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Chapter 28: Problem 67

The so-called Ruff degradation is a chain-shortening reaction in which an aldose chain is shortened by one C atom, hexoses, for example, being converted into pentoses. In the Ruff degradation, the calcium salt of an aldonic acid (the corresponding carboxylic acid of an aldose) is oxidized with hydrogen peroxide. Ferric ion catalyzes the reaction. The calcium salt of the aldonic acid necessary for the Ruff degradation is obtained by oxidizing an aldose with an aqueous solution of bromine and then adding calcium hydroxide. The reaction scheme is as follows where \(R\) represents the rest of the chain of the aldose. (a) Show that D-glucose can be degraded into D-arabinose. Which other aldose can be degraded into D-arabinose? (b) Which two monosaccharides can be degraded into D-glyceraldehyde by employing the Ruff degradation only once?

Short Answer

Expert verified
a) D-glucose and D-mannose can be degraded into D-arabinose. b) D-erythrose and D-threose can be degraded into D-glyceraldehyde.

Step by step solution

01

Convert D-glucose to D-arabinose

In order to show how D-glucose can be degraded into D-arabinose, let's apply the Ruff degradation process to D-glucose. D-glucose, being a hexose, loses one carbon atom producing an aldose pentose, which is D-arabinose.
02

Identify Other Aldose Convertible to D-arabinose

After successfully converting D-glucose to D-arabinose, let's look for other aldose that can be converted similarly. The other aldose that can be degraded to D-arabinose is D-mannose. D-mannose and D-glucose are epimers that differ only in the stereochemistry at carbon 2, hence D-mannose will also degrade to D-arabinose via the Ruff degradation.
03

Determine Monosaccharides Convertible to D-glyceraldehyde

The two monosaccharides that can be degraded into D-glyceraldehyde using Ruff degradation only once are D-erythrose and D-threose. Both are tetrose sugars having one carbon atom more than D-glyceraldehyde. Applying Ruff degradation to either of these would result in the triose sugar, D-glyceraldehyde.

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