[Homeslice]

This was right after spooning some of the soap into my glass beaker and adding some HCl (muriatic acid from Home Deopt).

[Homeslice]

Couple hours later, you can see the soap is breaking up a bit, but very slow.

[rolnor]

Nice with images! You should be carefull with the HCl, you fatty acid is sensitive, dont let it be to acidic for long time.

[Homeslice]

Thank you rolnor!

So the latest picture of the mix is below.

There is definitely two layers, the smaller darker one on top and the bigger lighter one on bottom, with some debris stuck in there. 

So is the top supposed to be pure free form fatty acids?  And the bottom NaCL/water/etc.?

rolnor, how would you suggest to be careful with the fatty acids?  Should I use an acid other than HCl?  Sulfuric acid maybe?  Or maybe use much less HCl so that there will be plenty of soap molecules to react with the HCl, with plenty of soap molecules left over, meaning no excess HCl in the mix to damage the fatty acids?

Thanks for any help everyone!!!

[rolnor]

You could controll pH of the solution when you add HCl, pH around 3 is acidic enough. You can use pH-paper if you dont have a pH-meter.

[Homeslice]

Thank you rolnor!

So what would you recommend I do with what is in that beaker?

I think I use a syringe or something to extract that top darker layer into a new beaker.  Then do a PH test on it with strips.  If its pure free fatty acids, or something close to it, I would guess its PH should be much closer to 7 than like 2 for HCl?  Then test what remains and I would guess it should be much purer to HCl PH.

Anyway to test what I skim off the top to make sure they are pure (or almost pure) free fatty acids?  Like some kind of spectrum (wrong word there) analysis or something?

On your point about controlling the PH of the solution when adding HCl, the problem is this - when I dumped the soap in the beaker, and started adding HCl, even just a little, when I held one of those PH strips even way above the mix, it turned very light, indicating a very, very low PH... and that was not any where close to dipped in the liquid, it was just the gassing of the HCl that made the PH strips show like PH 3 or 2 or even lower!

Here is what I am thinking, let me know what you think.  That layer at the top probably is the "good stuff", the free fatty acids.  The layer at the bottom is the "bad stuff", excess HCl that might denature the free fatty acids and what not.  So what if, by trial and error, I keep adding the same amount of soap every time, and slowly, each batch after the other, reduce the HCl amount, so that in the perfect version all I have is the dark liquid at the top (pure free fatty acids I hope) and none at the bottom (the unreacted HCl that could be denaturing the fatty acids)?  Does that make sense?

To speed the process, any problem using a stick blender to blend the two together each time?

Thoughts?

Thanks so much!!!

[rolnor]

You could have a very small amount of phenolphtalein as pH-indicator in the solution, this will turn from red to collorless when the pH is below 7.
If you have a separatory funnel it would be easy to wash you top-layer with water.
Then, as you suggest you need maybe a NMR-spektrum of your raw fatty acid.
I dont know the purity you will get, it depends on what other fatty acids are present in your starting material.

[Homeslice]

Thanks rolnor!

OK, so here is what I did.  I used a big syringe thing and slowly sucked the brownish top layer out of the beaker and into another one, leaving the more yellow liquid in its own beaker.  Then I used PH strips on both.  The brownish one is a PH of like 6 to 7 it looks like, the yellowish one is still like a 2 or something!

So there are three things that came out of it:

The brownish liquid

The yellowish liquid

Some white flakes that settled out on the bottom that you can see still in the beaker with the yellowish liquid.

So... is the brownish one pure free fatty acids, or something close to it?

Thanks!  Pics below!!!!

[Homeslice]

[Homeslice]

[rolnor]

Good!

I dont think its pure fatty acid but its probably a mixture of different fatty acids. Hopefully the strong HCl has not destroyed your product. Do you have access to some analytic instruments? NMR would be the most conclusive method.

[Homeslice]

Thank you rolnor!  I do not have any analytic instruments myself, I'll research NMR to see if it is something I can afford.  Or are there places that can do the testing for me at (hopefully) reasonable prices?  What should I search for on the internet if I am looking for them?

Also, check out this summary of a scientific process that is apparently aimed at doing just what I am trying to do:

Saponification and Purification of Free Fatty Acids
Procedure
Reflux for 15 minutes a mixture of 200 gr. oil and 400 ml. of a 20% alcoholic potassium hydroxide. (Note 1) Cool the flask under tap water and acidify the solution to Congo red paper with dilute sulfuric acid. (Note 2) Cool again if necessary; extract the fat acids repeatedly with a total of 1500 ml. of petroleum ether (bp 30°-60° C) and transfer the washings to a 2-liter separatory funnel  3  times, with 200 ml portions of distilled water or until the last wash is neutral to Congo red paper.  (Notes 3, 4) Then dry the washings with 50 gr. anhydrous calcium sulfate, filter and remove the solvent from a water bath. Final traces of solvent are removed by passing a stream of nitrogen or carbon dioxide through the fat acids in vacuo. The neutralization equivalent should be about 280, acid value 200. (Note 5)

Notes:

The alkali is prepared by dissolving 50grof potassium hydroxide in 50 ml of water and then adding 350 ml of commercial absolute ethanol. Sodium hydroxide should not be used because the sodium soaps formed on saponification will not be soluble in the volume of alcohol used.
The dilute sulfuric acid is prepared by pouring 50 ml onto 200 gr cracked ice.
Emulsions may be broken by adding salt to the funnel so that it falls through the interface.
Litmus paper should not be used since it frequently turns red due to the acidity of the fat acids.
If the neutralization equivalent is too high, the saponification should be repeated.




