Benzoic acid soluble in lotion base?

[PuddinAndPeanuts]

Ok, so I'm making an ointment for my nasty athletes foot. I'm using 6% benzoic acid with salicylic acid in a basic lotion base I got from WSP. Per the available literature, benzoic acid is soluble it hot water, alcohol, and in "volatile & fixed oils". I added the benzoic acid (which has a coarse crystalline texture kind of like kosher salt) to the lotion base, and it's currently grainy. I would imagine that the oils used in the lotion base are considered fixed oil (?), and the fragrance oil is possibly a volatile oil (?). (Total random guess there- but concocting bath and body products off the cuff based on intuition and random guesses seems like it might be a great way of adding excitement and adventure in my life... No? Bad idea???)
Anyway- would the chemists among you imagine there's a likelihood the benzoic acid will dissolve over the next day, or should I go ahead and just order the mortar and pestle?

Thanks!

 

[DeeAnna]

You can't assume just because something is soluble in a solvent that this means a lot will be soluble. You have to look at the specific solubility of the material in each of the solvents you're working with.

According to wikipedia, benzoic acid is soluble at 2.7 g/L in water at 20 C, and 4.2 g/100 g of olive oil. You can't look at elevated temps for solubility of the "Bacid" in water cuz you're using the product at room/body temps. If you got the Bacid to dissolve at higher temps, and cooled it down, some of it would crystallize back into solid form when cooler.

A basic lotion might be 70% water and perhaps 25% oils (yes, fixed oils). If you use essential oils (yes, volatile oil) at 1% or so, the EO content is so small, the EOs aren't going to do much. For the sake of this quick look-see, I'm going to ignore them.

100 g of base => Assume 25 g oils, 70 g water

2.7 g Bacid in 1000 g water => 2.7 X 70 / 1000 = 0.2 g Bacid in the water
4.2 g Bacid in 100 g oil => 4.2 X 25 / 100 = 1.1 g Bacid in the oil

Total Bacid = 0.2 + 1.1 = 1.3 g Bacid in 100 g base

That's a long ways from 6%. Also I have no idea how benzoic acid and salicylic acid might interact and affect each other's solubility. Might be no big deal, but I just don't know that. I haven't spent a lot of time analyzing this, but this should get you started. What is an ingredients list for a product that has this level of acids? Is it more of a salve (higher in fats)? Or are there products in lotion form?

Source: https://en.wikipedia.org/wiki/Benzoic_acid

 

[PuddinAndPeanuts]

You can't assume just because something is soluble in a solvent that this means a lot will be soluble. You have to look at the specific solubility of the material in each of the solvents you're working with.

According to wikipedia, benzoic acid is soluble at 2.7 g/L in water at 20 C, and 4.2 g/100 g of olive oil. You can't look at elevated temps for solubility of the "Bacid" in water cuz you're using the product at room/body temps. If you got the Bacid to dissolve at higher temps, and cooled it down, some of it would crystallize back into solid form when cooler.

A basic lotion might be 70% water and perhaps 25% oils (yes, fixed oils). If you use essential oils (yes, volatile oil) at 1% or so, the EO content is so small, the EOs aren't going to do much. For the sake of this quick look-see, I'm going to ignore them.

100 g of base => Assume 25 g oils, 70 g water

2.7 g Bacid in 1000 g water => 2.7 X 70 / 1000 = 0.2 g Bacid in the water
4.2 g Bacid in 100 g oil => 4.2 X 25 / 100 = 1.1 g Bacid in the oil

Total Bacid = 0.2 + 1.1 = 1.3 g Bacid in 100 g base

That's a long ways from 6%. Also I have no idea how benzoic acid and salicylic acid might interact and affect each other's solubility. Might be no big deal, but I just don't know that. I haven't spent a lot of time analyzing this, but this should get you started. What is an ingredients list for a product that has this level of acids? Is it more of a salve (higher in fats)? Or are there products in lotion form?

Source: https://en.wikipedia.org/wiki/Benzoic_acid

Deeanna- first, I want to thank you for your help. I've lost count of the number of times I've posted obscure questions like this, and you've taken a moment to educate me on something. You are incredibly generous with your time and knowledge and I always appreciate it.

I actually posted about this last week or the week before, and I think you were kind enough to help me get the info I needed to get started. It's Whitfield's ointment.

In the U.S. It's traditionally made with 6% benzoic acid and 3% salicylic acid in a petroleum jelly base. Someone or other (might have been you?) was sweet enough to post a link to a document that was published by (I think) the World Health Organization. Part of that document discussed the difference between the North American version and the version WHO recommends, which is 5% benzoic and 5% salicylic in a lotion base, which they seem to feel is a more effective formula.

I opted to make a version more similar to the WHO version, with 6% benzoic and 5% salicylic in a lotion base. (Let me stress- not for sale. Strictly for our household).

