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The Finkelstein reaction, named for the German chemist Hans Finkelstein, is an SN2 reaction
SN2 reaction

The SN2 reaction is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophile center and covalent bond to it, expelling another group called a leaving group....
 that involves the exchange of one halogen
Halogen

|}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
 atom for another. Halide exchange is an equilibrium reaction
Chemical equilibrium

In a chemical process, chemical equilibrium is the state in which the Activity or concentrations of the reactants and products have no net change over time....
, but the reaction can be driven to completion by taking advantage of differential solubility of halide salts, or by using a large excess of the halide salt.

R-X + X'- R-X' + X-


The classic Finkelstein reaction involves the conversion of an alkyl chloride or an alkyl bromide to an alkyl iodide by the addition of sodium iodide
Sodium iodide

Sodium iodide is a white, crystalline salt with chemical formula SodiumIodine used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction....
 in acetone
Acetone

Acetone is the organic compound with the chemical formula OC2. This colorless, mobile, flammable liquid is the simplest example of the ketones....
.






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The Finkelstein reaction, named for the German chemist Hans Finkelstein, is an SN2 reaction
SN2 reaction

The SN2 reaction is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophile center and covalent bond to it, expelling another group called a leaving group....
 that involves the exchange of one halogen
Halogen

|}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
 atom for another. Halide exchange is an equilibrium reaction
Chemical equilibrium

In a chemical process, chemical equilibrium is the state in which the Activity or concentrations of the reactants and products have no net change over time....
, but the reaction can be driven to completion by taking advantage of differential solubility of halide salts, or by using a large excess of the halide salt.

R-X + X'- R-X' + X-


The classic Finkelstein reaction involves the conversion of an alkyl chloride or an alkyl bromide to an alkyl iodide by the addition of sodium iodide
Sodium iodide

Sodium iodide is a white, crystalline salt with chemical formula SodiumIodine used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction....
 in acetone
Acetone

Acetone is the organic compound with the chemical formula OC2. This colorless, mobile, flammable liquid is the simplest example of the ketones....
. Because sodium iodide is soluble in acetone and sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
 and sodium bromide
Sodium bromide

Sodium bromide, also known as sedoneural is a salt with the formula sodiumbromine, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries....
 are not, the equilibrium is shifted by the precipitation of the insoluble salt. For example, bromoethane
Bromoethane

Bromoethane, also known as ethyl bromide is a chemical compound of the haloalkanes group. It is abbreviated by chemists as EtBr. This volatile compound has an ether-like odour....
 can be converted to iodoethane:

CH3CH2Br (acetone) + NaI (acetone) ? CH3CH2I (acetone) + NaBr (s)


Alkyl halides differ greatly in the ease with which they undergo the Finkelstein reaction. The reaction works well for primary (except for neopentyl) halides, and exceptionally well for allyl
Allyl

An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2....
, benzyl
Benzyl

In organic chemistry, benzyl is the term used to describe the substituent or molecular fragment possessing the structure C6H5CH2-....
, and a-carbonyl halides. Secondary substrates are marginal. Vinyl
Vinyl

A vinyl compound is any organic compound that contains a vinyl group , −CarbonHydrogenCovalent bondCH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group....
, aryl
Aryl

In the context of organic molecules, aryl refers to any functional group or substituent derived from a simple aromatic ring, may it be phenyl, thiophene, indole, etc ....
 and tertiary alkyl halides are unreactive. Below some relative rates of reaction (NaI in acetone at 60°):

Me-Cl Bu-Cl i-Pr-Cl t-BuCH2-Cl CH2=CH-CH2-Cl PhCH2-Cl EtOC(O)CH2-Cl MeC(O)CH2-Cl
179 1 0.0146 0.00003 64 179 1600 33000


In modern usage the definition of the reaction has been expanded to include the conversion of alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
s to alkyl halides by first converting the alcohol to a sulfonate
Sulfonate

A sulfonate is a Salt_ or ester of a sulfonic acid. It contains the functional group R-SO2O-....
 ester (tosylates or mesylate
Mesylate

In chemistry, a mesylate is any salt or ester of methanesulfonic acid . In salts, the mesylate is present as the CH3SO3- anion....
s are usually used), and then performing the substitution. The example below is from a synthesis of Chrysochlamic Acid.