Armstrong's acid (naphthalene-1,5-disulfonic acid) is a fluorescent organic compound with the formula C₁₀H₆(SO₃H)₂. It is one of several

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

s of naphthalenedisulfonic acid. It a colorless solid, typically obtained as the tetrahydrate. Like other

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s, it is a strong acid. It is named for British chemist Henry Edward Armstrong.

Production and use

It is prepared by disulfonation of naphthalene with

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: :C₁₀H₈ + 2 SO₃ → C₁₀H₆(SO₃H)₂ Further sulfonation gives The 1,3,5-trisulfonic acid derivative.Gerald Booth "Naphthalene Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. .

Reactions and uses

Fusion of Armstrong's acid in NaOH gives the disodium salt of 1,5-dihydroxynaphthalene, which can be acidified to give the

diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. The most common industrial diol is e ...

. The intermediate in this hydrolysis, 1-hydroxynaphthalene-5-sulfonic acid, is also useful. Nitration gives nitrodisulfonic acids, which are precursors to amino derivatives. The disodium salt is sometimes used as a divalent

counterion 160px, Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion.">cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typical ...

for forming salts of

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drug compounds, as an alternative to the related mesylate or tosylate salts. When used in this way such a salt is called a naphthalenedisulfonate salt, as seen with the most common salt form of the stimulant drug

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. The disodium salt is also used as an electrolyte in certain kinds of chromatography.Shigeru Terabe "Electrokinetic chromatography: An interface between electrophoresis and chromatography" TrAC Trends in Analytical Chemistry 1989, Volume 8, pp. 129–134.

References

{{DEFAULTSORT:Armstrong's Acid Reagents for organic chemistry Naphthalenesulfonic acids