Imine

Imines are a group of chemical compounds in which the oxygen atom of an aldehyde or ketone is formally replaced by a nitrogen atom. The nitrogen atom also bears a hydrogen atom or an organic residue, or R3; in the latter case one also speaks of a azomethine or a Schiff base. The structural design is so R1R2C = NR3. R1, R2 and R3 may be different or identical radicals and hydrogen atoms. Aldimines (R1 and / or R2 = H) N- analogs of aldehydes and ketimines (R1 and R2 = organyl radical, e.g. alkyl or aryl ), N- analogs of ketones.

Also as imines (especially in older literature ) heterocyclic amines such as piperidine ( Pentamethylenimin ) refers. Today, however, this term is inadmissible because genuine imines having the presence of the typical imine double bonds.

Properties

Imines are less basic than the corresponding amines, since the free electron pair of the sp2 nitrogen is less readily available for the addition of a proton. With appropriate substitution subject to the imine -enamine imine tautomerism.

Production

Imines are formed from primary amines with aldehydes or ketones; formed as intermediates semiaminals, the analogs of the hemiacetals.

The reaction is carried out by a nucleophilic reaction between a carbonyl compound and a primary amine. A zwitterion, which now has a positively charged nitrogen and negatively charged oxygen atom, an unstable hemiaminal formed. In three further steps, a proton ( protonation ) is first deposited on the oxygen, and the oxygen is replaced by a positive charge. After removal of the water at the carbon and the final hydrogen atom on the nitrogen azomethine is formed. Analogous runs, the formation of enamines. By Asinger reaction produces heterocyclic imines (eg, 3 - thiazoline ) with a C = N double bond as part of a five-membered ring system.

Use

In some multi-component reactions (for example, the Strecker synthesis, Ugi reaction ) for the production of amino acids or amino acid derivatives of imines to occur as intermediates or used as starting materials. From the BINOL derived Heterobimetallkatalysatoren be used in the enantioselective addition of Phosphornukleophilen to imines.