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
3D model (JSmol)
742134
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.712
EC Number
  • 205-182-7
27395
KEGG
RTECS number
  • QL2975000
UNII
UN number 3077
  • InChI=1S/C10H8O/c11-10-6-5-8-3-1-2-4-9(8)7-10/h1-7,11H checkY
    Key: JWAZRIHNYRIHIV-UHFFFAOYSA-N checkY
  • InChI=1/C10H8O/c11-10-6-5-8-3-1-2-4-9(8)7-10/h1-7,11H
    Key: JWAZRIHNYRIHIV-UHFFFAOYAV
  • Oc2ccc1c(cccc1)c2
  • c1ccc2cc(ccc2c1)O
Properties
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)
0.74 g/L
Acidity (pKa) 9.51
-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:
GHS07: Exclamation mark GHS09: Environmental hazard
Warning
H302, H332, H400
P261, P264, P270, P271, P273, P301+P312, P304+P312, P304+P340, P312, P330, P391, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored 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).
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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.

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
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[6] bromination,[7] and alkylations.[8] Ring-opening reactions have been documented.[9]

Safety

Naphthols (both the 1- and 2- isomers) are used as biomarkers for livestock and humans exposed to polycyclic aromatic hydrocarbons.[10]

References
  1. "MSDS safety data for 2-naphthol". Archived from the original on 3 March 2011.
  2. Booth, Gerald (2005). "Naphthalene Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_009.. full-text PDF
  3. Booth, Gerald; Zollinger, Heinrich; McLaren, Keith; Sharples, William G.; Westwell, Alan (2000). "Dyes, General Survey". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a09_073. ISBN 9783527306732.
  4. Melvin S. Newman; Frederick W. Hetzel (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". Organic Syntheses. 51: 139. doi:10.15227/orgsyn.051.0139.
  5. J. P. Schaefer; Jerry Higgins; P. K. Shenoy (1969). "2-Bromonaphthalene". Organic Syntheses. 49: 6. doi:10.15227/orgsyn.049.0006.
  6. "Nitroso-β-Naphthol C. S. Marvel and P. K. Porter". Organic Syntheses. 2: 61. 1922. doi:10.15227/orgsyn.002.0061.
  7. C. Frederick Koelsch (1940). "6-Bromo-2-Naphthol". Organic Syntheses. 20: 18. doi:10.15227/orgsyn.020.0018.
  8. Alfred Russell Luther B. Lockhart (1942). "2-Hydroxy-1-Naphthaldehyde". Organic Syntheses. 22: 63. doi:10.15227/orgsyn.022.0063.
  9. G. A. Page, D. S. Tarbell (1954). "β-(o-Carboxyphenyl)propionic Acid". Organic Syntheses. 34: 8. doi:10.15227/orgsyn.034.0008.
  10. 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. Bibcode:2013JPCA..11711261S. doi:10.1021/jp4081355. PMID 24093754.
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