Monosaccharides - Weak Oxidation (Aldonic Acid): Videos & Practice Problems

Weak oxidation of monosaccharides selectively converts aldehydes into carboxylic acids, forming aldonic acids. This reaction utilizes bromine water, which differentiates aldoses from ketoses, as ketoses lack aldehydes. For example, D-mannose oxidized with bromine water yields D-mannonic acid. The primary alcohols remain unchanged, highlighting the specificity of this oxidation process. Understanding this reaction is crucial for identifying sugar types and their functional groups in biochemical contexts.

Monosaccharides - Weak Oxidation (Aldonic Acid)

In the study of monosaccharides, understanding the process of weak oxidation is essential. Monosaccharides, which are polyols with a carbonyl group, can undergo various oxidation and reduction reactions due to their reactive functional groups, including alcohols and aldehydes. Weak oxidation specifically refers to the selective oxidation of the aldehyde group in monosaccharides to form a carboxylic acid, known as an aldonic acid.

This reaction is particularly significant because it does not affect other functional groups present in the monosaccharide. For instance, while a strong oxidizing agent could oxidize multiple hydroxyl groups to ketones or carboxylic acids, weak oxidation targets only the aldehyde. This selectivity is crucial for differentiating between aldoses (which contain aldehydes) and ketoses (which do not), as weak oxidation will not react with ketoses.

The reagent commonly used for this weak oxidation is bromine water, which is bromine dissolved in water, typically under mildly acidic conditions. This method serves as a basis for certain sugar tests that help identify the type of sugar present. For example, when D-mannose, a common aldose, is treated with bromine water, the aldehyde group is oxidized to a carboxylic acid, while the other hydroxyl groups remain unchanged. The resulting compound is referred to as an aldonic acid.

To name the product, the root name of the monosaccharide is combined with the suffix "-onic acid." Therefore, the aldonic acid derived from D-mannose is called D-mannonic acid, indicating that the aldehyde has been oxidized to a carboxylic acid. This transformation highlights the importance of weak oxidation in carbohydrate chemistry and its application in identifying different types of sugars.

Predict the product of the following reaction.

• A.
• B.
• C.
• D.

Answer: (D)

Here’s what students ask on this topic:

What is weak oxidation in the context of monosaccharides?

Weak oxidation in the context of monosaccharides refers to the selective oxidation of the aldehyde group in an aldose to form a carboxylic acid, resulting in an aldonic acid. This process uses bromine water as the oxidizing agent and is specific to aldoses because ketoses lack aldehyde groups. For example, D-mannose can be oxidized to D-mannonic acid using this method. The primary alcohols and other functional groups in the monosaccharide remain unchanged during this reaction.

How does bromine water differentiate between aldoses and ketoses?

Bromine water differentiates between aldoses and ketoses based on the presence of an aldehyde group. Aldoses contain an aldehyde group that can be selectively oxidized to a carboxylic acid by bromine water, forming an aldonic acid. In contrast, ketoses do not have an aldehyde group and therefore do not undergo this oxidation reaction with bromine water. This selective reaction is useful for identifying and distinguishing between these two types of sugars.

What is the product of weak oxidation of D-mannose?

The product of the weak oxidation of D-mannose is D-mannonic acid. In this reaction, the aldehyde group at the top of the D-mannose molecule is selectively oxidized to a carboxylic acid using bromine water. The primary alcohols and other functional groups in the molecule remain unchanged, resulting in the formation of D-mannonic acid.

Why is the mechanism of weak oxidation of monosaccharides not fully known?

The mechanism of weak oxidation of monosaccharides is not fully known because the exact steps and intermediates involved in the reaction have not been completely elucidated. While it is understood that bromine water selectively oxidizes the aldehyde group to a carboxylic acid, the detailed pathway and the role of any potential intermediates remain unclear. As a result, students are typically not required to draw the mechanism but should understand the overall transformation and the reagents involved.

How do you name the product of weak oxidation of a monosaccharide?

The product of weak oxidation of a monosaccharide is named by taking the root name of the original monosaccharide and adding the suffix '-onic acid.' For example, if D-mannose undergoes weak oxidation, the product is named D-mannonic acid. This naming convention reflects the conversion of the aldehyde group to a carboxylic acid while retaining the rest of the monosaccharide structure.