Lesson 27 of 34
Track every carbon when preparing an amine
Nitrile and amide reduction keep the original carbonyl or nitrile carbon in the product chain.
A-Level 9476 (2026-2027)
I can prepare the specified amines.Syllabus
Syllabus 9476, 11.9(a). Prepare the specified amines.
I can describe amine salt formation.Syllabus
Syllabus 9476, 11.9(b). Describe amine salt formation.
Track every carbon when preparing an amine
Nitrile and amide reduction keep the original carbonyl or nitrile carbon in the product chain.
| Target | Starting compound and conditions | Product accounting |
|---|---|---|
| Ethylamine from an amide | Ethanamide, CH3CONH2; LiAlH4 in dry ether, then aqueous work-up. | CH3CONH2 + 4[H] → CH3CH2NH2 + H2O. Both carbons remain. |
| Ethylamine from a nitrile | Ethanenitrile, CH3CN; LiAlH4 in dry ether then work-up, or H2/Ni. | CH3CN + 4[H] → CH3CH2NH2. The nitrile carbon becomes CH2 next to nitrogen. |
| Phenylamine from nitrobenzene | Sn and concentrated HCl with heating, then aqueous NaOH. | The acidic reduction mixture contains phenylammonium salt; NaOH liberates C6H5NH2. |
The reduction of nitrobenzene is C6H5NO2 + 6[H] → C6H5NH2 + 2H2O. The reaction mixture is acidic, so the amine forms as its protonated salt. That is why you add NaOH afterwards to get the free amine. Reduction turns the NO2 group into NH2. It does not put nitrogen into the ring.
The lone pair on an amine nitrogen accepts H+ to form a salt: C2H5NH2 + HCl → C2H5NH3+Cl-. Phenylamine forms phenylammonium salts in the same way. Adding aqueous base reverses this. Switching between the neutral amine and its charged salt can help separate an amine from neutral organic impurities.
Worked exampleChoose the carbon count before the reagent
To make propylamine by nitrile reduction, should the starting nitrile be ethanenitrile or propanenitrile?
Try it first. Then show the worked stepsHide the worked steps
- Nitrile reduction preserves the nitrile carbon as a CH2 carbon.
- Propylamine has three carbons, so the nitrile must also have three.
- Propanenitrile is CH3CH2CN, not CH3CN.
Use propanenitrile, CH3CH2CN. Its reduction gives CH3CH2CH2NH2.
Check your understanding
Which reduction gives ethylamine, CH3CH2NH2?
Show the answer
Reducing ethanenitrile, CH3CN, with LiAlH4 in dry ether
The nitrile carbon becomes the CH2 next to nitrogen, so CH3CN gives CH3CH2NH2. Reducing ethanamide, CH3CONH2, would also work.