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Topic: "Washing" versus "extraction"  (Read 36302 times)

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Offline astrapw

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"Washing" versus "extraction"
« on: October 21, 2006, 09:45:11 PM »
Can someone explain the difference between washing and extration?

Thanks

Offline Yggdrasil

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Re: "Washing" versus "extraction"
« Reply #1 on: October 21, 2006, 10:02:49 PM »
Both are pretty much the same thing.  You add a different solvent to your reaction mixture, shake them up to let the components of the solution go into the proper phase, let them separate the two phases.  The main difference is in where your compound of interest goes.  If the compound of interest stays in the original solvent, you are washing your reaction mixture to remove impurities.  However, if your compound moves into the new solvent, you are extracting your compound.

Say for example, you are trying to isolate an organic compound in a mixture of ether and NaOH. If you add a solution of hydrochloric acid to remove the NaOH from the organic phase, you are performing a wash, since your compound of interest stays in the ether.

Now, lets say you are trying to isolate an organic acid from a mixture of organic compounds in hexane.  If you add a solution of aqueous sodium hydroxide to remove the organic acid from the organic phase, you are performing an extraction because the compound of interest comes out from the hexane into the aqueous phase.

Offline astrapw

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Re: "Washing" versus "extraction"
« Reply #2 on: October 21, 2006, 10:09:57 PM »
To sum this up if I read it correctly...

wash: you remove a compound from a product that you are not trying to isolate (you discard this part)

extraction: you remove a compound from a product you are trying to isolate (you keep this part)

Offline Yggdrasil

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Re: "Washing" versus "extraction"
« Reply #3 on: October 21, 2006, 10:31:26 PM »
Somewhat close.

Lets say you perform a reaction and have your product x (which you want to isolate) along with some impurities y all in a solution of solvent A.  Let's denote this as:

A(x,y), which means x and y are disolved in A.

Now we add solvent B and perform either an extraction or wash

Extraction:
When we add B to A, mix, then separate A and B, we get:

A(y) and B(x)

Your product is now out of your original reaction mixture (A) and in a new solvent (B).  Plus, the impurities have been removed since they stay in solvent A.  Here, you discard solvent A and isolate your compound from solvent B.

Wash:
When we add B to A, mix, then separate A and B, we get:

A(x) and B(y)

Your product is still in A, but all of your impurities have been removed by solvent B.  Here, you discard solvent B and isolate your compound from solvent A.

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