1-Naphthol

1-Naphthol, or α-naphthol, is an organic compound with the formula C
10H
7OH. It is a fluorescent white solid. 1-Naphthol differs from its isomer 2-naphthol by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol. Both isomers are soluble in simple organic solvents. They are precursors to a variety of useful compounds.^[1]

1-Naphthol is prepared by two main routes.^[1] In one method, naphthalene is nitrated to give 1-nitronaphthalene, which is hydrogenated to the amine followed by hydrolysis:

C
10H
8 + HNO
3 → C
10H
7NO
2 + H
2O

C
10H
7NO
2 + 3H
2 → C
10H
7NH
2 + 2H
2O

C
10H
7NH
2 + H
2O → C
10H
7OH + NH
3

Alternatively, naphthalene is hydrogenated to tetralin, which is oxidized to 1-tetralone, which undergoes dehydrogenation.

Some reactions of 1-naphthol are explicable with reference to its tautomerism, which produces a small amount of the keto tautomer.^[2]

One consequence of this tautomerism is the Bucherer reaction: the ammonolysis of 1-naphthol to give 1-aminonaphthalene. Low temperature sulfonation of 1-naphthol gives 1-hydroxynaphthalene-2-sulfonic acid.

1-Naphthol biodegrades via formation of 1-naphthol-3,4-oxide, which converts to 1,4-naphthoquinone.^[3]

The 4-position of 1-naphthol is susceptible to electrophilic attack. This regioselective reaction is exploited in the preparation of diazo dyes, which are form using diazonium salts. Reduction of the diazo derivatives gives 4-amino-1-naphthol.^[4][5]

Partial reduction of 1-naphthol gives the tetrahydro derivative, leaving intact the phenol ring.^[6] Full hydrogenation is catalyzed by rhodium.^[7]

1-Naphthol is a precursor to a variety of insecticides including carbaryl and pharmaceuticals including nadolol^[8][9] as well as for the antidepressant sertraline^[10] and the anti-protozoan therapeutic atovaquone.^[11] It undergoes azo coupling to give various azo dyes, but these are generally less useful than those derived from 2-naphthol.^[1][12]

1-Naphthol is a metabolite of the insecticide carbaryl and naphthalene. Along with TCPy, it has been shown to decrease testosterone levels in adult men.^[13]

An agent called SBFI-26 is an ester that is formed between 1-naphthol and truxillic acid.

1-Naphthol is used in each of the following chemical tests, which predate the use of spectroscopic and chromatographic methods:

• Molisch's test gives a red- or purple-colored compound to indicate the presence of carbohydrate.
• rapid furfural test turns purple quickly (<30s) if fructose is present, distinguishing it from glucose.
• Sakaguchi test turns red to indicate the presence of arginine in proteins.
• Voges–Proskauer test changes color from yellow to red to indicate that glucose is being broken down into acetoin which is used by bacteria for external energy storage.

1-Naphthol has been described as "moderately toxic".^[1]

• NIST Chemistry WebBook 1-Naphthalenol

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