Kinetic studies of the reactions of phthalimide with ammonia and pyrrolidine

Abstract

The kinetics of the nucleophilic cleavage of phthalimide (PTH) in buffer solutions of ammonia and pyrrolidine were determined. The reaction rates for ammonolysis of PTH revealed a buffer‐catalysed second‐order term in the rate law, but the reaction rates for pyrrolidinolysis of PTH showed buffer‐catalysed second‐ and third‐order terms in the rate law. Both ammonia and pyrrolidine revealed nucleophilic reactivity towards ionized PTH (S−) only within the pH range of the present study. This is attributed to the occurrence of intramolecular general base–acid catalysis. General base catalysis is detected in the reactions of pyrrolidine with both non‐ionized PTH (SH) and S−. The general base‐catalysed third‐order rate constant for pyrrolidinolysis of SH is nearly 28 times larger than that of S−.

Structure−Reactivity Relationships in the Pyridinolysis of N-Methyl-N-arylcarbamoyl Chlorides in Dimethyl Sulfoxide

“…This type of ion-triplet formation in the S N 1 and S N 2 processes has been discussed in detail by Ritchie . Khan has observed a similar sharp initial rise in k obs for the alkaline hydrolysis of N -hydroxyphthalimide (NHP) with addition of salts (NaCl, KCl etc.) in aqueous acetonitrile solution.…”

Kinetic evidence for the occurrence of kinetically detectable intermediates in the cleavage of N‐ethoxycarbonylphthalimide under N‐methylhydroxylamine buffers

“…Significantly lower nucleophilic reactivity of CH 3 NHOH (p K a 6.24) compared with HNHOH (p K a 5.97) toward NCPH and NHPH is difficult to explain in terms of steric hindrance. If steric hindrance is the main cause for such characteristic difference in the nucleophilic reactivity of these nucleophiles, then it remains to explain almost similar nucleophilic reactivity of dimethylamine 32 and methylamine 12 toward phthalimide.…”

Kinetic studies on general base-catalyzed cleavage of phthalimide (PTH) in 2-hydroxyethylamine and 2-methoxyethylamine buffers

“…10.06 (0). 9.85 (b), and 9.61 (A).the change in the rate-determining step with the change in[RNH,],.…”

“…The simplest mechanism which may explain the observed data is shown in Scheme 11. The detailed mechanisms for the reactions of nonionized (SH) and ionized (S-) phthalimide with RNH, may be similar to the mechanisms for the corresponding reactions with R,NH[5,10]. The most likely preassociation stepwise mechanism for the reaction of RNH, with S-involves the association complex T,-.Theobserved rate law: rate = kObs[PTH], where [PTH], = [SHI + [S-1, and Scheme I1 can lead to eq.…”