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In this example the organic layer is the product, which is a liquid at room temperature. The bottom aqueous layer is removed with a pipette and discarded. The top layer is transferred to an Erlenmeyer flask where it is treated with anhydrous sodium sulfate to remove any remaining water.
Acid–base extraction is a subclass of liquid–liquid extractions and involves the separation of chemical species from other acidic or basic compounds. [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.
The resulting hydroquinone is poorly soluble in typical reaction solvents (dioxane, benzene, alkanes), which facilitates workup. Solutions of DDQ in benzene are red, due to the formation of a charge-transfer complex. [9]
The complex is destroyed upon aqueous workup to give the desired ketone. For example, the classical synthesis of deoxybenzoin calls for 1.1 equivalents of AlCl 3 with respect to the limiting reagent, phenylacetyl chloride. [14]
The mechanism of the reaction involves two steps. The first step is a nucleophilic addition to the nitrile with the aid of a polarizing Lewis acid, forming an imine, which is later hydrolyzed during the aqueous workup to yield the final aryl ketone. Hoesch reaction mechanism
Workup procedures may vary depending on the stability of the products. If the organic products of the reaction are stable to aqueous acid, aqueous hydrochloric acid may be used to quench the reaction. For workups involving acid-labile products, mildly basic solutions or pH 7–8 buffers may be used.
For example, nonylmagnesium bromide reacts with methyl p-chlorobenzoate to give p-nonylbenzoic acid, in the presence of Tris(acetylacetonato)iron(III) (Fe(acac) 3), after workup with NaOH to hydrolyze the ester, shown as follows. Without the Fe(acac) 3, the Grignard reagent would attack the ester group over the aryl halide. [21]
For instance, the production of glycolic acid typically follows this method, utilizing a base-induced reaction, followed by acid workup. Similarly, unsaturated acids and fumarate and maleate esters undergo hydration to yield malic acid derivatives from esters, and 3-hydroxypropionic acid from acrylic acid .