Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: pretzalisa on July 30, 2015, 08:02:25 AM
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Just a quick question regarding the ideal relative volume of organic solvent used to back extract from an aqueous layer? Can't find any information on this anywhere...
Cheers!
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Its hard to come up with a definitive answer. It seems the typical value is equal volumes, so you're maximizing contact area shaking in the sep. funnel. But you're going to do it 3 times, to get max extraction, based on partitioning coefficient. But can you handle that much volume? Or does it depend on solubility of compound in solvent, as well?
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Just a quick question regarding the ideal relative volume of organic solvent used to back extract from an aqueous layer? Can't find any information on this anywhere...
Cheers!
Re: ideal relative volume
The most effective would be a large volume extracting an infinite number of times, but that would use a lot of solvent. Reducing the volume of solvent would also be very effective, but a large number of extractions would be time consuming. For compounds not highly water soluble, I generally chose volumes that were comparable to my original extractions and would fit in my flask. If I had washed once with 50 mL and my organic layer was in a 125 mL flask, I'd back extract with a volume that would also fit in my 125 mL flask. Occasionally, I might have to change flask size, but I'd say flask size determined the relative volume I'd use. (I also didn't back extract except if I thought my compound had some water solubility. You can go crazy with washing the back extracts and re-extracting those, etc.)