[MNK]

Hi Folks

During the last step (evaporation of Dichloromethane to yield extracted alkaloids) of my standard alkaloid extraction procedure I have found that two distinct layers form. One of the layers is obviously unevaporated dichloromethane, the other is a colourless liquid (which floats on the surface). Is this the alkaloid

Just to give you a little background behind my procedure, I give a short description below


- Extract plant material with acidid water pH 2
- Filter
- Raise pH to 11
- Add dichloromethane
- Using seperating funnel seperate basic water layer from Dichloromethane layer
- Evaporate Dichloromethane to yield alkaloids (it is during this evaporation step that I find these two distinct liquid layers forming. As mentioned above, one of the layers is obviously unevaporated dichloromethane. Is the second (top) layer the alkaloid?

When I allow full evaporation a tiny amount of green goo remains. I am assuming that this is the alkaloid in non-liquid form.

Anyway, I am new at this (only my first year of study) so any help on the matter would be greatly appreciated.

Thanks

[Donaldson Tan]

It should be the alkaloid. You could extract a tiny sample and do some alkaloid-specific test to verify its identity.

[Sam (NG)]

Did you dry the dichloromethane layer before evaporation?  Could be water left over from the extraction.

[MNK]

Thanks for the responses guys

geodome - what types of tests could i do (simpler the better)


Sam - Im pretty careful when seperating the Dichloromethane layer from the Basified water layer. Would the Dichloromethane layer really hold water? The extraction works because the water layer naturally seperates from the dichloromethane.

I would say that the amount of colourless liquid floating at the top of the dichloromethane layer would by the end of the evaporation constitude about 1/20th the volume of the original amount, which is actually quite a large amount. I would say that a bear glass worth of dichloromethane becomes about a shot glass worth of this mystery colourless liquid. I guess one possible way of finding out whether or not it's water would be simply to ask whether or not water floats on dichloromethane, because if it does, it is still a possibility, if it sinks, we can be pretty sure its not water, because whatever this stuff is, it floats on the dichloromethane layer. One other thing, it has a potent smell, which is very hard to discribe.

[MNK]

Just to clarify, i obviously know that basified water floats on Dichloromethane. Im just not sure if water at different pH levels would act differently under these conditions. Im assuming that if it is water floating at the top of the dichloromethane layer during evaporation, it must be in some way different from the water which was discarded during the final seperation.

[nj_bartel]

One simple way to check and fix it if it's water is to take your entire sample, put in a copious amount of anhydrous MgSO₄, shake it thoroughly, vacuum filter it, then attempt to reseparate it.

[mreff555]

If you think it may be water nj_bartel is right. drying and vacuum filtering would be best. However, It sounds like you are at the step where the alkaloid would need to be extracted. Do you know what this theoretical alkaloid is? can you do a mp test, or maybe check it's refractive index?

[Donaldson Tan]

Chances are it is going to be a mixture of DCM, water and your alkaloid. If you know the identity of the alkaloid, why not do a TLC? Compare the R_f value you get to what's recorded in the Sigma Aldrich handbook. The TLC would be able to tell you if it is an organic mixture too.

[Fleaker]

Water will always float on DCM. Also, DCM is not entirely immiscible with water, and if you dissolve to.

Alkaloids have the amine function on them (hence the alk- part of their name, amines are bases).

Your alkaloid might be too polar for the DCM, or polar enough that it is dragging water molecules into the DCM layer.

I don't know how you do your extractions, but it's always a good idea to check the first extract with MgSO4 to see if there is water.
Take the organic and DCM layer and add anhydrous magnesium sulfate--if there is a lot of clumping, then there's a good bit of water, if there is not so much clumping, then it's probably fine.

It would probably help if you mentioned which alkaloid it is.