DIVALENT METAL-ION CATALYZED-HYDROLYSIS OF PICOLINANILIDES

The hydrolysis of N-methylpicolinanilides bearing electron-withdrawing substituents (4-nitro, 2,4-dinitro, and 5-chloro-2-nitro) was studied as a function of pH at 40.0-degrees-C in ethanol-water (1:2) in the absence and presence of divalent metal ions, in particular Cu(II). Plots of log k vs pH for uncatalyzed hydrolysis were linear with unit slope over the pH range 9-12, permitting the calculation of bimolecular k(OH) values for this region. Plots of log k vs pH in the presence of various concentrations of Cu-(NO3)2-bpy (1:1) increased linearly (slope = 1) over the pH range 5.0-6.2, plateaued over the pH region 7-9, and increased again at higher pH as the uncatalyzed reaction came to prominence. Catalysis by Cu(II) in the absence of bpy (for the 4-nitroanilide) could be followed only below pH 6, but log k increased linearly (slope = 1) in the pH range 4-6. The unit slope behavior at low pH for both the Cu(II)(bpy)- and Cu(II)-catalyzed reactions was interpreted in terms of Cu(II) catalysis of hydroxide-mediated hydrolysis. Second-order k(OH)(Cu) values could be calculated from the unit slopes, which, when compared to the uncatalyzed k(OH) values, indicate catalytic rate enhancements of 10(4)-10(5) induced by 10 mM Cu(II)(bpy). Saturation effects were seen for the 4-nitroanilide at high [Cu(II)] (+/- bpy), permitting an extrapolation to the maximum catalytic effect in these cases ((1-8) x 10(6)). These catalytic factors are discussed in comparison to related systems studied by other workers.