Question

para chloroaniline and anilinium hydrochloride can be distinguished by 1\. Sandmeyer reaction 2\. \(\mathrm{AgNO}_{3}\) 3\. Carbylamine reaction 4\. \(\mathrm{NaHCO}_{3}\) (a) \(1,3,4\) (b) \(1,2,4\) (c) \(1,2,3,4\) (d) \(2,3,4\)

Short answer

The correct answer is (c) 1, 2, 3, 4.

Step-by-step solution

Understanding the Compounds

Para chloroaniline (p-chloroaniline) is an aromatic amine with the formula C6H4ClNH2. Anilinium hydrochloride is an aniline derivative with an extra HCl group which gives it the structure C6H5NH3Cl.

Evaluating Sandmeyer Reaction

The Sandmeyer reaction is used for the substitution of an amino group in an aromatic ring with a halide. In p-chloroaniline, the amino group is directly attached to the aromatic ring, allowing it to undergo the Sandmeyer reaction, but not in anilinium hydrochloride where the amino group is protonated and forms a salt.

Evaluating 9AgNO_{3}

In the presence of 9AgNO_{3}, anilinium hydrochloride can react to form silver chloride as a precipitate due to the presence of chloride ions. P-chloroaniline does not have free chloride ions and thus does not form a precipitate.

Evaluating Carbylamine Reaction

The carbylamine reaction (or isocyanide test) is a chemical test for primary amines. It involves the formation of isocyanides. P-chloroaniline, being a primary amine, can undergo this reaction. Anilinium hydrochloride cannot, as the amino group is not free and is protonated.

Evaluating 9NaHCO_{3}

This test is used for substances that release carbon dioxide with 9NaHCO_{3}, like carboxylic acids. Neither p-chloroaniline nor anilinium hydrochloride will react with NaHCO3 since they don't release CO2.

Choosing the Correct Options

Based on the evaluations: Sandmeyer reaction (1) can distinguish p-chloroaniline, 9AgNO_{3} (2) can distinguish anilinium hydrochloride, and carbylamine reaction (3) can distinguish p-chloroaniline. NaHCO3 (4) does not distinguish either. So the correct options are 1, 2, and 3.

Key concepts

Sandmeyer Reaction

The Sandmeyer reaction is a classic chemical reaction used to transform an aromatic amine into an aryl halide by replacing the amino group with a different substituent, typically a halide. It proceeds through a diazonium salt intermediate, requiring the presence of primary amines in aromatic compounds. The key here is that the amino group must be directly bonded to the aromatic ring.

This makes p-chloroaniline, which has a free amino group attached to the aromatic ring, a perfect candidate for undergoing the Sandmeyer reaction. When exposed to copper(I) chloride (CuCl) or other similar reagents, the amino group in p-chloroaniline can be replaced effectively, distinguishing it from anilinium hydrochloride.

Anilinium hydrochloride, on the other hand, has its amino group protonated, making it form a salt structure (C6H5NH3Cl). Due to this protonation, it cannot form a diazonium salt under the standard Sandmeyer conditions, preventing any further reaction.

Primary Amines Test

The primary amines can be identified using the Carbylamine reaction (also called the isocyanide test). This reaction specifically targets primary amines by converting them into isocyanides (carbylamines) through a reaction with chloroform and an aqueous base like KOH.

This is a widely used test in organic chemistry for confirming the presence of primary amines. P-chloroaniline, having a primary amino group (-NH2), can engage in this reaction and produce a very characteristic and unpleasant odor of isocyanides, making it easily distinguishable.

In contrast, anilinium hydrochloride cannot participate in the Carbylamine reaction. This is because the amino group is not free; it is protonated (forming a salt) and therefore cannot interact with the reagents in the same way as p-chloroaniline.

AgNO3 Precipitation Test

The AgNO3 precipitation test is an essential chemical test utilized to detect the presence of chloride ions among other halides. It operates by forming a white precipitate of silver chloride (AgCl) when chloride ions are present.

For anilinium hydrochloride, the presence of these chloride ions is a key feature. When dissolved, the compound releases free chloride ions in solution. Thus, when AgNO3 is added, these chloride ions react with Ag+ ions forming an instantly noticeable white precipitate of AgCl.

On the other hand, p-chloroaniline does not possess free chloride ions that can dissociate in solution. Instead, it has a chloro group covalently bonded to the aromatic ring, thus it does not form any precipitate upon AgNO3 addition, making this test an effective way to distinguish between p-chloroaniline and anilinium hydrochloride.