Hofmann elimination
The Hofmann elimination (also Hofmann degradation ) is a name reaction in organic chemistry that was named after the German chemist August Wilhelm von Hofmann . In the Hofmann elimination of amines are obtained from amines by quaternization (= per- alkylation ) of the nitrogen and subsequent elimination reaction of alkenes .
Overview reaction
In Hofmann's elimination, an amine is converted into an alkene , with the nitrogen atom and a vicinal proton being split off.
mechanism
In the first step, an amine is "exhaustively" alkylated with an alkylating agent (e.g. methyl iodide ); d. h., the amine is in excess of CH 3 in the I quaternary ammonium compound converted. 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 ; That is, the alkene with the lowest number of alkyl groups is formed preferentially .
meaning
The Hofmann amine breakdown was an important means of elucidating 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).
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
- ↑ Stephen F. Mason: The Science and Humanism of Linus Pauling (1901-1994) . In: Chemical Society Reviews . tape 26 , no. 1 , 1997, p. 29-39 , doi : 10.1039 / CS9972600029 .
- ↑ Richard Willstätter , Ernst Waser: About Cyclo-octatetraen . In: Reports of the German Chemical Society . Vol. 44, No. 3 , 1911, pp. 3423-3445 , doi : 10.1002 / cber.191104403216 .