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An imine is a functional group or chemical compound containing a carbon-nitrogen double bond . Due to their diverse reactivity, imines are common substrates in a wide variety of transformations. An imine can be synthesised by the nucleophilic addition of an amine to a ketone or aldehyde giving a hemiaminal -C(OH)(NHR)- followed by an elimination of water to yield the imine. (see alkylimino-de-oxo-bisubstitution for a detailed mechanism) However, the equilibrium in this reaction usually lies in favor of the free carbonyl compound and amine, so that azeotrope distillation or use of a dehydrating agent such as molecular sieves is required to push the reaction in favor of imine formation.
Addition reactions with primary amines give imines that are stable under an inert atmosphere. In the presence of oxygen or water, such imines will quite readily hydrolyze or oligomerize. However, with an aryl group or certain stabilizing alkyl substituents on nitrogen, the imine formed is stable to oxygen and water and is called a Schiff base. In contrast, imine condensations using ammonia and a carbonyl compound do not lead to stable imines - the imine formed quickly oligomerizes such as in the reaction of formaldehyde and ammonia which gives hexamine instead of the corresponding imine. When a secondary amine is used, elimination of water from the hemiaminal leads to an iminium ion. This iminium ion can further react to form either an aminal, or enamine if there is an sp3-hybridized carbon in the alpha position. Addition of suitably activated carbonyl compounds to this imminium ion also leads to the corresponding Mannich base.
Additional recommended knowledge
imidates (R-N=C(OR)R) are imines with an oxygen atom connected to carbon. These compounds find use in organic synthesis as building blocks and intermediates for example in the Mumm rearrangement and the Overman rearrangement. An example of an imidate is benzyl 2,2,2-trichloroacetimidate used to protect an alcohol as a benzyl ether with release of trichloroacetamide.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Imine". A list of authors is available in Wikipedia.