[Homeslice]

I am a total chemistry novice.  I've read this study like 100 times, and I cannot figure out exactly what it is saying.  Here it is:

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:

1.  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.
2.  The dilute sulfuric acid is prepared by pouring 50 ml onto 200 gr cracked ice.
3.  Emulsions may be broken by adding salt to the funnel so that it falls through the interface.
4.  Litmus paper should not be used since it frequently turns red due to the acidity of the fat acids.
5.  If the neutralization equivalent is too high, the saponification should be repeated.



I understand the first sentence I think, that is saponifying the oils to make the free fatty acids. 

The second sentence I *THINK* is saying to keep adding sulfuric acid to the saponified mix until the congo red paper turns blue? 

Then after that I really have no clue.  Too short-hand for me, and my knowledge of chemistry is too limited.

I would sure appreciate any help on understanding all that!

Thanks!!!

[Borek]

https://www.youtube.com/watch?v=8bZl7mcG0Ew

Total of 1500 mL petroleum ether means more or less "do three extraction steps using 500 mL in each".

"Dry the washings" - add solid anhydrous CaSO₄, leave it for several hours, then filter the solid (that absorbed the water) out and you are left with mostly dry solution of fatty acids in the petroleum ether.

Solvent is then just boiled out in a controlled temperature (recover it using a condenser).

[Homeslice]

Thank you Borek!  OK, see if you think I have described it right:

1.  Make a 50 gram potassium hydroxide/50 gram distilled water/350ml ethanol solution (mix the PH and water first, add the ethanol once PH has been dissolved.

2.  Mix the solution make in #1 with 200 grams oil.

3.  Cool the solution from #2.

4.  Make a sulfuric acid solution by adding 50 ml of pure sulfuric acid onto 200 grams of distilled cold water/ice.

5.  Add the solution from #4 slowly to the solution cooled in #3 until congo red paper turns blue when you test it.

6.  Once the congo red paper turns blue, add the solution from #5 to a separatory funnel.

7.  After making sure the solution in the separatory funnel has cooled, do this three times:  add 500 ml of petroleum ether, shake the separatory funnel well, wait for several minutes, add 200 ml of distilled water, shake the funnel well again, wait for several minutes. Discard the water layer, add to each of the remainders 50 grams calcium sulfate, shake well, filter out the solids and you are left with the fatty acids in the petroleum ether.

8.  In a distillation condenser, boil each of the fatty acid/ether mixes at a relatively low temperature, say 60 degrees Celsius, which will cause the ether to be boiled off (and can be used again), with the remainder being mostly free fatty acids.

I have no idea about that last part about a stream of nitrogen or carbon dioxide, but it sounds like that would just purify the fatty acids a weeee bit more, not too worried about that.

How'd I do? 

Thanks Borek!!!

[Borek]

2.  Mix the solution make in #1 with 200 grams oil.

3.  Cool the solution from #2.

Keep it boiling under condenser (so that ethanol drops back) in between.

7.  After making sure the solution in the separatory funnel has cooled, do this three times:  add 500 ml of petroleum ether, shake the separatory funnel well, wait for several minutes

So far so good.

add 200 ml of distilled water

Nope. Separate two layers pouring the bottom one into flask. I am not sure which one will be witch, most likely the upper one will be the petroleum ether - so you need to first pout the lower layer into a flask, then the upper layer into another flask, then the first layer back to the funnel and here is where th eprocedure starts over.

Discard the water layer

Only if you are 100% percent which layer is which.

add to each of the remainders 50 grams calcium sulfate

Nope, combine all parts of the petroleum ether together, no need to keep them separate.

shake well, filter out the solids and you are left with the fatty acids in the petroleum ether.

8.  In a distillation condenser, boil each of the fatty acid/ether mixes at a relatively low temperature, say 60 degrees Celsius, which will cause the ether to be boiled off (and can be used again), with the remainder being mostly free fatty acids.

See above, work with one combined volume.

[Homeslice]

Thank you Borek!!!!

So see is this is right for a "revised" #7:

7.  After making sure the solution in the separatory funnel has cooled, do this three times:  add 500 ml of petroleum ether, shake the separatory funnel well, wait for several minutes.  Separate the two layers into two different flasks, one with the ether (and what has now been absorbed into it) and the other with the remainder.  Repeat twice, adding 500 ml more ether to the non-ether flask each time, shaking and separating.  After that is done three times, combine all the ether amounts into one flask.  Add 200 ml of distilled water to that flask, shaking well, and waiting for several minutes thereafter.  Assuming you can identify the water layer, discard it.  Add 50 grams calcium sulfate to the ether amount, shake well, filter out the solids and you are left with the fatty acids in the petroleum ether, boil off the ether in a vacuum distillation apparatus to recapture and be able to reuse the ether.

How'd I do?

Thanks!!!

[Borek]

Yes, sounds right now.