Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Oxidation of fructose with bromine water gives (a) gluconic acid (b) oxalic acid (c) trimethyl glutaric acid (d) tartaric acid

Step-by-Step Solution

Answer

The oxidation of fructose with bromine water gives (a) gluconic acid.

Step 1: Understand the Reaction

When fructose is oxidized with bromine water, it undergoes a gentle oxidation process. Bromine water selectively oxidizes the aldehyde group, if present, into a carboxylic acid group. Fructose, being a ketose, is first isomerized to glucose or mannose under bromine water conditions.

Step 2: Identify the Product of Isomerization

In the presence of bromine water, fructose, being a ketose, is converted to glucose or mannose, both of which are aldoses. Essentially, fructose rearranges into these forms which can then undergo oxidation.

Step 3: Determine the Oxidation Outcome

The bromine water oxidizes the resultant aldose (such as glucose) to form gluconic acid. This happens as the aldehyde group of glucose is converted into a carboxylic acid group.

Key Concepts

Fructose Oxidation

Fructose, a simple sugar or monosaccharide, undergoes a significant transformation when treated with an oxidizing agent. In the context of fructose oxidation, bromine water serves as a mild oxidant. Fructose itself does not directly contribute to oxidation in this reaction as it is not adequately reactive. Instead, it must first isomerize to enable oxidation. The reaction primarily occurs in aqueous solutions, which facilitates the isomerization process before the actual oxidation. Once fructose is converted into its respective aldose forms, such as glucose or mannose, the oxidation process can commence. The bromine water then smoothly oxidizes these aldoses to form gluconic acid, a carboxylic acid derived from the conversion of the aldehyde group of glucose into a carboxylic acid group.

Bromine Water Reaction

Bromine water is a solution of bromine in water and is commonly used as a mild oxidizing agent. It is famous for specific reactions where targeted oxidation is required without being overly vigorous.

• This solution is particularly effective in oxidizing aldehydic functional groups to carboxylic acids.
• In the reaction with fructose, bromine water first facilitates the isomerization of fructose into glucose or mannose before it acts as an oxidizing agent.

Once the isomerization occurs, bromine water converts the newly formed aldose into gluconic acid. Bromine, being less reactive than many other oxidants, ensures that this reaction proceeds without breaking apart other sensitive molecular structures, making it an ideal choice for precise oxidation processes.

Isomerization of Fructose

Isomerization is the process through which a molecule transforms into another molecule with the same atomic composition but a different structural configuration. For fructose, a ketose, isomerization is a crucial step before oxidation. Fructose initially exists in a form that is resistant to oxidation by bromine water, but under these conditions, it rearranges its molecular structure. The ketone group present in fructose becomes an aldose configuration, resulting in molecules like glucose or mannose. This conversion is a form of structural adjustment, moving from a ketose through a simple shift to form an aldose. The water present in the bromine solution acts as a medium for this molecular rearrangement. This ensures that when oxidation occurs, it does so on a structure appropriately configured to be oxidized into a carboxylic acid. Such isomerization is key to tapping into fructose's potential for chemical transformations in oxidation reactions.