Naphthol and its derivatives

In comparison with the 2-isomer, 1-naphthol is of relatively little importance as a dyestuff component. Its main use is in the production of the insecticide 1-naphthyl N-methylcarbamate (carbaryl), which was one of the most important organic pesticides used in the USA in the 1970 s. 

The most important process to obtain 1-naphthol has been developed by Union Carbide via tetralin to 1-naphthol (see Chapter 9.3.6). Processes applying alkali fusion of naphthalene-1-sulfonic acid, manufactured at 180 °C by selective sulfo-nation, and by pressure hydrolysis of 1-naphthylamine at 185 °C with 20% sulfuric acid are of less importance in terms of quantities. 

1-Naphthol production in the Western world is around 15,000 tpa, with the USA as the largest producer. 

The main derivative of 1-naphthol is carbaryl, which is produced by the reaction of 1-naphthol with methyl isocyanate. Methyl isocyanate, a toxic liquid boiling at 38 °C, is obtained, among other methods, by the reaction of phosgene with methylamine. Because of its toxicity, it should only be stored for short periods to avoid possible risks during storage (Bhopal accident). 

Another important derivative of 1-naphthol is propranolol, a P-receptor blocker developed by ICI and with a worldwide production of around 500 tpa. Synthesis takes place by the reaction of 1-naphthol with epichlorohydrin, followed by substitution of the chlorine in l-chloro-3-(l-naphthoxy)-2-propanol with isopropylamine to yield propranolol. 

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Further bromination of 3,4,6-tribromo-5-hydroxybenzo[6]thio-phene affords the 2,3,4,6-tetrabromo derivative in the absence of acetate ion, and 3,4,4,6-tetrabromo-4,5-dihydrobenzo[6]thiophen-5-one in the presence of acetate ion. 421 On treatment of 3,4-dibromo-, 4,6-dibromo-, 3,4,6-tribromo-, or 2,3,4,6-tetrabromo-5-hydroxybenzo-[6]thiophene with nitric acid in acetic acid, the corresponding unstable orange crystalline 4-bromo-4-nitro-4,5-dihydrobenzo[6]thio-phen-5-one is obtained.152,421 Hence, once both positions ortho to the hydroxyl group in 5-hydroxybenzo[6]thiophene are occupied by bromine, the properties of these compounds are analogous to the properties of l-bromo-2-naphthol which, on bromination in acetic acid in the presence of acetate ion, affords l,l-dibromo-l,2-dihydro-naphthalen-2-one whereas, in its absence, it affords l,6-dibromo-2-naphthol.616 The behavior of l-bromo-2-naphthol and its derivatives on nitration is similar to that of 4,0-dibromo-5-hydroxybenzo[6]thio-phene and its derivatives.162,616... 

The implications of the kinetics of the Se2 mechanism on the o/p-ratio of the azo coupling reaction of 1-naphthol and its derivatives with a sulfonic group in the 3-po-sition have already been discussed in detail in Sa tion 4.3. 

The most thoroughly studied compounds are derivatives of 2-naphthol. The emission spectra of 2-naphthol and its derivatives are shown in Fig. 12. The parent compound was found to have a rate of proton ejection (k) of about 5x10 s using phase fluorimetry, nanosecond emission... 

This carboxylation reaction is of importance mainly for the manufacture from 2-naphthol of P-oxynaphthoic acid (BON) acid, the parent acid of sodium 3-hydroxy-2-naphthoate (4-35). The carboxylation is achieved by heating the sodium salt of 2-naphthol under pressure in an atmosphere of carbon dioxide (Scheme 4.25). Under these conditions an equilibrium mixture of the naphthol and its carboxylated derivative is established, the mixture containing about 30% of the carboxylic acid. The desired product is extracted from the reaction mixture and the unchanged 2-naphthol is recycled. 

BINOL and its derivatives have been utilized as versatile chiral sources for asymmetric catalysis, and efficient catalysts for their syntheses are, ultimately, required in many chemical fields [39-42]. The oxidative coupling of 2-naphthols is a direct synthesis of BINOL derivatives [43, 44], and some transition metals such as copper [45, 46], iron [46, 47] and manganese [48] are known as active metals for the reaction. However, few studies on homogeneous metal complexes have been reported for the asymmetric coupling of 2-naphthols [49-56]. The chiral self-dimerized V dimers on Si02 is the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol. 

In this work we investigate such interactions by fluorescence spectroscopy. Probe molecules such as 2-naphthol and its 5-cyano-derivative are effective chromophores for studying acid/base interactions since both are relatively strong photo-acids. In addition, 2-naphthol is a common solute for which SCF solubility and physical property data exist. Ultimately, spectroscopic information will be used to develop a clearer picture of the specific interactions which induce large cosolvent effects on solubility in SCF solutions. 

