1,5-Naphthalenedisulfonic acid

Naphthalene-1,5-disulfonic acid [81-04-9]. Armstrong acid, C10H8O6S2, Mr 288.28, crystallizes as the tetrahydrate but dehydrates at 125 ℃ to give the anhydrous acid (mp 240 – 245℃). The disulfonic acid forms an anhydride when treated with oleum below 50℃. This anhydride reacts with ammonia to give a mixture of naphthalene-1,5-disulfonamide and naphthalene-1- sulfonamide-5-sulfonic acid. Treatment of the disodium salt of naphthalene-1,5-disulfonic acid with phosphorus pentachloride at 110℃ gives naphthalene-1,5-disulfonyl chloride (mp 184 ℃), which may also be prepared by chlorosulfonation of naphthalene. Reaction of an aqueous solution of naphthalene-1,5-disulfonic acid with bromide – bromate gives 1,5-dibromonaphthalene so readily that the yellow precipitate may be used to identify very low concentrations of the disulfonic acid.

The disodium salt of naphthalene-1,5- disulfonic acid gives 1-hydroxynaphthalene-5- sulfonic acid or 1,5-dihydroxynaphthalene (see Section 3.3) by fusion processes. Further sulfonation of the disulfonated reaction mixture gives naphthalene-1,3,5-trisulfonic acid, and nitration leads to 1- and 2-nitronaphthalene-4,8-disulfonic acids as intermediates to the corresponding aminonaphthalene disulfonic acids. Naphthalene-1,5-disulfonic acid is an important stabilizer for diazo compounds.

ChEBI: Naphthalene-1,5-disulfonic acid is a naphthalenesulfonic acid.

Naphthalene is mixed with 20 % oleum at 20 – 35 C followed by gradual addition of 65 % oleum and further naphthalene alternately. After heating for 6 h at 55 C the reaction mixture is added to water, and the product is precipitated as the free acid by cooling or as the disodium salt by the addition of alkaline sodium sulfate. In each case, the isolated yield is ca. 53 %. The 1,6-disulfonic acid can be recovered from the filtrate. Higher yields of 4 have been reported for alternative processes; for example, solvent sulfonation with sulfur trioxide and chlorosulfonic acid in a solvent such as tetrachloroethylene [24] or sulfonation with oleum through a double screw-feed apparatus.

Not classified

Very low oral toxicity. Whenheated to decomposition it emits toxic fumes of SOx. Seealso SULFONATES.