Sulfanilic acid (4-aminobenzenesulfonic acid) is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula H₃NC₆H₄SO₃. It is an off-white solid. It is a

zwitterion In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively and negatively charged functional groups. : (1,2- dipolar compounds, such as ylides, are sometimes excluded from ...

, which explains its high

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

. It is a common building block in organic chemistry."Sulphanilic acid". ''A Dictionary of Chemistry''. Oxford University Press, 2000. Oxford Reference Online. Oxford University Press.

Synthesis

Sulfanilic acid can be produced by sulfonation of

aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...

with concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

.Siegfried Hauptmann: ''Organische Chemie'', 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 511, . This proceeds via phenylsulfamic acid; a

with a N-S bond. Eugen Bamberger originally proposed a mechanism involving a series of intramolecular rearrangements, with phenylsulfamic acid forming orthanilic acid, which rearranged to sulfanilic acid on heating. Subsequent radiosulphur studies showed that the process is intermolecular, with the phenylsulfamic acid desulfating to generate

sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most conomicallyimportant sulfur oxide". It is prepared on an industrial scale as a precursor to ...

, which then reacts with aniline at the para position in manner similar to a Bamberger rearrangement. : Synthetic route of sulfanilic acid from aniline

Synthetic route of sulfanilic acid from aniline

Applications

As the compound readily forms diazo compounds, it is used to make dyes and sulfa drugs. This property is also used for the quantitative analysis of

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

and

nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

ions by diazonium coupling reaction with N-(1-Naphthyl)ethylenediamine, resulting in an

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C l ...

, and the concentration of

ions were deduced from the color intensity of the resulting red solution by colorimetry. : Formation of the diazonium derivative of sulfanilic acid

Formation of the diazonium derivative of sulfanilic acid

It is also used as a standard in combustion analysis and in the Pauly reaction.

Environmental aspects

Reflecting its wide use, sulfanilic acid is found in the leachates of landfills. It is produced by reduction of some azo dyes.

Derivatives

* Methyl orange (azo coupling with dimethylaniline) * Acid orange 7 (azo coupling with 2-naphthol). * Chrysoine resorcinol (azo coupling with

resorcinol Resorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or ''meta- (chemistry), meta''-isomer). Resorcinol crystallizes from benzene as co ...

)

References

{{Authority control Benzenesulfonic acids Anilines

Synthesis

Applications

Environmental aspects

Derivatives

See also

References