Acid/base extraction

[keikoblue2]

Say you have four compounds in a solution: benzoic acid (benzene with carboxyl group), phenol (benzene with alcohol group), aniline (benzene with amine group), and phenoxide (benzene with methoxide group).

TBR says to use a weak base first to extract the stronger acid (benzoic acid). If you use a strong base, it will extract both the phenoxide and benzoic acid.

Then they used a strong base to extract out the phenol, while the aniline and phenoxide remained in the organic layer.

Afterwards, a strong acid was used to extract the aniline and the phenoxide was in the organic layer.

My question is, do weak bases extract strong acids and vice versa, and strong bases extract weak acids and vice versa? And how come the phenoxide remained in the organic layer when HCl was added? (How come HCl has greater affinity for the aniline and not for the phenoxide, and how can you predict which compounds will be extracted by which reagents?)

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[FeinMS]

Say you have four compounds in a solution: benzoic acid (benzene with carboxyl group), phenol (benzene with alcohol group), aniline (benzene with amine group), and phenoxide (benzene with methoxide group).

TBR says to use a weak base first to extract the stronger acid (benzoic acid). If you use a strong base, it will extract both the phenoxide and benzoic acid.

Then they used a strong base to extract out the phenol, while the aniline and phenoxide remained in the organic layer.

Afterwards, a strong acid was used to extract the aniline and the phenoxide was in the organic layer.

My question is, do weak bases extract strong acids and vice versa, and strong bases extract weak acids and vice versa? And how come the phenoxide remained in the organic layer when HCl was added? (How come HCl has greater affinity for the aniline and not for the phenoxide, and how can you predict which compounds will be extracted by which reagents?)

I have not reviews lab techniques, but it makes complete sense for me. Phenoxide (C6H5OCH3) is neither acidic nor basic. Do you mean phenol by the bolded word?

If you add weak bases to the mixture, it's going to react with the strongest acid. Why? because to deprotonate an weak acid (who can but doesn't like to donate a proton) you need a strong base (who can and eager to accept a proton) With weak base, you can't really deprotonate weak acids. By adding weak bases, however, you can deprotonate strong acids. Phenoxide doesn't react with any base/acid because, as I said earlier, it's not acidic or basic, so it stays in the solution until all other acidic/basic compounds are precipitated and eliminated.

 

[keikoblue2]

I have not reviews lab techniques, but it makes complete sense for me. Phenoxide (C6H5OCH3) is neither acidic nor basic. Do you mean phenol by the bolded word?

If you add weak bases to the mixture, it's going to react with the strongest acid. Why? because to deprotonate an weak acid (who can but doesn't like to donate a proton) you need a strong base (who can and eager to accept a proton) With weak base, you can't really deprotonate weak acids. By adding weak bases, however, you can deprotonate strong acids. Phenoxide doesn't react with any base/acid because, as I said earlier, it's not acidic or basic, so it stays in the solution until all other acidic/basic compounds are precipitated and eliminated.

Oooh thank you! I was under the impression that both aniline and phenoxide were neutral, but I guess aniline is more basic (when protonated the N is less electronegative so it bears the positive charge better than an O would?). And I need to memorize the strengths of common acids and bases (thought phenol was a weak base like carboxylic acid; turns out phenol's a VERY weak base). Also, thanks for answering my other question floating around this board somewhere. Great explanations!

 

[FeinMS]

Oooh thank you! I was under the impression that both aniline and phenoxide were neutral, but I guess aniline is more basic (when protonated the N is less electronegative so it bears the positive charge better than an O would?). And I need to memorize the strengths of common acids and bases (thought phenol was a weak base like carboxylic acid; turns out phenol's a VERY weak base). Also, thanks for answering my other question floating around this board somewhere. Great explanations!

Phenol and carboxylic acids are ACIDS not bases

 

[keikoblue2]

Phenol and carboxylic acids are ACIDS not bases

Did I write base? Crap I did... goodness I must be losing it