Sciencemadness Discussion Board

Correlation between calculated logP and extraction solvent

marksev1 - 1-4-2009 at 11:20

Well i would like to know is there any correlation between calculated logP (say by ACD for example) and extraction solvent which could be used, since logP could also be taken as a measure of lipophilicity of a compound...

Nicodem - 2-4-2009 at 02:34

LogP is the logarithm of the partition coefficient of a substance between n-octanol and water. If logP is 2 then the substance is partitioned 100 times more in n-octanol than water. As such the logP (measured or predicted since ChemDraw and ChemSketch both quite convincingly give good predictions) is already the information that you are looking for, just antilogarithm it.

marksev1 - 2-4-2009 at 05:36

Yes i know that this is the partitioning coefficient between n-octanol and water...but i would like to know if this number also gives one some information about which solvent would somebody use for say an extraction from some solid material (say some plant). Since some solvents are more polar than others and one compound would be better extracted with one solvent and the other with some other solvent...and also for liquid-liquid extraction could this calc. partitioning coefficient give some information about the type of solvent to use when extracting out od aqueous phase. It would be nice to have a software which would calc. the partitioning coeficient for more solvent mixtures.

Nicodem - 2-4-2009 at 12:05

Of course the value of logP gives you a good information about what solvent is more appropriate for an extraction of a specific compound from aqueous solutions. However, this is not something that can be calculated. You need a specific case. Give me an example and I will tell you what solvent might be most appropriate. Properties of most solvents are easy to find in manuals and various property tables.

marksev1 - 3-4-2009 at 00:46

I know that this cannot be calculated,...i mean that it would look like a table of some sort, values of logP from 2 to 4 - you would use some solvents and for logP from 6 to 8 you would use different solvents and so on. Is there some kind of table in this manner. Or could you from your experience write it. I'm just talking about some basic extraction with an organic solvent, without the change of pH or something else.
Or is there maybe any other way to predict which solvent to use....Cause i want to really use this data which i get from software..
Thanks for the answers!

[Edited on 3-4-2009 by marksev1]

Nicodem - 5-4-2009 at 02:45

But it is already logical enough, even though you get the feeling only after some experience.
If a compound has a logP considerably bellow 0 you are hardly going to recover it efficiently with any given solvent without using a continuous extractor regardless of how appropriate solvent you use.
For compounds with logP<1 it is advisable, but not necessary, to saturate the aq. solution with NaCl prior to extraction (with these NaCl saturated aq. phases even water miscible solvents like isopropanol or acetone can be used for extractions, provided you later remove the taken over residual NaCl). With logP<1 you take solvents of higher polarity like ethyl acetate, methyl ethyl ketone, n-butanol (sometimes it helps to have a mixture of ethyl acetate with THF or (iso)propanol). But logP is not the only important parameter. Some compounds are too poorly soluble in ethyl acetate and remain solid during the extraction (which is very annoying). This is very common with some amides, heterocycles and other such compounds that have a large energy of the crystal lattice. Here a mixture of ethyl acetate with THF, acetone or propanol often helps (but keep in mind that all these solvents added to ethyl acetate also partitionate extensively into the aqueous phase, so saturating with NaCl is again advisable).
With logP between 1 and 5 you can use anything from ethyl acetate, dichloromethane, diethyl ether, toluene, and so on.
With logP>5 you can use petroleum ether. If the compound is liquid at room temperature you can use petroleum ether even for many compounds with logP>3.

This is just a rough guide based partly on experience, partly on theory, not to be taken too generally.

marksev1 - 5-4-2009 at 07:06

Very nice thank you very much for your effort, really..!

So does adding NaCl to for example water acetone mixture separate the mixture into 2 phases? Adding NaCl is to increase the difference in polarity and so promoting immiscibility right?

Nicodem - 7-4-2009 at 01:14

Monophasic mixtures of water with solvents like acetone, THF, isopropanol, even ethanol in some cases, do become biphasic when saturating them with ionic salts like NaCl and others such. One phase becomes rich in H2O+NaCl and poor in organic solvent, and the other becomes rich in organic solvent but poor in NaCl and H2O. This is a phenomenon usually called "salting out" where the monophasic solution is perturbed by the ions solvating in it. Ions, like Na<sup>+</sup> and Cl<sup>-</sup> for example, are always solvated in aq. solutions - that is, they get surrounded by H2O molecules. This way they compete with the solvation of the organic molecules and because they have a higher affinity for H2O molecules, the organic molecules remain without solvent, thus effectively crushing out of the solution. This way the partition coefficient of the organic solute increases in the favour of the extraction solvent when saturating the aq. solution with ionic salts (unless the organic compound is able to chelate with such ions! hence NaCl is most commonly used to prevent this to occur). See also the attached review.

