Kinetics and Mechanism of Hydrolysis of N-Arylphthalimides

Abstract

The values of pseudo-first-order rate constants, kobs, for hydrolysis of N-(2'-methoxyphenyl)phthalimide (1) increase linearly with increase in [HCl] over the range 5 × 10−3 - 1.0M at 8.0 × 10−5 M 1, 0.5M μ (by NaCl) and in the temperature range 30-40°C. The rate of acidic hydrolysis of N-(4'-methoxyphenyl)phthalimide (2) reveals behaviour similar to that found for 1, N-(2'-hydro-xyphenyl)phthalimide (3) and N-(4 ‘-aminophenyl)phthalimide (4). The values of kobs at 35°C and varying [HCl] give the respective rate constants for the [HCl]-independent ( k0) and the [HCl]-dependent ( kH) hydrolysis of 1 (at [10] = 8.0 × 10−5 M, μ = 0.5 M) as 6.74 ×10−7 s−1 and 5.47 × 10−6 M−1 s−1, 2 (at [20] = 3.0 × 10−5M, μ = 0.5 M) as 12.2 × 10−7 s−1 and 4.61 × 10−6 M−1 s−1 and 4H+ (at [40] = 2.0 × 10−4 M, μ = 1.0 M) as 5.83 × 10−7 s−1 and 15.2 × 10−6 M−1 s−1. The values of kw/ k0min are of the order of 102 for 1, 2 and 4 where k0min represents the sum of the contributions of H+ - and HO- -catalysed hydrolysis towards k0 (first-order rate constant for pH-independent hydrolysis of imide) and kw is the pseudo-first-order rate constant for the uncatalysed reaction of H2O with imide.