The hydrolysis of N-methyl-4'-nitro-6-carboxypicolinanilide (1) was studied in water at 40.0 OC in the absence and presence of Cu(II), Zn(II), Ni(II), and Co(II), and the results are compared to those obtained for the des-6-carboxy compound (2). The ''spontaneous'' hydrolysis exhibits a linear unit slope pH-rate profile between pH 9 and 11, indicative of a straightforward HO--dependent reaction. Parallel, leftward-shifted lines in the pH-rate profile are seen in the presence of divalent metal ions between pH 5 and 7, implicating the dominance of a M(II)-catalyzed HO- reaction in this pH range. The dimensionless rate enhancement factors for 1 at saturating concentrations of M(II) are about 2 x 10(4) for Ni(II), 4 X 10(4) for Co(II), 7 X 10(5) for Zn(II), and 1 X 10(6) for Cu(II). There is little difference between the kinetic behaviors of 1 and 2 except that the carboxylate ligand in 1 results in saturation at lower M(II) concentrations and permits the kinetics to be studied over a wider pH range, though the intrinsic catalytic effectiveness of the bound metal ion is actually somewhat reduced. The product pyridine-2,6-dicarboxylic acid binds M(II) more strongly than does the reactant 1, but not by a sufficient margin to preclude the observation of true catalytic reactions (to 100% hydrolysis) using as little as 0.1 equiv of Cu(II) and Zn(II), though there is a progressive slowing in rate at high percent conversion as the amount of M(II) used decreases. Inhibition of the M(II)-catalyzed hydrolysis by so-called ''biological buffers'' is seen above pH 7.5, to a degree which increases with decreasing Lewis acidity of M(II). The switchover from pH-dependent to pH-independent behavior for Cu(II) catalysis at pH similar to 7 appears to reflect titration of the metal-bound water, producing 1-Cu(II)-OH or a kinetically equivalent form as the species undergoing hydrolysis.
