Mechanism and Reactivity of Hydrolysis of Aliphatic Sulfonate Esters

Abstract It was shown with a five-membered sultone that the hydrolysis of aliphatic sultones in water proceeds substantially by BAL1-E1 mechanism, and that it is a nucleophilic substitution reaction caused by hydroxyl ion and water. We carried out a kinetic experiment on the hydrolysis of 1,4-butanesultone and ethyl ethanesulfonate, both in water and in water-acetone mixed solvent. It was found that these aliphatic sulfonate esters were hydrolyzed substantially by BAL1-E1 mechanism as in the case of a five-membered sultone, and in particular, ethyl ethanesulfonate was hydrolyzed by complete BAL1-E1 mechanism. The results seem to be justified by a tracer experiment with H218O. Namely, the ratios of the C–O fission to the S–O fission in 1,3-propanesultone and ethyl ethanesulfonate were 85.6:14.4 and 100:0, respectively. In strong alkaline solutions and approtic solvent-water systems, the SN2 reaction involving attack of the nucleophile on sulfur atom took place partly in sultones, but practically not in linear sulfonate esters. On the other hand, the ratio of relative reaction rates of a five-membered sultone, a six-membered sultone, and a linear sulfonate ester in water is 37:1:7. Since Ea is nearly the same for these three compounds, the contribution of strain in the molecular structure to the reactivity is small, and in consequence the above ratio seems to be attributed to ΔS\eweq.