Generation of glycopyranosyl cations in the spontaneous hydrolyses of 2,4-dinitrophenyl glycopyranosides. Evidence for the general intermediacy of glycopyranosyl cations in the acid-catalysed hydrolyses of methyl glycopyranosides

Abstract

The rate of liberation of 2,4-dinitrophenol from 2,4-dinitrophenyl βD-galactopyranoside at 25.0 °C is independent of pH between pH 1.6 and 8.4: catalysis by buffer is absent. Above pH 8.4, 2,4-dinitrophenolate is liberated by a specific base-catalysed process. At 25 °C, the rates of spontaneous hydrolysis of a series of four homeomorphs each of 2,4-dinitrophenyl β-D-gluco- and -galacto-pyranoside at pH 6.5 exhibit a linear free energy relationship (|r|= 0.92) with the rates of hydrolysis of the corresponding methyl glycopyranosides in 2.0M-hydrochloric acid. The 2-acetamido-2-deoxy-β-D-glucopyranosyl system obeys this relationship.