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

✍ Scribed by M. Niyaz Khan

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 172 KB
• Volume: 34
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.10023

✦ Synopsis

Abstract

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