Problem 143 - A Complete Resource Book in Chemistry for JEE Main

Question

Mild oxidizing agents, e.g. bromine water, Tollen's reagent, Fehling's solution etc, oxidize aldoses into aldonic acid. Both glucose and fructose can be oxidized by Tollen's reagent and Fehling's solution despite the presence of a keto group in Fructose. Strong oxidizing agents like conc. \(\mathrm{HNO}_{3}\) oxidizes glucose to a dibasic acid. Fructose under similar conditions is also oxidized. All carbohydrates are quantitatively oxidized by lead tetraacetate or periodic acid. This reaction is used to elucidate the structure of carbohydrates. Both glucose and fructose can be reduced by red \(\mathrm{P} / \mathrm{HI}\), Lial \(\mathrm{H}_{4}\), Clemmensen and Wolff - Kishner reduction. Fructose on oxidation with conc. \(\mathrm{HNO}_{3}\) gives (a) Tartaric acid (b) Saccharic acid (c) Glycolic acid (d) Both (a) and (c)

Step-by-Step Solution

Answer

The correct answer is (b) Saccharic acid.

Step 1: Understand Oxidation with Conc. HNO3

Concentrated nitric acid (HNO3) is a strong oxidizing agent that oxidizes carbohydrates such as fructose to form specific acids. When fructose undergoes oxidation by this reagent, it forms different polycarboxylic acids depending on the structure and conditions.

Step 2: Evaluate Expected Products

Fructose, when oxidized by concentrated HNO3, typically yields a primary product, which in this case is saccharic acid. This is due to the complete oxidation of the aldose structure into a corresponding dibasic (two carboxylic groups) acid form.

Step 3: Recognize Saccharic Acid Formation

Know that the primary acid formed when fructose is oxidized by strong oxidizing agents like concentrated HNO3 is saccharic acid. Recognizing saccharic acid as one of the options helps in identifying the correct answer among multiple choices.

Key Concepts

Aldoses

Aldoses are a type of carbohydrate that contain an aldehyde group (-CHO). These carbohydrates are known as monosaccharides, which are the simplest form of sugars. Common examples of aldoses include glucose and galactose. The structural feature of the aldehyde group at the end of the carbon chain is what allows aldoses to participate in oxidation reactions.

Oxidation of aldoses involves the conversion of the terminal aldehyde group into a carboxylic acid group. Mild oxidizing agents like bromine water can convert aldoses into aldonic acids. The general reaction is an important chemical process that alters the functionality of these sugars. This ability to transform is vital in carbohydrate chemistry, as it can provide information regarding the structure and reactivity of the sugar molecules in biological systems.

Oxidizing Agents

Oxidizing agents are substances that cause other molecules to lose electrons during a chemical reaction. In the context of carbohydrate chemistry, they play a crucial role in converting sugars into acids.

Some mild oxidizing agents such as bromine water, Tollen's reagent, and Fehling's solution selectively oxidize the aldehyde group present in aldoses to produce aldonic acids. Strong oxidizing agents like concentrated nitric acid (\(\text{HNO}_3\)) are more aggressive and can further oxidize sugars to form dibasic acids.

These agents help elucidate the structure of carbohydrates by breaking them into smaller, more manageable parts or by converting them into specific products that are easier to analyze. Understanding the role of oxidizing agents is essential for manipulating sugar molecules to suit various chemical and industrial needs.

Glucose and Fructose Oxidation

Both glucose and fructose can undergo oxidation, despite fructose containing a ketone group rather than an aldehyde group. When treated with Tollen's reagent or Fehling's solution, both of these sugars can be oxidized, which is intriguing given the difference in their structure.

While glucose easily yields products due to its aldose nature, fructose can isomerize to form glucose in the presence of these reagents, allowing for its oxidation. A more extensive oxidation of both sugars occurs when using strong oxidizing agents like concentrated nitric acid. In such cases, glucose and fructose are converted into dibasic acids, which are compounds containing two carboxylic acid groups.

• This property of oxidation makes glucose and fructose versatile in chemical reactions.
• Understanding the oxidation behavior of glucose and fructose aids in deciphering their roles in biological systems and industrial applications.

Saccharic Acid Formation

The formation of saccharic acid occurs when fructose is oxidized by strong oxidizing agents like concentrated \(\text{HNO}_3\). This oxidation results in the conversion of fructose into a dibasic acid with two carboxyl groups.

Recognizing saccharic acid as the primary product helps identify the outcome of such reactions in sugar chemistry. Fructose undergoes complex oxidation leading to the cleaving and reformation of bonds that result in saccharic acid.

• Saccharic acid, also known as glucaric acid, is an important compound due to its potential applications in sustainable polymers and biodegradables.
• Understanding the oxidation process leading to this acid is key in producing and utilizing it for commercial purposes.