Question

Unpleasant smell of carbylamine is produced when chloroform and alcoholic KOH are heated with (a) any amine (b) any aliphatic amine (c) any aromatic amine (d) any primary amine

Short answer

(d) any primary amine

Step-by-step solution

Recognize the Chemical Reaction

The reaction in question is the carbylamine reaction, which is a test for primary amines. In this reaction, chloroform (CHCl₃) reacts with an alcoholic solution of potassium hydroxide (KOH) to produce an isocyanide (carbylamine), which has a distinct and unpleasant smell. This reaction occurs in the presence of primary amines.

Identify the Reactants and Conditions

Ensure you understand what each reactant contributes to the reaction: chloroform provides the halogen, and alcoholic KOH acts as the strong base initiating dehalogenation. Heating is required to facilitate the reaction.

Determine Which Amines React

The carbylamine reaction is specific to primary amines. Other types of amines, such as secondary and tertiary amines, do not react to give carbylamines. Therefore, the unpleasant smell is specifically produced when primary amines are used in the reaction.

Conclude Based on Reaction Specificity

Make your conclusion based on the specificity of the reaction. Since the unpleasant smell of carbylamine is only produced with primary amines, they are the only type capable of undergoing this specific transformation with chloroform and alcoholic KOH under heating conditions.

Key concepts

Primary Amines

Primary amines are a type of organic compound that contain a nitrogen atom connected to a single alkyl or aryl group and two hydrogen atoms. They are represented by the general formula R-NH₂, where R is the alkyl or aryl group.
They are notable for their role in the carbylamine reaction, which is used to identify them due to their unique ability to produce isocyanides when reacting with chloroform and alcoholic KOH.

• The nitrogen atom in primary amines has a lone pair of electrons, which makes them reactive.
• Primary amines are versatile and can participate in various reactions, but the carbylamine reaction specifically identifies their presence.

Understanding primary amines is crucial since only these compounds give the distinct odor of carbylamines when involved in this specific chemical reaction.

Isocyanide Production

Isocyanide production is a signature reaction known for its distinct and often unpleasant odor. This reaction is prominently utilized in the carbylamine reaction to identify primary amines.
During the process, a primary amine reacts with chloroform and alcoholic KOH to form an isocyanide, which is responsible for the sharp odor.

• This reaction serves as a qualitative test, providing a clear indication for the presence of primary amines through smell.
• The formation of isocyanides is characterized by a nucleophilic substitution, involving the nitrogen atom of the amine.

The practical application of this reaction lies in its specificity to primary amines, making it a valuable tool in chemical analysis.

Chloroform

Chloroform, chemically known as trichloromethane (CHCl₃), plays a vital role as a reactant in the carbylamine reaction. It is a colorless, volatile liquid with a sweet smell and was historically used as an anesthetic.
However, in the context of the carbylamine reaction, chloroform functions as the source of the halogen atom required for the reaction.

• Chloroform is involved in the reaction by providing chlorine atoms that are crucial for forming the intermediate that's needed to produce an isocyanide.
• It needs to be handled with care due to its potential health hazards, including central nervous system effects and possible liver and kidney damage.

Thus, chloroform is essential not just for its role in the reaction but also as an intermediate in the specific transformation to isocyanide.

Alcoholic KOH

Alcoholic KOH, which is potassium hydroxide dissolved in alcohol, acts as a crucial reagent in the carbylamine reaction. Its primary role is to serve as a strong base to facilitate the reaction by deprotonating the primary amine and promoting dehalogenation of chloroform.
This environment helps the nitrogen atom in the amine attack the carbon atom in chloroform, setting off the chain of reactions leading to isocyanide formation.

• Alcohol serves as a solvent, ensuring that the reactants are adequately mixed and react effectively.
• KOH being in alcoholic form rather than aqueous is vital, as water could interfere or diminish the reaction efficiency.

Therefore, alcoholic KOH is indispensable in the reaction setup, empowering the process to yield isocyanides effectively through its basic and catalytic properties.