Sulfanilic acid (4-aminobenzenesulfonic acid) is an organic compound with the formula H₃NC₆H₄SO₃. It is an off-white solid. It is a zwitterion, which explains its high melting point. 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 the sulfonation of

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile startin ...

with concentrated sulfuric acid.Siegfried Hauptmann: ''Organische Chemie'', 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 511, . This proceeds via phenylsulfamic acid; a zwitterion 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, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...

, which then reacts with aniline at the para position in manner similar to a

Bamberger rearrangement The Bamberger rearrangement is the chemical reaction of phenylhydroxylamines with strong aqueous acid, which will rearrange to give 4-aminophenols. It is named for the German chemist Eugen Bamberger (1857–1932). The starting phenylhydroxylami ...

Synthetic route of sulfanilic acid from aniline

Applications

As the compound readily forms

diazo The diazo group is an organic moiety consisting of two linked nitrogen atoms ( azo) at the terminal position. Overall charge neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes ...

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 . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolubl ...

and

nitrite The nitrite 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 nitrite also re ...

ions by diazonium coupling reaction with N-(1-Naphthyl)ethylenediamine, resulting in an azo dye, and the concentration of

ions were deduced from the color intensity of the resulting red solution by

colorimetry Colorimetry is "the science and technology used to quantify and describe physically the human color perception". It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...

. It is also used as a standard in

combustion analysis Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions where the resul ...

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 Methyl orange is a pH indicator frequently used in titration because of its clear and distinct color variance at different pH values. Methyl orange shows red color in acidic medium and yellow color in basic medium. Because it changes color at the ...

(azo coupling with dimethylaniline) *

Acid orange 7 Acid Orange 7, also known as 2-naphthol orange is an azo dye. It is used for dyeing wool. It is produced by azo coupling of β-naphthol and diazonium derivative of sulfanilic acid Sulfanilic acid (4-aminobenzenesulfonic acid) is an organic co ...

(azo coupling with 2-naphthol). * Chrysoine resorcinol (azo coupling with resorcinol)

References

{{Authority control Benzenesulfonic acids Anilines

Synthesis

Applications

Environmental aspects

Derivatives

See also

References