I am trying to extract some essential oil from spearmint leaves, I've done a steam distillation and now i'd like to carry out a solvent extraction on
the distillate. I think hexane is best solvent but I don't currently have any. I do have a few cans of lighter fluid though... do you think naptha
would work to extract the oil?Yttrium2 - 30-8-2022 at 12:25
Not all lighter fluid is the sameYttrium2 - 30-8-2022 at 12:26
I’d bet a vacuum fractional distillation if the essential oil would yield the best productOneEyedPyro - 30-8-2022 at 14:18
I'd guess naptha would pull out a lot of undesired compounds.
Naphta will do
Organikum - 30-8-2022 at 14:31
As pure Hexane and the other aliphatic hydrocarbons which make up petrol ether aka VM Naphta or "Wundbenzin" in German are horrible expensive here I
afford them only for chromatography and analytical purposes and use when ever Hexane or another small hydrocarbon is called for in extractions or
similar, in special when large amounts are needed just petrol ether 40/60 or if bp is no issue even the 80/100 variation ("Reinigungsbenzin" in
German) and I had no problems whatsoever up to now. Naphta is already a very selective solvent as the mix it is, the difference to pure Hexane is
marginal. Aromatics, well thats an complete different story then.
Naphta will do, I would bet on it. Chemgineer - 30-8-2022 at 15:01
@Organikum Thanks for confirming my thoughts, also I think I should buy a few litres of petrol to have on standby.PirateDocBrown - 31-8-2022 at 05:54
If you are in the States, Coleman stove fuel.
But I'd prefer a polar solvent first, like absolute ethanol or ethyl acetate.Tsjerk - 31-8-2022 at 10:28
But I'd prefer a polar solvent first, like absolute ethanol or ethyl acetate.
It is a liquid liquid extraction, so ethanol won't do. Ethyl acetate takes up a lot of water, so be sure to dry it. Also, if hexane seems best, a
non-polar would be better.
If you have some random naphtha and want to be sure, you can evaporate some to see if it leaves a residue.j_sum1 - 31-8-2022 at 18:33
I distil petrol (gasoline) and collect a suitable fraction for extractions like this.
You can also clean it up with KMnO4 to get rid of any unsaturated hydrocarbons. And then distil a second time.
You will end up with a mixture of (probably) hexane and heptane isomers with a small amount of benzene, but it should be suitable for your purposes.
The heads and tails I pop back in the car. It does not seem to have any ill effect whatsoever.
And the good thing is, this process is a cheap and relatively quick way of obtaining useful solvent. Yttrium2 - 31-8-2022 at 20:09
Why wouldn’t ethanol work?
What’s the Kmno4 do?j_sum1 - 31-8-2022 at 20:55
Ethanol will not be suitable in this case because it is miscible in water and the OP is attempting a liquid-liquid extraction.
KMnO4 reacts with unsaturated hydrocarbons to form various oxidated species. These are generally soluble in water and so tend to stay in solution
with the permanganate. However, I still like to redistil to make sure my solvent is as pure as possible.
There may be some aromatics. But these tend to be in relatively low concentration in gasoline. Additionally, they generally have a much higher BP.
Toluene has BP of 110. The only one that will come over in a hexane-heptane fraction will be benzene -- at less than 3% where i live.
If you need something with no aromatics, it is better to start with kerosene. I hope this weekend to get an aliphitic mix with BP between 150C and
180C for a project. Kero will be my starting material. I will collect and clean some lighter fractions while I am at it.PirateDocBrown - 1-9-2022 at 04:40
Ah, I didn't perceive it would be a a liquid-liquid. I thought he was gonna do a do-over. I would extract from leaves in this manner via Soxhlet, then
go from there.
But he's done a steam distillation, and has collected the insoluble oil off the top of the distillate? Sounds like he needs a frac distil more than an
additional extraction.
J_sum is correct, Yttrium2. KMnO4 generally reacts with alkene bonds to replace them with paired oxo groups. (AKA carbonyls) Redistillation there is
usually effective, as he says, not only because of greater solubility of carbonyls, but it also raises the BP over the origin material. (example:
butylene would go to acetone, BP goes from 19 to 56)
j_sum, you'd be surprised how much toluene is in unleaded motor fuel. I did a survey back in undergrad instrumental analysis class of gasoline samples
and found toluene concentrations over 30%, with a few % benzene, as well.
Coleman stove fuel is largely straight run distilate, without refinery reformation.
But "odorless" painters naphtha should also be very low in aromatics, as well.
[Edited on 9/1/22 by PirateDocBrown]j_sum1 - 1-9-2022 at 05:31
j_sum, you'd be surprised how much toluene is in unleaded motor fuel. I did a survey back in undergrad instrumental analysis class of gasoline samples
and found toluene concentrations over 30%, with a few % benzene, as well.
I am sure there is a bit.
But if I collect the fraction below 85°C say, then there should be little toluene as its BP is a lot higher.
The problem I have here in Oz is that there are a large number of paint thinners, laquers, solvents, white spirits etc products. All of them say
"petroleum distillate" on the label and on the SDS. So, without buying one of each and running some sophisticated lab tests, I do not know what is in
what product. I have not seen Coleman fuel for years although it might be around. So, there is undoubtedly a more concentrated source of hexanes out
there. What I have however is a relaiable method for obtaining a suitable clean solvent for extractions. To be fair, I have not run it through its
paces properly yet, but it seems to have worked on the few occasions I have used it.Tsjerk - 1-9-2022 at 08:06
But he's done a steam distillation, and has collected the insoluble oil off the top of the distillate? Sounds like he needs a frac distil more than an
additional extraction.
[Edited on 9/1/22 by PirateDocBrown]
Fractional distillation of the essential oil? Spearmint oil contains mostly carvone, which boils at 231 degrees. You would have to do a vacuum
distillation, but why would you if you don't want one specific component? When you extract with a low boiling non-polar you only have to dry and
evaporate the solvent. Which you can do under atmospheric pressure or under vacuum, but still a whole lot easier than doing a vacuum distillation.
Also a liquid liquid extraction with a non-polar is much more efficient as the volume of the organic layer becomes bigger and you extract all the
goodies from the (probably large volume) water.PirateDocBrown - 1-9-2022 at 11:33
Well, around here, car starter fluid, from which I extract diethyl ether, is also 50%+ n-heptane. It might be easiest to distil a few cans of this
(Doug did a video of this), and use the heptane. As a bonus, you get some ether, too!
