Need advice on extracting carboxylic acids from an NaOH Mixture

  1. I have an amino carboxylic acid that is practically insoluble in most alcohols and in water, but supposedly soluble in an 20% NaOH solution.

    A basic reaction is run with an organic solvent/reactant, and the amino carboxylic acid dissolved in the NaOH solution. After the reaction the layers are easily separated. With the NaOH layer separate, by what method is the carboxylic acid able to be extracted from the NaOH layer?

    I've read one way to do this is to neutralize the base with equal parts Hydrochloric acid but I am unsure if the carboxylic acid will dissolve in HCL, and if possible, I would want to avoid such acids all together.

    Any ideas?
  2. jcsd
  3. Borek

    Staff: Mentor

    What will happen if you neutralize the base in water solution, and if the acid is insoluble?
  4. That is a possibility but then I face the problem of the formed salt(from the NaOH being neutralized by an acid) potentially being unseparable from the carboxylic-acid. This of course could be done if the salt can be filted out from the acid with water rinses, but this would assume that the acid is totally insoluble in water, which, I won't know until I try.
  5. Borek

    Staff: Mentor

    There is no such thing as "completely insoluble", and separation is always a matter of finding a good compromise between what is left and what is lost.

    Too low pH can probably dissolve the acid back (you have mentioned the amine group, it will get protonated).

    You can neutralize and try to extract the acid into some non-polar, immiscible solvent. It may require good pH control.
  6. Ah, so, if I carefully control the PH, I can add acid until the PH is neutral, and then I could decant off mixture and be left with the remaining carboxylic acid? Will this acid-base neutralization leave any solid residual products in the mistd of my carboxylic?

    I realize that NaOH + HCL will produce a NaCl salt, but this salt will likely be dissolved in the mixture and easily separable from the nondissolved carboxylic, correct?
  7. Borek

    Staff: Mentor

    Depends on what was present in the solution, but as most chlorides are well soluble I would not expect any other solids. Unless you happen to have other, weakly soluble acid in the solution.

    That's the idea. It is all in the fine print - a lot depends on the acid itself, and its pKa values.
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?

Draft saved Draft deleted