The "Salting out" of Non-electrolytes from Aqueous Solutions
Paul M. Gross
Chem. Rev., 13 (1933), 91–101. DOI: 10.1021/cr60044a007

Attachment: The Salting out of Non-electrolytes from Aqueous Solutions.pdf (599kB)
This file has been downloaded 988 times

marksev1 - 7-4-2009 at 06:05

I've heard of the salting out principle for precipitating some solid material out of solution, but i couldn't realise that this would work for 2 liquids too, nice...thank you for the info.

One last question that is maybe a little bit " out of thread " but do you maybe (or anyone else) know a book where some procedures for isolation of compounds from natural sources are described. I would like it in such manner...To obtain for example Vitamin K you take this plant,...use this and this solvent and so on....Does such a book exist?

Nicodem - 7-4-2009 at 07:56

The information about which biological material contains what and how much, can be obtained, like every other scientific information, from the primary literature. There you have described also the procedure used for the isolation as well as all the characterization data.
Extraction can not be used on its own since it is not a method that separates compounds with similar properties. Extraction is just the first step to remove cellulose, proteins, lignins, lipids, chlorophyll and other macromolecular stuff as well as water/acid/base soluble stuff from the sample. The so obtained mixture must then be subject to a real separation technique like recrystallization (solids) or fractionation (liquids) if such a crude mixture is actually rich in the target material. Otherwise, chromatographic separation is most commonly used (today it is practically the only method used). This includes anything from flash column chromatography to preparative HPLC. The point of most research is to characterize a compound present in the biological material, for which you need as little material as 1mg if it crystallizes since single crystal XRD requires just one crystal (but even modern 800MHz NMR machines can give you an excellent spectra from <1mg material, while for mass spectroscopy almost nothing is already too much).

marksev1 - 8-4-2009 at 13:18

I found one interesting practic case which i could try out...if you have maybe time to guide me a bit through..I read on wikipedia that capers have a lot of quercetin (1800mg/1kg). So next I calculated logP on ACD and got the next result: 2,07 +- 0,72...first i would have to investigate if this quercetin in the oil of the capers or in the other material (since flavonoids are pigments i would think that they are in the actual fruit and they are not that lipophilic also another point) and then possibly if it is not in the oil...i could first defat the res of the material with petroleum ether and then extract with diethyl ether for instance...

[Edited on 8-4-2009 by marksev1]

Nicodem - 8-4-2009 at 22:59

First find the papers describing its isolation. If it is in a journal you can not access in the library, remember that we have a References section here...

marksev1 - 12-4-2009 at 23:50

I found one from Phytomedicine. I could send it here if you want?

I have a lot of article's to contribute to the references section if you are interested? I don't know if you have every single one which i have, but nontheless,...btw how much post must one have to get access to the references section? or is there any other request to be satisfyed...

[Edited on 13-4-2009 by marksev1]

DJF90 - 13-4-2009 at 02:33

There is a book I have in german that details the extraction of compounds from natural sources, I think. The title is "Isolierung und Charakterisierung von Naturstoffen" which I take to mean "Isolation and Characterisation of Natural summat or anothers"...

As you can probably tell I cant read German and so I will have to use a Chemistry dictionary in order to make sense of it. I think its written by Egon Stahl and Werner Schild.

[Edited on 13-4-2009 by DJF90]

Nicodem - 13-4-2009 at 02:45

Quote: Originally posted by marksev1  
I found one from Phytomedicine. I could send it here if you want?
btw how much post must one have to get access to the references section? or is there any other request to be satisfyed...

Yes, sure upload the paper.
To obtain access to the Reference section you need to ask an administrator (Polverone or vulture). If you fit the conditions by being an active member (= at least two helpful replies and two month from registration) or you convince them you desperately need it right now because whatever reason...

marksev1 - 15-4-2009 at 09:57

Thank you very much for the info both of you. DJF90 i downloaded the book it has some examples but not enough for me hehe:D..i would like more... Here's the article about quercetin.

Attachment: isol of quercetin.pdf (76kB)
This file has been downloaded 899 times

[Edited on 15-4-2009 by marksev1]

[Edited on 15-4-2009 by marksev1]

Nicodem - 17-4-2009 at 04:19

Do you already have a source of quercetin?
What solvents do you have?
Can you do column chromatography?
What kind of analysis can you perform? TLC, mp, NMR, IR, MS...?
Are you sure you do not want to first start with something more abundant, being present in at least 1% in dry material? It would be smarter to start with something like caffeine from tea for a beginner, and then move to other stuff.

marksev1 - 18-4-2009 at 00:20

I'm planning to isolate it from Rutae herba, which is a quite common plant where i come from. Some grandmas use it to flavour their coffee or tee:D. According to Egon: Isolierung und Charakterisierung von Naturstoffen, it contains about 7-8% of Rutin which is a glycoside of quercetin, i have the chemical which are described in the extraction in the book, also i have most of the reagents described in the article. I could do melting point, TLC and maybe IR...although i first have to aquire a soxhlett to begin really doing extractions.

[Edited on 18-4-2009 by marksev1]