Hofmann rearrangement

Hofmann rearrangement

The Hofmann rearrangement is the organic reaction of a primary amide to a primary amine with one fewer carbon atom. [Hofmann, A. W. v. "Ber." 1881, "14", 2725.] [Wallis, E. S.; Lane, J. F. "Org. React." 1949, "3", 267-306. (Review)] [Shioiri, T. "Comp. Org. Syn." 1991, "6", 800-806. (Review)]

The reaction of bromine with sodium hydroxide forms sodium hypobromite in situ, which transforms the primary amide into an intermediate isocyanate. The intermediate isocyanate is hydrolyzed to a primary amine giving off carbon dioxide.

The reaction is named after its discoverer: August Wilhelm von Hofmann. This reaction is also sometimes called the Hofmann degradation, and should not be confused with the Hofmann elimination.

Variations

Several reagents can substitute for bromine. N-Bromosuccinimide and [1,8-Diazabicycloundec-7-ene|1,8-Diazabicyclo [5.4.0] undec-7-ene (DBU)] can effect a Hofmann rearrangement. In the following example, the intermediate isocyanate is trapped by methanol forming a carbamate. [Keillor, J. W.; Huang, X. "Organic Syntheses", Coll. Vol. 10, p.549 (2004); Vol. 78, p.234 (2002). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=v78p0234 Article] )]

A mild alternative to bromine is also (bis(trifluoroacetoxy)iodo)benzene. [Almond, M. R.; Stimmel, J. B.; Thompson, E. A.; Loudon, G. M. "Organic Syntheses", Coll. Vol. 8, p.132 (1993); Vol. 66, p.132 (1988). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv8p0132 Article] )]

References

ee also

* Beckmann rearrangement
* Curtius rearrangement
* Iodoform reaction
* Lossen rearrangement
* Schmidt reaction
* Weerman degradation


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