Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: pcm81 on September 15, 2018, 07:25:14 PM
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In many youtube videos of soxhlet extraction of oils from plants i see n-hexane being used. In some rare cases i see acetone being used. Why would someone use n-hexane over isopropyl alcohol or ethanol? Just looking at physical properties of these solvents nothing obvious is jumping out at me to justify using hexane over an ethanol or easier accessible isopropyl alcohol.
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I quote from WIKI
Hexanes are significant constituents of gasoline. They are all colorless liquids, odorless when pure, with boiling points between 50 and 70 °C (122 and 158 °F). They are widely used as cheap, relatively safe, largely unreactive, and easily evaporated non-polar solvents.
Just as a start looking at properties.
Do you think polarity is a factor?
https://en.wikipedia.org/wiki/Solubility#Polarity (https://en.wikipedia.org/wiki/Solubility#Polarity)
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Compare their water solubility.
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I looked at wiki before posting this thread and nothing major jumped out at me.
Hexane boiling point is 69*C
Isopropyl alcohol boiling point is: 82.6 *C
Unless you are extracting a compound that decomposes somewhere between 69 and 82 degrees C I don't see disadvantage of isopropyl alcohol vs hexane. And if you really need to go low boiling point, acetone boils at 56*C so it would be even better choice than hexane.
Isopropyl alcohol is miscable in water, while hexane is basically insoluble, but I am failing to see why this comes into play. Where is water going to come from in the first place for this difference to matter?
I'd think the solvent would get boiled off from what ever it extracted, after extraction is complete,so why worry about water?
I agree that there must be some advantage to hexane, which is why people use it, i just don't see it. For that matter, even ethanol, which is safe enough for people to drink is close enough in physical properties.
EDIT:
Polarity is most certainly important factor in solubility. Isopropyl alcohol has structure similar to surfactants, that is a polar head (OH) and non-polar tail. Hexane is completely unpolar. Either way, both of them would dissolve non-polar oils and other organic compounds. Not seeing what makes hexane so special...
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What do you think of this possibility
Separatory funnel
https://en.wikipedia.org/wiki/Separatory_funnel (https://en.wikipedia.org/wiki/Separatory_funnel)