Liquid-liquid extraction (solvent extraction)

[MedPR]

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I don't really understand the experimental procedure. I mean, I understand that you use two solvents, water and an organic solvent, in an attempt to isolate a solute that will react in only one of them.

Do you just pour both solvents into the separating funnel, then add the solute, then shake it up and wait for the layers to separate? Then open the stopcock until the bottom layer drains out and what you have left is a flask full of the more dense solvent (water, usually) and a separating funnel full of the less dense solvent?

 

[milski]

That's very close to it. Usually you already have what you want to separate in some sort of solvent, since it's a result of some sort of reaction. You put that in a separation funnel. Then you add some strong acide - that is supposed to protonate your compounds, making some of them polar (NH-based) and some of them not very polar (-OH, -COOH). If you were already in organic solvent, you have now water too, since that came as a solvent for the strong acid. You shake and wait for the layers to separate.

Drain the bottom layer. If you care about what's there, you can add strong base, deprotonate it and make it precipitate since you just changed it from polar to non-polar.

You can repeat the same procedure with what's left in the separation funnel and strong base.

That allows you to extract three types of compounds:
- polar at low pH, non-polar at high pH
- polar at high pH, non-polar at low pH
- stable garbage which does not change polarity (alkyls for example)

 

[MedPR]

That's very close to it. Usually you already have what you want to separate in some sort of solvent, since it's a result of some sort of reaction. You put that in a separation funnel. Then you add some strong acide - that is supposed to protonate your compounds, making some of them polar (NH-based) and some of them not very polar (-OH, -COOH). If you were already in organic solvent, you have now water too, since that came as a solvent for the strong acid. You shake and wait for the layers to separate.

Drain the bottom layer. If you care about what's there, you can add strong base, deprotonate it and make it precipitate since you just changed it from polar to non-polar.

You can repeat the same procedure with what's left in the separation funnel and strong base.

That allows you to extract three types of compounds:
- polar at low pH, non-polar at high pH
- polar at high pH, non-polar at low pH
- stable garbage which does not change polarity (alkyls for example)

Starting to creep over from PS into BS, huh? Thank you 🙂

 

[milski]

Starting to creep over from PS into BS, huh? Thank you 🙂

Half way done with the required 1 year of ochem lab. 😀 The final was brutal. Or at least the grading was.

There's something to be said about doing something instead of reading about it. I have to admit that there is some usefulness in making all sorts of white powders after all.

 

[MedPR]

Half way done with the required 1 year of ochem lab. 😀 The final was brutal. Or at least the grading was.

There's something to be said about doing something instead of reading about it. I have to admit that there is some usefulness in making all sorts of white powders after all.

Yea, doing it really makes it easier to remember than reading about it. I took organic 4 years ago and even when I was in it I had no idea what was going on.