[Homeslice]

I was looking at the boiling point of various fatty acids.  Gamma linolenic acid, its boiling point is listed here at 125 degrees Celsius:

https://www.tuscany-diet.net/lipids/list-of-fatty-acids/gamma-linolenic/

"In purified form its melting point is from -11.3 (11.66 °F; 261.85 K) to -11 °C (12.2 °F; 262.15 F) and boiling point at 125 °C (257 °F; 398.15 K) at 0.05 mm Hg."


I've seen at least one other place list is at 125 degrees Celsius as well.

But then here it is listed as ~379 degrees Celsius:

https://www.chemicalbook.com/ProductChemicalPropertiescb3238150_EN.htm


And any many, many other places it lists as ~379 degrees Celsius as well.

So what gives?  They are both talking about the exact same thing so far as I can tell.  Why one earth do they list such different boiling points (especially when they agree exactly on the melting point!)?

Thanks!

[Homeslice]

I am seeing gigantic differences for other fatty acids as well.  Linoleic acid is said in some places to have a boiling point of like 230 Celsius but other places is listed at like 386 Celsius and others like 446 Celsius!

And I don't think they are talking about different forms, I'm looking at their molecular formula and they are all showing the same....

What gives?!?!

[mjc123]

Note that reference says 379±11°C (a large uncertainty) - "predicted". That is, not measured.
The other says 125°C at 0.05mmHg. Do you appreciate the point of specifying the pressure?

[Homeslice]

Thanks mjc123!  I saw the +- thing, no big deal.  On the .05mmHg, I had no clue what that meant, I assumed it had to be something at least a little close to a standard 1 atmospheric pressure.  But I googled that, and it seems 760mmHg is 1 atmospheric pressure, so that was just a tiny, tiny fraction of an atmospheric pressure?  Wow, I guess that explains that!  Why would they quote something so weird?

Thanks!

[Homeslice]

Still, other things not adding up.  I mentioned linoleic acid, seeing different numbers for that one too.  Check out this site:

http://www.chemspider.com/Chemical-Structure.4444105.html


If I click on "properties", then "experimental boiling point", is gives two sources of it being 407.82 Celsius at 760 mmHg, which is one atmosphere I believe (what would be relevant to someone actually trying to convert it to a gas).

But then this link:

http://www.thegoodscentscompany.com/data/rw1045901.html

Lists the boiling point at 365 to 366 degrees Celsius at the same 760 mmHg!  That is a big difference.

Any ideas?

Thanks!

[Borek]

These numbers are not 'real' - fatty acids will decompose long before boiling. Most likely these are attempts at predicting boiling points, there are different methods that give different results. None of these guesses has a practical meaning.

[Babcock_Hall]

Some compounds are purified by distillation under reduced pressure, especially when then would decompose if one attempted to distill them at atmospheric pressure.  I do not know from experience whether or not it would be possible to distill this compound at reduced pressure, but I have my doubts.

[Homeslice]

These numbers are not 'real' - fatty acids will decompose long before boiling. Most likely these are attempts at predicting boiling points, there are different methods that give different results. None of these guesses has a practical meaning.

Thank you Borek, understood!

[Homeslice]

Some compounds are purified by distillation under reduced pressure, especially when then would decompose if one attempted to distill them at atmospheric pressure.  I do not know from experience whether or not it would be possible to distill this compound at reduced pressure, but I have my doubts.

Thank you Babcock_hall!  So, if I wanted to separate those two, how could I realistically go about it?  Thanks!!!

[Babcock_Hall]

On an analytical scale, I would look into reverse-phase HPLC.

[rolnor]

I think you can forget about separation, you need expensive equipment. Maybe if you find some neat procedure in the litterature but I think you need very low vacuum distillation with a good distillation column.