Sciencemadness Discussion Board

Ideas to run a chromathography column (menthol / camphor)

JoseTineo - 11-10-2019 at 13:11

I need to separate an ointment (mentol and camphor) to verify the quantity of both, and I don't have acces to a GC-MS or HPLC. I'm thinking in run a column and I don't have much experience in that.

Ideas on the better solvent system and treatment to carry the column the best i can.

DraconicAcid - 11-10-2019 at 13:37

That's should be do-able; camphor is a ketone, and menthol is an alcohol, so the menthol should stick to the silica/alumina stationary phase significantly more. The big thing to worry about is what's else in the ointment?

Also, how will you detect the compounds in the eluent? Menthol, at least, won't absorb UV, so you can't use a TLC to check the fractions (unless you're staining it another way).

If you've got TLC, run different solvent mixtures with that to see what separates them best.

PirateDocBrown - 11-10-2019 at 13:48

Stain your TLC with iodine vapor.

But seriously, if you are doing quantitative analysis, why do chromatography at all?

Just separate a sample with wet lab techniques.

[Edited on 10/11/19 by PirateDocBrown]

DraconicAcid - 11-10-2019 at 16:04

Quote: Originally posted by PirateDocBrown  

But seriously, if you are doing quantitative analysis, why do chromatography at all?

Just separate a sample with wet lab techniques.
[Edited on 10/11/19 by PirateDocBrown]


What wet techniques do you have in mind? I doubt their solubilities are sufficiently different for separating by extraction.

SWIM - 11-10-2019 at 21:08

Camphor ought to be more easily reduced than menthol, right?

So could you reduce the mixture in moderate conditions and separate the menthol from the resultant norborneol by distillation?

30 degree boiling point difference.

I would also wonder about differences in sublimation rates.
Camphor sure looks more sublimate-y than menthol to me.

And Menthol looks like it ought to crystallize better than camphor, so maybe it can be isolated by fractional crystallization.


Maybe you could do a reductive amination on the camphor in the mixture without messing the menthol up?
I have no idea what the result would be called, but it ought to be easy to isolate from menthol.


draculic acid69 - 12-10-2019 at 04:26

Distillation? Steam distillation will carry camphor but I'm not sure bout menthol as I seen a post about mint distillation not working but it might have been carvone they were talking about. Fractional crystallizing might work.as an ointment it will have other gunk in there that would mess with any attempt to purify either product out of it I reckon.

unionised - 12-10-2019 at 07:06

Both materials smell.
So, it's pretty clear that they both sublime.

You might be able to separate them by something like oxime formation.

PirateDocBrown - 12-10-2019 at 12:50

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by PirateDocBrown  

But seriously, if you are doing quantitative analysis, why do chromatography at all?

Just separate a sample with wet lab techniques.
[Edited on 10/11/19 by PirateDocBrown]


What wet techniques do you have in mind? I doubt their solubilities are sufficiently different for separating by extraction.


Since one is an alcohol, and the other a ketone, there surely must be some solvent one is far more soluable in than the other.

Alternatively, doing a reaction that only one can participate in, but not the other, could make a mixture that's easy to seperate. Such as making an ester. Or reacting the carbonyl to make a hydrazone, or some similar product.

PirateDocBrown - 12-10-2019 at 13:01

Did a bit of a look-up.

Menthol melts at the low 40s, but camphor at a much higher temp, 170 or so. Just melt the stuff.

DraconicAcid - 12-10-2019 at 13:40

Quote: Originally posted by PirateDocBrown  
Did a bit of a look-up.

Menthol melts at the low 40s, but camphor at a much higher temp, 170 or so. Just melt the stuff.


And you don't think the camphor will dissolve at all in the liquid menthol?

You might be able to crystallize camphor from a mixture using the right solvent, but it's also possible that you'd get them both precipitating as an oily mixture.

draculic acid69 - 12-10-2019 at 19:48

First step for getting these two substances out is to use a solvent to dissolve them and not dissolve the gel or cream or thickening agent or petroleum jelly or whatever it is that they're mixed with.acetone or metho or DCM or something.do u know what else is in the mix?

JoseTineo - 13-10-2019 at 18:34

Quote: Originally posted by draculic acid69  
First step for getting these two substances out is to use a solvent to dissolve them and not dissolve the gel or cream or thickening agent or petroleum jelly or whatever it is that they're mixed with.acetone or metho or DCM or something.do u know what else is in the mix?


Just petroleum jelly Aka "vaseline"

Ubya - 14-10-2019 at 10:45

if you already have a column it is quite easy, youtube is full of videos about the practical aspect of a chromatography column run.
you should silica or allumina, vaseline will elute first with the apolar solvent (a mix of petroleum ether and ethyl acetate or methanol to make it more polar). you should try the various combinations of eluents with a tlc, if you don't have tlc plates you could make a a few with a bit of time and work.
as a stain you could use iodine or vanilin, again a quick google search will give you all the info about making the solutions and how to apply them

SWIM - 14-10-2019 at 18:11

Just wondering,

If the menthol is synthetic in origin it will be racemic.

If that's the case then could one determine the camphor content of the mixture with a polarimeter?

Ubya - 15-10-2019 at 12:46

Quote: Originally posted by SWIM  
Just wondering,

If the menthol is synthetic in origin it will be racemic.

If that's the case then could one determine the camphor content of the mixture with a polarimeter?


synthetic and natural menthol is not reacemic. menthol is industrially made through an asymetric synthesis or if the reaction produces a racemic mixture it is then resolved and purified. only L-Menthol

SWIM - 15-10-2019 at 15:57

I didn't know L -menthol was made synthetically.

DL -menthol is, however, an ingredient in numerous cosmetics and personal hygiene products as well.

Dr.Bob - 16-10-2019 at 16:36

Just run a column on silica gel (or alumina) and go from hexane to ethyl acetate. Use TLC to decide the best mixture (you want the spots to move about 1/3 of the way up the solvent front, with iodine, UV, or whatever as a stain. Then use that mixture or a gradient that passes through it to elute the column, with about 20 times the volume of the silica gel (use about 50 times the weight of your mixed material in silica gel for a good separation).

Collect test tubes of what eludes from the column, and then let them evaporate some, the ones with a small film or ring at the top are likely the separated materials. This may let you get a guess as the amount of each compound, but it is more of a preparative method than quantitative. You will also need a way to determine what each the identity of each tube is.

A simple GC, HPLC, or NMR of the extracted organics would be much faster, more accurate, and simpler, but requires access to the equipment. Finding friends at a university or other research facility would be good.