[Aqueous Maqueous]

I've thought it out, and I know that the anhydrous magnesium sulfate would probably extract any water molecules from the 1-propanol solution (which has caffeine, NaCl to increase polarity of water, and Ca(OH)₂ to make the solution basic, and NaOH to remove any impurities).

Is there anything it can do to the 1-propanol or caffeine (or any of the chemicals listed).

[macman104]

Nah, not really.  You are just trying to remove the water from the solution.  But I haven't heard of using anhydrous magnesium sulfate on a solvent that is miscible with water like this, unless there is only a very small amount compared to the amount of 1-propanol you have...

This procedure is typically used when you have an aqueous and a organic solvent layer.  You drain the aqueous layer, and take the organic layer and treat it with anhydrous magnesium sulfate to remove any water that may be dissolved in the layer (because most things have some degree of solubility with water, just not much).

However, you probably didn't have a two-phase mixture, because 1-propanol is completely miscible with water...

[Aqueous Maqueous]

This procedure is typically used when you have an aqueous and a organic solvent layer.  You drain the aqueous layer, and take the organic layer and treat it with anhydrous magnesium sulfate to remove any water that may be dissolved in the layer (because most things have some degree of solubility with water, just not much).

That's exactly what happened. Thank you very much!

[macman104]

Really?  Are you sure you used 1-propanol then?  Wikipedia says it is completely miscible...and a MSDS sheet backs that up too.

[Aqueous Maqueous]

I'm sure.

Also, I was following this guide: http://fido.pcc.edu/reserves.archived/Moffett,Gabriella/Fall02/CH241LABS/ExtractionofCaffeinefromTeaLeaves.pdf

[macman104]

Very interesting, I suppose it would work, using the salt and the conditions to decrease the solubility enough.  Kinda neat!

So, yes in this case, you had an organic layer, but due to solubility, there was still some in that layer.  So the anhydrous MgSO₄ will remove any of the extra water.  It should have gone from being floaty to being very clumpy, and then you would have added more until you saw it floating freely again, yea?

When we did this, we used CH₂Cl₂, but I guess this is the new green chem way to introduce this lab.

[nj_bartel]

Side question - why do compounds that form hydrates, such as MgSO₄, not react in a similar manner with alcohols?

[expert]

Alcohols do react with MgSO4, although less efficient than water. MeOH>EtOH>PrOH, etc. That's why MgSO4 is not a good drying agent for alcohols. By the way, Ca(OH)2 and NaOH will substantially remove your caffeine from the solution too.

[typhoon2028]

I remember doing this same type of lab years ago.  I don't believe we used an alcohol as the solvent.  I think we may have use methylene chloride or hexane, because I remember having to extract the organic phase.  We may have then passed the organic phase through an anhydrous salt to remove any water.  Then we blew nitrogen across the solution.  I remember this evaporation step, because it was cold in my hand.

[expert]

Methylene chloride most likely. Hexane won't dissolve/extract caffeine.