Aminolysis of sulfamate esters in non-aqueous solvents. Use of Bronsted coefficients (beta(nuc)) to assign E2 and E1cB mechanisms

A series of Hammett rho(acyl) values for the aminolysis in chloroform and acetonitrile at 37 degrees C of the sulfamate esters RNHSO2OC6H4NO2-4 (R = XC6H4-, X = 4-MeO, 4-Me, 3-Me, H, 4-Br and 3-Cl) have been measured using piperidine and a set of five pyridines. Hammett rho(pyr) values have also been measured for various esters using a set of pyridines with varying substituents in the pyridine ring. A series of Bronsted beta(nuc) values have been measured for the sulfamate esters. All the available beta(nuc) values for sulfamate ester aminolysis have been compared and from this it has been possible to make mechanistic assignments to ElcB (beta(nuc) Ca 0.7 and ca. 0) and E2 (beta(nuc) 0.17 to 0.54) pathways. In the case of the E2 mechanism those reactions with lower beta(nuc) values are thought to have little N-beta-H bond-breaking but this process is well advanced giving carbanionic ElcB-like characteristics to the E2 mechanism for reactions with larger beta(nuc) values. Thermodynamic data (Delta H double dagger and Delta S double dagger) support these interpretations.