The kinetics of the reaction of 4-nitrophenyl sulfamate NH2SO2OC6H4NO2-4 (1a) in acetonitrile (ACN) with a series of pyridines (pK(a) range ca. 8 units) and alicyclic amines (pK(a) range ca, 3.6 units) has been studied in the presence of excess amine at various temperatures. The compounds 1a-1f are important as model substrates for the medicinally important sulfamate esters 667-coumate and emate and analogues. Pseudo-first-order rate constants (k(obsd)) have been obtained mainly by the release of 4-nitrophenol/4-nitrophenoxide. Slopes of plots of k(obsd). vs. [amine] gave second-order rate constants (k(2)), and Bronsted plots were biphasic for the aminolysis (with alicyclic amines) with an initial slope beta(1) = 0.53 and a subsequent slope beta(2) = 0.19. The change in slope occurs near the first pK(a) of 1a (17.9) in ACN, Leaving-group effects were probed by using the same series of phenyl sulfamates, i.e. 1a-f and the alicyclic amines N-formylpiperazine and pyrrolidine. The reactions were considered to be dissociative in nature involving E2- and E1cB- type mechanisms with the phenyl sulfamate anion 2 being involved in pyridine and in the weaker alicyclic amines (beta(1) segment) and a phenyl sulfamate dianion 3 being involved with the stronger alicyclic bases (beta(2) segment). The calculation of Leffler indices (a) for bond-forming (base center dot center dot center dot H+) and bond-breaking (S-OAr) steps allows fuller interpretation of the mechanisms occurring, which are seen as having the N-sulfonylamines, HN=SO2 and -N=SO2 on the reaction pathways leading to products. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).