Kinetic evidence for the occurrence of kinetically detectable intermediates in the cleavage of N ‐ethoxycarbonylphthalimide under N ‐methylhydroxylamine buffers

The kinetics of the aqueous cleavage of N ‐ethoxycarbonylphthalimide (NCPH) in CH 3 NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH $\buildrel{k_{1\,{\rm obs}}}\over\longrightarrow$ ENMBC $\buildrel{k_{2\,{\rm obs}}}\over\longrightarrow$ A $\buildrel{k_{3\,{\rm obs}}}\over\longrightarrow$ B , where ENMBC, A , and B represent ethyl N ‐[ o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)benzoyl]carbamate, N ‐hydroxyl group cyclized product of ENMBC, and o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k 1 obs at a constant pH, obeys the relationship k 1 obs = k w + k n app [Am] T + k b [Am] T 2 , where [Am] T is the total concentration of CH 3 NHOH buffer and k w is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant k b shows the presence of both general base and general acid catalysis. Both the rate constants k 2 obs and k 3 obs are independent of [Am] T (within the [Am] T range of present study) at a constant pH and increase linearly with the increase in a OH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002