Anyway, it's been several hours, and from what I can tell, the benzoic acid seems to be well on the way to dissolving. I didn't touch it, but to stir and look at it now, it seems almost (but not quite) completely smooth.

My dad actually ordered some Whitfield's ointment for me from an online pharmacy and had it sent (North American formula). I'm really looking forward to using a version on each foot and doing a side by side comparison.

 

[DeeAnna]

Hey, if it seems to be dissolving, that's good! Math can take a person only so far -- the proof of the pudding is real life testing. I hope you'll share your results with the two types of products. I've seen differences in oil-based and water-alcohol based versions of my bug repellent as far as which one lasts longer (oil) and which one feels better (water-alcohol). So I'm curious to see what you find out!

 

[PuddinAndPeanuts]

Hey, if it seems to be dissolving, that's good! Math can take a person only so far -- the proof of the pudding is real life testing. I hope you'll share your results with the two types of products. I've seen differences in oil-based and water-alcohol based versions of my bug repellent as far as which one lasts longer (oil) and which one feels better (water-alcohol). So I'm curious to see what you find out!

Will do. Remember- the two versions I'm using differ not only in their base, but also in whether 3% or 5% of salicylic acid was used.

Between the lotion vs. ointment base, I believe that the lotion base is supposed to be more effective for treatment, but have a shorter shelf life due to the ingredient becoming inert after time. (I can't recall if that was from the WHO document, or a conclusion I came to after talking to my dad who was a pharmacist once upon a time). Regardless, yes, I'll make sure to share the results.

 

[PuddinAndPeanuts]

Update: the benzoic acid was not nearly as dissolved as it looked yesterday. There's still lots and lots of very large grains. Im running to Walmart to get a mortar and pestle and remake it.

 

[cmzaha]

Could you not make a lotion and use sodium benzoate in the the water phase and white willow bark in the water phase, since both are water soluble? You would have to do some research and find how to preserve the lotion. At least then you will be assured of getting the ingredients dissolved. Lotioncrafter has White Willow bark extract. With a premade base I would worry about affecting the preservation system and the possibility of the product not dissolving. Sodium Benzoate which becomes benzoic acid when dissolved is most effective in products with a ph of 4.5% or less. As ph goes higher the effectiveness decreases. So the use of a ph meter is really necessary

I really think I would just purchase the OTC cream/ointment that is proven to work.

 

[PuddinAndPeanuts]

Just an update on this experiment.

I ended up making another batch where I ground the benzoic with a mortar and pestle. Though it seemed powdery at the moment, I dont think it was ground as much as I thought it was. Still big grains.

I found that the foot with the pharmacy prepared version was healing better than mine. I don't think my benzoic acid was ground fine enough and I'm nearly certain that my salicylic acid is something else. I need to find out how to test salicylic acid to get an idea if that's what this is... Seems chemically inert to me.

In the end, after a few weeks of one preparation on each foot, I went to the podiatrist for an unrelated issue. Both feet still showed signs of athletes foot, but the non-homemade version was clearly more effective. I now have a prescription cream that cleared it up in about a week.

 

[Soapmaker145]

Suspending a finely ground chemical in a medium is not the same as dissolving a chemical to make a solution. A suspended chemical is not likely to do much of anything. The most you can hope for in a suspension is that some of the chemical will get dissolved over time and become reactive.

 

[PuddinAndPeanuts]

Suspending a finely ground chemical in a medium is not the same as dissolving a chemical to make a solution. A suspended chemical is not likely to do much of anything. The most you can hope for in a suspension is that some of the chemical will get dissolved over time and become reactive.

I see your point, but the basic recipe was found in a World Health Organization document- surely WHO isn't recommending crap recipes?

 

[Soapmaker145]

Mistakes happen even when experts write highly technical documents. There might be omissions that are critical to achieving the desired outcome. They may expect pharmacists to have technical skills that the average person doesn't necessarily have.

When I made a salicylic acid solution, I added SA slowly to various liquids and measured how many grams I can dissolve in each liquid. I had a highly technical paper that gave me an idea what to expect. I even tried some of the solutions I made to see how my skin reacts to them. If you want something that works for you, there is no substitute for doing your own testing with the chemicals that you have available. All the advice and the printed documents can take you only so far.

 

[The Efficacious Gentleman]

Could be. Even in cookbooks, a knowledge of methods is often assumed. "Blanch the vegetables....." Is fine, if one knows what blanching is. Apparently it has nothing to do with one of The Golden Girls.

In this case, how thick is your product?

 

[Soapmaker145]

In this case, how thick is your product?

I don't know if this is a question for me or the OP. For SA, I ended up using propylene glycol and the final product has the same viscosity as PG. I tested commercial products first but ended up making my own because the commercial products had added herbal extracts of questionable value and unknown safety.