The hydrolysis of N-methylisatin: on how a simple rate-pH profile may mislead.

Alkaline hydrolysis of the title isatin 4 in unbuffered solution obeys a rate law such that kobs varies; is directly proportional to [OH-]2 at pH 10 changes smoothly to kobs varies; is directly proportional to [OG-] by pH 13. As in the case of other isatins, this inflection in the pH profile is traced to ionisation of the substrate by addition of OH-; the UV spectrum of the anion has been recorded. Hydrolysis is also very sensitive to general base catalysis, which has mechanistic implications and would probably have prevented any development of this compound as a potential drug.