Problem 58 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

When glucose reacts with bromine water, the main product is: [BHU 2004] (a) acetic acid (b) saccharic acid (c) glyceraldehyde (d) gluconic acid

Step-by-Step Solution

Answer

The main product is gluconic acid.

Step 1: Understand the Reaction

When glucose reacts with bromine water, the aldehyde group (\(-CHO\), right) in glucose is oxidized to a carboxylic acid group (\(-COOH\), right). Bromine water is commonly used to oxidize aldehydes into acids.

Step 2: Recall the Oxidation Outcome

In the presence of bromine water, glucose, which is an aldohexose, gets its aldehyde group oxidized. This results in the conversion of glucose into gluconic acid.

Step 3: Identify the Correct Option

Based on the oxidation of the aldehyde group in glucose to form a carboxylic acid, the main product when glucose reacts with bromine water is gluconic acid. Thus, the correct option is (d) gluconic acid.

Key Concepts

Oxidation of aldehydes

When glucose undergoes a reaction with bromine water, an important transformation occurs. The aldehyde group on glucose is targeted by bromine water. This reaction leads to an oxidation process. An aldehyde is a functional group characterized by the presence of a carbon atom double-bonded to an oxygen atom (i.e., the carbonyl group), and a single hydrogen atom attached to this carbon. In the context of glucose, this aldehyde group is found at the end of the glucose molecule.

The oxidation of aldehydes involves the increase of oxygen bonds, typically transforming the aldehyde into a different functional group. Bromine water acts as an oxidizing agent in this reaction. As it oxidizes the aldehyde group of glucose, it transforms into a carboxylic acid group. This occurs while bromine water is used in place of more aggressive oxidants, making it a gentle yet effective method to achieve this reaction. Thus, the oxidation of the aldehyde in glucose is a key step in transforming the molecule.

• The aldehyde group ( ce{-CHO}) is commonly subjected to oxidation.
• Carbon increases its number of bonds to oxygen during this process.
• This conversion is crucial for changing the chemical properties of glucose.

Formation of carboxylic acids

One significant outcome of the oxidation process is the formation of a carboxylic acid group from the aldehyde group. A carboxylic acid is characterized by the ce{-COOH} group, which is a combination of carbonyl ( ce{C=O}) and hydroxyl ( ce{OH}) groups bonded to the same carbon. During the oxidation of glucose, the aldehyde is converted to this carboxylic acid group.

This transformation is crucial for altering the structure and function of the molecule. In the context of glucose, the addition of the ce{-COOH} group marks a shift from a simple sugar's basic structure to a more complex compound with different chemical behaviors. Carboxylic acids are known for their acidic properties, which are distinct from the characteristics of aldehydes.

• A ce{-COOH} group replaces the ce{-CHO} group in molecules.
• This changes the reactivity and solubility of the molecule.
• Such transformations are common in organic chemistry, facilitating the synthesis of new compounds.

Gluconic acid synthesis

The reaction where glucose is converted to gluconic acid is a prime example of this oxidation process yielding a carboxylic acid. Gluconic acid is a compound derived by the oxidation of the aldehyde group in glucose. As glucose, an aldohexose, reacts with bromine water, the aldehyde at the end of the glucose molecule is oxidized to form the ce{-COOH} group, resulting in gluconic acid.

Gluconic acid has numerous applications, ranging from its use in food and pharmaceuticals to its role in cleaning agents. Its synthesis from glucose is not only a chemical transformation but also a demonstration of how altering a functional group can lead to entirely new substances with diverse uses. Thus, knowing this reaction is foundational for students studying organic and biochemical reactions.

• The aldehyde group in glucose is oxidized to form gluconic acid.
• This reaction utilizes bromine water for its specificity and mild conditions.
• Gluconic acid has varied uses, showcasing the importance of such transformations.