Master gas-phase vs aqueous basicity order of aliphatic amines and synthetic conversions via benzene diazonium chloride.
Amines are nitrogen-containing organic compounds derived from ammonia. This chapter covers preparation methods, basicity trends, qualitative chemical distinction tests, and synthetic applications of diazonium salts.
Basicity Order of Amines: Nitrogen lone pair availability determines basic strength. In gas phase, basic strength follows 3° > 2° > 1° > NH3. In aqueous solution, due to combined inductive, solvation, and steric effects, the order for methyl-substituted amines is 2° > 1° > 3° > NH3 (213), and for ethyl-substituted amines is 2° > 3° > 1° > NH3 (231). Aniline is far weaker than ammonia due to resonance delocalization of lone pair into benzene ring.
Distinction Tests: Hinsberg Test (Benzenesulphonyl chloride) distinguishes 1°, 2°, and 3° amines. Primary aliphatic amines form soluble salts in alkali; secondary amines form insoluble precipitates; tertiary amines do not react.
Benzene Diazonium Chloride (Ar-N2+ Cl-): Formed by diazotization of primary aromatic amines with NaNO2 + HCl at 0-5 °C. Serves as a versatile synthetic intermediate for Sandmeyer reaction, Gattermann reaction, Iodination, Fluorination (Balz-Schiemann), and Azo dye coupling reactions. Dr. Aarzoo Saini details synthetic roadmaps at We-Gyaan Classes.
Key Takeaways for Students
- Memorize aqueous basicity orders: 213 for methyl-substituted amines, 231 for ethyl-substituted amines.
- Use Hinsberg test to differentiate primary, secondary, and tertiary amines.
- Perform diazotization strictly between 0 and 5 °C to prevent decomposition to phenol.
- Master azo dye coupling reactions with phenol (orange dye) and aniline (yellow dye).
Authored by Dr. Aarzoo Saini
Founder & Lead Educator at We-Gyaan Classes Roorkee, with over 20 years of teaching excellence in Science and Chemistry for Board Exams, NEET, JEE, and CUET.