Additive Tendency of Substituent Effects onto Rate Constant of Acidic Hydrolysis of Methyl 4‐O‐Methyl‐β‐d‐Glucopyranoside

Abstract

All eight types of differently methyl-substituted methyl 4-Omethyl-b-d-glucopyranosides were chemically synthesized, analytically characterized including 13 C NMR analysis, and subjected to acid-catalyzed hydrolytic cleavage of the glucosides. The 13 C NMR resonances of the ring-carbons shift apprx. 10 ppm down-field by methyl substitution. Acid hydrolysis (3 mol·L À1 DCl/D 2 O) was followed by 1 H NMR to determine the rate constants (k) which all were of first order. Methyl substitution at any position (2-O, 3-O and 6-O) was found to have a simple additive effect on the reaction rate. This was also shown as a linear free energy relationship (LFER). The substituent effects upon mono-substitution depend on the substitution position: 2-O-methyl or 6-O-methyl substitution decreased the reaction rate, while 3-O-methyl substitution accelerated the hydrolysis. In cases of di-or tri-substitutions these effects were additive.[a] Dr. Scheme 1. Two proposed acid hydrolysis mechanisms of glycosides.

Comparative hydrolysis analysis of cellulose samples and aspects of its application in conservation science

“…glucose vs. mannose vs. xylose), anomer (a/b), linkage (e.g. b-O-3 vs. b-O-4, vs. b-O-6), neighboring activating or deactivating groups (such as ether, keto or carboxylic acid moieties) and their position, and the surrounding hydrogen bond system are major influencing factors (Yoneda et al 2016). Hydrolysis efficiency is of course also affected by the conditions, such as the type, strength and concentration of acid used, duration of the hydrolysis treatment, and reaction temperature (Panagiotopouos 2005).…”