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seperating compounds

I have a solution of 3 compounds, 4-nitrobenzoic acid, ethyl 4-nitrobenzenoate and ethyl 4-aminobenzoate. ( I need to isolate the ethyl 4-nitrobenzoate and ethyl 4-aminobenzoate)

I'm going to be using a separating funnel to separate the compounds and have a few solvents and solutions I can use

Diethyl ether
Dichloromethane
Water
NaOH (aq)
HCl (aq)
Saturated NaHCO3
Saturated NaCl

I was going to use DCM as the organic layer and NaOH(aq) as the aqueous layer as the 4-nitrobenzoic acid will dissolve in this dissolve in this, then I can run the aqueous layer off (and repeat?) and I will be left with the 2 compounds I need, then I could add HCl(?) to seperate the two, ethyl 4-nitrobenzoate will be in the organic layer and ethyl 4-aminobenzoate in the aquous. Then i'm not sure if I would need to add anything to do the ethyl 4-aminobenzoate to remove the hydrogen ion or not.

Does this sound ok? i'm also not sure as to the difference between using diethyl ether and DCM, and NaOH or NaHCO3

Reply 1

KombatWombat

I think you've got the general idea. To recover solid 4-nitrobenzoic acid, you'll need to add HCl until pH is low enough to reprotonate the carboxylic acid. Since it's not soluble in water, it'll crash out. Same with recovering the amino benzoate; add base to deportonate the conjugate base and it will crash out. Make sure you're careful to use as little solvent as possible though, otherwise extracting will be difficult.

Then I guess you'll want to recover the ethyl 4-nitrobenzenoate which you can just rotovap off (I'm assuming this is undergrad so you'll have access to one?).

I think the point about DCM vs diethyl ether is that DCM is pretty hazardous! You don't really want to be using it in such abundance, and you'd use a fair bit doing these extractions. NaOH or NaHCO3 depends on whether any of the compounds are sensitive to the harsher hydroxide. I don't think any of them are especially, but you might want to double check.

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