Monosaccharides - Weak Oxidation (Aldonic Acid) - Online Tutor, Practice Problems & Exam Prep

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 this video, we're going to learn how to perform a weak oxidation on monosaccharides to yield a functional group called an aldonic acid. Let's get going. So guys, monosaccharides are essentially polyols with carbonyls attached, or with one carbonyl attached. That means they can undergo a series of oxidation and reduction reactions because we have so many reactive functional groups. We have alcohols that can be oxidized, we have ketones that can be reduced, all kinds of stuff. Okay?

Well, it turns out that one of those possible oxidations is called weak oxidation. And what weak oxidation is defined as it's the selective oxidation of monosaccharide aldehydes to carboxylic acid. The selective oxidation of just the aldehyde to carboxylic acid is known as weak oxidation. Now, guys, think about it. All of these different OHs could potentially be oxidized. They could be; this OH could be oxidized to a ketone. This OH is a primary alcohol that could be oxidized to a carboxylic acid. If I use a strong enough oxidizing agent, I could turn this whole thing into ketones, carboxylic acids, etc. But with the special oxidizing agent, I can simply select the very top aldehyde and turn it into a carboxylic acid. Okay?

In fact, this reaction doesn't even work with ketoses because ketoses don't have aldehydes, right? So it's selective for aldehydes to carboxylic acids. And the reagents that we use for this are actually just called bromine water. Okay? So it's bromine in water. This method can be used to differentiate between aldoses and ketoses because it doesn't work on ketoses, you can't do anything with them. It works on aldoses but doesn't work on ketoses. So it's kind of the basis, the principle of this is the basis for some tests of sugars, some sugar tests to test whether you have one type of functional group or another. This is kind of like one of the tests. Okay.

Now, guys, we're in luck. The mecha

Predict the product of the following reaction. 

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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.