Chemistry:Armstrong's acid

Armstrong's acid

Names
Preferred IUPAC name Naphthalene-1,5-disulfonic acid
Other names Armstrong's acid
Identifiers
CAS Number	81-04-9 Y
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30890 Y
ChemSpider	6414 Y
PubChem CID	6666
UNII	E8FPK78470 Y
InChI InChI=1S/C10H8O6S2/c11-17(12,13)9-5-1-3-7-8(9)4-2-6-10(7)18(14,15)16/h1-6H,(H,11,12,13)(H,14,15,16) Y Key: XTEGVFVZDVNBPF-UHFFFAOYSA-N Y InChI=1/C10H8O6S2/c11-17(12,13)9-5-1-3-7-8(9)4-2-6-10(7)18(14,15)16/h1-6H,(H,11,12,13)(H,14,15,16) Key: XTEGVFVZDVNBPF-UHFFFAOYAR
SMILES O=S(C2=CC=CC1=C(S(=O)(O)=O)C=CC=C12)(O)=O O=S(=O)(O)c1cccc2c1cccc2S(=O)(=O)O
Properties
Chemical formula	C10H8S2O6
Molar mass	288.299 g/mol
Appearance	colorless solid
Hazards
Main hazards	corrosive
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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Armstrong's acid (naphthalene-1,5-disulfonic acid) is a fluorescent organic compound with the formula C₁₀H₆(SO₃H)₂. It is one of several isomers of naphthalenedisulfonic acid. It a colorless solid, typically obtained as the tetrahydrate. Like other sulfonic acids, 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:

C₁₀H₈ + 2 SO₃ → C₁₀H₆(SO₃H)₂

Further sulfonation gives The 1,3,5-trisulfonic acid derivative.

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. 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 for forming salts of basic 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 CFT. The disodium salt is also used as an electrolyte in certain kinds of chromatography.