Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

In the following reaction: Glucose \(+3 \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}-\mathrm{NH}_{2} \stackrel{\mathrm{H}^{+} / \mathrm{U}}{\longrightarrow}\) Osazone \(+\mathrm{X}+\mathrm{Y}\) \((\mathrm{X})\) and \((\mathrm{Y})\) are (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) and \(\mathrm{NH}_{2} \mathrm{OH}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) and \(\mathrm{NH}_{3}\) (c) \(\mathrm{NH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}-\mathrm{NHOH}\) and \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

The byproducts X and Y are aniline (C_{6} H_{5} NH_{2}) and ammonia (NH_{3}), so the answer is (b).

Step 1: Understand the Reaction

The given reaction is the formation of osazone from glucose and phenylhydrazine (C_{6} H_{5} NH-NH_{2}). Typically, two molecules of phenylhydrazine react with the glucose to form an osazone.

Step 2: Identify Byproducts

In osazone formation, one of the byproducts is ammonia (NH_{3}), released when the phenylhydrazine reacts with the carbonyl group of glucose. The other byproduct is aniline (C_{6} H_{5} NH_{2}), which results from the degradation of the phenylhydrazine.

Step 3: Match with Given Options

Review the final products based on the osazone synthesis: they are aniline (C_{6} H_{5} NH_{2}) and ammonia (NH_{3}). These correspond with option (b) in the provided choices.

Key Concepts

Glucose Reaction Mechanism

To understand the formation of osazone from glucose, it is important to delve into the reaction mechanism at play. Glucose is a type of simple sugar, more formally known as a monosaccharide. It contains a carbonyl group (C=O), which can either be an aldehyde or a ketone group. In this context, glucose reacts with phenylhydrazine, a specific derivative of hydrazine known for its reactivity with aldehydes and ketones.

When glucose is mixed with phenylhydrazine under acidic conditions, a fascinating transformation occurs. Here's a simplified look at the process:

• Two molecules of phenylhydrazine initially attack and replace the oxygen in the carbonyl group of glucose to form a hydrazone.
• Subsequently, another molecule of phenylhydrazine attacks this hydrazone to give osazone.

This sequence of reactions results in the formation of osazone, characterized by its crystalline and yellow appearance. The formation of osazone from glucose is a classical method used to identify and differentiate between different sugars, thanks to the unique osazones each sugar forms.

Phenylhydrazine

Phenylhydrazine is a crucial reagent in the osazone formation process with glucose. It is an organic compound with the formula \( C_{6}H_{5}NH-NH_{2} \), displaying notable properties that make it effective for such reactions.

This compound is similar to hydrazine but with a phenyl group \( (C_{6}H_{5}-) \) attached, which introduces specific reactivity characteristics:

• Phenylhydrazine readily reacts with carbonyl groups, such as those in sugars, to generate hydrazones.
• In the synthesis of osazone, it can further react with pre-formed hydrazones, highlighting its function in multiple reaction stages.

The balanced combination of nucleophilic sites in phenylhydrazine and its aromatic phenyl group improves its efficiency in capturing and modifying simple sugars. During the reaction, some phenylhydrazine is degraded to form aniline, a byproduct alongside ammonia.

Byproducts Identification

In any chemical reaction, identifying byproducts is just as critical as understanding the main product formation. In the osazone formation from glucose, two principal byproducts emerge: aniline \( (C_{6}H_{5}NH_{2}) \) and ammonia \( (NH_{3}) \).

Here's how these byproducts come about:

• Aniline results from the breakdown of phenylhydrazine during the reaction process. As phenylhydrazine undergoes transformation, the nitrogen-hydrogen bonds rearrange, releasing aniline as a fragment.
• Ammonia is freed when one of the hydrazine moieties, originally derived from phenylhydrazine, reacts with the glucose and is cleaved off in subsequent reaction steps.

Spotting and recognizing these byproducts is crucial not only for identifying the right reaction conditions but also for ensuring the accuracy of expected results. In our provided exercise, option (b) correctly lists the byproducts as aniline and ammonia, affirming their presence during osazone synthesis.