Question

Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.

1. α-D-glucopyranose
2. β-D-ribofuranose

Short answer

1. penta-O-acetyl-α-D-glucopyranose
2. tetra-O-acetyl-β-D-ribofuranose

Step-by-step solution

Formation of acetate esters

The hydroxy (-OH) groups of a sugar can be converted to acetate esters by the treatment with acetic anhydride and pyridine. The stereochemistry is usually retained at the anomeric carbon.

Pyranose and furanose

Pyranose is a six-membered cyclic hemiacetal while a furanose is a five-membered cyclic hemiacetal.

Formation of product

1. α-D-glucopyranose on treatment with excess acetic anhydride and pyridine gives penta-O-acetyl-α-D-glucopyranoside as the product.
   
   Reaction
2. β-D-ribofuranose on treatment with excess acetic anhydride and pyridine gives tetra-O-acetyl-β-D-ribofuranoside as the product.
   
   Reaction