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.

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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] The use of tetrafluoroborate delivers the halide-substituted product, fluorobenzene. Substituting thiols or water for the copper salts generates thioethers or phenols, respectively.

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.
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.
3. ^ Ludwig Gattermann (1890). "Untersuchungen über Diazoverbindungen". Berichte der deutschen chemischen Gesellschaft 17 (1): 1218-1228. doi:10.1002/cber.189002301199.
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.