Reduction of Monosaccharides: Study with Video Lessons, Practice Problems & Examples

The reduction of aldose or keto sugars involves converting the carbonyl group into a hydroxyl group, resulting in sugar alcohols. This process uses hydrogen (H₂) as a reducing agent, facilitated by metal catalysts like nickel, platinum, or palladium. The carbonyl carbon and oxygen each gain an H atom, transforming the sugar structure. Sugar alcohols are named by changing the suffix from -ose to -itol. Understanding this reduction is essential for grasping carbohydrate metabolism and the properties of these compounds in biological systems.

Reduction of Monosaccharides Concept 1

Now when it comes to the reduction of an aldose or keto sugar, we're going to say the carbonyl group is reduced via a reducing agent to a hydroxyl group to create a sugar alcohol. Now when I say hydroxyl group, I just mean an OH group. A sugar alcohol is just a monosaccharide that has all carbons connected to a hydroxyl group. Now when it comes to this reduction, the reducing agent is H₂, and the reduction is facilitated by the use of a metal catalyst in the form of nickel, platinum, or palladium. What happens in this reaction is that our carbonyl oxygen gains an H, and the carbonyl carbon also gains an H. So we go from an aldose or keto sugar to our sugar alcohol.

Reduction of Monosaccharides Concept 2

So, let's look and see what this reduction of monosaccharides would resemble. If we take a look here, we have an Aldo sugar to begin with, and we're going to say we're reducing it with H₂ with one of our metal catalysts, nickel, palladium, or platinum. Remember, the carbonyl carbon will gain an H, and this carbonyl oxygen is still present, and it also gains an H. And in that way, we've gone from an Aldo sugar to just a sugar alcohol. Now, let's look at our keto sugar. Same thing. We're using H₂ with one of our three metal catalysts. We're going to say here that our carbonyl carbon gains an H, and then the carbonyl oxygen is still present, it also gains an H. And again, we've created a sugar alcohol, this time from a ketose sugar. So remember, we're making sugar alcohols because now all the carbons within this structure have an OH connected to it. Right? So just keep that in mind. We're going from an Aldo sugar to a keto sugar. Our carbonyl group is being transformed into a COH group.

Reduction of Monosaccharides Example 1

Here it says determine the sugar alcohol product formed from the reduction of the following monosaccharide. So here's our monosaccharide, which is a keto sugar. Remember, in its reduction, it's the carbonyl carbon or the carbonyl group that's being transformed. We're going to say here that that carbonyl carbon gains an H, and the carbonyl oxygen is still there, it also gains an H. And then the rest of the structure stays the same. So we'd still have this C with an H here and an OH here, this C with an OH here and an H here, and then our CH₂OH group. So this would be our sugar alcohol product formed from the reduction of this ketose sugar.

Determine which aldose reactant should be used to produce the following sugar alcohol.

• A.
• B.
• C.
• D.

Common Naming of Sugar Alcohols Concept 3

We know the reduction of an aldose or keto sugar creates a sugar alcohol. With this, we have to be able to name these sugar alcohols. Now we're going to say the common naming of sugar alcohols is that the set of rules for naming them are similar to aldose and keto sugars. The way we do it is we modify the ending of our aldose or keto sugars, which typically end with "os", and we change it to "-itol." All because it's an alcohol. So remember, when we have an aldose or keto sugar, their ending is "os". When they get reduced to a sugar alcohol, the ending transforms to "itol".

Reduction of Monosaccharides Example 2

Here it says, "Provide the structure and common name for the sugar alcohol created from the reduction reaction." So, we're starting out with D-ribose. We know that when it comes to reduction, we're reducing the aldehyde group. Now remember the aldehyde group is C double bond O connected to an H. When it comes to reduction, the carbonyl carbon would gain an H and the carbonyl oxygen, which is still there, would also gain an H. This would transform the aldehyde group into a CH2OH group. So we're gonna have CH2OH now, and the rest of the structure would stay the same. So, we'd still have this carbon connected to OHH, and the same with the others. And then CH2OH here on the bottom. Remember, when it comes to naming the common naming of sugar alcohols, we change the 'ose' ending to 'itol.' So, this would be called D-ribitol. This would be the common name of this sugar alcohol.

What is the common name of the sugar alcohol produced when D-galactose is reduced?

• A. L-galactose
• B. D-galactitol
• C. D-galactaric acid
• D. L-galactitol

Draw the Fischer projection for the reduction product of D-mannose, the C-2 epimer of glucose. What is the structure and common name of the sugar alcohol produced? 

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the process of reducing aldose and keto sugars?

The reduction of aldose and keto sugars involves converting the carbonyl group (C=O) into a hydroxyl group (OH), resulting in sugar alcohols. This process uses hydrogen (H₂) as a reducing agent, facilitated by metal catalysts like nickel, platinum, or palladium. During the reaction, the carbonyl carbon and oxygen each gain an H atom, transforming the sugar structure. For example, an aldose or ketose sugar is reduced to a sugar alcohol, where all carbons are connected to hydroxyl groups. This transformation is crucial for understanding carbohydrate metabolism and the properties of these compounds in biological systems.

What are the common catalysts used in the reduction of monosaccharides?

The common catalysts used in the reduction of monosaccharides are metals such as nickel (Ni), platinum (Pt), and palladium (Pd). These catalysts facilitate the reduction process by enabling the hydrogen (H₂) to effectively add to the carbonyl group of the sugar, converting it into a hydroxyl group. This results in the formation of sugar alcohols from aldose or ketose sugars. The choice of catalyst can influence the efficiency and specificity of the reduction reaction.

How are sugar alcohols named after the reduction of aldose or keto sugars?

Sugar alcohols are named by modifying the suffix of the original aldose or ketose sugar. Typically, aldose and ketose sugars end with the suffix -ose. When these sugars are reduced to sugar alcohols, the suffix changes to -itol. For example, glucose (an aldose) becomes glucitol, and fructose (a ketose) becomes fructitol. This naming convention helps in identifying the compound as a sugar alcohol, which is important for understanding its chemical properties and biological functions.

What is the role of hydrogen in the reduction of monosaccharides?

Hydrogen (H₂) acts as the reducing agent in the reduction of monosaccharides. During the reaction, hydrogen atoms are added to the carbonyl group of the sugar. Specifically, the carbonyl carbon gains one hydrogen atom, and the carbonyl oxygen gains another hydrogen atom. This addition converts the carbonyl group (C=O) into a hydroxyl group (OH), resulting in the formation of a sugar alcohol. The presence of a metal catalyst like nickel, platinum, or palladium facilitates this hydrogenation process.

What is the significance of sugar alcohols in biological systems?

Sugar alcohols play a significant role in biological systems due to their unique properties. They are often used as low-calorie sweeteners in food products because they provide sweetness without the same caloric content as regular sugars. Additionally, sugar alcohols do not cause a rapid spike in blood glucose levels, making them suitable for diabetic-friendly diets. In metabolism, sugar alcohols can be intermediates in various biochemical pathways, contributing to energy production and storage. Understanding their formation and function is essential for studying carbohydrate metabolism and nutrition.