Skip to content
qorganica.es qorganica.comOrganic Chemistry made transparent Course map Español

Topic 5Amines, anilines and other nitrogen functions

Amines are ammonia derivatives in which one or more hydrogens have been replaced by alkyl or aryl groups. The lone pair of the nitrogen explains their basicity and nucleophilicity, which dominate their chemistry. The topic also covers anilines and other nitrogen functions: nitroalkanes, isocyanates and azides.

YouTube video: structure and properties of amines▶ Watch the video on YouTube
YouTube video: amino acids▶ Watch the video on YouTube
YouTube video: basicity and nucleophilicity of nitrogen▶ Watch the video on YouTube

Amines

Biologically important amines: adrenaline (secondary amine) and norepinephrine (primary amine), hormones that stimulate the nervous system; nicotine, with an aromatic and a secondary amine; and the general formula of amino acids

Nomenclature

 Animation of the inversion of ammonia

Physical and Bond Properties of Amines

 Basicity of aniline (pKb = 9.4) and acidity of the anilinium ion (pKa = 4.6), with the resonance forms that delocalize the nitrogen lone pair to the ortho and para positions of the ring

Acid-Base Properties

 Gabriel synthesis: potassium phthalimide displaces the halide of R–X and hydrazine releases the primary amine R–NH₂ and phthalhydrazide

Preparation

 Double Hofmann degradation of 1,2-dimethylpiperidine: methylation with MeI, Ag₂O and heat open the ring; a second sequence gives 1,5-hexadiene

Reactivity

Anilines

Examples of aniline nomenclature: 3-ethylaniline, 4-nitroaniline, 3-chloro-5-methylaniline, o-, m- and p-phenylenediamine, 2-aminobenzoic and 3-aminobenzenesulfonic acids and 1,2,3- and 1,3,5-phenylenetriamine

Nomenclature

 Basicity of aniline (pKb = 9.4) and acidity of the anilinium ion (pKa = 4.6)

Physical Properties

 Reduction of nitrobenzene to aniline with Zn(Hg)/HCl, H₂/Ni or Fe/HCl, and the reverse oxidation with CF₃CO₃H: the nitro group is deactivating and meta-directing; the amino group, activating and ortho-para-directing

Preparation

 Arenediazonium salts, formed from anilines with NaNO₂/HCl, are converted into phenols (H₂O), iodides (HI), chlorides and bromides (CuX), nitriles (CuCN), fluorides (HBF₄), arenes (H₃PO₂) and azo compounds (with another arene)

Reactivity

Other Nitrogenated Functions

Preparation of 1-nitrooctane with AgNO₂ (83%) and acidity of nitromethane (pKa = 10): its conjugate base is resonance-stabilized by the nitro group

Nitroderivatives

 Reactions of isocyanates: with water they give carbamic acids, which lose CO₂ to give amines; with amines, ureas; with alcohols, carbamates (urethanes); and with diols, polyurethanes

Isocyanates

 Azides: opening of propylene oxide with NaN₃, formation of an acyl azide from an acyl chloride and reduction of an azide to an amine with LiAlH₄

Azides