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Topic: Extraction, liquid-liquid  (Read 3540 times)

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Offline yxyx

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Extraction, liquid-liquid
« on: April 10, 2011, 06:29:02 AM »
Hi!
I'm new here so sorry if there is a similar post.

I have trouble understanding a extraction lab that we had a couple of days ago.
We've got a solution of 2-chlorophenol, benzoic acid and benzophenon in dichloromethane.

In step 1 we extract the solution with NaHCO3 (B). The TLC showed that only benzophenon and 2-chlorophenol was present in the organic phase (is it called that in english?).

In step 2 the water phase of (B) was washed with dichloromethane twice. On the TLC of the organic phase it looked like only 2-chlorophenol was left in this phase.

In step 3 we put some HCl in the water phase+washed it again with dichloromethane and the TLC showed that we had separated benzoic acid in the organic phase!

The thing i don't understand are the steps of getting the benzoic acid. Was it really 2-chlorophenol i saw in step 2?

Sorry if it looks messy, english is not my first language (duh  :P)

Offline Dan

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Re: Extraction, liquid-liquid
« Reply #1 on: April 10, 2011, 08:16:54 AM »
You're English is very good don't worry.

Think about what happens to benzoic acid when it comes into contact with bicarbonate. How does this affect the solubility?
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Offline yxyx

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Re: Extraction, liquid-liquid
« Reply #2 on: April 10, 2011, 09:19:48 AM »
You're English is very good don't worry.

Think about what happens to benzoic acid when it comes into contact with bicarbonate. How does this affect the solubility?

Hmm.. if i understand it correct the benzoic acid gets deprotonated (?) and there for gets uncharged and soluble in solvents that are base (i'm not sure of the english word for the opposite of acid solvents :P)?

Does that mean that it wasn't 2-chlorophenol that i saw on the TLC, just a deprotonated benzoic acid?

Offline Dan

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Re: Extraction, liquid-liquid
« Reply #3 on: April 10, 2011, 10:34:16 AM »
Quote
Does that mean that it wasn't 2-chlorophenol that i saw on the TLC, just a deprotonated benzoic acid?

No, don't worry about that for now, that can be explained later.

Hmm.. if i understand it correct the benzoic acid gets deprotonated (?) and there for gets uncharged and soluble in solvents that are base (i'm not sure of the english word for the opposite of acid solvents :P)?

Almost. The benzoic acid is deprotonated to produce benzoate ion (which is charged).

PhCOOH + HCO3- --> PhCOO- + CO2 + H2O

The charged benzoate is more polar than benzoic acid, and is therefore more soluble in polar solvents (such as water).

Adding acid to an aqueous solution of benzoate causes protonation, re-forming benzoic acid. This acid is uncharged and therefore less polar and more soluble in less polar solvents (like DCM).

Think about the acitity of chlorophenol compared to benzoic acid, and see if you can see what's happening.
My research: Google Scholar and Researchgate

Offline yxyx

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Re: Extraction, liquid-liquid
« Reply #4 on: April 12, 2011, 10:25:08 AM »
Think about the acitity of chlorophenol compared to benzoic acid, and see if you can see what's happening.

Hi and thank you so much!
I know that the chlorophenol is less acid than the benzoic acid, and therefor less polar?

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