Sandmeyer reaction

Sandmeyer reaction

The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. [cite journal
author = Traugott Sandmeyer
title = Ueber die Ersetzung der Amidgruppe durch Chlor in den aromatischen Substanzen
year = 1884
journal = Berichte der deutschen chemischen Gesellschaft
volume = 17
issue = 3
pages = 1633–1635
doi = 10.1002/cber.18840170219
url = http://gallica.bnf.fr/ark:/12148/bpt6k90700r/f56.chemindefer
] [cite journal
author = Traugott Sandmeyer
title = Ueber die Ersetzung der Amid-gruppe durch Chlor, Brom und Cyan in den aromatischen Substanzen
year = 1884
journal = Berichte der deutschen chemischen Gesellschaft
volume = 17
issue = 4
pages = 2650–2653
doi = 10.1002/cber.188401702202
url = http://gallica.bnf.fr/ark:/12148/bpt6k90700r/f1073.chemindefer
] [cite journal
author = Ludwig Gattermann
title = Untersuchungen über Diazoverbindungen
year = 1890
journal = Berichte der deutschen chemischen Gesellschaft
volume = 17
issue = 1
pages = 1218–1228
doi = 10.1002/cber.189002301199
url = http://gallica.bnf.fr/ark:/12148/bpt6k90720c/f1220.chemindefer
] It is named after the Swiss chemist Traugott Sandmeyer.

An aromatic (or heterocyclic) amine quickly reacts with a nitrite to form an aryl diazonium salt, which decomposes in the presence of copper(I) salts, such as copper(I) chloride, to form the desired aryl halide. [cite journal | author = J. K. Kochi | title = The Mechanism of the Sandmeyer and Meerwein Reactions | year = 1957 | journal = J. Am. Chem. Soc. | volume = 79 | issue = 11 | pages = 2942–2948 | doi = 10.1021/ja01568a066] [cite journal | author = H. H. Hodgson | title = The Sandmeyer Reaction | year = 1947 | journal = Chem. Rev. | volume = 40 | issue = 2 | pages = 251–277 | doi = 10.1021/cr60126a003] The reaction is a radical-nucleophilic aromatic substitution.

Several improvements have been made to the standard procedures. [cite journal | author = M. P. Doyle, B. Siegfried and J. F. Dellaria | title = Alkyl nitrite-metal halide deamination reactions. 2. Substitutive deamination of arylamines by alkyl nitrites and copper(II) halides. A direct and remarkably efficient conversion of arylamines to aryl halides | year = 1977 | journal = J. Org. Chem. | volume = 42 | issue = 14 | pages = 2426–2431 | doi = 10.1021/jo00434a017] [Suzuki, N. "et al." "Perkins Trans. I" 1987, 645.]

Variations

The majority of variations of the Sandmeyer reactions consist of using various copper salts. [OrgSynth | collvol = 3 | collvolpages = 185 | year = 1955 | prep = cv3p0185 | title = "o"-Chlorobromobenzene | author = Jonathan L. Hartwell] [OrgSynth | collvol = 4 | collvolpages = 160 | year = 1963 | prep = cv4p0160 | title = 1-Chloro-2,6-dinitrobenzene | author = F. D. Gunstone and S. Horwood Tucker] For example, using cuprous cyanide produces benzonitriles. [OrgSynth | collvol = 1 | collvolpages = 514 | year = 1941 | prep = cv1p0514 | title = "o"-Tolunitrile and "p"-Tolunitrile | author = H. T. Clarke and R. R. Read] Substituting thiols or water for the copper salts generates thioethers or phenols, respectively.

The Schiemann reaction uses tetrafluoroborate and delivers the halide-substituted product, fluorobenzene, which is not obtained by the use of copper fluorides.

Sandmeyer reactions with copper salts used in catalytic amounts are also known. One bromination protocol employs a 0.2 equivalent Cu(I)/Cu(II) mixture with additional amounts of the bidentate ligand phenanthroline and phase-transfer catalyst dibenzo-18-crown-6 [cite journal | title = Catalytic Sandmeyer Bromination | author = P. Beletskaya, Alexander S. Sigeev, Alexander S. Peregudov, Pavel V. Petrovskii | journal = Synthesis | year = 2007 | volume = 2007 | pages = 2534–2538 | doi = 10.1055/s-2007-983784] :

References


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