Amines Identification

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Identification of Primary Amines

Amines are classified into different categories namely, primary, secondary, and tertiary depending on the number of carbons which are bonded directly to the nitrogen atom. Primary amines have just one carbon that is bonded to the nitrogen. Secondary amines, on the other hand, have two carbons which are bonded to the nitrogen. And lastly, the tertiary amines have three carbons that are bonded to the nitrogen. The system of classification of all these amines is superficially similar in the way we have classified alcohols. 

However, the important difference is that in alcohols we count bonds to the carbon that carry the OH group. In the case of amines, we count the carbons which are bonded to the nitrogen. All of these primary, secondary and tertiary amine show varying chemical properties and have observable physical changes. They have their uses typically in the commercial and industrial applications. Today, we will learn about the identification of primary amine, secondary amine, tertiary amine, the primary amine, secondary aromatic amine and tertiary amine definition, and the primary, secondary, tertiary amine formula.

Structure of Primary Amine, Secondary Amine, Tertiary Amine

Let us look at how primary amine and secondary amine and tertiary aromatic amine look like. Take a look at the figure given below.

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Properties of Primary and Secondary Amines

Amines, irrespective of them being primary, secondary, or tertiary amine groups, usually have specific distinct properties about them, for example, their characteristic odours. These odours usually resemble that of rotten eggs or fishes. Aliphatic amines are known to be less dense than water and are stronger bonds of ammonia compared to the aromatic amines. 

The major industrial applications of the primary, secondary amine are to make dyes, rubber, synthetic fibres and resins, and pharmaceuticals. However, specific tests are done for the identification of primary amines, secondary amines, and tertiary amines. Amongst the most popular tests is the Hinsberg test. The reaction which is produced from this test is known as the Hinsberg reaction. Let us learn about the Hinsberg test and Hinsberg reaction in detail.

Hinsberg Test

The Hinsberg test is a test to identify the primary, secondary and tertiary amines. In this test, the given amine is to be shaken well along with Hinsberg reagent in the presence of an aqueous alkali, which can be either NaOH or KOH. Then, a reagent constituting of benzenesulfonyl chloride and an aqueous sodium hydroxide solution is to be added to a substrate. A primary amine will tend to form a soluble sulfonamide salt. Acidification of this salt precipitates then the sulfonamide of this primary amine. A secondary amine is to undergo the same reaction which will directly tend to form an insoluble sulfonamide. A tertiary amine, however, will not react with the sulfonamide but it is insoluble. On adding dilute acid, this particular insoluble amine gets converted to a soluble ammonium salt. In this manner, the reaction can distinguish between all the three types of amines.

You must know that the tertiary amines can react with the benzenesulfonyl chloride under various conditions since the Hinsberg test described above is not absolute. However, the Hinsberg test for identification of different types of amines is only valid when the reaction speed, temperature, concentration, and solubility are taken into consideration.

The Hinsberg reaction is shown in the figure below.

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Hence, the Hinsberg test is highly effective for the identification of primary amines, secondary amines, and tertiary amines. Amines are generally used for many different purposes, for example, a great variety of different medicines, photographs, etc. not only this but also the amine used for the synthesis of insecticides and rocket propellants. Hence, amines have an entire host of several different uses in the industry apart from their traditional chemical uses. Amines also have their use in the heavy-duty military functions, for example, the production of synthetic fibres, and the production of Kevlar. This is known to be the main component in making bulletproof vests and helmets to protect the soldiers in warfare.

FAQ (Frequently Asked Questions)

1. What are the different chemical reactions involved to identify Primary, Secondary and Tertiary Amines?

Ans: The primary, secondary and tertiary amines are identified and distinguished with the help of Hinsberg's test. In this test, amines are reacted with the Hinsberg's reagent, which is benzenesulphonyl chloride (C6H5SO2Cl). All three types of amines tend to react differently to the Hinsberg's reagent. Hence, they can be easily identified with the help of Hinsberg's reagent.

The primary amines react with the benzenesulphonyl chloride and form N-alkylbenzenesulphonyl amide. This is soluble in alkalis.

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As a strong electron-withdrawing sulphonyl group is present in the sulphonamide, the H-atom which is attached to nitrogen is easily released as a proton. Hence, it is acidic and tends to get dissolved in the alkali.

Secondary amines on the other hand tend to react with the Hinsberg's reagent and produce a sulphonamide. This is insoluble in alkali.

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There is no hydrogen atom which is attached to the N-atom in sulphonamide. Hence, it is not acidic and is insoluble in alkali.

On the other hand, the tertiary amines do not tend to react with the Hinsberg's reagent at all.

2. List all the Secondary Amines.

Ans: The secondary amine is amine wherein the amino group tends to directly bond to two carbons of any hybridization. However, these carbons cannot be of the carbonyl group carbons. The secondary amines have two organic substituents, alkyl, an aryl, or even both, that are attached to the nitrogen along with one hydrogen atom. The list of some of the secondary amines is given as follows. These contain both the names and the nomenclatures of the secondary amines.

  1. Dimethylamine

  2. Diphenylamine 

  3. Cyclen

  4. N,N′-Diisopropylethylenediamine

  5. N,N′-Diisopropyl-1,3-propanediamine

  6. N,N′-Dimethyl-1,3-propanediamine

  7. N,N′-Diphenyl-p-phenylenediamine

  8. 2-Isopropyl-2-oxazoline

  9. 1,4,8,12-Tetraazacyclopentadecane

  10. 1,4,8,11-Tetraazacyclotetradecane-5,7-dione

These are some of the examples of secondary amines.