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2-Naphthol

| NFPA-H = 2 | NFPA-F = 1 | NFPA-R = 0

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.

Production

Traditionally, 2-naphthol is produced by a two-step process that begins with the sulfonation of naphthalene in sulfuric acid: :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.

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. Sudan dyes I–IV and Sudan Red G consist of arylazo-substituted naphthols.

File:Sudan I.svg|Sudan I File:Sudan II.svg|Sudan II File:Sudan III.svg|Sudan III File:Sudan IV.svg|Sudan IV File:Oil Red O.svg|Oil Red O File:Naphthol AS.svg|Naphthol AS

Reactions

Some reactions of 2-naphthol are explicable with reference to its tautomerism, which produces a small amount of the keto tautomer. :[[File:Beta-naphthol tautomerism.svg|thumb|Tautomeric equilibrium for beta-naphthol|left|384px]] One consequence of this tautomerism is the Bucherer reaction, the ammonolysis of 2-naphthol to give 2-aminonaphthalene.

2-Naphthol can be oxidatively coupled to form BINOL, a C2-symmetric ligand popularized for use in asymmetric catalysis.

2-Naphthol converts to 2-naphthalenethiol by reaction with dimethylthiocarbamoyl chloride via the Newman–Kwart rearrangement. The OH→Br conversion has been described.

Electrophilic attack occurs characteristically at the 1-position as indicated by nitrosylation to give 1-nitroso-2-naphthol. Bromination and alkylations proceed with similar regiochemistry. Ring-opening reactions have been documented.

Carbonation of 2-naphthol gives 2-hydroxy-1-naphthoic acid.

2-Naphthol is used in the synthesis of a compound that is called 6-Methoxy-1-tetralone [1078-19-9]. This is a critically important starting material in the total synthesis of many gonane and estrane steroids, such as Estrone methyl ether, for example.

Methlation of 2-Naphthol gives a compound that is called 2-Methoxynaphthalene (Nerolin) [93-04-9].

Safety

2-Naphthol has been described as "moderately toxic".

References

References

  1. "MSDS safety data for 2-naphthol".
  2. Booth, Gerald. (2005). "Naphthalene Derivatives".
  3. (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". [[Organic Syntheses]].
  4. (1969). "2-Bromonaphthalene". Organic Syntheses.
  5. (1922). "Nitroso-β-Naphthol". Organic Syntheses.
  6. C. Frederick Koelsch. (1940). "6-Bromo-2-Naphthol". Organic Syntheses.
  7. Alfred Russell Luther B. Lockhart. (1942). "2-Hydroxy-1-Naphthaldehyde". Organic Syntheses.
  8. G. A. Page, D. S. Tarbell. (1954). "β-(o-Carboxyphenyl)propionic Acid". Organic Syntheses.
  9. Zou Xiaomao, et al. CN120398657 (2025 to Nankai University).
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2-naphthols 2-naphthyl-compounds
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