Formula C10H8O Density 1.22 g/cm³ | ||
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Appearance Colorless crystalline solid | ||
Preparation of azo dye 2 naphthol aniline dye
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.
Contents
Production
Traditionally, 2-naphthol is produced by a two-step process that begins with the sulfonation of naphthalene in sulfuric acid:
C10H8 + H2SO4 → C10H7SO3H + H2OThe sulfonic acid group is then cleaved in molten sodium hydroxide:
C10H7(SO3H) + 3 NaOH → C10H7ONa + Na2SO3 + 2 H2ONeutralization of the product with acid gives 2-naphthol.
2-Naphthol can also be produced by a method analogous to the cumene process.
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. Sudan dyes I -IV and Sudan Red G consist of arylazo-substituted naphthols.
Precursor to BINOL
They can be also used in the production of dyes and in organic synthesis. For example, 2-naphthol reacts to form BINOL.
Safety
Naphthols (both 1 and 2 isomers) are used as biomarkers for livestock and humans exposed to polycyclic aromatic hydrocarbons.