Sandmeyer reaction

The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts.^[1][2][3] 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.^[4][5] The reaction is a radical-nucleophilic aromatic substitution.

Several improvements have been made to the standard procedures.^[6][7]

Variations

The majority of variations of the Sandmeyer reactions consist of using various copper salts.^[8][9] For example, using cuprous cyanide produces benzonitriles.^[10] 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 ^[11]:

References

1. ^ Traugott Sandmeyer (1884). "Ueber die Ersetzung der Amidgruppe durch Chlor in den aromatischen Substanzen". Berichte der deutschen chemischen Gesellschaft 17 (3): 1633–1635. doi:10.1002/cber.18840170219. http://gallica.bnf.fr/ark:/12148/bpt6k90700r/f56.chemindefer. 
2. ^ Traugott Sandmeyer (1884). "Ueber die Ersetzung der Amid-gruppe durch Chlor, Brom und Cyan in den aromatischen Substanzen". Berichte der deutschen chemischen Gesellschaft 17 (4): 2650–2653. doi:10.1002/cber.188401702202. http://gallica.bnf.fr/ark:/12148/bpt6k90700r/f1073.chemindefer. 
3. ^ Ludwig Gattermann (1890). "Untersuchungen über Diazoverbindungen". Berichte der deutschen chemischen Gesellschaft 17 (1): 1218–1228. doi:10.1002/cber.189002301199. http://gallica.bnf.fr/ark:/12148/bpt6k90720c/f1220.chemindefer. 
4. ^ J. K. Kochi (1957). "The Mechanism of the Sandmeyer and Meerwein Reactions". J. Am. Chem. Soc. 79 (11): 2942–2948. doi:10.1021/ja01568a066. 
5. ^ H. H. Hodgson (1947). "The Sandmeyer Reaction". Chem. Rev. 40 (2): 251–277. doi:10.1021/cr60126a003. 
6. ^ M. P. Doyle, B. Siegfried and J. F. Dellaria (1977). "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". J. Org. Chem. 42 (14): 2426–2431. doi:10.1021/jo00434a017. 
7. ^ Suzuki, N. et al. Perkins Trans. I 1987, 645.
8. ^ Jonathan L. Hartwell (1955). "o-Chlorobromobenzene". Org. Synth.; Coll. Vol. 3: 185. 
9. ^ F. D. Gunstone and S. Horwood Tucker (1963). "1-Chloro-2,6-dinitrobenzene". Org. Synth.; Coll. Vol. 4: 160. 
10. ^ H. T. Clarke and R. R. Read (1941). "o-Tolunitrile and p-Tolunitrile". Org. Synth.; Coll. Vol. 1: 514. 
11. ^ P. Beletskaya, Alexander S. Sigeev, Alexander S. Peregudov, Pavel V. Petrovskii (2007). "Catalytic Sandmeyer Bromination". Synthesis 2007: 2534–2538. doi:10.1055/s-2007-983784.