82-75-7

Dark green powder

Intermediate of dyestuff

Naphthalene is converted to naphthalene-1-sulfonic acid. The crude sulfonation product is diluted with sulfuric acid, and 67.5 % nitric acid is added slowly at 30℃ to give the 5- and 8-nitro derivatives. The products are converted to the readily soluble magnesium salts by addition of a slurry of dolomite. The reaction mixture is neutralized with chalk and filtered hot. The filtrate is run into a suspension of iron powder in boiling water, which is kept slightly acidic with sulfuric acid. When reduction is complete, dissolved iron is precipitated by addition of magnesia, the iron residues are filtered off while hot, and the resulting liquor is acidified to pH 4.5 with sulfuric acid to give 99 % pure Peri acid in 48 % yield. The filtrates are further acidified to precipitate crude Laurent’s acid. This may be purified via its magnesium salt to give a 17 % yield of pure 1,5-isomer.