Naphthalene Chemical properties

Reactions with electrophiles

Naphthalene reacts more readily than benzene in electrophilic aromatic substitution reactions.For example, the chlorination and bromination of naphthalene proceed without catalysts to 1-chloronaphthalene and 1-bromonaphthalene, respectively.Likewise, while both benzene and naphthalene can be alkylated using the Friedel Crafts reaction, naphthalene can also be easily alkylated by reaction with olefins or alcohols using sulfuric or phosphoric acid catalysts.In terms of regiochemistry, electrophiles attack the alpha position. The selectivity of the alpha-substituted beta-substitution can be rationalized based on the resonance structures of the intermediates: for the alpha-substituted intermediate, seven resonance structures can be drawn, four of which retain the aromatic ring.For β substitution, the intermediate has only six resonance structures, only two of which are aromatic.Sulfonation gives the “alpha” product naphthalene-1-sulfonic acid as the kinetic product but naphthalene-2-sulfonic acid as the thermodynamic product.The 1-isomer is mainly formed at 25 °C and the 2-isomer at 160 °C. Sulfonation to 1- and 2-sulfonic acids occurs readily:

H2SO4 + C10H8 → C10H7SO3H + H2O.Further sulfonation affords di-, tri-, and tetra-sulfonic acids.

Lithiation

An analogous synthesis of phenyllithium is the conversion of 1-bromonaphthalene to 1-lithium naphthalene by lithium-halogen exchange:C10H7Br + BuLi → C10H7Li + BuBr

In contrast to the behavior of phenyl lithium, the resulting lithium naphthalene undergoes a second lithiation.These 1,8-dilithium derivatives are precursors to a large number of cyclonaphthalene derivatives.

Production

Most naphthalene comes from coal tar.Large quantities of naphthalene were also produced from heavy petroleum fractions during petroleum refining from the 1960s to the 1990s, but current production comes primarily from coal tar.Approximately 1.3 million tons are produced annually.Naphthalene is the most abundant single component in coal tar.The composition of coal tar varies depending on the type of coal and how it was processed, but a typical coal tar contains about 10% naphthalene by weight.In industrial practice, the distillation of coal tar produces an oil that contains about 50% naphthalene along with 12 other aromatic compounds.After the oil is washed with aqueous sodium hydroxide solution to remove acidic components (mainly various phenols) and basic components with sulfuric acid, it is subjected to fractional distillation to separate naphthalene.The crude naphthalene produced by this process is approximately 95% by weight of naphthalene.The main impurities are sulfur-containing aromatic compounds benzothiophene (< 2%), indane (0.2%), indene (< 2%), and methylnaphthalene (< 2%). Petroleum derived naphthalene is generally purer than coal tar derived naphthalene. If desired, crude naphthalene can be further purified by recrystallization from any of a variety of solvents to yield 99% by weight naphthalene, referred to as 80 °C (melting point) and the major oil producer is Monument Chemical.In Western Europe, well-known producers are Koppers, Ruetgers and Deza.In Eastern Europe, naphthalene is produced by various integrated metallurgical complexes in Russia (Severstal, Evraz, Mechel, MMK), specialized naphthalene and phenol manufacturer INKOR, Yenakievsky Metallurgical Plant in Ukraine, and ArcelorMittal Temirtau in Kazakhstan.