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chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, work-up refers to the series of manipulations required to isolate and purify the product(s) of a
chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
. The term is used colloquially to refer to these manipulations, which may include: * deactivating any unreacted reagents by quenching a reaction. * cooling the reaction mixture or adding an '' antisolvent'' to induce
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
, 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. * separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction. * removal of solvents by
evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...
. * purification by
chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...
, distillation or recrystallization. The work-up steps required for a given chemical reaction may require one or more of these manipulations. Work-up steps are not always explicitly shown in reaction schemes. Written experimental procedures will describe work-up steps but will usually not formally refer to them as a work-up.


Examples


Isolation of benzoic acid

The Grignard reaction between phenylmagnesium bromide (1) and
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
in the form of
dry ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and Sublimation (phase transition), sublimes directly from the solid state to the gas ...
gives the conjugate base of benzoic acid (2). The desired product, benzoic acid (3), is obtained by the following work-up: * 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 (3) from an
alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...
(1). 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 (2). The product is isolated from the mixture by the following work-up: * A concentrated solution of
sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
in water, known as 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. 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 Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 mill ...
to remove any remaining water. * The sodium sulfate is filtered out leaving the pure liquid product.


Synthesis of an amide

The reaction between a secondary amine (1) and an acyl chloride (2) yields the desired amide (4) as shown below. The acyl chloride is added slowly to a solution of the amine and triethylamine in dichloromethane at 0 °C. The reaction is allowed to warm to room temperature and is stirred for 14 hours. The following manipulations are then performed on the crude reaction mixture (3) to isolate the desired product:{{Cite journal , last=Kaiser , first=Daniel , last2=Teskey , first2=Christopher J. , last3=Adler , first3=Pauline , last4=Maulide , first4=Nuno , date=2017-11-15 , title=Chemoselective Intermolecular Cross-Enolate-Type Coupling of Amides , url=https://pubs.acs.org/doi/10.1021/jacs.7b08813 , journal=Journal of the American Chemical Society , language=en , volume=139 , issue=45 , pages=16040–16043 , doi=10.1021/jacs.7b08813 , issn=0002-7863 , pmc=5691317 , pmid=29099184 * A concentrated solution of sodium bicarbonate is added to the reaction mixture. This will promote the migration of impurities and byproducts to the aqueous layer and leave the product in the dichloromethane (organic layer). The aqueous and organic layers are allowed to separate. This process is typically performed in a separatory funnel. * The aqueous layer is collected and extracted once with dichloromethane. * The organic phase is collected and dried with anhydrous sodium sulfate. * The solid is filtered off and the organic layer is concentrated under reduced pressure to yield the desired amide. * Further purification is achieved by flash column chromatography.


References

Chemical reactions