Question

Write short notes on chain-shortening and chain-lengthening reactions for sugars.

Answer 1

Chain shortening and lengthening of glucose:

• Chain shortening and lengthening are the chemical processes that are employed for decreasing or increasing the carbon chain length of glucose.
• The Kiliani-Fischer Synthesis is employed by extending a carbohydrate chain by a single carbon.
• The Ruff Degradation is a method employed for shortening a carbohydrate chain by a single carbon.

The killiani-Fischer synthesis for chain lengthening of Glucose:

• The Kiliani-Fischer Synthesis includes adding cyanide to an open-chain aldehyde (in the case of aldoses), which is then partially reduced and hydrolyzed to yield a new aldehyde.
• The cyanide ion ${\mathrm{CN}}^{-}$can be a highly effective tool for adding a single carbon to carbon chains.
• A mixture of diastereomers will be formed in the absence of chiral reagents.
• The mixture s reduced with hydrogen in palladium and then hydrolysed to give the product.

The Ruff Degradation for chain shortening of Glucose:

• The aldose chain length reduces by one carbon in this process.
• Bromine and water selectively oxidize aldehyde to a carboxylic acid.
• It involves adding an $\mathrm{Fe}\left(\mathrm{III}\right)$ salt ${\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3$with hydrogen peroxide, which involves the loss of carbon