Proton transfer is sensitive to the local solute environment in liquid solutions as evidenced by the water quenching curves for 2-naphthol and its cyano- derivatives. We have used proton transfer as a mechanism to probe the cosolvent composition around a solute in supercritical fluids to discern any difference between local and bulk concentrations. No proton transfer was observed from either 2-naphthol or 5-cyano-2-naphthol, presumably indicating insufficient structure in the SCF to solvate the proton. Although significant cosolvent effects on the fluorescence emission were observed, these appear to be independent of the thermodynamic variables. 

This chiral column has been shown successfully to resolve enantiomeric mixtures (or racemates) of aromatic alcohols including l,l -bi-2-naphthol and its analogues (p. 836), aromatic hydroxy (or alkoxy) carboxylic esters and amides, amino acid derivatives, sulphoxides, cyclic imides and amides, lactones, etc. Even this list should not be regarded as limiting. The potential of this method, coupled with the simplicity of operation will undoubtedly be extensively developed and explored in the coming years. 

An important coupling component for paper dyes is 2-amino-5-naphthol-7-sulfonic acid (12) and its derivatives (R= H, acetyl, benzoyl, aryl, imidazoyl, thi-azolyl, triazolyl, etc.). 

The principal red couplers are 3-aminophenol [591-27-5], 5-amino-2-methyl-phenol [2835-95-2], and 1-naphthol [90-15-3]. Yellow-green couplers include resorcinol [108-46-3], 4-chlororesorcinol 195-88-5, benzodioxoles, and 2-methyl-resorcinol [608-25-3] and its derivatives. The importance of the yellow-green couplers lies in the broad-band absorption of the dyes produced, which makes natural-looking hair shades possible. Table 5.4 lists a range of colors obtained by reaction of primary intermediates with different couplers. 

An analogous approach has been used in assigning H and 13C NMR chemical shifts in anthracenedione phenylhydrazones,50 l,3-bis(phenylazo)-2-naphthol and its precursors.51 Azo and hydrazone compounds 13 derived from Fischer base (l,3,3-trimethyl-2-methylidene-2,3-dihydroindole) were studied by two groups.52,53... 

Both 2-naphthol (35) and its derivative B-, or 2-oxynaphthoic acid are important coupling components in the production of azo pigments. The latter is used for several reds,... 

Naphthol and its 3,6-disulfonate derivative show consistency in their spectral feamres in both the photoacid and base sides, while much less consistency is evident in the spectral features of the 1-naphthol derivatives in the acid side, where the fluorescence spectrum appears to be much narrower and more structured than the absorption spectrum (Figure 21). This points to more extensive electronic rearrangements in the acid side of... 

Dr Schupphaus found that propyl and isobutyl alcohols with camphor were active solvents, and the ketones, palmitone, and stearone in alcohol solution, also alpha- and beta-naphthol, with alcohol and anthraquinone (diphenylene diketone) in alcoholic solution, and also iso-valeric aldehyde and its derivatives, amyliden-dimethyl and amyliden-diethyl ethers. 

A tris(4-bromophenyl)ammonium hexachloroantimonate catalyst has been utilized to promote a cation radical mechanism in the Diels-Alder cycloaddition polymerization of a bis(diene) with an ionizable bis(dienophile) (Scheme 2). The polymers were obtained with molecular weights up to ca 10 000 and a polydispersity index of ca 2. The electron-transfer reactions of phenols and its derivatives are also important to the polymer industry for the stabilization of polymers, fats and oils. Pulse radiolysis of naphthols and hydroxybiphenyls in n-butyl chloride at room temperature forms two species-phenol-type radical cations and phenoxyl-type radicals. Two different electron-transfer channels are proposed. The naphthol and hydroxybiphenyl radical cations show increased stability compared with phenol radical cations, presumably due to extensive delocalization over the whole aromatic system. 

Dehydration is carried out with sulfuric acid, hydrochloric acid, or phosphoric acid. Among phenols, phenol, thymol, guaiacol, resorcinol, orcinol, catechol, phloroglucinol, a-naphthol, and naphthoresorcinol have been proposed. Among amines, aniline, p-anisidine, benzidine, 3,3 -di-methoxybenzidine, diphenylamine, indole and its derivatives, carbazole, N-ethylcarbazole, a,a-dinaphthylamine, and 1,2,7,8-dibenzocarbazole have been found valuable. In its classical form (Molisch reaction) the test for saccharides is carried out With 1-naphthol and cone, sulfuric acid (70). It is supposed that under the conditions of the reaction corresponding triphenylmethane dyes are formed, although the course of the reaction might be more complicated (71). 

Conant and Peterson123 made the first kinetic study of the coupling of diazonium ions with aromatics, and measured the rates of reaction of diazotised aniline and its 2-MeO, 4-Me, 4-Br and 4-S03H derivatives with the sodium salts of 4-hydroxybenzenesulphonic acid, 2-naphthol-3,6-disulphonic acid, 1-naphthol-3,8-disulphonic acid, and l-naphthol-4-sulphonic acid. The reaction was second-order, viz. 

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