arylamino

Arylamino refers to a nitrogen-containing substituent in which an aryl group is bonded to nitrogen. In practice, arylamino compounds include arylamines such as Ar-NH2 and their substituted derivatives Ar-NHR, Ar-NR2, where Ar denotes an aryl group (commonly a phenyl ring). The term is used to describe the arylamino functional group present in many organic molecules, including dyes, pharmaceuticals, and ligands.

Synthesis and occurrence: Arylamines are most commonly prepared by reduction of nitroarenes to give Ar-NH2. They can also be formed via Buchwald–Hartwig amination, where an aryl halide couples with ammonia or an amine, or by reductive amination of aryl aldehydes. The arylamino group is prevalent in industrially important compounds, especially anilines used as precursors to dyes and polymers.

Properties and reactivity: The lone pair on nitrogen in arylamino groups is conjugated with the attached aryl ring, which reduces basicity compared with aliphatic amines. Substituents on the aryl ring can modulate both basicity and nucleophilicity: electron-donating groups increase the electron density on nitrogen, while electron-withdrawing groups decrease it. The N–H bond in primary arylamines is moderately acidic for an amine, and secondary and tertiary arylamines display varying steric and electronic effects that influence their reactivity.

Applications: Arylamines are key intermediates in the production of dyes (notably azo dyes), pharmaceuticals, and polymers. They also serve as ligands in coordination chemistry and as building blocks in organic synthesis for more complex molecules.

Safety: Some arylamines and their derivatives can be toxic or carcinogenic, with certain industrial arylamines requiring careful handling, containment, and waste management. Proper safety data and regulations apply to their use and disposal.