9.6.6. Reaction with arylsulphonyl chloride

Benzenesulphonyl chloride (C6H5SO2Cl), which is also known as Hinsberg’s reagent, reacts with primary and secondary amines to form sulphonamides.

Benzenesulphonyl chloride, commonly called Hinsberg's reagent, is a chemical compound that plays a vital role in identifying and differentiating between primary and secondary amines. When this reagent reacts with amines, it produces sulphonamides, which are formed from this chemical interaction. Understanding the nature of this reaction is crucial for distinguishing between types of amines.

Think of Hinsberg's reagent like a specific test for understanding different types of amines. Just as a teacher grades students based on their assignments to see who has done well, this reagent helps chemists identify whether an amine is primary or secondary based on how they react.

(a) The reaction of benzenesulphonyl chloride with primary amine yields N-ethylbenzenesulphonyl amide.

When benzenesulphonyl chloride reacts with primary amines, the result is the formation of a sulphonamide. In this case, for a primary amine like ethylamine, the product is N-ethylbenzenesulphonyl amide. This means that the nitrogen atom from the amine gets bonded to the sulphonyl group (–SO2), resulting in a new compound that has distinct properties.

Imagine a puzzle where one piece (the primary amine) fits perfectly with another piece (benzenesulphonyl chloride) to create a new picture (the sulphonamide). This new picture represents a unique compound made from the initial pieces.

The hydrogen attached to nitrogen in sulphonamide is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.

Sulphonamides, resulting from the reaction between primary amines and benzenesulphonyl chloride, contain a hydrogen atom attached to the nitrogen. This hydrogen bond becomes quite acidic due to the influence of the sulphonyl group that withdraws electron density from the nitrogen. As a consequence, sulphonamides can dissolve in alkaline solutions, which is a useful property in various chemical processes.

Picture pouring sugar into a cup of coffee. When you add sugar (the sulphonyl group) to the coffee (the nitrogen), the coffee becomes sweet (the acidity of the hydrogen) because of the interaction, making it more enjoyable and easier to drink (the solubility in alkali).

(b) In the reaction with secondary amine, N,N-diethylbenzenesulphonamide is formed.

When benzenesulphonyl chloride reacts with secondary amines, it leads to the formation of N,N-diethylbenzenesulphonamide. Here, both ethyl groups attached to the nitrogen come from the secondary amine, resulting in a compound that does not contain any hydrogen atoms attached to nitrogen, which influences its chemical behavior.

Think of secondary amines as a special dining table that can only accommodate a certain number of guests (the two ethyl groups). When you invite the benzenesulphonyl chloride to the table (the reaction), you end up with a unique and complete dining experience (the sulphonamide), which is different from when you invite a primary amine.

(c) Tertiary amines do not react with benzenesulphonyl chloride.

Tertiary amines, which have three organic groups attached to the nitrogen atom, do not participate in the reaction with benzenesulphonyl chloride, unlike primary and secondary amines. This lack of reactivity is because there is no hydrogen atom on the nitrogen that can participate in forming sulphonamides.

Imagine a three-tiered cake (the tertiary amine). Since all the tiers (the organic groups) are already covered (attached to the nitrogen), there's no room to add frosting (the sulphonamide formation) like you can with a two-tiered or single-tier cake (the primary and secondary amines).

This property of amines reacting with benzenesulphonyl chloride in a different manner is used for the distinction of primary, secondary and tertiary amines and also for the separation of a mixture of amines.

The unique way in which primary, secondary, and tertiary amines react with benzenesulphonyl chloride provides a crucial method for distinguishing between these types of amines in a mixture. This distinction is important in synthesizing compounds and purifying chemical mixtures.

Consider a chemistry lab where different colored liquids represent the different amines. When you add a reagent (benzenesulphonyl chloride), it acts like a filter that shows you which colors belong to which group, helping you separate and identify each liquid accurately.

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