Usually imines refer to compounds with the connectivity R2C=NR, as discussed below. In the older literature, imine refers to the aza analogue of an epoxide. Thus, ethyleneimine is the three-membered ring species C2H4NH. The relationship of imines to amines having double and single bonds carries over to imides and amides, as in acetamide vs succinimide.
Imines are related to ketones and aldehydes by replacement of the oxygen with an NR group. When R = H, the compound is a primary imine, when R is hydrocarbyl, the compound is a secondary imine. Imines exhibit diverse reactivity and are commonly encountered throughout chemistry. When R3 is OH, the imine is called an oxime, and when R3 is NH2 the imine is called a hydrazone.
A primary imine in which C is attached to both a hydrocarbyl and a H is called a primary aldimine; a secondary imine with such groups is called a secondary aldimine. A primary imine in which C is attached to two hydrocarbyls is called a primary ketimine; a secondary imine with such groups is called a secondary ketimine.
Aziridine and its derivatives are sometimes referred to as imines.
One way of naming aldimines is to take the name of the radical, remove final "e", and add "-imine", for example ethanimine. Alternately, an imine is named as a derivative of a carbonyl, adding the word "imine" to the name of a carbonyl compound whose oxo group is replaced by an imino group, for example sydnone imine and acetone imine (an intermediate in the synthesis of acetone azine).
N-Sulfinyl imines are a special class of imines having a sulfinyl group attached to the nitrogen atom.
An iminium cation is a related functional group in which the nitrogen has a fourth bond, giving it a positive charge.
An aldimine is an imine that is an analog of an aldehyde.
As such, aldimines have the general formula R-CH=N-R'. Aldimines are similar to ketimines, which are analogs of ketones.
Somewhat like the parent amines, imines are mildly basic and reversibly protonate to give iminium salts. Iminium derivatives are particularly susceptible to reduction to the amines using transfer hydrogenation or by the stoichiometric action of sodium cyanoborohydride. Since imines derived from unsymmetrical ketones are prochiral, their reduction is a useful method for the synthesis of chiral amines.
Imine polymers (polyimines) can be synthesised from multivalent aldehydes and amines. This polymerisation reaction is feasible because it generally proceeds immediately when mixing the relevant components. Also, because no additional chemicals are required and the only formed side product is water, this reaction is very environmentally friendly. Polyimines are particularly interesting materials because of their application as vitrimers. They are known to be easily recyclable and self-healing.
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