Kinetics and mechanism for the formation of o ‐carboxy( N ‐methyl)‐benzohydroxamic acid in the cleavage of ethyl N ‐[ o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)‐benzoyl]carbamate in N ‐methylhydroxylamine, acetate, and phosphate buffers

The rate of cleavage of ethyl N ‐[ o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)benzoyl]‐ carbamate (ENMBC) in the buffer solutions containing N ‐methylhydroxylamine, acetate + N ‐methylhydroxylamine, and phosphate + N ‐methylhydroxylamine followed an irreversible consecutive reaction path: ENMBC where A and B represent N ‐hydroxyl group cyclized product of ENMBC and o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)benzoic acid, respectively. Both rate constants k 1 obs and k 2 obs showed the presence of buffer catalysis, but buffer catalysis turned out to be weak in the presence N ‐methylhydroxylamine buffer, while it was strong in the presence of acetate and phosphate ones. Buffer‐independent rate constants k 10 and k 20 increased linearly with the increase in a OH with definite intercepts. The values of molar absorption coefficient of A , obtained under varying total buffer concentrations at a constant pH, showed the presence of a fast equilibrium: A + CH 3 NHOH ⇆ C , where C represents N ‐[ o ‐( N ‐methyl‐ N ‐hydroxycarbamoyl)methyl]benzohydroxamic acid. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 427–437, 2003