Intermediates in the reaction of aniline with formaldehyde catalyzed by acids

The relative stabilities and reactivities of possible intermediates in the reaction of aniline with formaldehyde under conditions of acid catalysis were estimated by the semiempirical MNDO method. According to the calculation results, protonated N-(hydroxymethyl)aniline and ortho-, meta-, and paraσ-complexes are formed through the ion-dipole complex. Further transformations of these intermediates, which determine the structure of the final products, depend on the possibility of proton abstraction from the σ-complexes with formation of a quinonimine structure, as well as on the lability of the hydroxymethyl group in the protonated amino alcohol.