Intramolecular carboxylic group-assisted cleavage of N-(2-hydroxyphenyl)-phthalamic acid (7) and N-(2-methoxyphenyl)-phthalamic acid (8): Absence of intramolecular general acid catalysis due to 2-OH in 7
Document Type
Article
Publication Date
1-1-2006
Abstract
The values of pseudo first-order rate constants (k(obs)) for the cleavage of N-(2-hydroxyphenyl)phthalamic acid (7), obtained at 4.9 x 10(-2) M HCl, 35 degrees C, and within CH(3)CN content range 2-80% (v/v) in mixed aqueous solvent are smaller than k(obs) for the cleavage of N-(2-methoxyphenyl)phthalamic acid (8), obtained under almost similar experimental conditions, by nearly 1.5- to 2-fold. These observations show the absence of expected intramolecular general acid catalysis due to 2-OH group in 7. The values of k(obs) for the cleavage of 7 and 8 decrease by more than 20-fold with the increase in the content of CH(3)CN from 2 to 80-82% (v/v) in mixed aqueous solvent. The kinetic data reveal that in acidic aqueous cleavage of 7, N-cyclization (leading to the formation of imide) and O-cyclization (leading to the formation of phthalic anhydride) vary from similar to 10 to 15% and similar to 90 to 85%, respectively, with the increase in CH3CN content from 2 to 80% (v/v). Similar increase in CH3CN content causes increase in N-cyclization from similar to 0 to 5% and decrease in O-cyclization from similar to 100 to 95% in the acidic aqueous cleavage of 8. Some speculative, yet conceivable, reasons for nearly 10 and 0% N-cyclization in the cleavage of respective 7 and 8 at low content of CH3CN have been described. (c) 2006 Wiley Periodicals, Inc.
Keywords
rate-determining step, amide hydrolysis, phthalic-anhydride, phenyl salicylate, aqueous cleavage, alkaline-hydrolysis, base catalysis, mechanism, solvents, kinetics
Divisions
CHEMISTRY
Publication Title
International Journal of Chemical Kinetics
Volume
38
Issue
12
Additional Information
Department of Chemistry, Faculty of Science Building, University of Malaya, 50603 Kuala Lumpur, MALAYSIA