What is Hoffmann Elimination Reaction

Hofmann elimination

In the Hofmann elimination (also Hofmann dismantling) is a name reaction in organic chemistry that was named after the German chemist August Wilhelm von Hofmann. In the Hofmann elimination of amines, alkenes are obtained from amines by quaternization (= per-alkylation) of nitrogen and a subsequent elimination reaction.

Overview reaction

Hofmann elimination converts an amine into an alkene, cleaving the nitrogen atom and a vicinal proton.

mechanism

In the first step, an amine is "exhaustively" alkylated with an alkylating agent (e.g. methyl iodide); d. that is, the amine is in excess of CH3I converted into the quaternary ammonium compound. The ammonium salt (counterion: iodide) is converted into the ammonium salt with the counterion hydroxide with silver (I) oxide, which serves as a base in aqueous solution. By evaporating the aqueous solution or heating, the latter then decomposes in an E2 reaction with the formation of the corresponding alkene.


If there are several β-H atoms, different alkenes can be formed. In many cases the elimination follows Hofmann's rule; H. the alkene preferentially arises with the least Number of alkyl groups.

importance

The Hofmann amine breakdown was an important means of determining the structure of nitrogen-containing natural substances (alkaloids).

One example is the breakdown of pseudopelletierin to 1,3,5,7-cyclooctatetraene by Richard Willstätter (Munich, 1905).[1][2]

Importance in medicine

In anesthesiology, Hofmann elimination is important in relation to the inactivation of certain muscle relaxants: the muscle relaxants atracurium and cisatracurium are broken down in the body independently of the organs: they break down depending on the pH value and temperature. Laudanosine and acrylate also arise as degradation products, but through an alternative degradation path: hydrolysis by unspecific plasma esterases.

source

  • Organikum, VEB Deutscher Verlag der Wissenschaften, Berlin 1976.

Individual evidence

  1. ↑ Mason, S. "The Science and Humanism of Linus Pauling (1901-1994)", Chemical Society Reviews 26, 1 (February 1997).
  2. Richard Willstätter, Ernst Waser: About cyclo-octatetraene. In: Reports of the German Chemical Society. 44, No. 3, 1911, pp. 3423-3445. doi: 10.1002 / cber.191104403216.