Electrophilic Catalysis of Glycoside Hydrolysis

5 and the idea was so firmly entrenched that protons from the aluminium hydration sphere were the depolymerisation catalyst that massive programmes of document deacidification, such as much of the stock of the US Library of Congress, were set in train. In fact, a steep dependence of kobs for hydrolysis of 

5- anhydrocellobiitol on the concentration of added Al at constant pH demonstrates the culprit is in all likelihood aluminium acting as an electrophile, not protons. 

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Electrophilic catalysis of the departure of halogens in the century-old Koenigs-Knorr reaction is implicit in the use of heavy metal bases such as silver oxide and mercuric cyanide, but the first demonstration of electrophilic catalysis in water (in the hydrolysis of the p-glucoside of 8-hydroxyquinoline by first-row transition metals (Cu Np > C")) was by Clark and Hay in 1973. The observations were expanded to the more conveniently followed (because more labile) benzaldehyde methylacetals or tetrahydropyranyl derivatives of 8-hydroxyquinoline, whose hydrolysis is now known to give solvent-equilibrated oxocarbenium ions (Figure 3.19). Surprisingly, however, the observation of electrophilic catalysis of glycoside hydrolysis itself was not picked up by paper... 

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