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Unexpected rate enhancement in the intramolecular carboxylic acid‐catalyzed cleavage of o ‐carboxybenzohydroxamic acid
Author(s) -
Niyaz Khan M.
Publication year - 1998
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199803)11:3<216::aid-poc992>3.0.co;2-9
Subject(s) - chemistry , hydrolysis , reaction rate constant , catalysis , aqueous solution , phthalic anhydride , phthalic acid , carboxylic acid , intramolecular force , solvent , medicinal chemistry , solvent effects , organic chemistry , kinetics , physics , quantum mechanics
Phthalic anhydride was detected spectrophotometrically in the hydrolysis of o ‐carboxybenzohydroxamic acid (OCBA) in CH 3 CN–H 2 O solvent containing 0.03 mol dm −3 HCl. Pseudo‐first‐order rate constants ( k 1 ) for hydrolysis of OCBA are almost independent of the change in CH 3 CN content from 10 to 80% (v/v) in mixed aqueous solvents. The rate constants k 1 are more than 10‐fold larger than the corresponding rate constants for hydrolysis of phthalamic acid. These observations are explained in terms of a mechanism slightly different from the mechanism for hydrolysis of phthalamic acid. The activation parameters, Δ H * and Δ S *, are not affected appreciably by an increase in CH 3 CN content from 10 to 80% in mixed aqueous solvents. © 1998 John Wiley & Sons, Ltd.