Kolbe nitrile synthesis

The Kolbe- nitrile is a process for the preparation of 1 alkyl nitriles by reacting corresponding alkyl halides with alkali. As a by- product of this reaction caused isonitriles 2, as the cyanide ion can react as a nucleophile, according to the ambifunctional Ambident or Kornblum control both the carbon and the nitrogen atom.

The reaction is named after its discoverer Hermann Kolbe.

Reaction mechanism

Since it is a Ambident or ambifunctional nucleophile when cyanide ion, there are two possibilities for the attack.

Firstly, the reaction of the attack on the carbon atom of the cyanide ion can proceed. The result is a nitrile.

On the other hand, the reaction of the attack on the nitrogen atom of the cyanide ion may pass. This creates an isocyanide (by-product ).

The ratio of the two isomers depends mainly on the solvent and reaction type. The reaction proceeds with the use of alkali metal cyanides (e.g. sodium cyanide, NaCN ) in polar solvents by an SN2 mechanism, the halide by the nitrogen atom is attacked over more nucleophilic carbon atom. With silver cyanide ( AgCN ) in diethyl ether, the reaction proceeds through a SN1 mechanism runs as a solvent; obtained mainly isonitriles, which arise at the carbenium ion by attack of the more nucleophilic nitrogen atom now.

Above all, primary alkyl halides and benzyl halides react in good yields with alkali to nitrites. Secondary halides react against it only in poor yields and tertiary halides are no longer in the desired manner.

The nitriles formed can be easily performed via hydrolysis to the corresponding carboxylic acid in other functional groups, which is why the Kolbe nitrile synthesis is also an important method for lengthening alkyl chain by one carbon atom.