Organic Compounds Containing Nitrogen - Methods of preparation and properties

Classification of Amines: Nitrogen compounds are classified as primary ($1^\circ$), secondary ($2^circ$), and tertiary ($3^\circ$) based on the number of alkyl or aryl groups attached to the nitrogen atom: $RNH_2$, $R_2NH$, and $R_3N$.

Preparation from Nitro Compounds: Nitro compounds are reduced to amines using hydrogen gas in the presence of finely divided nickel, palladium, or platinum, or by using metals in acidic medium like $Sn/HCl$ or $Fe/HCl$.

Gabriel Phthalimide Synthesis: This method is used for the preparation of pure primary aliphatic amines. Phthalimide reacts with ethanolic $KOH$ to form potassium phthalimide, which then reacts with an alkyl halide followed by alkaline hydrolysis.

Hofmann Bromamide Degradation Reaction: An amide is treated with bromine in an aqueous or ethanolic solution of sodium hydroxide, resulting in a primary amine with one carbon atom less than the parent amide: $R-CONH_2 \rightarrow R-NH_2$.

Basic Character of Amines: Amines are basic due to the presence of a lone pair of electrons on the nitrogen atom. In the aqueous phase, the basic strength order for methyl-substituted amines is $(CH_3)_2NH > CH_3NH_2 > (CH_3)_3N > NH_3$.

Carbylamine Reaction: Aliphatic and aromatic primary amines, when heated with chloroform and ethanolic potassium hydroxide, form isocyanides (carbylamines) which have a foul smell. This serves as a test for primary amines.

Hinsberg's Test: Used to distinguish between $1^\circ$, $2^\circ$, and $3^\circ$ amines using benzenesulfonyl chloride ($C_6H_5SO_2Cl$). $1^\circ$ amines form a precipitate soluble in alkali; $2^\circ$ amines form a precipitate insoluble in alkali; $3^\circ$ amines do not react.

Diazonium Salts: Formed by the reaction of aniline with nitrous acid ($NaNO_2 + HCl$) at $273-278 K$. They are vital intermediates for synthesizing substituted benzene derivatives via Sandmeyer or Gattermann reactions.