Reactions of (E)-O-Arylbenzaldoximes with Secondary Amines in Acetonitrile. Competition between E2 and S_NAr Reactions

Reactions of (E)-O-arylbenzaldoximes in which the O-aryl group is 2,4-dinitrophenyl (1) and picryl (2) with secondary amines in acetonitrile have been studied kinetically. The reactions proceed via competing E2 and S_NAr mechanism. The second rate-determining step of the S_NAr reactions involves both uncatalyzed and base-catalyzed pathways. The sensitivity of the S_NAr reaction to base catalysis was greater for 2 and increased with base strength. The rates of E2 and S_NAr reactions increased by approximately 10³ and 10⁴ fold, respectively, with the variation of the substrate from 1 to 2. The yield of S_NAr product increased with base concentration, electron-withdrawing ability of O-aryl group, and base strength. From these results, factors that influence the competition between E2 and S_NAr reaction pathways are assessed.