Nucleophilic Attacks on Carbon-Nitrogen Double Bonds. 2 Diversity of Mechanisms for the Substitution of Diarylimidoyl Chlorides by Amines in Benzene

The reactions of diarylimidoyl chlorides ArC(Cl)=NC6H4Y with piperidine, morpholine, diethylamine which form the corresponding amidines were studied in benzene. Either only first-order term in the amine (mostly with piperidine) or both first- and second-order terms in the amine (mostly with morpholine) were found. The Hammett plots show a minimum when Y = p-Cl with piperidine and when Y = m-Cl with morpholine, and the element effect k(PhC(Br)=NPh)/k(PhC-(Cl)=NPh) for the reaction with piperidine is 440. Analysis of the substituent effects, the Hammett-type correlations, the catalyzed route, the effect of the nucleophile and the element effect, and the activation parameters suggest that the bimolecular substitution proceeds via the Sn2(IP) mechanism for electron-donating substituents and via nucleophilic addition-elimination for electron-attracting substituents. Superimposed on these routes are less important variants of third-order amine-catalyzed routes, where the amine may serve as a basic, electrophilic, or bifunctional catalyst.