Studies on the Hydrolysis of Glucuronosides. II : The Effect of Aglycone on Acid Hydrolysis Rate of β-D-Glucopyranosiduronic Acids

Effect of the electron affinity of the aglycone group in the rate of acid hydrolysis of alkyl-β-D-glucopyranosiduronic acid was examined. Electron-attracting aglycone was found to decrease the acid hydrolysis rate greatly, while the electron releasing aglycone greatly increased the rate. The Hammet-Taft rule was applied to the acid hydrolysis rate of glucopyranosiduronic acid and glucopyranoside, and the result suggested that the mechanism of hydrolysis was the same for glucopyranosiduronic acid (ρ*) and for glucopyranoside (ρ1*) having an electron releasing aglycone, but differed from that of glycopyranoside(ρ2*)having an electron-attracting aglycone. The activation energy has the greatest effect on the acid hydrolysis rate constant of glucopyranosiduronic acid and the entropy of activation has no part in it.