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Naphthalene-2,6-disulfonic Acid can be used in in geothermal reservoirs as new fluorescent tracers.

ChEBI: Naphthalene-2,6-disulfonic acid is a naphthalenesulfonic acid.

Naphthalene is added to sulfuric acid – monohydrate (SO3 H2O) mixture at 135 ℃, and the reaction is completed by heating at 170 – 175 ℃ for 5 h. After quenching in water, the disodium salt of Naphthalene-2,6-disulfonic acid is precipitated at 90 C by adding sodium chloride and sodium sulfate. Filtration at 95℃ followed by washing with sodium sulfate solution gives the required product, free from the 2,7-isomer, in 21 % yield. The 2,7-isomer is then isolated from the filtrates.