Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.
Solution and Explanation
Primary, secondary and tertiary amines can be identified and distinguished by Hinsberg's test. In this test, the amines are allowed to react with Hinsberg's reagent, benzenesulphonyl chloride (C6H5SO2Cl). The three types of amines react differently with Hinsberg's reagent. Therefore, they can be easily identified using Hinsberg's reagent.
Primary amines react with benzenesulphonyl chloride to form N-alkylbenzenesulphonyl amide which is soluble in alkali.
Due to the presence of a strong electron-withdrawing sulphonyl group in the sulphonamide, the H-atom attached to nitrogen can be easily released as proton. So, it is acidic and dissolves in alkali.
Secondary amines react with Hinsberg's reagent to give a sulphonamide which is insoluble in alkali.
There is no H-atom attached to the N-atom in the sulphonamide. Therefore, it is not acidic and insoluble in alkali. On the other hand, tertiary amines do not react with Hinsberg's reagent at all
Top Questions on Amines
- Arrange the following compounds as asked:
(a) In decreasing order of pKb, values: C$_6$H$_5$NH$_2$, (C$_2$H$_5$)$_2$NH, C$_6$H$_5$NHCH$_2$CH$_3$, C$_6$H$_5$NH$_3$
(b) Increasing order of boiling point: C$_6$H$_5$OH, C$_2$H$_5$NH$_2$, (C$_2$H$_5$)$_2$NH, C$_6$H$_5$NH$_2$
(c) Increasing order of solubility in water: C$_6$H$_5$NH$_2$, (C$_2$H$_5$)$_2$NH, C$_6$H$_5$NHCH$_2$CH$_3$ - Give plausible explanation for each of the following:
Amides are less basic than amines. Amines are usually formed from amides, imides, halides, nitro compounds, etc. They exhibit hydrogen bonding which influences their physical properties. In alkyl amines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia. Amines being basic in nature, react with acids to form salts. Aryldiazonium salts, undergo replacement of the diazonium group with a variety of nucleophiles to produce aryl halides, cyanides, phenols and arenes.
How can you convert the following:
(i) Ethanoic acid to methanamine- Give the structures of A, B, and C in the following reaction sequences: (i)\; \(\mathrm{CH_3CH_2I} \xrightarrow[\ ]{\mathrm{NaCN}} A \xrightarrow[\ ]{\;\;HO^-\;/\;H_2O\;\;} B \xrightarrow[\;Br_2/NaOH\;]{} C\)
(ii)\; \(\mathrm{C_6H_5N_2^+Cl^-} \xrightarrow[\ ]{\mathrm{CuCN}} A \xrightarrow[\ ]{\;H_3O^+\;} B \xrightarrow[\ \Delta\ ]{\;NH_3\;} C\)
(iii)\; \(\mathrm{CH_3CH_2Br} \xrightarrow[\ ]{\mathrm{KCN}} A \xrightarrow[\ ]{\mathrm{LiAlH_4}} B \xrightarrow[\;273\,K\;]{\;HNO_2\;} C\) - How can you obtain the following?
(a) Aniline from ammonium benzoate
(b) Benzene diazonium chloride from nitrobenzene
(c) 2,4,6-Tribromoaniline from aniline
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Concepts Used:
Amines - Chemical Properties
There are many chemical properties of amines.
The primary and secondary amines, including several amine derivatives, have a direct impact on their properties due to the presence of hydrogen bonding. The compounds containing phosphorus have a lower boiling point and the compounds containing amines and alcohol have a higher boiling point. The structure of alkanols is immensely similar to that of amine except the presence of the hydroxyl group. In such a case, oxygen has a higher electronegativity than that of nitrogen, so alkanol compounds are more acidic in nature in comparison to the amines.
On account of the ability to form hydrogen bonds, the amines have tendencies of high solubility in water. The amine molecules such as Ethyl, diethyl, triethyl, and Methyl are gaseous in nature. Whereas, higher weight amines have a solid structure and alkyl amines have a liquid structure. There is an ammonia smell to gaseous amines and a fishy smell to liquid amines. The solubility of amines entirely depends upon the number of carbon atoms in the molecule.