View source for Chemistry:Finkelstein reaction

{{Short description|Chemistry}}
{{Reactionbox
| Name = Finkelstein reaction
| Type = Substitution reaction
| NamedAfter = Hans Finkelstein
| Section3 = {{Reactionbox Identifiers
   | OrganicChemistryNamed = finkelstein-reaction
   | RSC_ontology_id = 0000155
 }}
}}
[[File:Finkelstein_Reaction_in_Flask.jpg|thumb|right]]
The '''Finkelstein reaction''', named after the German chemist Hans Finkelstein,<ref>{{cite journal|first = Hans|last = Finkelstein|journal = Ber. Dtsch. Chem. Ges.|year = 1910|volume = 43|issue = 2|pages = 1528–1532|title = Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden|language = German|doi = 10.1002/cber.19100430257|url = https://zenodo.org/record/1426411}}</ref> is an [[Chemistry:SN2 reaction|S<sub>N</sub>2 reaction]] (Substitution Nucleophilic Bimolecular reaction) that involves the exchange of one [[Chemistry:Halogen|halogen]] atom for another. It is an [[Chemistry:Chemical equilibrium|equilibrium reaction]], but the reaction can be driven to completion by exploiting the [[Chemistry:Solubility#Differential solubility|differential solubility]] of halide salts, or by using a large excess of the halide salt.<ref>{{March6th}}</ref>

:R&ndash;X &nbsp; + &nbsp; X′<sup>−</sup> &nbsp; {{eqm}} &nbsp; R&ndash;X′ &nbsp; + &nbsp; X<sup>−</sup>

==Method==
The classic Finkelstein reaction entails the conversion of an alkyl chloride or an alkyl bromide to an alkyl iodide by treatment with a solution of [[Chemistry:Sodium iodide|sodium iodide]] in [[Chemistry:Acetone|acetone]].  Sodium iodide is soluble in acetone while [[Chemistry:Sodium chloride|sodium chloride]] and [[Chemistry:Sodium bromide|sodium bromide]] are not.<ref>{{cite journal | last = Ervithayasuporn | first =  V. | year = 2013 | title = One-pot synthesis of halogen exchanged silsesquioxanes: octakis(3-bromopropyl)octasilsesquioxane and octakis(3-iodopropyl)octasilsesquioxane | journal = Dalton Trans. | volume = 42 | issue = 37 | pages = 13747–13753 | doi = 10.1039/C3DT51373D | pmid = 23907310 }}</ref> The reaction is driven toward products by [[Chemistry:Law of mass action|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[[Chemistry:Valeric acid|valeric acid]] to the iodide:<ref>{{cite journal|title=Copper-catalyzed Conjugate Addition of Functionalized Organozinc Reagents to α,β-Unsaturated Ketones: Ethyl 5-(3-oxocyclohexyl)pentanoate|author1=B. H. Lipshutz |author2=M. R. Wood |author3=R. Tirado
|journal=Org. Synth.|year=1999|volume=76|page=252
|doi=10.15227/orgsyn.076.0252}}</ref>
:EtO<sub>2</sub>C(CH<sub>2</sub>)<sub>4</sub>Br  +  NaI   →   EtO<sub>2</sub>C(CH<sub>2</sub>)<sub>4</sub>I + NaBr

[[Chemistry:Potassium fluoride|Potassium fluoride]] is used for the conversion of chlorocarbons into [[Chemistry:Fluorocarbon|fluorocarbon]]s.<ref>{{OrgSynth  | last1= Vogel| first1=A. I.| last2=Leicester| first2=J.| last3=Macey| first3=W. A. T. | title = n-Hexyl Fluoride | volume =  36|year=1956 | pages = 40| doi= 10.15227/orgsyn.036.0040}}</ref> Such reactions usually employ polar solvents such as dimethyl formamide, [[Chemistry:Ethylene glycol|ethylene glycol]], and [[Chemistry:Dimethyl sulfoxide|dimethyl sulfoxide]].<ref>Han, Q.; Li, H-Y. "Potassium Fluoride" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons,New York. {{doi|10.1002/047084289X.rp214}}</ref>

==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) halides, and exceptionally well for [[Chemistry:Allyl|allyl]], benzyl, and α-carbonyl halides. Secondary halides are far less reactive. [[Chemistry:Vinyl group|Vinyl]], [[Chemistry:Aryl|aryl]] 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&nbsp;°C):<ref>{{cite journal | last = Streitwieser | first =  A. |  year = 1956 | title = Solvolytic Displacement Reactions at Saturated Carbon Atoms | journal = [[Chemistry:Chem. Rev.|Chem. Rev.]] | volume = 56 | pages = 571–752 | doi = 10.1021/cr50010a001 | issue = 4}}</ref><ref>{{cite journal | title = The Effect of the Carbonyl and Related Groups on the Reactivity of Halides in S<sub>N</sub>2 Reactions |last1=Bordwell|first1 = F. G. |last2=Brannen|first2 = W. T. | journal = J. Am. Chem. Soc. | year = 1964 | volume = 86 | pages = 4645–4650 | doi = 10.1021/ja01075a025 | issue = 21}}</ref>

{| class="wikitable"
|-
! [[Chemistry:Chloromethane|Me&ndash;Cl]]
! Bu&ndash;Cl
! ''i''-Pr&ndash;Cl
! ''t''-BuCH<sub>2</sub>&ndash;Cl
! [[Chemistry:Allyl chloride|CH<sub>2</sub>=CH&ndash;CH<sub>2</sub>&ndash;Cl]]
! [[Chemistry:Benzyl chloride|PhCH<sub>2</sub>&ndash;Cl]]
! [[Chemistry:Ethyl chloroacetate|EtOC(O)CH<sub>2</sub>&ndash;Cl]]
! [[Chemistry:Chloroacetone|MeC(O)CH<sub>2</sub>&ndash;Cl]]
|-
| 179
| 1
| 0.0146
| 0.00003
| 64
| 179
| 1600
| 33000
|}

==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 [[Chemistry:Copper(I) iodide|copper(I) iodide]] in combination with diamine ligands.<ref>{{cite journal |first1=A.|last1 = Klapars |first2=S. L.|last2 = Buchwald | title = Copper-Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein Reaction | journal = J. Am. Chem. Soc. | volume = 124 | pages = 14844–14845 | doi = 10.1021/ja028865v | year = 2002 | issue = 50 | pmid = 12475315|s2cid = 11338218 }}</ref> Nickel bromide and tri-''n''-butylphosphine have been found to be suitable catalysts as well.<ref>{{cite journal | doi = 10.1039/c2cc30956d | title = Nickel-catalysed aromatic Finkelstein reaction of aryl and heteroaryl bromides | year = 2012 | last1 = Cant | first1 = Alastair A. | last2 = Bhalla | first2 = Rajiv | last3 = Pimlott | first3 = Sally L. | last4 = Sutherland | first4 = Andrew | journal = Chem. Commun. | volume = 48 | issue = 33 | pages = 3993–5 | pmid = 22422214}}</ref>

==See also==
* [[Chemistry:Halex process|Halex process]], also a salt metathesis, but for conversion of aryl chlorides to aryl fluorides

==References==
{{Reflist}}

[[Category:Halogenation reactions]]
[[Category:Substitution reactions]]
[[Category:Name reactions]]

{{Sourceattribution|Finkelstein reaction}}