User:CorrelationSpec/Work-Up Sandbox

In chemistry, work-up refers to the series of manipulations required to isolate and purify the product(s) of a chemical reaction.^[1] Typically, these manipulations may include:

deactivating any unreacted reagents by quenching a reaction.
cooling the reaction mixture or adding an antisolvent to induce precipitation, and collecting or removing the solids by filtration, decantation, or centrifugation.
changing the protonation state of the products or impurities by adding an acid or base
removal of solvents by evaporation.
separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction.
purification by chromatography, distillation or recrystallization

Workup steps are not always explicitly shown in reaction schemes. The term work-up is used colloquially to describe the process of isolating the desired material from the crude reaction mixture. Written experimental procedures will describe the work-up steps but will usually not formally refer to them as a work-up.

examples of

Examples

Isolation of Benzoic Acid

The Grignard reaction between phenylmagnesium bromide and carbon dioxide in the form of dry ice gives the conjugate base of benzoic acid. The desired product, benzoic acid, is obtained by the following work-up:^[2]

Synthetic route of benzoic acid with workup step in red.

The reaction mixture containing the Grignard reagent is allowed to warm to room temperature in a water bath to allow excess dry ice to evaporate
Any remaining Grignard reagent is quenched by the addition of water
Dilute hydrochloric acid is added to the reaction mixture to protonate the benzoate salts, as well as to dissolve the magnesium salts. White solids of impure benzoic acid are obtained.
The benzoic acid is decanted to remove the aqueous solution of impurities, more water is added, and the mixture is brought to a boil with more water added to give a homogeneous solution.
The solution is allowed to cool slowly to room temperature, then in an ice bath to recrystallize benzoic acid.
The recrystallized benzoic acid crystals are collected on a Buchner funnel and are allowed to air-dry to give pure benzoic acid.

Dehydration of 4-methylcyclohexanol

This dehydration reaction produces the desired alkene from the alcohol. The reaction is performed in a distillation apparatus so the formed alkene product can be distilled off and collected as the reaction proceeds. The water produced by the reaction as well as some acid will co-distill, giving a distillate mixture. The product is isolated from he mixture by the following work-up:^[3]

A brine solution is added to the mixture and the layers are allowed to separate. The brine is used to remove any acid or water from the organic layer.
The bottom aqueous layer is removed with a pipette and discarded.
The top product layer is transferred to an Erlenmeyer flask where it is treated with anhydrous sodium sulfate to remove any remaining water.
The sodium sulfate is filtered out leaving the pure liquid product.

Tert-butyl Ester Hydrolysis

In the hydrolysis of a tert-butyl ester, the starting material is treated with trifluoracetic acid. If the product is not volatile relative to the TFA

Once the reaction is complete, a simple workup can be completed by evaporation, which leaves the desired carboxylic acid.

Liquid-Liquid Extraction

References

^ Stevenson, Angus; Lindberg, Christine A., eds. (2010). "Workup". New Oxford American Dictionary (3rd ed.). Oxford University Press. ISBN 9780199891535.
^ Donald L. Pavia (2004). Introduction to Organic Laboratory Techniques: A Small Scale Approach. Thomson Brooks/Cole. pp. 312–314. ISBN 0-534-40833-8.
^ Pavia, Donald L.; Lampman, Gary M.; Kriz, George S.; Engel, Randall G. (2011). A Small Scale Approach to Organic Laboratory techniques (3rd ed.). Belmont, CA: Brooks/Cole. pp. 179–182. ISBN 978-1-4390-4932-7.

[1] Stevenson, Angus; Lindberg, Christine A., eds. (2010). "Workup". New Oxford American Dictionary (3rd ed.). Oxford University Press. ISBN 9780199891535.

[2] Donald L. Pavia (2004). Introduction to Organic Laboratory Techniques: A Small Scale Approach. Thomson Brooks/Cole. pp. 312–314. ISBN 0-534-40833-8.

[3] Pavia, Donald L.; Lampman, Gary M.; Kriz, George S.; Engel, Randall G. (2011). A Small Scale Approach to Organic Laboratory techniques (3rd ed.). Belmont, CA: Brooks/Cole. pp. 179–182. ISBN 978-1-4390-4932-7.

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