Question

Primary amine, secondary amine and tertiary amine can be separated by (A) Hinsberg reagent (B) Carbyl amine test (C) Ethyl oxalate (D) Fractional distillation

Short answer

In summary, primary, secondary, and tertiary amines can be separated by using the Hinsberg reagent (A) method. This reagent consistently provides distinct reactions with primary, secondary, and tertiary amines, allowing them to be easily separated from one another.

Step-by-step solution

Understand primary, secondary, and tertiary amines

Primary amines have the general formula RNH2, where R is an alkyl or aryl group. Secondary amines have the general formula R₂NH, where R is an alkyl or aryl group. Tertiary amines have the general formula R₃N, where R is an alkyl or aryl group.

Analyze Option A: Hinsberg reagent

Hinsberg reagent is benzene sulfonyl chloride (C₆H₅SO₂Cl). It reacts with primary, secondary, and tertiary amines differently, allowing for their separation. Primary amines form a soluble sulfonamide salt, secondary amines form an insoluble sulfonamide, and tertiary amines do not react with Hinsberg reagent.

Analyze Option B: Carbyl amine test

The carbyl amine test, also known as the isocyanide test, involves chloroform (CHCl₃) and an alkali such as KOH or NaOH. In this test, only primary amines produce foul-smelling carbyl amines or isocyanides. Secondary and tertiary amines do not react in this test.

Analyze Option C: Ethyl oxalate

Ethyl oxalate is seldom used for separating amines, as it mostly deals with the formation of crystalline oxalates when reacting with alkaloids and other nitrogen-containing compounds. However, this is not a selective method for separating primary, secondary, and tertiary amines.

Analyze Option D: Fractional distillation

Fractional distillation separates components in a mixture based on their boiling points. This method can separate mixtures of diverse chemical compounds but is not a selective method for primary, secondary, and tertiary amines.

Choose the correct method

Based on our analysis of the four given options, the Hinsberg reagent (A) is the most suitable method for separating primary, secondary, and tertiary amines. This is due to the distinct reactivity of primary, secondary, and tertiary amines with the Hinsberg reagent, allowing for their separation.

Key concepts

Hinsberg Reagent

The Hinsberg reagent, also known as benzene sulfonyl chloride ((C_6H_5SO_2Cl)), is essential for distinguishing between primary, secondary, and tertiary amines. The concept is simple: this reagent reacts differently with each type of amine, allowing for an easy separation.

When a primary amine encounters the Hinsberg reagent, it forms a sulfonamide salt which is soluble in alkali. This solubility arises due to the free amino group in primary amines which can react with benzene sulfonyl chloride to form sulphonamides, easily separated by basic extraction.

Reactivity with Secondary and Tertiary Amines

Secondary amines, having two organic groups attached to the nitrogen, form an insoluble sulfonamide when treated with this reagent, making it possible to separate them from the mixture via filtration. Tertiary amines, on the other hand, have no hydrogen atoms attached to the nitrogen and do not react with the Hinsberg reagent, thus remaining unchanged in the reaction mixture.

The beauty of this method is in its specificity – each outcome provides a clear indication of the type of amine present, which is why it is favored for such separations.

Primary Amine

Understanding primary amines is pivotal when we discuss the separation of amines. A primary amine has the general formula (RNH_2), where R represents an alkyl or aryl group attached to a nitrogen atom featuring two hydrogen atoms.

Primary amines are notably reactive due to their two N-H bonds. The presence of these hydrogen atoms makes primary amines good nucleophiles and susceptible to reactions such as acylation and alkylation.

Importance in Separation

This nucleophilicity is taken advantage of in separation processes, like when using the Hinsberg reagent, as primary amines generate a product that behaves differently (in terms of solubility) from secondary and tertiary amines. Also, in the carbyl amine test, which is specific to primary amines, they form foul-smelling isocyanides, making the test both a qualitative and a separation technique.

Carbyl Amine Test

Known as the isocyanide test, the carbyl amine test is a chemical reaction utilized to detect primary aliphatic and aromatic amines. The test is quite distinctive due to the strong and unpleasant smell of the isocyanides formed in the reaction.

The process involves heating the suspect amine with chloroform (CHCl_3) and an alkali like KOH or NaOH. Primary amines react to form the malodorous isocyanides, a reaction that secondary and tertiary amines do not undergo due to the absence of a hydrogen atom bonded to the nitrogen atom.

Results of the Carbyl Amine Test

This reaction is denoted by the sharp, 'fishy' smell, serving as a qualitative measure of primary amines' presence. This test offers a simple and quick method to distinguish primary amines from secondary and tertiary ones, with the added benefit of separating them based on their chemical reactivity.