[DoctorDomo]

I have a few questions about this. I'll ask the most important one first, the others are just for the sake of knowledge.

So I'm wondering what other aqueous solvents are good for liquid-liquid extractions? According to the miscibility charts:

water is the only one that is immiscible with a wide range of solvents. Methanol is immiscible with a few of them. If you have a mixture of products, some of them soluble in methanol, some only soluble in hexane, would this not be a good system since methanol can easily be rotavapped off, so you could obtain products from both the organic and aqueous layers? Also, would it be possible to make methanol even less miscible with non polars by saturating it with salt?

DMSO is immiscible with a good few solvents too, and in my experience DMSO dissolves all kinds of compounds, regardless of their polarity so I'm wondering if this can be used to your advantage, in order to wash non polar materials out of your organic phase, while leaving compounds that happen to be insoluble with DMSO. Can these charts be trusted though? I think I tried mixing hexane with DMF before and didn't see any biphase formation. Maybe you just need to give it time to separate into layers though. I've been using DMF a lot lately, and have been using liquid-liquid extractions with water to get rid of the DMF. If DMF is immiscible with things like hexane and pentane, couldn't I just do a DMF-hexane extraction?

Next question: Lets say you're doing a liquid-liquid extraction and you add a less dense solvent like diethyl ether or ethyl acetate to water. What happens if you add say n-Hexane to the mix. Will that simply make the organic layer (top layer in this case) less polar, or are there more complex interactions that occur.

Secondly, what happens if I add a more dense immiscible like chloroform to the mix, will the organic layer just sink to the bottom as it gradually becomes more dense? What happens when the net density reaches 1.0, will an emulsion form?

Thirdly, what happens if you add a miscible solvent like acetone to the mix? Will it cause the two layers to merge? If so, can you add more hexane to make the mixture seperate into 2 layers again? In the labs, someone had an issue when they added THF to their aqueous solution, they thought it was immiscible with water, but it turned out that it didn't separate into two layers. I suggested adding hexane to see if it would split into two layers, and it did. In this case, I'm guessing the partition coefficient will determine how much THF goes into what layer. If he was to then add more THF, would the layers merge together again? If so, would an emulsion form, or would be the THF help solvate the hexane better so that a homogenous solution can be obtained?

[Hunter2]

Polar likes polar and inpolar likes inpolar.

[DoctorDomo]

That much I've established Hunter2. I should break this thread into seperate threads cuz it probably turns people away when they see the length of it.

Anyway, I found out the answer to one of the questions. I added hexane to water to form two layers, hexane on top, water at the bottom. Then I added chloroform to see if it split into 3 layers, but it didn't. Instead an emulsion formed. I should have tried it the other way around, adding the chloroform and water first. Either way, this isn't gonna be useful for extractions cuz shaking it up with produce an emulsion.

I attempted to answer the first question, I added an alliquot of DMF reaction mixture to a vial, then added hexane and shook it up. The hexane layer turned yellow, while the DMF layer remained green. Had to shake like mad to get the hexane to change colour, and a bit of an emulsion formed between the two layers. I tried adding salt, but its not too soluble in DMF. I'll collect the hexane layer and rotavap it to see whats in there. My compounds have intermediate polarity (DCM and ethyl acetate dissolve them well, hexane not as well), this would work much better for less polar compounds.

[Arkcon]

Good.  I'm glad you figured out some of your questions.  Your posting is long, and contains a number of simply wrong conclusions, that would take too long to correct.  So if you want to try again, with what you still don't know, we're ready for you.

[zsinger]

Remember Dr. Domo,
HCl, one might notice is higher on the B/L acid base table than is H2SO4, leading to the obvious conclusion that it is the stronger acid.  NOT SO!  This does NOT keep with thermodynamic studies done to correctly tackle system pH.  So what am I getting at?  Often times, things such as the true behavior of matter is hard to measure.  Now, the flip side of that coin is that the thermodynamic studies targeted at getting these pKa values may have been wrong! (Chemistry is confusing sometimes huh!  )  One must experiment instead of looking at "in theory" ideas to get answers.  One of the board members here (forget which one) has a good saying of "chemistry is an experimental science".  Try these mixes and make careful observation in a laboratory notebook.  Only experimentation will make the knowledge yours.  Hope this helps, and slow down in making so many conclusions!
                 -Zack