1,5-Dihydroxy naphthalene

Grey powder 1,5-Naphthalenediol [83-56-7], 1,5-dihydroxynaphthalene, Azurol, C10H8O2, Mr 160.16, forms colorless needles (from aqueous methyl cellosolve). The compound is sublimable, readily soluble in ether and acetone, but only sparingly soluble in water and hydrocarbons. It is oxidized to 5-hydroxy-1,4-naphthoquinone ( juglone) by CrO3. Amination gives 1,5-naphthalenediamine; coupling with diazotized anilines occurs in the 2- or 4-position.

1,5-Dihydroxynaphthalene is an intermediate of synthetic mordant azo dyes. It is an intermediate used in organic synthesis, pharmaceuticals, dyestuff fields and photograph industry. It is used as a coupling component in azo dyes as exemplified in the metallizable (Cr) wool dye, C.I. Mordant Black 9.

The sodium salt of naphthalene-1,5-disulfonic acid is added gradually to excess 75 % sodium hydroxide. The mixture is heated under pressure to 276℃ over the course of 7 h and the reaction is completed by heating for a further 5 h at this temperature. After precipitation with sulfuric acid, the product is isolated in 90 % yield.

The diol (~30g) is purified by making into a thick paste with H2O and suspending this in 3L of H2O containing 200mL of EtOH, boiling under reflux for 3hours, cooling to 30o, saturating with SO2, digesting below the boiling point for 1hour and filtering fast through a large hot filter paper. The hot filtrate is poured onto crushed ice whereby the diol (15-20g) separates as colourless needles (m 258o) [Wheeler & Ergle J Am Chem Soc 52 4873 1930]. Recrystallise it from H2O or nitromethane under N2 to avoid oxidation. The dibenzoyl derivative has m 245o (from EtOH). The 5-methoxy-1-naphthol derivative [prepared from the diol in MeOH/HCl (1:30 weight to volume ratio) and set aside at 25o for 9-10days] crystallised from pet ether (m 135-136o) or from CH2Cl2/hexane (needles m 140o) [Bell & McCaffrey Aust J Chem 46 731 1993]. [Beilstein 6 I 477, 6 II 950, 6 III 5265, 6 IV 6554.]