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

All eight types of differently methyl‐substituted methyl 4‐O‐methyl‐β‐d‐glucopyranosides were chemically synthesized, analytically characterized including 13C NMR analysis, and subjected to acid‐catalyzed hydrolytic cleavage of the glucosides. The 13C NMR resonances of the ring‐carbons shift apprx....

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Bibliographic Details
Published in:ChemistrySelect (Weinheim) 2016-11, Vol.1 (18), p.5715-5720
Main Authors: Yoneda, Yuko, Hettegger, Hubert, Rosenau, Thomas, Kawada, Toshinari
Format: Article
Language:English
Subjects:
acid hydrolysis
kinetics
linear free energy relationship
methyl 4-O-methyl-β-d-glucopyranoside
rate constant
substituent effect
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Summary:All eight types of differently methyl‐substituted methyl 4‐O‐methyl‐β‐d‐glucopyranosides were chemically synthesized, analytically characterized including 13C NMR analysis, and subjected to acid‐catalyzed hydrolytic cleavage of the glucosides. The 13C NMR resonances of the ring‐carbons shift apprx. 10 ppm down‐field by methyl substitution. Acid hydrolysis (3 mol⋅L−1 DCl/D2O) was followed by 1H 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. Methyl substitution on 2‐, 3‐ and 6‐OH affects independently and additively in acid hydrolysis (3 mol⋅L−1 DCl/D2O) of methyl 4‐O‐methyl‐β‐d‐glucopyranosides.
ISSN:2365-6549
2365-6549
DOI:10.1002/slct.201601125