[lucas89]

Hey forum,

Just reading over my procedure for my Bio-Organic Chemistry lab tomorrow, and I have a few questions about the procedure I was hoping someone would be able to help clarify for me (or even just help easy my tension, it's been way too long since I've stepped foot in an organic chemistry lab).

Tomorrow we're oxidizing 9-hydroxyfluorene to 9-fluorenone using NaOCl, and monitoring the progress of the oxidation by using TLC. Simple enough. However, after the reaction is gone to completion, we have to extract the reaction solution with hexane, and then wash the organic layer with various items (In our reaction vessel, we had 9-hydroxyfluorene, acetone, acetic acid and Javex before the reaction begun.)

Since it's been way too long since I've done this, and the lab book gives no insight into the process, my questions/ideas are:

1. I remember using a separatory funnel for this. Now, I also remember the fact that more dense layer is on bottom. I can find a density value for hexane, however a density value for 9-fluorenone hasn't been as easy to find. I did find one value of 1.0728, though I can't confirm this as correct. If this is the case, our bottom layer with our product would be our organic layer. Thus, by adding the hexane, and shaking, any non-polar impurities will dissolve in this (top) layer? Or will the hexane combine with the product layer? Considering the product appears to be polar, I wouldn't assume so?

I'll leave it at this until I get a reply, and then maybe we can work through the process/theory together? Thanks

[Yggdrasil]

The product will be dissolved in hexane which is less dense than water (even if the product is more dense than water, it likely will not be present in a large enough quantity to make the organic phase heavier than the water phase).  As a general rule, organic solvents will be less dense than water unless the organic solvents are halogenated (e.g. chloroform, dichloromethane).

For the purpose of the extraction, however, you have the right idea.  The non-polar components will migrate into the hexane while the polar components will stay in the water.  However, I would consider 9-fluorenone to be fairly non-polar (remember, water is very polar and unless your compound is charged or contains many very polar groups capable of hydrogen bonding, the compound will prefer the organic phase).

[lucas89]

thanks for the *delete me* Though I figured it out in the lab (after MANY tense minutes trying to make a decision on which layer to work with), it's always nice to read an explanation as to why I did what I did. And I did not know that little tidbit about most organic solvents being less dense than water, but thinking about it in my head, it makes perfect sense. That will save myself much time and anguish from here on in

 

[Yggdrasil]

Here's a trick I like to do.  If you can't figure out which phase is the water phase and which phase is the organic phase, squirt a little water into one of the liquids.  If the water dissolves, that phase is the water phase.  If the water separates, that phase is the organic phase.

[UnintentionalChaos]

Here's a trick I like to do.  If you can't figure out which phase is the water phase and which phase is the organic phase, squirt a little water into one of the liquids.  If the water dissolves, that phase is the water phase.  If the water separates, that phase is the organic phase.

This is a good trick, which has saved me several times in lab. When using saturated brine and the like, the layers are not always where you expect.