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Unexpected rate enhancement in the intramolecular carboxylic acid-catalyzed cleavage of o-carboxybenzohydroxamic acid

✍ Scribed by M. Niyaz Khan

Publisher: John Wiley and Sons
Year: 1998
Tongue: English
Weight: 125 KB
Volume: 11
Category: Article
ISSN: 0894-3230
DOI: 10.1002/(sici)1099-1395(199803)11:3<216::aid-poc992>3.0.co;2-9

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✦ Synopsis

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 À3 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, DH* and DS*, are not affected appreciably by an increase in CH 3 CN content from 10 to 80% in mixed aqueous solvents.

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