Acid–base extraction

[1] It is typically performed during the work-up step following a chemical synthesis to purify crude compounds[2] and results in the product being largely free of acidic or basic impurities.

[3] Acid-base extraction utilizes the difference in solubility of a compound in its acid or base form to induce separation.

[4] Typically, the desired compound is changed into its charged acid or base form, causing it to become soluble in aqueous solution and thus be extracted from the non-aqueous (organic) layer.

[3][7] The following procedure is typically followed when performing an acid-base extraction for a mixture containing an acidic and/or basic compound: Acid-base extraction is frequently used as the first step in a work-up procedure following a chemical synthesis[2] to remove acidic and basic starting materials or impurities.

[3] Acid-base extraction is typically a precursor to more complicated purification techniques, such as recrystallization, if the product synthesized is still not completely pure.

The post-reaction mixture often consists of small amounts of leftover acid and alcohol, in addition to the desired ester.

Another common example of acid-base extraction occurs following peptide coupling, where the amide product must be separated from leftover carboxylic acid and amine.

Example of acid base extraction. A 3-component system is separated into its acid component (benzoic acid), base component (benzylamine), and neutral component (biphenyl).
Example of acid-base extraction of two components: acidic phenol, and basic phenylamine. Phenylamine is first collected in the organic layer, then phenol is collected from the aqueous layer. The green layer in the separatory funnel indicates the organic layer, while the colourless layer indicates the aqueous layer.