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
Preferred IUPAC name Naphthalen-2-ol
Other names 2-Hydroxynaphthalene; 2-Naphthalenol; beta-Naphthol; Naphth-2-ol
Identifiers
CAS Number	135-19-3 Y
3D model (JSmol)	Interactive image Interactive image
Beilstein Reference	742134
ChEBI	CHEBI:10432 Y
ChEMBL	ChEMBL14126 Y
ChemSpider	8341 Y
ECHA InfoCard	100.004.712
EC Number	205-182-7
Gmelin Reference	27395
KEGG	C11713 Y
PubChem CID	8663
RTECS number	QL2975000
UNII	P2Z71CIK5H Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID5027061
InChI InChI=1S/C10H8O/c11-10-6-5-8-3-1-2-4-9(8)7-10/h1-7,11H Y Key: JWAZRIHNYRIHIV-UHFFFAOYSA-N Y 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/cm3
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 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Harmful when inhaled or swallowed; dangerous to environment, esp. aquatic organisms.[1]
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H332, H400
Precautionary statements	P261, P264, P270, P271, P273, P301+P312, P304+P312, P304+P340, P312, P330, P391, P501
NFPA 704 (fire diamond)	2 1 0
Flash point	161 °C (322 °F; 434 K)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) 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

Some reactions of 2-naphthol are explicable with reference to its tautomerism, which produces a small amount of the keto tautomer.

Tautomeric equilibrium for beta-naphthol

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.

Coupling of beta-naphthol using CuCl2

2-Naphthol converts to 2-naphthalenethiol by reaction with dimethylthiocarbamoyl chloride via the Newman–Kwart rearrangement.^[4] The OH→Br conversion has been described.^[5]

Electrophilic attack occurs characteristically at the 1-position as indicated by nitrosylation to give 1-nitroso-2-naphthol.^[6] Bromination^[7] and alkylations proceed with similar regiochemistry.^[8] Ring-opening reactions have been documented.^[9]

Carbonation of 2-naphthol gives 2-hydroxy-1-naphthoic acid.^[2]

Safety

2-Naphthol has been described as "moderately toxic.^[2]