[rhm95]

I would like to know if I am making the correct decision in this matter.
I am used to being spoon fed directions from my procedure outlines of my experiment, but this experiment gives no directions and relies on my ability to outline my own procedure.  Something I'm not used to and would like some guidance on.

The mixture I received was clear liquid with yellow tint and somewhat viscous. I was informed that it contains equal volume of two unknown liquids.  I preformed solubility tests, ph test, IR spectrum, and a TLC plate with 80% ethyl acetate and 20% hexanes.  The compound was not soluble in HCl, NaOH, or water at various temperatures.  The ph gave a reading of 7.  The TLC showed two separate dots on a silica gel plate.  I was led to believe that due to the differing polarities that I could do flash chromatography, but my GTA told me not to with no explanation as to why.

I really want to do flash column chromatography because it seems most viable, the other available options don't seem to be of any use.  I can't do acid/base extraction because of ph neutral.  I cant do distillation because lack of proper equipment.  I can't do sublimation cause we never were even taught about that, and I dont know if its even applicable.  I cant do re crystallization because its a liquid.  I'm at a loss for what to do.

Should I ignore my GTA and do it anyway?  Or is there something I am forgetting or an incorrect assumption I am making?

[rhm95]

It might be useful to know the purpose of this lab, sorry bout that. We are supposed to determine the components of this mixture.

[TheUnassuming]

In theory the assignment should be solvable with the material you have covered so far.  What methods of separation have you covered in class?

If the TA says no to chromatography, then don't do it.  What were the Rf's of the spots you see by TLC in your 20% EtoAc/Hex run?

[rhm95]

We didnt actually calculate those, but we can next lab because we kept the plates. Didnt think that information would be particularly useful since there is such a large variance in Rf values from laboratory to laboratory.

Our methods learned so far have been recrystallization, acid base extraction, distillation, flash column chromatography, and some sort of solvent based enabtiomer separation.

[TheUnassuming]

I ask about the RF's more in a general sense.  If they are relatively similar in polarity by TLC, then they will probably be miscible in the same solvents unless you can change the charge state of one of them.

So lets try to narrow this down a bit.  Your TA says chromatography is out and you don't have the equipment for a distillation (I'm assuming your TA isn't assuming you will go out and source your own equipment), which leaves you extraction and crystallization of the methods you have covered to isolate your compounds.

Crystallization is generally only done with solids, but have you taken the mixture to temps below room temperature to see if one of the compounds freezes while the other stays in liquid form? 

On the extraction side, how did you measure the pH and how did you determine neither are soluble in acidic/basic water?

[rhm95]

The Rf values, although im not sure of the relativity of your similarity, weren't too similar. There was a clear separation between the two compounds. I can give exacts after my monday lab.

We have not cooled the liquid as of right now. We are limited to 2mL of total mixture, so is it correct to assume to perform this on a smaller sample or to use the entire mixture? Also, how do we know both compounds will not  percipitate.

Ph was measured with ph paper indicators. The wide variety, not blue or red litmus. We retested the pH with the same paper, but wetting with DI water first.  Solubility was tested by taking a portion of the mixture and the HCl, NaOH, and room temperature water and mixing in 3 test tubes.  The solubility was determined from visual inspection. There was a clear separation between the liquid and the yellow mixture even after vortex mixing.

[kriggy]

How do you know that one of the compounds didnt dissolve in the HCl or NaOH? One of the compounds could possible be extracted into the HCl/NaOH solutions

[rhm95]

I guess we really dont know if they dissolved solely based off visuals because one of the compounds could have have dissolved. So far in this class we have only done solubility tests on solids.  So thanks kriggy for pointing out that we don't know if the liquid is soluble just based off a visual indication. Today we mainly focused on our other mixture that I didnt mention, but isn't relevant other than to update that we didn't spend much time on the yellow mixture.

I found the Rf values. They were .80 and .87.  We tried mixing the mixture with both acid and base in different vials. Since we couldn't think of anything else we tested the mixture to see if we could do acid base extraction. We then added diethyl ether to both and extracted the potential aqueous and neutral organic layers. We found that the addition of NaOH was able to separate the compounds of the mixture. We dotted the diluted aqueous and organic layer on a TLC plate.

The TLC plate showed a single dot for the organic layer and extremely dense dot at the starting point with a long streak for the aqueous. I believe this means that we can do base extraction on this mixture. I think the long streak and dense dot is due to the salt. These TLC results line up with our IR results, which showed there is a carboxylic acid functional group in one of the compounds.