Studies on Sulfate Esters. I. Nucleophilic Reactions of Amines with p-Nitrophenyl Sulfate

The nucleophilic reactivity of a series of amines toward p-nitrophenyl sulfate exhibits a small sensitivity to the basicity of the amine (β = 0.20). The reactivity is in the order tertiary > secondary > primary amine; steric hindrance increases rapidly with α substitution. A comparison of the reactions of the same amines with p-nitrophenyl phosphate reveals a striking similarity in their nucleophilic reactivity and the mechanism of the displacement. Both appear to involve transition states which feature little bond formation between substrate and amine. The spontaneous hydrolysis of p-nitrophenyl sulfate is discussed in terms of a possible elimination of sulfur trioxide in analogy to monomeric metaphosphate formation in the hydrolysis of certain phosphate dianions.