Formula sheet: Amines
Amines12 min readLesson 1 of 5
1.1 Preparation routes
| Route | Reagents and conditions | Product |
|---|---|---|
| Ammonolysis | Alkyl halide with excess ammonia, sealed tube, heat | Mixture of primary, secondary, tertiary amine and quaternary salt |
| Reduction of nitriles | Nitrile with LiAlH4, or H2 with Ni, or Na and alcohol | Primary amine with the same number of carbons |
| Reduction of amides | Amide with LiAlH4 | Primary amine |
| Hofmann bromamide | Amide with Br2 and concentrated NaOH | Primary amine with one carbon less |
| Gabriel phthalimide | Phthalimide with KOH, then alkyl halide, then hydrolysis | Pure primary amine |
| Reduction of nitro compounds | Nitro compound with H2 and Ni, or Sn and HCl, or Fe and HCl | Primary aromatic amine |
| Reduction of oximes | Oxime with LiAlH4 or Na and alcohol | Primary amine |
| From acid azides and amides | Curtius and Schmidt reactions | Primary amine |
1.2 Reactions with name labels
| Reaction | What happens |
|---|---|
| Hinsberg test | Benzenesulphonyl chloride with an amine; primary gives a product soluble in alkali, secondary gives an insoluble product, tertiary gives no reaction |
| Carbylamine test | Primary amine with chloroform and alcoholic KOH gives an isocyanide with a foul smell |
| Acetylation | Amine with acid chloride or anhydride gives an amide |
| Diazotisation | Aromatic primary amine with NaNO2 and HCl at 273 to 278 K gives a diazonium salt |
| Sandmeyer | Diazonium salt with CuCl or CuBr gives aryl chloride or bromide |
| Gattermann | Diazonium salt with HCl or HBr in the presence of copper powder gives aryl halide |
| Coupling | Diazonium salt with phenol or aniline gives an azo dye |
| Hofmann elimination | Quaternary ammonium hydroxide heated gives the less substituted alkene |
1.3 Basicity data
The strength of an amine is measured by Kb or by pKb, and a lower pKb means a stronger base. In aqueous solution the usual order for the methylamines is secondary above primary above ammonia above tertiary, because solvation of the ammonium ion and steric hindrance to hydrogen bonding pull in opposite directions. In the gas phase the order is tertiary above secondary above primary above ammonia, because there is no solvent to hydrogen bond the ion.