
September 4, 2017 at 7:38 am

@Zink
I know this is an old discussion, but very relevant to me.
How have your experiments with differents solvents for the salicylic acid been going?

I tried 20% propylene glycol with 1% sodium citrate as buffer at a pH of 4.0 - 4.2 (to 75% water). No such luck. Precipitation starts within about 5 days when I keep it in the fridge.

Edit: I see you use castor oil and ethanol in an anhydrous system. You had no problems with it so far?
em88

Member
September 4, 2017 at 12:47 pm

How much SA do you want to dissolve? What do you want to obtain?
Propylene glycol + ethanol + glycerine should do the job.
Doreen

Member
September 8, 2017 at 9:43 am

@em88
A BHA exfoliant with 1% salicylic acid. I have gotten a few tips I’ll start working on (also keep it out of the fridge). To be continued!
em88

Member
September 8, 2017 at 2:49 pm

Waiting for a feedback!
Good luck!
ozgirl

Member
October 12, 2017 at 11:56 pm

I was looking up some old information on betaine today and came across the following information that may be useful to someone.

Betafin BP20 (betaine) is a co-solubilizer for salicylic acid and allantoin.

Salicylic acid

•Use
levels from 2 to 10
%.

•
Solubility in water is 0.2 % at room temperature

•
Betaine was found to increase the solubility of salicylic acid to 5 %

Allantoin

•solubility
in water 0.7 % at RT

•
Betaine was found to increase the solubility of allantoin to 2 %
Doreen

Member
October 13, 2017 at 12:53 pm

@ozgirl
Coincidentally I have received this information about betaine very recently, I’ll order it from a supplier in the UK.
http://www.theformulary.co.uk/betaine-839-p.asp

On their site they state: “We have no empirical data on using betaine as a solubilising agent for salicylic acid but will carry out tests and publish our findings here.”

Looking forward to experiment with it and find out what % are needed for both allantoin and salicylic acid.
If I know more, I’ll let it know here on CC.
Cst4Ms4Tmps4

Member
November 21, 2020 at 4:10 am

This is an old discussion I know and I do not know whether I have something valueble to add or not. More like question/s. Depending on the individuals - Some people think that my questions give them ah ha moment. Some people think that I am stupid.

I must say the same as what @Doreen mentioned “Very relevant to me”. LOL! Because it is!

You see, I am going back to one of my first/oldest formulation dealing with Salicylic Acid. I found this page and wow…Only then I realise I could actually use that little solvent! It is because my formulation has damn high amount of Propylene Glycol and PEG-40 Hydrogenated Castor Oil. 0% Water. Result is very stick and felt weird. So, I left it.

When I tried solubilising 2% Salicylic Acid with 10g Propylene Glycol (according to the chart @ngarayeva001 share on here. I round 9.09g PG up to 10g instead for easy calculation and measurement). It works beautifully!

However, SA crystallises as soon as I add water to SA + PG!
THIS shows exactly it. Which is the reason why that lady says adding Sodium Citrate is imperative. This is a cheat! Sodium Citrate basically neutralises some SA and raises pH a bit.

Question: Am I doing/calculating it correctly?

According to my calculations:

(a) if 2% SA + 10g PG =>16.666% SA (Total final ‘volume’ is 12g)

(b) if 2% SA + 10% PG + 88% Water => 2% SA(Total final ‘volume’ is 100g or 100%)

Because it is in % so I naturally would go for (b).

Next, I replaced Water with 52% Ethanol. Et voila! Nice and clear solution!
And next, I replaced PG with PEG-40 HCO. Nice and clear solution as well!
Shines big time on skin but way way less sticky and uneasy feeling than my initial formulation!

But, I do not want water in it and I do not want too much PG.
In other words, I want to stay as close as what the chart shows which is using only 10g PG and SA stays 2% and is fully solubilised. Is this even possible to do so? Am I understanding the chart incorrectly?