Sciencemadness Discussion Board

dcm-water separation

jeremyirons - 15-3-2019 at 08:26

Good day!
I have got amine as a result of reductive animation, basified it until ph 12 and extracted with dcm.
Next the idea was to wash it with water since water is not miscible with dcm. So I added water, but no separation happened. I added more and more but still nothing. Then I added some dcm thinking that it might extract amine from the mix, but it settled as a clear layer of the same volume I added.
Where am I wrong and how is it that they don't separate?

Sigmatropic - 15-3-2019 at 09:33

Did you take the lower layer of the initial basic biphasic mixture? It appears you have collected the upper aq. Layer instead.

Or maybe you did things so concentrated that the aq layer was more dense than the dcm layer. Anyway I would check your other layer and see whether that is not your organic layer.

DraconicAcid - 15-3-2019 at 09:55

Mistaking the top layer for the organic layer is a very common mistake- I've had entire classes of students do that.

jeremyirons - 15-3-2019 at 10:14

No, I took the bottom layer several times(it was same volume as dcm I poured in, so obviously correct). After a while I started noticing that the bottom layer is less volume than I am pouring in, so I added some water and it pushed dcm out, but to the top.

jeremyirons - 15-3-2019 at 10:21

Also I should add that I evaporated half or little more of the base solution before extracting with dcm

Sigmatropic - 15-3-2019 at 11:39

Ya, your aq. solution will have been very concentrated and thus more dense than the DCM. Check miscibility of your phases before moving on to the next step(!). Simply always taking the top layer with halogen free solvents or always the bottom layer with chlorinated solvents is bound to end in something like this.

And it is not hard to do, just add a drop of water to your presumed organic layer, if your guess was off it will dissolve. Very much like how you describe it.

Sigmatropic - 15-3-2019 at 11:43

This gets interesting when you have an organic salt in there, I've had a three layer system with ethyl acetate organic layer on top, water in the middle and product at the bottom as an ionic liquid. Quite a sight and surprise to behold!

jeremyirons - 15-3-2019 at 12:29

Quote: Originally posted by Sigmatropic  
Simply always taking the top layer with halogen free solvents or always the bottom layer with chlorinated solvents is bound to end in something like this.

Please elaborate on this. I'm not a chemist, but trying to understand =) I was adding the same solvent both times. There might be some IPA leftover though.
Quote: Originally posted by Sigmatropic  
And it is not hard to do, just add a drop of water to your presumed organic layer, if your guess was off it will dissolve. Very much like how you describe it.

So how should I proceed in case they are miscible?
And why are they miscible?

happyfooddance - 15-3-2019 at 16:42

He's saying that when you mixed your base + amine and your dcm, the dcm and your product were probably the TOP LAYER. Hope you saved that top layer ;)

fusso - 15-3-2019 at 18:28

Quote: Originally posted by jeremyirons  
Quote: Originally posted by Sigmatropic  
Simply always taking the top layer with halogen free solvents or always the bottom layer with chlorinated solvents is bound to end in something like this.

Please elaborate on this. I'm not a chemist, but trying to understand =) I was adding the same solvent both times. There might be some IPA leftover though.
Quote: Originally posted by Sigmatropic  
And it is not hard to do, just add a drop of water to your presumed organic layer, if your guess was off it will dissolve. Very much like how you describe it.

So how should I proceed in case they are miscible?
And why are they miscible?
H2O and DCM isn't miscible unless you have very huge amount of iPrOH.
DCM is almost always the bottom unless a lot of very dense material is dissolved in H2O &/or a lot of very light material is dissolved in DCM.
To separate the monophasic mixture just add DCM until 2 layers separate.

jeremyirons - 16-3-2019 at 01:59

Quote: Originally posted by fusso  
To separate the monophasic mixture just add DCM until 2 layers separate.

When DCM added it doesn't break the mixture, just sits as a separate layer. Or do you mean a lot more DCM?

fusso - 16-3-2019 at 06:48

Quote: Originally posted by jeremyirons  
Quote: Originally posted by fusso  
To separate the monophasic mixture just add DCM until 2 layers separate.

When DCM added it doesn't break the mixture, just sits as a separate layer. Or do you mean a lot more DCM?
Just mix the mixture until reach equilibrium, if it still remain as another layer then that's what you want.

jeremyirons - 16-3-2019 at 10:18

I took half of the mix to boil down and see what I get.
Other half I acidified, washed with DCM, basified, extracted with toluene. Toluene looks almost translucent and the water layer left behind is yellow. Is this ok? I'm under the impression that amine layer should be yellow-ish

jeremyirons - 16-3-2019 at 12:21

Quote: Originally posted by DraconicAcid  
Mistaking the top layer for the organic layer is a very common mistake- I've had entire classes of students do that.

I realized you are right :o noob mistake, thanks everyone!