Aminolysis of sulfamate esters in non-aqueous solvents. Evidence consistent with a concerted E2-type mechanism

Abstract

Aminolysis of 4-nitrophenyl sulfamate, N-phenylmethylsulfamate and N-phenylsulfamate esters in chloroform and acetonitrile at 37 °C using a series of pyridine, quinuclidine and cyclic amine bases has been studied. Second-order kinetics were observed and k₂ constants were obtained from plots of k_obsvs. [amine]. Brønsted-type plots gave slopes of ∼ 0.27 for the pyridines and ∼ 0.5 for the stronger bases. The failure of the N,N-dimethylsulfamate, Me₂NSO₂OC₆H₄NO₂-4, to react and the absence of steric effects when hindered pyridines were used support an elimination rather than a substitution mechanism and thus the amines act as general base catalysts. Negative entropies of activation support a bimolecular mechanism and an isokinetic temperature of 541 K was obtained from a plot of ΔH^‡vs.ΔS^‡. A β_1g of –1.25 (ρ=+2.8) has been obtained for reaction of a series of five N-phenylmethyl esters, PhCH₂NHSO₂OC₆H₄X (X = 4-NO₂, 3-NO₂, 3-Cl, 4-Cl and H with tert-butylamine in chloroform and a ρ_acyl, of –0.91 for reaction of the phenyl esters, XC₆H₄NHSO₂OC₆H₄X (X = 4-MeO, 4-Me, 3-Me, H and 3-Cl) with 4-dimethylaminopyridine in chloroform. These reactions are seen as being E2 type processes with some ElcB-like character but they are not thought to involve N-sulfonylamines, RNSO₂.