Abstract
The reactions of N-succinimidyl benzoates (1) with aliphatic primary amines (2) (RNH2 : R= n-Pr, iso-Pr, n-Bu, s-Bu, t-Bu, and n-Am) were studied kinetically at 25 °C in aqueous solution (7.0≤pH≤10.5).N-arylcarbonylation was competitive with the decomposition of (1) and the rate is expressed as V= (k1, d+k2 [2]) [1], where k1, d and k2 are the rate constants for the decomposition and N-arylcarbonylation, respectively.
The reactivity of (2) was in the order of n-Pr > iso-Pr, iso-Bu > n-Bu > s-Bu > t-Bu n-Pr_??_n-Bu_??_n-Am and iso-Pr_??_s-Bu because of the inductive and steric effects of the alkyl group in (2). Plots of log k2 vs. pH (pH profiles) for N-arylcarbonylation gave a good linear relationship in the range of 7.0≤pH≤10.0, with a slope of 1.0. The rate (k2) correlated with Hammett δ, giving a positive ρ of 1.21.3 for meta-substituted (1). The rates for ortho-substituted (1) were slower than those expected from the ionization constant of the corresponding benzoic acid, and the reactivity was in the order of o-F > o-Cl > o-Br due to the steric effect of the substituents. The rate ratios, 10-3k2/k1, d increased with basicity of the solvent (pH) for both ortho- and meta-substituted (1). These ratios exceeded unity for (2) with a straight chain but less than unity for 1-alkylated (2).
Based on the above observations, a possible mechanism is proposed and discussed.
