A Mechanistic Study of the Alkaline Hydrolysis of Diaryl Sulfate Diesters

Nearly all of the reported studies of reactions of sulfate diesters are for dialkyl or alkyl aryl diesters, which undergo reaction by carbon−oxygen bond fission. Sulfuryl transfer reactions of sulfate diesters (RO−SO₂−OR‘) proceeding by attack at sulfur have been little explored. When both ester groups are aryl groups the hydrolysis reaction (sulfuryl transfer to water) occurs by way of attack at sulfur. The alkaline hydrolysis of diaryl sulfate diesters was shown to obey first-order kinetics with respect to [^-OH] and proceed through S−O bond fission, in a mechanism that is most likely concerted. Activation parameters for 4-chloro-3-nitrophenyl phenyl sulfate and 4-nitrophenyl phenyl sulfate gave the following respective values:  ΔH^⧧ = 88.0 ± 0.1 and 84.83 ± 0.06 kJ mol^-1 and ΔS^⧧ = −37 ± 1 and −50.2 ± 0.5 J mol^-1 deg^-1. The dependence of the second-order rate constant for hydrolysis on leaving group pK_a was analyzed giving a β_lg slope of −0.7 ± 0.2 and a Leffler α parameter value of 0.36. A ¹⁵k kinetic isotope effect (KIE) for the hydroxide attack on 4-nitrophenyl phenyl sulfate of 1.0000 ±0.0005 and an ¹⁸k_lg KIE value of 1.003±0.002 were obtained.