Deathunter88
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Separating a Mixture of 1-Octanol and Octyl Acetate
Greetings,
Today I attempted to perform the synthesis of octyl acetate from 1-Octanol and glacial acetic acid with concentrated sulphuric acid as a catalyst.
Below are the amounts used.
• 72ml Glacial Acetic Acid
• 104ml Octyl alcohol (1-Octanol)
• 18ml Concentrated sufuric acid, 8ml added at the start, another 10ml added about 1 hour later.
I refluxed everything in a 500 RBF for about 1.5 hours and everything turned a deep black. I then dumped everything in a 1L beaker and added 200ml of
distilled water, stirred it and let it separate. It separated into two layer, the aqueous layer on the bottom being deep gray with the layer of
1-octanol and acetyl acetate completely black. I did this 2 more times but every time the wash water is still dark grey and the 1-octanol and octyl
acetate is still deep black. The mixture smells horrible and makes me nauseous so I want to handle it as little as possible. Thus comes my question;
How do I separate the mixture of unreacted 1-Octanol, acetic acid and sulphuric acid from the Octyl acetate? I am assuming the mixture I have contains
mostly 1-octanol and octyl acetate because most of the sulphuric acid and acetic acid should have been washed away. These two substances have very
similar characteristics which makes it hard to separate. I could attempt fractional distillation but they only have a difference of 8 degrees C at
worst and a difference of 16 degrees C at best which would be a challenge. Is there any other way of separating the two other than distillation?
1-Octanol:
BP-195 degrees C
Density: 0.824g/cm^3
Solubility in water: 0.460 g/liter
Soluble in: Ethanol
Octyl Acetate
BP-203–211.3 °C
Density: 0.863–0.87 g/cm^3
Solubility in water: 0.018 g/100 g
Soluble in: Ethanol, Diethyl Ether
My procedure is modified from:
http://www.chemicalforums.com/index.php?topic=10300.0
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Cou
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Fischer esterifications sometimes result in a dark brown reaction mixture because of impurities. That's why you always distill the ester once you
isolate it from workup, to remove the organic crap.
You can ensure almost all of the 1-octanol is consumed by using a large molar excess of acetic acid (five fold), and/or doing the reaction in toluene
so a Dean-stark trap removes water and drives the reaction further.
This semester I'm hoping to do some research on this issue of purifying esters made from long-chain alcohols. Typical workup may not be effective
because the long-chain alcohol isn't soluble in water. Since 1-octanol is much more soluble in water than octyl acetate, you may be able to remove it
with several washes with a large volume of water. I'll find out if washing with water is effective, by using TLC chromatography or GC-MS to see if
there are two components in the ester product. If water washes don't work, you may have to do column chromatography to separate them.
Deep eutectic solvents have been used to separate alcohols and esters.
https://www.sciencedirect.com/science/article/pii/S004040391...
[Edited on 13-3-2020 by Cou]
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Dr.Bob
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If you wash the mix with sat'd NaHCO3, it will help remove any traces of acetic or sulfuric acid, which will help clean it up. If you have any
organic solvent, this will help partition the ester away from the water, but not likely needed, as it is its own solvent. If you have any silica gel
available, just pushing it through a short plug of it, will remove much of the polar stuff, which is likely the grey or black stuff. Distillation
would also do a great job as well. You may also have some octyl sulfonate or similar material as well.
[Edited on 13-3-2020 by Dr.Bob]
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UC235
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Sounds like you had some charring due to high reaction temp and a relatively large amount of sulfuric acid. Probably some octanal was formed and
condensation resulted. I would use a considerable excess of acetic acid if you're going to repeat it. Also, I would recommend p-TsOH which is
non-oxidizing. For this particular compound, the boiling points make things really difficult to separate. Both are effectively insoluble in water. To
clean up a product with only a little octanol in it, the easiest option if you have it available, is probably just to treat with acetic anhydride and
a little acid catalyst. The overall usage would be much less than making it all from anhydride.
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