getafix
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extraction
Could anyone please fill me in on the advantages/disadvantages of using different solvent in extration processes.
Are dichloromethane, toluene and diethyl ether all interchangable and is this purely based on the compounds bp that you are extracting (assuming you
separate the desired compound from the solvent by distillation obviously)
Any hints or tips wouldbe appreciated!
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Marvin
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Usually it depends what you are trying to seperate from what.
Ok, that sounds obvios, but this includes not only the reactants and other products, but side products in reaction as well.
Different solvents dissolve differering amounts of other compounds and diethyl ether will dissolve very differently to pet ether or to water or to
ethyl acetate etc depending on functional groups, how polar a substance is, these things tend to make the biggest difference.
Often how solvents behave doesnt seem to make sense. For example cellulose is essentially insoluable in acetone. Partially nitrated cellulose is
fairly soluable, but fully nitrated cellulose is hardly soluable at all.
For purification steps, solubilities need to be in a useful range, for simple extractions the requirements are less strict, simply knowing what will
and wont dissolve is usually justification enough, frequently this is as simple as forming salts selectivly by altering the ph of a water solution in
contact with a non polar solvent.
This reply sounds confused and rushed, and thats because it is confused and rushed. This is a huge area to cover and I cant do it justice in a forum
post. Essentially, there are reasons for choosing say chloroform over ether in a specific extraction beyond non reactivity, but they dont tend to get
discussed.
For home experiements, most related solvents can be substituted with not much in the way of additional problems. Confusing classes of solvents would
be a mistake though, eg, trying to substitute pet ether for diethyl ether or acetone for dichloromethane.
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getafix
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Thanks for the reply.
Most of it does make sense, but I have question. With the limitless number of compounds out there - how does one determine the solubility of a
specific compound in a solvent. Are there any general guidelines/properties for classes of compounds and their solubilities in different solvents. If
so and you know where I can find out this sort of info - please tell!!
I get the concept of like disolves like etc but as you are probably aware, some solvents are easier to obtain than others.
For the experiments I have in mind I know the solvents recommended but I guess all I really want to know is can non-polar solvents on the whole be
interchanged?
Oils should generally be soluble in any non-polar solvent to a much greater degree than in a polar one.
anyways - if you have any further thoughts then let me know
cheers
[Edited on 7-8-2003 by getafix]
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Marvin
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Oils and fats dont seem to show a lot of difference between them becuase they are very similar chemicals. Organic compounds generally are more
diverse.
An experienced chemist would probably have no trouble trying different solvents and determining if the extraction worked as well afterwards.
In general changing extraction solvents isnt a good idea. On the other hand that can be compaired to changing solvents for a reaction, which is a
very very bad idea.
If you have to, go for a solvent in the same class, not just any non-polar solvent.
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getafix
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Thanks.
I've been looking around and yes - staying in the same class definitely seems the way to go.
For example the chlorinated solvents are innert and won't produce any secondary products when gassing or brominating etc
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adroit_synth
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good link
this will answer many questions
http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Solvent...
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