2-Naphthol

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.

2-Naphthol

Names
IUPAC name Naphthalen-2-ol
Other names 2-Hydroxynaphthalene; 2-Naphthalenol; beta-Naphthol; Naphth-2-ol
Identifiers
CAS Number	135-19-3
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:10432
ChEMBL	ChEMBL14126
ChemSpider	8341
ECHA InfoCard	100.004.712
KEGG	C11713
PubChem CID	8663
UNII	P2Z71CIK5H
CompTox Dashboard (EPA)	DTXSID5027061
InChI InChI=1S/C10H8O/c11-10-6-5-8-3-1-2-4-9(8)7-10/h1-7,11H Key: JWAZRIHNYRIHIV-UHFFFAOYSA-N InChI=1/C10H8O/c11-10-6-5-8-3-1-2-4-9(8)7-10/h1-7,11H Key: JWAZRIHNYRIHIV-UHFFFAOYAV
SMILES Oc2ccc1c(cccc1)c2 c1ccc2cc(ccc2c1)O
Properties
Chemical formula	C10H8O
Molar mass	144.173 g·mol^−1
Appearance	Colorless crystalline solid
Density	1.280 g/cm^3
Melting point	121 to 123 °C (250 to 253 °F; 394 to 396 K)
Boiling point	285 °C (545 °F; 558 K)
Solubility in water	0.74 g/L
Acidity (pKa)	9.51
Magnetic susceptibility (χ)	-98.25·10^−6 cm^3/mol
Hazards
Main hazards	Harmful when inhaled or swallowed; dangerous to environment, esp. aquatic organisms.[1]
R-phrases (outdated)	R20 R22 R50
S-phrases (outdated)	S24 S25 S61
NFPA 704 (fire diamond)	1 2 0
Flash point	161 °C (322 °F)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Production

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

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]

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.[3] Sudan dyes I -IV and Sudan Red G consist of arylazo-substituted naphthols.

• Selected 2-Naphthol-derived dyes
• 
  Sudan I
• 
  Sudan II
• 
  Sudan III
• 
  Sudan IV
• 
  Oil Red O
• 
  Naphthol AS

Reactions

2-Naphthol reacts to form BINOL, a C2-symmetric ligand popularized for use in asymmetric catalysis.

2-Naphthol converts to 2-naphthalenethiol via reaction with dimethylthiocarbamoyl chloride via the Newman-Kwart rearrangement.[4]

Safety

Naphthols (both 1 and 2 isomers) are used as biomarkers for livestock and humans exposed to polycyclic aromatic hydrocarbons.[5]

References

1. Safety data for 2-naphthol
2. Gerald Booth (2005). "Naphthalene Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_009..
3. Booth, Gerald (2000). "Dyes, General Survey". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a09_073. ISBN 978-3527306732.
4. Melvin S. Newman; Frederick W. Hetzel (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". Org. Synth. 51: 139. doi:10.15227/orgsyn.051.0139.
5. Sreekanth, R.; Prasanthkumar, Kavanal P.; Sunil Paul, M. M.; Aravind, Usha K.; Aravindakumar, C. T. (7 November 2013). "Oxidation Reactions of 1- and 2-Naphthols: An Experimental and Theoretical Study". The Journal of Physical Chemistry A. 117 (44): 11261–11270. doi:10.1021/jp4081355. PMID 24093754.

External links

• NIST Chemistry WebBook 2-Naphthalenol