naphthalene(redirected from Naphtalene)
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an aromatic hydrocarbon; colorless lamellar crystals with a characteristic odor. Melting point, 80.3°C; boiling point, 218°C; density, 1.1517 g/cm3 (15°C).
Naphthalene is volatile; it sublimes at 50°C. It is poorly soluble in water but dissolves readily in most organic solvents; it is distilled over steam. In general, naphthalene is prepared commercially from coal tar (8–10 percent naphthalene content) and from products of petroleum pyrolysis; naphthalene extracted from the latter is considerably purer than that derived from coal tar.
Naphthalene readily enters into elecrophilic substitution reactions (for example, halogenation, nitration, sulfonation, alkylation, and acylation). The substitution rate in the α-position is higher than in the β-position, although β-substituted naphthalenes have greater thermodynamic stability than α-substituted forms. Therefore, mixtures of isomers are usually produced; their composition depends on the reagent, catalyst, and solvent used, and also on the temperature and reaction time. For example, both α-chloronaphthalene and 1,4- and 1,5-dichloronaphthalenes are produced upon cold chlorination of naphthalene in the presence of FeCl3. The reaction of naphthalene and acetyl chloride in ethylene dichloride upon action of AlCl3. produces α-acetylnaphthalene; a mixture of α- and β-derivatives is formed when no solvent is used. Sulfonation of naphthalene at low temperatures yields α-naphthalenesulfonic acid, which converts to the β-isomer upon heating. Further sulfonation produces a mixture of disulfonic and polysulfonic acids of naphthalene; this process yields no sulfonic acids containing sulfo groups in the ortho-, para-, and peri- (that is, 1,8 or 4,5) positions. Naphthalene nitration yields α-nitronaphthalene, and the β-isomer is obtained by an indirect method.
Hydrogenation of naphthalene yields Tetralin (I) and Decalin (II), whereas oxidation yields phthalic anhydride (III)—for example,
In industry, α-naphthylamine is prepared by reduction of α-nitronaphthalene, acid hydrolysis of α-naphthylamine yields α-naphthol, and alkaline fusion of β-naphthalenesulfonic acid produces β-naphthol:
Naphthalene is a valuable source material in the preparation of many organic intermediates (primarily phthalic anhydride) and dyes (based on naphthols, naphthylamines, and their sulfonic acids).
Methyl naphthalenes, the closest homologues of naphthalene, are also found in coal tar and have properties similar to those of naphthalenes. These homologues are used in the synthesis of plant growth regulators, whereas polymethyl naphthalenes are used as insecticides, and the sulfonic acid salts of higher naphthalene homologues are used as emulsifiers.
B. L. DIATKIN