title: Efficient rate enhancement due to intramolecular general base (IGB) assistance in the hydrolysis of N-(o-hydroxyphenyl)phthalimide.
abstract: The rates of the hydrolyses of N-(o-hydroxyphenyl)phthalimide (1) and N-(o-methoxyphenyl)phthalimide (2), studied at different pH, show that the hydrolysis of 1 involves intramolecular general base (IGB) assistance where the o-O- group of ionized 1 acts as IGB and H2O as the reactant. The rate enhancement due to the IGB-assisted reaction of H2O with ionized 1 is>8x10(4)-fold. Pseudo-first-order rate constant for the reaction of water with 2 is approximately 2x10(3)-fold smaller than the first-order rate constant (0.10 s-1) for pH-independent hydrolysis of 1 within the pH range of 9.60-10.10. Second-order rate constants (kOH) for hydroxide ion-assisted hydrolysis of ionized 1 and 2 are 3.0 and 29.1 M-1 s-1, respectively. The solvent deuterium kinetic isotope effect (dKIE) on the rate of alkaline hydrolysis of 1 and 2 reveals that the respective values of kOH/kOD are 0.84 and 0.78, where kOD represents the second-order rate constant for DO--assisted cleavage of these imides (1 and 2). The value of kwH2O/kdD2O is 2.04, with kwH2O and kdD2O representing pseudo-first-order rate constants for the reactions of ionized 1 with H2O and D2O, respectively.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia.
authors.forename: Yoke-Leng
authors.initials: YL
authors.lastname: Sim
authors.forename: Azhar
authors.initials: A
authors.lastname: Ariffin
authors.forename: M Niyaz
authors.initials: MN
authors.lastname: Khan
mesh_terms: D000468:Alkalies / Q000737:chemistry; D002021:Buffers; D003500:Cyclization; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D015394:Molecular Structure; D010797:Phthalimides / Q000737:chemistry*; D012997:Solvents
chemical_list: D000468:Alkalies; D002021:Buffers; C519419:N-(o-hydroxyphenyl)phthalimide; D010797:Phthalimides; D012997:Solvents; C037431:phthalimide