2-Naphthol, or β-naphthol, is a fluorescent colorless (or occasionally yellow) crystalline solid with the formula C10H7OH. It is an isomer of 1-naphthol, differing by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol, but more reactive. Both isomers are soluble in simple alcohols, ethers, and chloroform. 2-Naphthol is a widely used intermediate for the production of dyes and other compounds.
Traditionally, 2-naphthol is produced by a two-step process that begins with the sulfonation of naphthalene in sulfuric acid:[1]
C10H8 + H2SO4 → C10H7SO3H + H2O
The sulfonic acid group is then cleaved in molten sodium hydroxide:
C10H7(SO3H) + 3 NaOH → C10H7ONa + Na2SO3 + 2 H2O
Neutralization of the product with acid gives 2-naphthol.
2-Naphthol can also be produced by a method analogous to the cumene process.[1]
2-Naphthol-derived dyes
The Sudan dyes are popular dyes noted for being soluble in organic solvents. Several of the Sudan dyes are derived from 2-naphthol by coupling with diazonium salts.[2] Sudan dyes I–IV and Sudan Red G consist of arylazo-substituted naphthols.
Electrophilic attack occurs characteristically at the 1-position as indicated by nitrosylation to give 1-nitroso-2-naphthol.[5] Bromination[6] and alkylations proceed with similar regiochemistry.[7] Ring-opening reactions have been documented.[8]
