119-79-9

Purple Solid

Fluorescent reagent.

Intermediate of dyestuff

ChEBI: 5-aminonaphthalene-2-sulfonic acid is an aminonaphthalenesulfonic acid.

Sulfonation of 1-naphthylamine with concentrated sulfuric acid at 130℃ gives mainly 1-aminonaphthalene-6-sulfonic acid. However, the latter is always made, together with the 1,7-isomer, by nitration of naphthalene-2-sulfonic acid to give the mixed 5- and 8- nitronaphthalene-2-sulfonic acids follwed by reduction to ‘‘mixed Cleve’s acids.’’ A b-sulfonation mass is diluted with sulfuric acid, then 67.5 % nitric acid is added slowly at 34℃. After being quenched and neutralized with calcium carbonate, the filtered liquor is reduced by boiling with iron powder, slight acidity being maintained with sulfuric acid. After basification with magnesia the iron residues are filtered off and the filtrate is evaporated until the magnesium salt of the product crystallizes on cooling. Filtration followed by washing with magnesium sulfate gives a 34 % yield of the magnesium salt of 1,6-Cleve’s acid. Purification by dissolution in hot water, acidification, and filtration of the free acid while hot reduce the yield to 25 % based on naphthalene.