Sciencemadness Discussion Board

Synthesis of Oleic Acid from Olive Oil

Mindchemist - 28-3-2011 at 16:53

Extraction of triolein from olive oil – 3 liters of extra virgin olive oil are poured into a 5 liter one necked boiling flask and the flask is set up for fractional vacuum distillation. The air is evacuated until the pressure is only 8 torr and the boiling flask heated gradually to 240C. Collect what comes over from 230-240C. What has been collected is reasonably pure (>97%) triolein.

Conversion of triolein to glycerol and oleic acid – (Scale up conversion as necessary) 1 liter of triolein created in the last step is placed in a 5 liter flask and 1,300 grams of a 10% sodium hydroxide solution is added. The solution is heated and stirred with reflux at 100C for 3 hours. The solution is then heated to 100C to boil off the water. What should be left is sodium oleate in glycerol. Cool to room temperature and filter off glycerol. The glycerol can be further purified by a fractional distillation if glycerol is desired. Weigh the sodium oleate and add ten times that weight in water to the powder. Add one molar equivalent of 12M hydrochloric acid and stir for about thirty minutes. After this, let the solution settle for about a hour. Decant off the water and wash with more water until a clear, thick liquid is obtained (this is your oleic acid product, if you haven't already guessed). Distill the oleic acid if a very pure product is desired.

[Edited on 3-27-2011 by Mindchemist]

gsd - 28-3-2011 at 20:16


Nice write-up.

Have you analyzed the resulting fatty acid mixture?

How will it be "pure" oleic acid ? What happens to linoleic & stearic acids?
This wiki page is quite informative.
http://en.m.wikipedia.org/wiki/Olive_oil

Gsd

Mindchemist - 29-3-2011 at 16:21

The first distillation should get rid of any other fatty acids or triglycerides in the olive oil.

UnintentionalChaos - 29-3-2011 at 16:34

Did you actually do this, copy it from some paper, or are you making stuff up (seems like a lot of details for that though)?

If you did it, where is the procedure from, if a paper, can you give a reference/attach the paper.

gsd - 29-3-2011 at 16:57

Quote: Originally posted by Mindchemist  
The first distillation should get rid of any other fatty acids or triglycerides in the olive oil.

???
The first distillation will only get rid of FREE FATTY ACIDS including any free oleic acid - as a light cut.

Could you please explain how it will remove other acids which are combined with glycerol?

Mindchemist - 29-3-2011 at 17:26

Since the first distillation is done under a 8 torr vacuum the boiling points of the triglycerides differ enough to be separated by distillation.

gsd - 29-3-2011 at 18:23

Quote: Originally posted by Mindchemist  
Since the first distillation is done under a 8 torr vacuum the boiling points of the triglycerides differ enough to be separated by distillation.


You seem to be under impression that in an oil, all the three -OH of glycerol are combined with same fatty acid. Even in that case I fail to understand that how a triglyceride of stearic acid will distill ahead of that of oleic acid.

I suggest you first read some material on this subjest before trying to explain the "unexplainable"

Gsd

Nicodem - 30-3-2011 at 10:14

Mindchemist, please explain what this thread is about. Have you actually performed what you claim or is it just the product of your imagination? If the first, then provide the characterization data and references in support to your claims. If the second, then explain what was the purpose of all this.

bbartlog - 30-3-2011 at 13:30

Quote:
all the three -OH of glycerol are combined with same fatty acid. Even in that case I fail to understand that how a triglyceride of stearic acid will distill ahead of that of oleic acid.


While I also find it annoying when people post lab procedures without explicitly indicating whether or not they have, in fact, done what is described (shades of Anders Hoveland!), these particular objections seem irrelevant. Given that the substantial majority of the fatty acids in olive oil are oleic acid, a significant chunk of the triglyceride content will in fact be triolein. The writeup seems to recognize this. Further, there is no suggestion that stearic acid triglycerides are coming over ahead of triolein (where did you get this?). In short the writeup seems perfectly plausible, as far as I can tell; but like Nicodem I wonder what the purpose is. The detail (while decent enough) and references fall short of it being useful as something others can refer to in turn, and it doesn't seem like the author has any questions...

jon - 30-3-2011 at 17:51

what are you shooting for?
just heat the triglyceride with hydroxyethylamine under a shit load of heat and pressure.
ammonolysis of esters to make amides i think that's what you want.


[Edited on 31-3-2011 by jon]

gsd - 31-3-2011 at 05:39

Quote: Originally posted by bbartlog  
.......these particular objections seem irrelevant. Given that the substantial majority of the fatty acids in olive oil are oleic acid, a significant chunk of the triglyceride content will in fact be triolein. The writeup seems to recognize this. Further, there is no suggestion that stearic acid triglycerides are coming over ahead of triolein (where did you get this?).


The average composition of olive oil is: (Wiki)

Unsaturated Acids:
Linoleic acid : 12 %
Oleic acid : 72 %

saturated Acids:
Palmitic acid: 14%
Stearic acid: 4%

Anybody who has cared to study basics of Oleochemistry will know that the fatty acids are in a form of RANDOM triglycerides (see any text book on oils & fats - say Bailey)

Given the above composition, a gusstimate gives average composition of pure triolein not more that about 45 % in olive oil.

In absence of any actual boiling point data of triglecerides, it is logical to assume that the BPs of them will vary as per the BPs of corresponding fatty acids. The BP order of fatty acids is:

Palmitic(351 °C) < Oleic(360 °C) < Linoleic(365°C) < Stearic(383 °C)

So during distillation, triglyceride of Palmitic (not Stearic - that was my mistake) will come ahead of triolein.

The write-up doesn't show any attempt at fractionation. Hence the distilled triglycerides will in fact be a cocktail having all fatty acids and not 97+ triolein as the writer has presumed.

This is where I got it.
Quote: Originally posted by bbartlog  
In short the writeup seems perfectly plausible, ...


This is what I acknowledged at the beginning of my post.




bbartlog - 1-4-2011 at 04:28

'pure triolein not more that about 45 % in olive oil.'
Or even lower (wouldn't .72^3 be the baseline estimate, ignoring molecular weights?); but still a decent enough chunk.

'The write-up doesn't show any attempt at fractionation.'
...actually, he does:
Quote:
and the flask is set up for fractional vacuum distillation.


The point about palmitic acid is a good one, but it's still possible that pure palmitic acid triglycerides will come over below 230C at 8 torr, so that the temperature range specified in the writeup (230-240C) would give a decent cut. However, I suspect that you are basically right about this and that mixed triglycerides (how about palmitic, linoleic and oleic acid together?) would pass over in the same temperature range as the triolein, even with a good attempt at fractionation.

Eclectic - 1-4-2011 at 07:21

You might get good results with the fractionation if a little transesterification catalyst is added, say a prill of NaOH.

UnintentionalChaos - 1-4-2011 at 08:58

I would think that converting the oil to it's methyl esters via base catalysis and an excess of methanol before distilling would give best results. Of course, given the high and fairly close b.p. of the acids, you better be fractionating under vacuum with a damn good column.

jon - 1-4-2011 at 11:46

i was thinking the same damn that would be a hassle
rule of thumb (does'nt always apply) boils over 150 C use a vacum.


[Edited on 1-4-2011 by jon]