Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Homeslice on November 13, 2021, 01:45:21 PM
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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/ (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 (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!
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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?!?!
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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?
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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!
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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 (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 (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!
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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.
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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.
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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!
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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!!!
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On an analytical scale, I would look into reverse-phase HPLC.
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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.