Chapter 27: Organic Nitrogen Compounds

Organic Nitrogen Compounds explores organic nitrogen compounds, detailing the structure, synthesis, and reactions of amines, amides, and biologically vital amino acids. Amines are categorized as primary, secondary, or tertiary and exhibit basic properties because the nitrogen atom’s lone pair of electrons is available to accept a proton, leading to the formation of salts. The relative basicity varies significantly; alkyl amines, such as ethylamine, are stronger bases than ammonia due to the electron-donating positive inductive effect of the alkyl group, which enhances the lone pair's availability. Conversely, phenylamine is a weaker base than ammonia because the nitrogen lone pair is delocalized into the aromatic ring structure, diminishing its ability to bond with a proton. Alkyl amines can be prepared by reacting ammonia with halogenoalkanes or through the reduction of nitriles or amides, often using lithium tetrahydridoaluminate in dry ether or hydrogen over a nickel catalyst. Phenylamine is specifically synthesized by reducing nitrobenzene using tin and concentrated hydrochloric acid, followed by treatment with aqueous alkali. A major application of phenylamine is in the synthesis of azo dyes, which begins with diazotisation—the reaction with unstable nitric(III) acid to form a diazonium salt, a process critically maintained below ten degrees Celsius to prevent decomposition. This diazonium ion then participates in an electrophilic coupling reaction with an aryl compound like phenol to form the stable, highly colored azo dye, which is characterized by the central nitrogen double bond nitrogen group linking two rings. The chapter also examines amides, which are notably weaker bases than amines because the lone pair on the nitrogen is pulled toward the electron-withdrawing oxygen atom. Amides are formed from acyl chlorides and can be broken down by hydrolysis using either acid or alkali. Finally, the chapter introduces amino acids, which are amphoteric compounds containing both a basic amino group and an acidic carboxylic acid group. In solution, they exist primarily as zwitterions, carrying both positive and negative charges internally, which explains their nature as soluble crystalline solids. Amino acids condense to form dipeptides and tripeptides via the formation of an amide link, known as a peptide bond, through the elimination of water. The separation of these charged species is achieved through electrophoresis, an analytical technique where ions migrate in an electric field; this separation is highly dependent on controlling the solution's pH, especially relative to the amino acid's isoelectric point where its net charge is zero.