aniline

aniline
Name	Aniline
Caption	Structural formula of aniline
IUPAC name	Benzenamine
Other names	Phenylamine; Aminobenzene
Formula	C6H7N
Molar mass	93.13 g·mol−1
Appearance	Colorless to brown oily liquid
Density	1.021 g·cm−3
Melting point	−6.2 °C
Boiling point	184.13 °C
Solubility	Slightly soluble in water; miscible with organic solvents
Refractive index	1.586 (20 °C)

aniline is an aromatic amine consisting of a phenyl group attached to an amino group, with the molecular formula C6H5NH2. It is a primary intermediate in the manufacture of dyes, pharmaceuticals, and agrochemicals, and serves as a building block in organic synthesis. The compound is historically significant in the development of the synthetic dye industry and remains important in contemporary chemical manufacturing.

Structure and properties

The molecule comprises a six-membered Benzene ring bonded to an amino substituent, adopting resonance-stabilized structures that delocalize the lone pair on nitrogen into the aromatic system, affecting basicity and reactivity. Physical properties include a boiling point around 184 °C and a density near 1.02 g·cm−3; it is a colorless to brown oily liquid that oxidizes on exposure to Air and light, often acquiring a brown tint. Electronic effects from the amino substituent influence electrophilic aromatic substitution patterns, directing ortho and para positions relative to the substituent; these patterns are central to transformations used by manufacturers such as BASF, Dow Chemical Company, Eastman Chemical Company, and DuPont. Spectroscopic signatures include characteristic absorptions in IR for N–H stretching and distinct peaks in 1H NMR and 13C NMR, while Mass spectrometry fragments reflect loss of the amino group and phenyl fragments, important for analysts at institutions like SRI International, Sandia National Laboratories, and universities such as Massachusetts Institute of Technology, University of Cambridge, and Stanford University.

Production and synthesis

Industrial production historically involved reduction of nitrobenzene via catalytic hydrogenation using catalysts developed by firms and researchers linked to Bayer AG and ICI; modern processes employ hydrogenation over metals like palladium, platinum, iron, or catalytic systems optimized by companies such as Haldor Topsoe and Johnson Matthey. Alternative methods include the reduction of diazonium salts in reactions first studied by chemists associated with Friedrich Wöhler and Justus von Liebig, and methods using hydride reagents in laboratory practice taught at institutions like University of Oxford. Synthesis routes are integrated into larger value chains for dye manufacture at historical centers such as Leverkusen and Duisburg, and for pharmaceutical intermediates in clusters in Basel and Shanghai. Process safety, catalyst recovery, and waste minimization have been addressed by regulators and organizations including the European Chemicals Agency and the United States Environmental Protection Agency.

Chemical reactions and derivatives

Aniline participates in electrophilic aromatic substitution to give diazonium salts via nitrosation, enabling coupling reactions that led to important dyes such as those discovered by William Henry Perkin; diazonium chemistry links to syntheses of azo dyes and compounds used by firms like Clariant and Dystar. Acylation of the amino group yields amides (e.g., acetanilide), transformations studied by researchers at Harvard University and University of California, Berkeley. Oxidation can produce azobenzene and quinone imines, reactions relevant to pigment manufacture at companies like Huntsman Corporation. Derivatization includes nitration, sulfonation, and alkylation to produce materials for DuPont-era fibers, and reduction pathways furnish substituted anilines that serve as precursors to pharmaceuticals developed by organizations such as Pfizer, Roche, GlaxoSmithKline, and Merck & Co..

Uses and applications

Principal uses include production of methylene blue and a broad class of azo dyes that transformed textile industries connected historically to cities like Manchester and Essen. Aniline derivatives are central to pharmaceuticals, agrochemicals, rubber processing chemicals, and antioxidants utilized by manufacturers such as Goodyear and Bridgestone. It is a precursor to polyurethane catalysts and pesticides developed by companies like Bayer and Syngenta. Research institutions and corporations including AstraZeneca, Novartis, and Eli Lilly and Company employ aniline chemistry in medicinal chemistry programs for lead optimization. Laboratory reagents and intermediates derived from aniline support methodologies published in journals affiliated with societies such as the American Chemical Society and the Royal Society of Chemistry.

Safety and environmental impact

Aniline is toxic by inhalation, ingestion, and skin absorption, causing methemoglobinemia and lesions described in clinical reports from hospitals such as Mayo Clinic and Johns Hopkins Hospital; occupational exposure limits are set by agencies including OSHA and NIOSH. Environmental releases have been regulated under frameworks administered by the EPA and the European Commission, with contamination incidents investigated by state authorities and remediation performed by contractors certified under programs associated with UNEP and regional agencies. Wastewater containing aniline is treated by chemical oxidation, biodegradation in activated sludge systems informed by research at Eawag, and advanced oxidation processes deployed by engineering firms like AECOM and Bechtel. Chronic exposure studies have been conducted in laboratories affiliated with National Institutes of Health and international toxicology panels advising the World Health Organization.

History and etymology

The compound was first isolated from indigo-bearing materials and coal-tar derivatives during the 19th century, with early work by chemists such as Friedlieb Runge and August Wilhelm von Hofmann contributing to characterization and naming; the term derives from the Latin anil meaning indigo, itself traced to trade routes involving ports like Lisbon and Calcutta. Aniline played a foundational role in the birth of the synthetic dye industry after William Henry Perkin's discovery of mauveine, transforming textile manufacturing in urban centers including London and Berlin and spurring enterprises like BASF and Hoechst. Subsequent developments in industrial chemistry and organic synthesis at universities such as Heidelberg University and ETH Zurich expanded applications into pharmaceuticals and materials that characterize modern chemical industry clusters in Ruhr (region) and the Yangtze River Delta.

Category:Anilines