The Finkelstein reaction named after the German chemist
Hans Finkelstein, is an
SN2 reaction (Substitution Nucleophilic Bimolecular reaction) that involves the exchange of one
halogen atom for another. It is an
equilibrium reaction
In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the s ...
, but the reaction can be driven to completion by exploiting the
differential solubility of halide salts, or by using a large excess of the halide salt.
:R–X + X′
− R–X′ + X
−
Method
The classic Finkelstein reaction entails the conversion of an
alkyl chloride or an
alkyl bromide
Organobromine compounds, also called organobromides, are organic compounds that contain carbon Chemical bond, bonded to bromine. The most pervasive is the naturally produced bromomethane.
One prominent application of synthetic organobromine comp ...
to an
alkyl iodide
Organoiodine compounds are organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are relatively rare in nature. The thyroxine hormones are organoiodine compounds that are required for he ...
by treatment with a solution of
sodium iodide
Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions ...
in
acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour.
Acetone is miscib ...
. Sodium iodide is soluble in acetone while
sodium chloride and
sodium bromide
Sodium bromide is an inorganic compound with the formula Na Br. It is a high-melting white, crystalline solid that resembles sodium chloride. It is a widely used source of the bromide ion and has many applications.Michael J. Dagani, Henry J. Ba ...
are not. The reaction is driven toward products by
mass action due to the precipitation of the poorly soluble NaCl or NaBr. An example involves the conversion of the ethyl ester of 5-bromo
valeric acid
Valeric acid or pentanoic acid is a straight-chain alkyl carboxylic acid with the chemical formula . Like other low-molecular-weight carboxylic acids, it has an unpleasant odor. It is found in the perennial flowering plant ''Valeriana officin ...
to the iodide:
:EtO
2C(CH
2)
4Br + NaI → EtO
2C(CH
2)
4I + NaBr
Potassium fluoride
Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide and occurs naturally as the rare ...
is used for the conversion of
chlorocarbon
An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens substituted by chlo ...
s into
fluorocarbons. Such reactions usually employ polar solvents such as
dimethyl formamide
Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the major ...
,
ethylene glycol
Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
, and
dimethyl sulfoxide.
Use for analysis
Alkyl halides differ greatly in the ease with which they undergo the Finkelstein reaction. The reaction works well for primary (except for
neopentyl
Pentyl is a five-carbon alkyl group or substituent with chemical formula -C5H11. It is the substituent form of the alkane pentane.
In older literature, the common non-systematic name amyl was often used for the pentyl group. Conversely, the name ...
) halides, and exceptionally well for
allyl,
benzyl
In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group.
Nomenclature
In IUPAC nomenclature, the prefix benzyl refers to a substi ...
, and α-carbonyl halides. Secondary halides are far less reactive.
Vinyl
Vinyl may refer to:
Chemistry
* Polyvinyl chloride (PVC), a particular vinyl polymer
* Vinyl cation, a type of carbocation
* Vinyl group, a broad class of organic molecules in chemistry
* Vinyl polymer, a group of polymers derived from vinyl ...
,
aryl
In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...
and tertiary alkyl halides are unreactive; as a result, the reaction of NaI in acetone can be used as a qualitative test to determine which of the aforementioned classes an unknown alkyl halide belongs to, with the exception of alkyl iodides, as they yield the same product upon substitution. Below some relative rates of reaction (NaI in acetone at 60 °C):
Aromatic Finkelstein reaction
The aromatic chlorides and bromides are not easily substituted by iodide, though they may occur when appropriately catalyzed. The so-called "aromatic Finkelstein reaction" is catalyzed by
copper(I) iodide
Copper(I) iodide is the inorganic compound with the formula CuI. It is also known as cuprous iodide. It is useful in a variety of applications ranging from organic synthesis to cloud seeding.
Copper(I) iodide is white, but samples often appe ...
in combination with diamine ligands.
Nickel bromide
Nickel(II) bromide is the name for the inorganic compounds with the chemical formula NiBr2(H2O)''x''. The value of ''x'' can be 0 for the anhydrous material, as well as 2, 3, or 6 for the three known hydrate forms. The anhydrous material is a yel ...
and
tri-''n''-butylphosphine have been found to be suitable catalysts as well.
See also
*
Halex process
In chemistry, the Halex process is used to convert aromatic chlorides to the corresponding aromatic fluorides. The process entails ''Hal''ide ''ex''change, hence the name. The reaction conditions call for hot (150-250 °C) solution of the aryl ch ...
, also a salt metathesis, but for conversion of aryl chlorides to aryl fluorides
References
{{Reflist
Halogenation reactions
Substitution reactions
Name reactions