It looks like they do pretty much what I did to start (only using sulfuric acid rather than HCl, which would probably make you happy since it would be less likely to destroy the fatty acids, your concern , but they didn't just stop where I did, they went a step further and apparently used ether to try and extract the fatty acids from what is I assume the dark brown layer in my experiment.  Does that make sense to you?  I think they are implicitly saying that the dark brown layer is several things in addition to fatty acids, and to get anything close to pure fatty acids you have to use the ether to extract them (which presumably will not extract those other things).  Then I assume I can boil off the ether and be left with something close to pure free form fatty acids (of different kinds, whatever the oil started with of course).

Does that make sense to you?  Also, do you feel pretty comfortable that it is the dark brown layer that contains the fatty acids in my experiment, not the yellow layer (which I can't imagine it does given its super low PH, seems like it is the left over HCL), but also not those white solids at the bottom - any idea what those white solids are?

Here is a link to the study above, it is the first one on the page.

https://lipidlibrary.aocs.org/chemistry/physics/lipid-chemistry/methods-of-preparation-of-fatty-acids-and-their-derivatives-laboratory-exercises#Saponification

Thanks again!!!

[rolnor]

They neutralize to congorred pH-paper and that was my concern, if you use to much acid you can destroy the product. Sulphuric acid or hydrchloric acid is probably OK but it should be diluted, its easier to dose. It is better to use petroeum ether, its easier to wash the fatty acid-layer but its probably not important  for purification, if you have by-product it will also go in the ether-layer. NMR-instruments are expensive even if very small so you need to contact a university. There are some companies that sell these services but thats also expensive.

[Homeslice]

Thank you rolnor!  So let me see if I got this right about that procedure they described.  I can't really follow some of it.  Here is what I am thinking about each step, let me know how you think I did?

___________

"Reflux for 15 minutes a mixture of 200 gr. oil and 400 ml. of a 20% alcoholic potassium hydroxide." and the associated note:  "The alkali is prepared by dissolving 50grof potassium hydroxide in 50 ml of water and then adding 350 ml of commercial absolute ethanol. Sodium hydroxide should not be used because the sodium soaps formed on saponification will not be soluble in the volume of alcohol used."

I think I have this one.  Dissolve grams of potassium hydroxide in 50 ml of distilled water, then add 350 ml of "commercial absolute ethanol".  Just stir/shake this until it dissolves/mixes.  I have no idea what "commercial absolute ethanol" is, but I have Everclear by me that is 90% ethanol so that should be pretty close, and I think the other 10% is water so I can just adjust accordingly. 


_________


"Cool the flask under tap water and acidify the solution to Congo red paper with dilute sulfuric acid." and the note:  "The dilute sulfuric acid is prepared by pouring 50 ml onto 200 gr cracked ice."

The note is easy.  Just mixt 50 ml of sulfuric acid and 200 grams of very cold distilled water (or even frozen distilled water).  But when it says "acidify the solution to Congo red paper", what does THAT mean?  Congo red paper is a PH indicator paper I understand, but the color changes the higher the PH goes higher.  So is that saying that you keep adding the sulfuric acid solution until the paper stops turning red when you test it, and stays blue (i.e. when its PH 3.0 or below)?

___________________

"Cool again if necessary; extract the fat acids repeatedly with a total of 1500 ml. of petroleum ether (bp 30°-60° C) and transfer the washings to a 2-liter separatory funnel  3  times, with 200 ml portions of distilled water or until the last wash is neutral to Congo red paper.  (Notes 3, 4) "


This is also confusing to me.  By extract the fat acids repeatedly, I take it he is saying you pour a total of 1500 ml of petroleum ether on top, which should extract the fatty acids, then transfer that ether to the separatory funnel?  But then he gives the 200 ml x 3 figure, but that does not equal 1500 ml.  Maybe the 3 x 200 referred to distilled water, but I am not sure.  That whole description seems to be off, missing something.  Any idea?


__________

"Then dry the washings with 50 gr. anhydrous calcium sulfate, filter and remove the solvent from a water bath. Final traces of solvent are removed by passing a stream of nitrogen or carbon dioxide through the fat acids in vacuo. The neutralization equivalent should be about 280, acid value 200. (Note 5)"

So, I think he is saying you mix 50 grams of calcium sulfate (I don't know what anhydrous means, but I'm assuming regular calcium sulfate will do the trick) with SOMETHING, the "solvent".  I thought calcium sulfate was a drying agent to remove the last vestiges of water from the ether and fatty acid mix, which would make sense, but the language "remove the solvent the water bath" makes me think I have the whole thing wrong. 



Actually I realize I understand very little of that after typing that all out.

Can you help me understand it further rolnor?

Thanks!!!