Armstrong's acid (naphthalene-1,5-disulfonic acid) is a fluorescent

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 C₁₀H₆(SO₃H)₂. It is one of several

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

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

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

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

oleum Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Ol ...

: :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 may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...

. 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 In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemica ...

counterion 160px, cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion. In chemistry, a counterion (sometimes written as "counter ...

for forming salts of

basic Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...

drug compounds, as an alternative to the related

mesylate In organosulfur chemistry, a mesylate is any salt or ester of methanesulfonic acid (). In salts, the mesylate is present as the anion. When modifying the international nonproprietary name of a pharmaceutical substance containing the gr ...

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 CFT. The disodium salt is also used as an electrolyte in certain kinds of

chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...

.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