title: Kinetic and theoretical studies on alkaline ethanolysis of 4-nitrophenyl salicylate: effect of alkali metal ions on reactivity and mechanism.
abstract: Pseudo-first-order rate constants (k(obsd)) for reactions of 4-nitrophenyl salicylate (7) with alkali metal ethoxides (EtOM, M = K, Na, and Li) in anhydrous ethanol have been measured spectrophotometrically. Interestingly, the k(obsd) value decreases significantly as the concentration of EtOM increases. Because the phenolic moiety of substrate 7 would be deprotonated and exist as an anionic form (i.e., 7(-)) under kinetic conditions, the ground-state stabilization of 7(-) through formation of a six-membered cyclic complex with M(+) (i.e., 8) is proposed to be responsible for the decreasing k(obsd) trend. The k(obsd) value at a given concentration of EtOK increases steeply upon addition of [18]crown-6 ether (18C6) up to [18C6]/[EtOK] = 1 in the reaction mixture and then remains relatively constant thereafter. In contrast, k(obsd) decreases upon addition of salts (e.g., LiClO(4) or KSCN) to the reaction mixture, which indicates that M(+) ions inhibit the reaction. However, in the presence of 18C6, the k(obsd) value is independent of the concentration of EtOK but remains constant, which indicates that the reaction proceeds through a unimolecular mechanism in the presence of the complexing agent. Although two conceivable unimolecular pathways (formation of ketene 9 and lactone 10) can account for the kinetic results, the reaction has been concluded to proceed via formation of ketene 9 as the reactive intermediate on the basis of theoretical calculations.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea. ihum@ewha.ac.kr
authors.forename: Ik-Hwan
authors.initials: IH
authors.lastname: Um
authors.forename: Jin-A
authors.initials: JA
authors.lastname: Seo
authors.forename: Masaaki
authors.initials: M
authors.lastname: Mishima
mesh_terms: D007700:Kinetics; D008672:Metals, Alkali / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D009596:Nitrophenols / Q000138:chemical synthesis / Q000737:chemistry*; D012459:Salicylates / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: C557246:4-nitrophenyl salicylate; D008672:Metals, Alkali; D009596:Nitrophenols; D012459:Salicylates; C024719:4-nitrophenyl