β-naphthol
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2-Naphthol, or β-naphthol, is a
fluorescent Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...
colorless (or occasionally yellow) crystalline solid with the formula C10H7OH. It is an
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
of
1-naphthol 1-Naphthol, or α-naphthol, is an organic compound with the formula . 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 ...
, differing by the location of the
hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
on the
naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...
ring. The naphthols are naphthalene homologues of
phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...
, but more reactive. Both isomers are soluble in simple
alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...
s,
ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R†...
s, and
chloroform Chloroform, or trichloromethane (often abbreviated as TCM), is an organochloride with the formula and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and po ...
. 2-Naphthol is a widely used intermediate for the production of
dye Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...
s and other compounds.


Production

Traditionally, 2-naphthol is produced by a two-step process that begins with the
sulfonation In organic chemistry, aromatic sulfonation is a reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid () group. Together with nitration and chlorination, aromatic sulfonation is a widely used electrophilic aromatic substi ...
of naphthalene in
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
:
full-text PDF
/ref> :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 The cumene process (cumene-phenol process, Hock process) is an industrial process for synthesizing phenol and acetone from benzene and propylene. The term stems from cumene (isopropyl benzene), the intermediate material during the process. It ...
.


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 salt Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. The parent, comp ...
s. Sudan dyes I–IV and Sudan Red G consist of arylazo-substituted
naphthol Naphthol may refer to: * 1-Naphthol 1-Naphthol, or α-naphthol, is an organic compound with the formula . It is a fluorescent white solid. 1-Naphthol differs from its isomer 2-naphthol by the location of the hydroxyl group on the naphthalene ...
s. File:Sudan I.svg,
Sudan I Sudan I (also known as CI Solvent Yellow 14 or Solvent Orange R) is an organic compound typically classified as an azo dye. It is an orange-red solid, used to color waxes, oils, petrol, solvents, and polishes. Historically, Sudan I used to serve ...
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 Oil Red O (Solvent Red 27, Sudan Red 5B, C.I. 26125, C26H24N4O) is a lysochrome (fat-soluble dye) diazo dye used for staining of neutral triglycerides and lipids on frozen sections and some lipoproteins on paraffin sections. It has the appearance ...
File:Naphthol AS.svg,
Naphthol AS Naphthol AS is an organic compound with the formula C10H6(OH)C(O)NHC6H5. It is the anilide of 3-hydroxy-2-carboxynaphthalene. Many analogous compounds are known, designated with a differing suffix. For example, in Naphthol AS-OL, the aryl sub ...


Reactions

Some reactions of 2-naphthol are explicable with reference to its tautomerism, which produces a small amount of the keto tautomer. : One consequence of this tautomerism is the
Bucherer reaction The Bucherer reaction in organic chemistry is the reversible conversion of a naphthol to a naphthylamine in the presence of ammonia and sodium bisulfite. The reaction is widely used in the synthesis of dye precursors aminonaphthalenesulfonic ac ...
, the ammonolysis of 2-naphthol to give
2-aminonaphthalene 2-Naphthylamine or 2-aminonaphthalene is one of two isomeric aminonaphthalenes, compounds with the formula C10H7NH2. It is a colorless solid, but samples take on a reddish color in air because of oxidation. It was formerly used to make azo dyes, b ...
. 2-Naphthol can be oxidatively coupled to form BINOL, a ''C''2-symmetric ligand popularized for use in
asymmetric catalysis Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of Chirality (chemistry), chirality are formed ...
. 2-Naphthol converts to
2-naphthalenethiol 2-Naphthalenethiol is an organosulfur compound with the formula C10H7SH. It is a white solid. It is one of two monothiols of naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, ...
by reaction with
dimethylthiocarbamoyl chloride Dimethylthiocarbamoyl chloride is an organosulfur compound with the formula (CH3)2NC(S)Cl. A yellow solid, it is often encountered as a yellow syrup. It is a key reagent in the synthesis of arylthiols via the Newman-Kwart rearrangement. Synthes ...
via the
Newman–Kwart rearrangement The Newman–Kwart rearrangement is a type of rearrangement reaction in which the aryl group of an ''O''-aryl thiocarbamate, ArOC(=S)NMe2, migrates from the oxygen atom to the sulfur atom, forming an ''S''-aryl thiocarbamate, ArSC(=O)NMe2. The ...
. 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.


Safety

2-Naphthol has been described as "moderately toxic.


References


External links


NIST Chemistry WebBook 2-Naphthalenol
* {{DEFAULTSORT:Naphthol, 2- 2-Naphthyl compounds