Kolbe nitrile synthesis
The Kolbe nitrile synthesis is a process for the preparation of alkyl nitriles 1 by reacting corresponding alkyl halides with alkali metal cyanides. As a by-product of this reaction caused isonitriles 2 , because the cyanide - ion as ambident or ambifunctional nucleophile in accordance Kornblum rule may react with both the carbon and the nitrogen atom.
The reaction is named after its discoverer Hermann Kolbe .
Reaction mechanism
Since this is the cyanide - ion to a ambident or ambifunctional nucleophile is, there are two possibilities for the attack.
On the one hand, the reaction can about the attack on the carbon atom of the cyanide - ion run. This creates a nitrile:
On the other hand, the reaction can about the attack on the nitrogen atom of cyanide - ion run. This creates an isocyanide (by-product):
The ratio of the two isomers depends primarily on the solvent and type of reaction. When using alkali metal cyanides (e.g. sodium cyanide , NaCN) in polar solvents, the reaction proceeds according to an S N 2 mechanism , the halide being attacked by the carbon atom, which is more nucleophilic than the nitrogen atom. With silver cyanide (AgCN) in diethyl ether as the solvent, the reaction proceeds via an S N 1 mechanism ; predominantly isonitriles are obtained, which are formed by attack of the now more nucleophilic nitrogen atom on the carbenium ion.
Primary alkyl halides and benzyl halides in particular react with alkali metal cyanides to form nitriles in good yields. Secondary halides, on the other hand, only react in poor yields and tertiary halides no longer react in the desired manner.
The nitriles formed can easily be converted into further functional groups via hydrolysis into the corresponding carboxylic acid , which is why the Kolbe nitrile synthesis is also an important method for lengthening alkyl chains by one carbon atom.
Individual evidence
- ^ Wang, Z .: Comprehensive Organic: Name Reactions and Reagents , Wiley Verlag, 2009, pp. 1661–1663, ISBN 978-0-471-70450-8 .
literature
- Organikum , 22nd edition, Wiley-VCH, Weinheim, 2004, ISBN 3-527-31148-3