Aminolysis of sulfamate esters in chloroform - Nonlinear kinetics

Aminolysis in chloroform of sulfamate esters RNHSO₂OC₆H₄NO₂-4 principally with a series of imidazoles gives good k_obs first-order rate constants under pseudo-first-order conditions. Plots of k_obs vs. [amine] display downward curvature leading to saturation and these plots can be fitted to the rate law k_obs = K_mk¹[amine]/{1 + K_m[amine]} where K_m and k¹ are defined by eqn. (i). The Hammett ρ value for the S + Amine ⇌^Km [S·Amine] →^k1_rds Products (i) formation of the complex [S·Amine] is +1.64. Using data derived for the rate-determining step, the breakup of the intermediate is shown to be unimolecular with a ρ_acyl (substituents in the R part of S) of -1.78 consistent with an E1cB process. Steric effects of the bound-amine in the complex are negligible.