Imines are typically prepared by the condensation of primary amines and aldehydes. Ketones undergo similar reactions, but less commonly than aldehydes. In terms of mechanism, such reactions proceed via the nucleophilic addition giving a hemiaminal -C(OH)(NHR)- intermediate, followed by an elimination of water to yield the imine (see alkylimino-de-oxo-bisubstitution for a detailed mechanism). The equilibrium in this reaction usually favors the carbonyl compound and amine, so that azeotropic distillation or use of a dehydrating agent, such as molecular sieves or magnesium sulfate, is required to favor of imine formation. In recent years, several reagents such as Tris(2,2,2-trifluoroethyl)borate [B(OCHCF)], pyrrolidine or titanium ethoxide [Ti(OEt)] have been shown to catalyse imine formation.
Rarer than primary amines is the use of ammonia to give a primary imine. In the case of hexafluoroacetone, the hemiaminal intermediate can be isolated.