Entropy furanosides

Many investigations have shown that furanosides are hydrolyzed faster than pyranosides, and acid-catalyzed hydrolysis of furanosides has been discussed in detail by Green. Additional discussion is given in Section III,la. Overend and coworkers have determined the entropy of activation for one furanoside, ethyl 3-D-galactofuranoside, and found it to be... 

Capon and Thacker have determined the entropies of activation for several methyl furanosides. These values (see Table IVA) range from... 

Entropies of Activation for the Acid-catalyzed Hydrolysis of Furanosides"... 

Hydrolysis of acetals by acid is considered to proceed normally via the A1 mechanism. Electron release in the aldehyde facilitates reaction, the p value being —3.5, indicating stabilization of a cationic intermediate. The solvent isotope-effect k H2O/ D2O is approximately 2.6, which indicates that the acidic property of the solvent is more important than its nucleophilicity. The entropy of activation is positive, 5-20 K l mol-1. Glycopyranosides fit into this generalization, but the acidic hydrolysis of the corresponding furanosides shows negative entropies of activation, indicating a difference in mechanism. 

Volumes of activation have been determined for the acid-catalyzed hydrolysis of 19 glycosides, both furanosidic and pyranosidic, and were found to parallel closely the trend in entropies of activation, positive for pyranosides and negative... 

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