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Chapter 13: Problem 6

Carbylamine test is performed in alcoholic KOH by heating a mixture of: (a) Trihalogenated methane and a primary amine (b) An alkyl halide and a primary amine (c) An alkyl cyanide and a primary amine (d) Chloroform and silver powder

Short Answer

Expert verified
The mixture used in the carbylamine test is chloroform and a primary amine, which is described by option (b) in a generalized form. Option (d) may be considered if we strictly adhere to the description but it lacks a primary amine.

Step by step solution

01

Understanding the Carbylamine Test

The Carbylamine test, also known as the isocyanide test, is a qualitative reaction that is used to detect the presence of primary amines. In this test, chloroform (CHCl3) reacts with primary amines in the presence of alcoholic potassium hydroxide (alcoholic KOH) to form a foul-smelling isocyanide (carbylamine). This reaction does not occur with secondary or tertiary amines.
02

Examining the Options

To determine which mixture is used in the carbylamine test, we must find the one that contains all the necessary reactants for the reaction to occur. The necessary reactants are a primary amine, chloroform (CHCl3), and alcoholic KOH. While other options include constituents that might be used in other amine detection tests, only one option contains the correct reagents for the carbylamine test.
03

Selecting the Correct Option

Comparing the given options with the requirements of the carbylamine reaction, we observe that option (d) chloroform and silver powder is lacking the primary amine and silver powder is not a reactant in carbylamine test. Option (a) trihalogenated methane might seem a relevant choice but the term 'trihalogenated methane' is less specific and usually does not refer to chloroform which is crucial for the test. Option (c) alkyl cyanide and a primary amine does not involve chloroform. Therefore, the only option that includes chloroform and a primary amine is option (b) an alkyl halide and a primary amine, with the understanding that the alkyl halide in this context should be chloroform which is an alkyl halide itself. However, it should be noted that 'an alkyl halide' is a general term and not all alkyl halides would react to form a carbylamine; specifically, chloroform is the alkyl halide needed for the reaction.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Primary Amines Detection
Primary amines are organic compounds with the general formula RNH2, where R is an alkyl or aryl group. Detecting these molecules is crucial in organic chemistry as they form the building blocks for a variety of more complex molecules such as drugs, dyes, and polymers. One noteworthy method of detecting primary amines is the Carbylamine test. This test uniquely identifies primary amines due to their ability to react with chloroform in the presence of alcoholic potassium hydroxide, producing a distinct and pungent isocyanide odor. It's also important to highlight that this test does not react with secondary and tertiary amines, attesting to its specificity.

This test can, therefore, be a quick and unequivocal way to identify primary amines in a sample, which is invaluable when trying to confirm or deduce the structure of an organic compound within a mixture.
Isocyanide Test
The Isocyanide test, broadly known as the Carbylamine test, is key for detecting primary amines through the mechanism of isocyanide formation. In this reaction, the primary amine interacts with chloroform and an alkali, specifically alcoholic KOH, to create an isocyanide compound. This chemical conversion releases a strong odor that is easy to detect, facilitating confirmation of the presence of a primary amine.

Reaction Mechanism

The reaction pathway involves the deprotonation of the primary amine followed by an alpha-substitution with chloroform, which after several steps, results in the isocyanide compound. As is typical with qualitative tests, the presence of a distinct physical change—in this case, the smell—confirms the presence of the desired analyte.
Qualitative Organic Reactions
Qualitative organic reactions are a cornerstone of analytical chemistry, providing chemists with the ability to identify the functional groups within molecules. Such reactions often lead to changes that are observable through color change, precipitate formation, or, as with the Carbylamine test, scent emission. A clear indication from these responses can swiftly inform a chemist about the presence or absence of certain functional groups.

These tests are vital since they form initial guidelines before conducting more in-depth, often instrumental analyses. They are the rudimentary tools that assist in building an understanding of the molecular structure and thus play a significant role in the world of organic synthesis and identification of organic compounds.
Chemical Tests in Organic Chemistry
Organic chemistry heavily relies on chemical tests to assess the presence of different functionalities in compounds. These tests are necessary for the classification and characterisation of organic substances, and they offer instant insights into the richness of organic transformations.
  • The Carbylamine test distinguishes primary amines from other amine classes.
  • The Tollen's test can identify aldehydes.
  • The Bromine test is used to detect carbon-carbon double bonds.
Each test in the vast toolkit of a chemist has specific requirements regarding reactants and conditions and gives a particular type of response when positive. Preference for these tests stems from their simplicity, cost-effectiveness, and promptness, making them invaluable in both educational and research labs for preliminary analysis before resorting to more sophisticated techniques like spectroscopy or chromatography.

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Most popular questions from this chapter

Which of the following is most basic in nature? (a) Benzylamine (b) Acetamide (c) Aniline (d) None of these

Electrolytic reduction of nitrobenzene in strongly acidic medium gives: (a) Azoxybenzene (b) Aniline (c) p-aminophenol (d) Phenylhydroxyl amine

Nitrobenzene gives azoxybenzene and hydrazobenzene when reduced: (a) In neutral medium (b) Is acidic medium (c) In alkaline medium (d) Electrolytically

Which of the following reactions does not yield an amine? (a) \(\mathrm{R}-\mathrm{X}+\mathrm{NH}_{3} \longrightarrow\) (b) \(\mathrm{R}-\mathrm{CH}=\mathrm{NOH}+[\mathrm{H}] \stackrel{\mathrm{Na}, \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}}{\longrightarrow}\) (c) \(\mathrm{R}-\mathrm{CN}+\mathrm{H}_{2} \mathrm{O} \stackrel{\mathrm{H}^{+}}{\longrightarrow}\) (d) \(\mathrm{R}-\mathrm{CONH}_{2}+4[\mathrm{H}] \stackrel{\mathrm{LiAlH}_{4}}{\longrightarrow}\)

Amongst the following, the most basic compound is: (a) Benzylamine (b) Aniline (c) Acetanilide (d) p-nitroaniline
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