Orgo Destroyer Q #180

[hope_to_match]

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From 2013 version. It is asking for the compound that will be most soluble in water. The answer is B (carboxy acid) because it has the greatest ability to H-bond to water.

My question is, why then Chad says (in his lecture on lab techniques and spec) that in order for carboxylic acids to be soluble they need to be charged and the proton needs to be removed with NaHCO3 or NaOH first before it will be soluble?

 

[Minion]

Carboxylic acid is capable of hydrogen bonds, "like-dissolve-like" in this case.

Also whenever you are comparing two molecules that are capable of hydrogen bonding, then the most dipole will dissolve in water more readily because it is more polar.

 

[getsome111]

So what chad is talking about is doing an extraction, its the same concept. The reason why a carboxylic acid will be soluble in water because, 1; it has a low pka resulting in a negative charge (this is the most important reason) and 2; because it can H-bond.

now for the extraction, when you're doing one you want to get as close to 100% of the chemical as possible.. usually out of ether. Ether is something that a carboxylic acid will be slightly soluble in, thus, to ensure you get as much into the aqueous phase as possible you use a base to make the already preferable aqueous phase more preferable. The principle of acid base extraction is to put a charge on whatever you want in the aqueous phase, and remove the charge from whatever you want in the organic 🙂