Cou
National Hazard
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Plan to analyze amount of unreacted 1-octanol in crude ester, and test if DES extracts 1-octanol
from what i've seen in the journal of chemical education, 1000 ppm seems to be the max concentration of organic analytes to avoid overloading a GC-MS,
in general.
I'm concerned that if making a series of external standards to find concentration of an unknown, concentrations like 25 ppm might be too low to get a
reliable peak height for 1-octanol. Don't know yet, i'll find out on tuesday. This tuesday we played around with the GC-MS but mostly wasted lots of
time.
a quick equilibrium calculation with Keq = 1 shows that in fischer esterification, with a 3 fold molar excess of acetic acid, only about 75% of the
1-octanol would be reacted, and there would still be 25% of unreacted 1-octanol which is difficult to remove. The goal is to find if DES can be used
to do this. https://www.sciencedirect.com/science/article/abs/pii/S00404...
[Edited on 10-14-2020 by Cou]
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Fery
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Cou you can shift equilibrium towards ester product using Dean-Stark trap adapter and adding e.g. hexane or benzene or maybe toluene...
or using acid anhydride instead of acid itself to avoid H2O formation completely...
just my theoretical ideas... keep up your good work
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Cou
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Quote: Originally posted by Fery  | Cou you can shift equilibrium towards ester product using Dean-Stark trap adapter and adding e.g. hexane or benzene or maybe toluene...
or using acid anhydride instead of acid itself to avoid H2O formation completely...
just my theoretical ideas... keep up your good work |
Using a dean-stark apparatus only works when the boiling points of both reactants are a good amount higher than the boiling point of the dean-stark
solvent.
For example, using toluene with acetic acid would cause acetic acid to boil into the trap, which screws up water separation because acetic acid and
water are miscible. Hexane might work, since its azeotrope BP is around 61 C whereas formic acid boils at 100.8 C. But I haven't tested this yet. It
doesn't take much acetic acid vapor to mess up water separation.
Yea you could probably use a dean-stark trap to react all 1-octanol, but I already got started on this project of DES extraction.
another thing is that using a dean-stark solvent just adds more tedious distillation steps in purification of the ester. I hate distillation, myself.
Low MW acids such as acetic acid, formic acid, etc, are cheap enough that it might be more convenient to use them in excess, and do a simple DES wash
to remove unreacted alcohol.
[Edited on 10-15-2020 by Cou]
[Edited on 10-15-2020 by Cou]
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Cou
National Hazard
Posts: 958
Registered: 16-5-2013
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Mood: Mad Scientist
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