The kinetics and mechanism of alkaline hydrolysis of N‐substituted phthalimides

Abstract

AbstractThe aqueous cleavage of N‐(2‐bromoethyl)phthalimide (NBEPH), N‐(3‐bromopropyl)phthalimide (NBPPH), and N‐carbethoxyphthalimide (NCPH) have been studied within the [ŌH] range of 5 × 10−4 M to 2 × 10−3 M, pH range of 8.82 to 10.62 and 8.06 to 8.66, respectively. The observed pseudo‐first‐order rate constants, kobs, reveal a linear relationship with [ŌH] with essentially zero intercept. The alkaline hydrolysis of N‐(hydroxymethyl)phthalimide (NHMPH) has been studied within the [ŌH] range of 5.64 × 10−6 M to 2.0 M. The [OH]‐rate profile reveals that both ionized and nonionized NHMPH are reactive toward ŌH. The second‐order rate constant, kOH, for the reaction of ŌH with non‐ionized NHMPH is ca. 104 times larger than that with ionized NHMPH. The values of kOH obtained for NBEPH, NBPPH, NCPH, and nonionized NHMPH show a reasonable linear relationship with Taft substituent constants, and the slope (ρ*) of the plot is 1.01 ± 0.10. The low value of ρ* of 1.01 is attributed to nucleophilic attack as the rate‐limiting. The kOH value for ionized NHMPH reveals nearly 103‐fold negative deviation from the linear Taft plot.